101
|
Li Y, Xiang B, Xiong W. Heterodyne transient vibrational SFG to reveal molecular responses to interfacial charge transfer. J Chem Phys 2019; 150:114706. [DOI: 10.1063/1.5066237] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Affiliation(s)
- Yingmin Li
- Materials Science and Engineering Program, University of California, San Diego, La Jolla, California 92093, USA
| | - Bo Xiang
- Materials Science and Engineering Program, University of California, San Diego, La Jolla, California 92093, USA
| | - Wei Xiong
- Materials Science and Engineering Program, University of California, San Diego, La Jolla, California 92093, USA
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA
| |
Collapse
|
102
|
Park Y, Baeg KJ, Kim C. Solution-Processed Nonvolatile Organic Transistor Memory Based on Semiconductor Blends. ACS APPLIED MATERIALS & INTERFACES 2019; 11:8327-8336. [PMID: 30707007 DOI: 10.1021/acsami.8b20571] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Solution-processed nonvolatile organic transistor memory devices are fabricated by employing semiconductor blends of p-channel 6,13-bis(triisopropylsilylethynyl)pentacene and n-channel poly{[ N, N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-2T); N2200) on polystyrene-brush as a polymer electret. Electret-based memory characteristics are significantly changed depending on the frontier molecular orbitals of the active semiconductors because the charge-trapping efficiency is mainly determined by the energy barrier to transfer electrons and holes from the active channel to the electret layer. A semiconductor mixture with an optimized blending ratio results in an efficient programming and erasing process. Thus, we obtained a remarkably high ratio of ON/OFF current (memory ratio) about 107 and a large amount of shifts in the threshold voltage (memory window) between the programmed and erased states of 55 V, while single-component N2200 showed only writing-once-read-many (WORM)-type memory. Especially, the programmed data can be stably retained more than 10 years with a sufficient memory ratio of 103. Furthermore, our semiconductor blend system leads to preferable vertical phase separation, which affords good reliability under a sequential memory operation condition as well as stability in ambient air. It is expected that our memory devices can be applied for versatile data storage in printed and flexible electronic applications.
Collapse
Affiliation(s)
- Yonghan Park
- Department of Chemical and Biomolecular Engineering , Sogang University , 35 Baekbeom-ro , Mapo-gu, Seoul 04107 , Republic of Korea
| | - Kang-Jun Baeg
- Department of Graphic Arts Information Engineering , Pukyong National University , 45 Yongso-ro , Nam-gu, Busan 48513 , Republic of Korea
| | - Choongik Kim
- Department of Chemical and Biomolecular Engineering , Sogang University , 35 Baekbeom-ro , Mapo-gu, Seoul 04107 , Republic of Korea
| |
Collapse
|
103
|
Chen J, Messing ME, Zheng K, Pullerits T. Cation-Dependent Hot Carrier Cooling in Halide Perovskite Nanocrystals. J Am Chem Soc 2019; 141:3532-3540. [DOI: 10.1021/jacs.8b11867] [Citation(s) in RCA: 130] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Junsheng Chen
- Chemical Physics and NanoLund, Lund University, Box 124, 22100 Lund, Sweden
- Nano-Science Center & Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - Maria E. Messing
- Solid State Physics and NanoLund, Lund University, Box 118, 22100 Lund, Sweden
| | - Kaibo Zheng
- Chemical Physics and NanoLund, Lund University, Box 124, 22100 Lund, Sweden
- Department of Chemistry, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - Tonu Pullerits
- Chemical Physics and NanoLund, Lund University, Box 124, 22100 Lund, Sweden
| |
Collapse
|
104
|
Ultrafast hole transfer mediated by polaron pairs in all-polymer photovoltaic blends. Nat Commun 2019; 10:398. [PMID: 30674887 PMCID: PMC6344565 DOI: 10.1038/s41467-019-08361-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2018] [Accepted: 01/08/2019] [Indexed: 11/24/2022] Open
Abstract
The charge separation yield at a bulk heterojunction sets the upper efficiency limit of an organic solar cell. Ultrafast charge transfer processes in polymer/fullerene blends have been intensively studied but much less is known about these processes in all-polymer systems. Here, we show that interfacial charge separation can occur through a polaron pair-derived hole transfer process in all-polymer photovoltaic blends, which is a fundamentally different mechanism compared to the exciton-dominated pathway in the polymer/fullerene blends. By utilizing ultrafast optical measurements, we have clearly identified an ultrafast hole transfer process with a lifetime of about 3 ps mediated by photo-excited polaron pairs which has a markedly high quantum efficiency of about 97%. Spectroscopic data show that excitons act as spectators during the efficient hole transfer process. Our findings suggest an alternative route to improve the efficiency of all-polymer solar devices by manipulating polaron pairs. All-polymer solar cells have shown high efficiencies but the ultrafast charge transfer processes are less known. Here Wang et al. show that polaron pairs play vital role facilitating the hole transfer, which is quite different from the exciton dominated pathway in polymer-fullerene blends.
Collapse
|
105
|
Li Y, Xiao B, Chen R, Chen H, Dong J, Liu Y, Chang S. Single-molecule conductance investigation of BDT derivatives: an additional pattern found to induce through-space channels beyond π–π stacking. Chem Commun (Camb) 2019; 55:8325-8328. [DOI: 10.1039/c9cc02998b] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Beyond π–π stacked benzene rings, non-bonded conducting channels are also confirmed in non-strict face-to-face aligned thiophenes or phenyl-thiophene in BDT derivatives.
Collapse
Affiliation(s)
- Yunchuan Li
- The State Key Laboratory of Refractories and Metallurgy
- and Institute of Advanced Materials and Nanotechnology
- Wuhan University of Science and Technology
- Wuhan 430081
- China
| | - Bohuai Xiao
- The State Key Laboratory of Refractories and Metallurgy
- and Institute of Advanced Materials and Nanotechnology
- Wuhan University of Science and Technology
- Wuhan 430081
- China
| | - Rongsheng Chen
- The State Key Laboratory of Refractories and Metallurgy
- and Institute of Advanced Materials and Nanotechnology
- Wuhan University of Science and Technology
- Wuhan 430081
- China
| | - Haijian Chen
- The State Key Laboratory of Refractories and Metallurgy
- and Institute of Advanced Materials and Nanotechnology
- Wuhan University of Science and Technology
- Wuhan 430081
- China
| | - Jianqiao Dong
- The State Key Laboratory of Refractories and Metallurgy
- and Institute of Advanced Materials and Nanotechnology
- Wuhan University of Science and Technology
- Wuhan 430081
- China
| | - Yichong Liu
- The State Key Laboratory of Refractories and Metallurgy
- and Institute of Advanced Materials and Nanotechnology
- Wuhan University of Science and Technology
- Wuhan 430081
- China
| | - Shuai Chang
- The State Key Laboratory of Refractories and Metallurgy
- and Institute of Advanced Materials and Nanotechnology
- Wuhan University of Science and Technology
- Wuhan 430081
- China
| |
Collapse
|
106
|
Cocchi C, Breuer T, Witte G, Draxl C. Polarized absorbance and Davydov splitting in bulk and thin-film pentacene polymorphs. Phys Chem Chem Phys 2018; 20:29724-29736. [PMID: 30462114 DOI: 10.1039/c8cp06384b] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Pentacene is one of the most studied organic materials and in particular its optical properties have been the subject of intense research during the last two decades. In spite of such a widespread interest and of the extensive knowledge achieved so far, a number of issues are still debated. One of the most relevant questions concerns the role of polymorphism and how it affects the lowest-energy exciton, which appears in the visible region and is subject to a sizable Davydov splitting. We address this problem in a combined theoretical and experimental work, where the optical absorption properties of three pentacene polymorphs are investigated within the whole energy range of visible light. Optical spectra computed from first principles in the framework of many-body perturbation theory are directly compared with the polarization-resolved absorbance, measured for three different pentacene phases (the two bulk polymorphs and the thin-film phase). In this way, we unambiguously identify the two Davydov components of the first exciton and the optical fingerprints of each considered phase. With very good agreement between theory and experiment, we show that all polymorphs exhibit common features at the absorption onset, while phase-dependent characteristics appear only above 2 eV. We discuss the character of the lowest-lying singlet and triplet excitons, including dark ones, highlighting the contributions from the electronic bands and the role of the electron-hole interaction and of the local-field effects.
Collapse
Affiliation(s)
- Caterina Cocchi
- Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Germany and European Theoretical Spectroscopic Facility (ETSF), Germany.
| | | | | | | |
Collapse
|
107
|
Wang Y, Jiang C, Chen Q, Zhou Q, Wang H, Wan J, Ma L, Wang J. Highly Promoted Carrier Mobility and Intrinsic Stability by Rolling Up Monolayer Black Phosphorus into Nanoscrolls. J Phys Chem Lett 2018; 9:6847-6852. [PMID: 30449107 DOI: 10.1021/acs.jpclett.8b02913] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Rolling up two-dimensional (2D) materials into nanoscrolls could not only retain the excellent properties of their 2D hosts but also display intriguing physical and chemical properties that arise from their 1D tubular structures. Here, we report a new class of black phosphorus nanoscrolls (bPNSs), which are stable at room-temperature and energetically more favorable than 2D bP. Most strikingly, these bPNSs hold tunable direct band gaps and extremely high mobilities (e.g., the mobility of the double-layer bPNS is about 20-fold higher than that of 2D bP monolayer). Their unique self-encapsulation structure and layer-dependent conduction band minimum can largely prevent the entrance of O2 and the production of O2- and thereby suppress the possible environmental degradation as well. The enhanced intrinsic stability and promoted electronic properties render bPNSs great promise in many advanced electronics or optoelectronics applications.
Collapse
Affiliation(s)
- Yitian Wang
- School of Physics , Southeast University , Nanjing 211189 , China
| | - Chenghuan Jiang
- School of Physics , Nanjing University , Nanjing 210093 , China
| | - Qian Chen
- School of Physics , Southeast University , Nanjing 211189 , China
| | - Qionghua Zhou
- School of Physics , Southeast University , Nanjing 211189 , China
| | - Haowei Wang
- Mechanical Engineering Department , California State University Fullerton , Fullerton , California 92831 , United States
| | - Jianguo Wan
- School of Physics , Nanjing University , Nanjing 210093 , China
| | - Liang Ma
- School of Physics , Southeast University , Nanjing 211189 , China
| | - Jinlan Wang
- School of Physics , Southeast University , Nanjing 211189 , China
| |
Collapse
|
108
|
Yang W, Yao Y, Guo P, Sun H, Luo Y. Optimum driving energy for achieving balanced open-circuit voltage and short-circuit current density in organic bulk heterojunction solar cells. Phys Chem Chem Phys 2018; 20:29866-29875. [PMID: 30468215 DOI: 10.1039/c8cp05145c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Organic bulk heterojunction solar cells generally suffer from a trade-off between the open circuit voltage (Voc) and the short circuit current density (Jsc) under a given donor/acceptor (D/A) interfacial energetic offset (or the so-called driving force). Here we theoretically investigate the optimum driving energy required for achieving the balanced Jsc and Voc simultaneously. To this end, the Jscversus the driving force ΔE curves are calculated under two different charge separation mechanisms by employing the drift-diffusion method. For the Marcus incoherent mechanism, the curve features a high plateau in a broad range of ΔE starting from 0.2 eV, which is due to the accumulation of undissociated excitons within their lifetime and signifies the possibility of obtaining a sizable Jsc under a ΔE value much smaller than the reorganization energy. After incorporating both the electron and hole transfer pathways into the device model, the calculated J-V curves are comparable to experimentally measured ones foractual blended systems of different driving forces. For the coherent mechanism, it is demonstrated that the maximum Jsc can also be achieved under the ΔE of 0.2 eV if a large proportion of the high-lying delocalized states are harvested through tuning the density of states for the charge transfer excitons to reduce the sub-gap states. This theoretical work revealed quantitatively the relationship between the interfacial energy offsets and device performance, and also provides some guidelines for identifying the macroscopic features of the actual charge separation mechanisms in bulk heterojunction solar cells.
Collapse
Affiliation(s)
- Wenchao Yang
- Key Laboratory of Microelectronics and Energy of Henan, School of Physics and Electronic Engineering, Xinyang Normal University, Xinyang, 464000, China.
| | | | | | | | | |
Collapse
|
109
|
Prampolini G, Ingrosso F, Segalina A, Caramori S, Foggi P, Pastore M. Dynamical and Environmental Effects on the Optical Properties of an Heteroleptic Ru(II)–Polypyridine Complex: A Multilevel Approach Combining Accurate Ground and Excited State QM-Derived Force Fields, MD and TD-DFT. J Chem Theory Comput 2018; 15:529-545. [DOI: 10.1021/acs.jctc.8b01031] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Giacomo Prampolini
- Istituto di Chimica dei Composti OrganoMetallici (ICCOM-CNR), Area della Ricerca, via G. Moruzzi 1, I-56124 Pisa, Italy
| | - Francesca Ingrosso
- Université de Lorraine, CNRS, Laboratoire de Physique et Chimie Théoriques, F-54000 Nancy, France
| | - Alekos Segalina
- Université de Lorraine, CNRS, Laboratoire de Physique et Chimie Théoriques, F-54000 Nancy, France
| | - Stefano Caramori
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Ferrara, Via Luigi Borsari 46, I-44100, Ferrara, Italy
| | - Paolo Foggi
- European Laboratory for Non Linear Spectroscopy (LENS), Università di Firenze, Via Nello Carrara 1, I-50019 Sesto Fiorentino Florence, Italy
- INO−CNR, Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche, Largo Fermi 6, I-50125 Florence, Italy
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Via Elce di Sotto 8, I-06123 Perugia, Italy
| | - Mariachiara Pastore
- Université de Lorraine, CNRS, Laboratoire de Physique et Chimie Théoriques, F-54000 Nancy, France
| |
Collapse
|
110
|
Fujita T, Alam MK, Hoshi T. Thousand-atom ab initio calculations of excited states at organic/organic interfaces: toward first-principles investigations of charge photogeneration. Phys Chem Chem Phys 2018; 20:26443-26452. [PMID: 30306163 DOI: 10.1039/c8cp05574b] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Predicting electronically excited states across electron-donor/electron acceptor interfaces is essential for understanding the charge photogeneration process in organic solar cells. However, organic solar cells are large and disordered systems, and their excited states cannot be easily accessed by conventional quantum chemistry approaches. Moreover, a large number of excited states must be obtained to fully understand the charge separation mechanism. Recently, we have developed a novel fragment-based excited state method which can efficiently calculate a large number of states in molecular aggregates. In this article, we demonstrate the large-scale excited-state calculations by investigating interfacial charge transfer (ICT) states across the electron-donor/electron acceptor interfaces. As the model systems, we considered the face-on and edge-on configurations of pentacene/C60 bilayer heterojunction structures. These model structures contain approximately 1.8 × 105 atoms, and their local interface regions containing 2000 atoms were treated quantum mechanically, embedded in the electrostatic potentials from the remaining parts. Therefore, the charge delocalization effect, structural disorder, and the resulting heterogeneous electrostatic and polarizable environments were taken into account in the excited-state calculations. The computed energies of the low-lying ICT states are in reasonable agreement with experimental estimates. By comparing the edge-on and face-on configurations of the pentacene/C60 interfaces, we discuss the influence of interfacial morphologies on the energetics and charge delocalization of ICT states. In addition, we present the detailed characterization of excited states and highlight the importance of hybridization effects between pentacene excited states and ICT states. The large-scale ab initio calculations for the interface systems enabled the exploration of the ICT states, leading to first-principles investigation of the charge separation mechanism in organic solar cells.
Collapse
Affiliation(s)
- Takatoshi Fujita
- Institute for Molecular Science, Okazaki, Aichi 444-0865, Japan.
| | - Md Khorshed Alam
- Department of Physics, University of Barisal, Barisal-8200, Bangladesh
| | - Takeo Hoshi
- Department of Applied Mathmatics and Physics, Tottori University, Tottori 680-8550, Japan
| |
Collapse
|
111
|
A series of oxyfluoride chains containing asymmetric basic building units of both early- and late-transition metal cations. J SOLID STATE CHEM 2018. [DOI: 10.1016/j.jssc.2018.08.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
|
112
|
Häse F, Roch LM, Aspuru-Guzik A. Chimera: enabling hierarchy based multi-objective optimization for self-driving laboratories. Chem Sci 2018; 9:7642-7655. [PMID: 30393525 PMCID: PMC6182568 DOI: 10.1039/c8sc02239a] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2018] [Accepted: 08/04/2018] [Indexed: 12/23/2022] Open
Abstract
Finding the ideal conditions satisfying multiple pre-defined targets simultaneously is a challenging decision-making process, which impacts science, engineering, and economics. Additional complexity arises for tasks involving experimentation or expensive computations, as the number of evaluated conditions must be kept low. We propose Chimera as a general purpose achievement scalarizing function for multi-target optimization where evaluations are the limiting factor. Chimera combines concepts of a priori scalarizing with lexicographic approaches and is applicable to any set of n unknown objectives. Importantly, it does not require detailed prior knowledge about individual objectives. The performance of Chimera is demonstrated on several well-established analytic multi-objective benchmark sets using different single-objective optimization algorithms. We further illustrate the applicability and performance of Chimera with two practical examples: (i) the auto-calibration of a virtual robotic sampling sequence for direct-injection, and (ii) the inverse-design of a four-pigment excitonic system for an efficient energy transport. The results indicate that Chimera enables a wide class of optimization algorithms to rapidly find ideal conditions. Additionally, the presented applications highlight the interpretability of Chimera to corroborate design choices for tailoring system parameters.
Collapse
Affiliation(s)
- Florian Häse
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , Massachusetts 02138 , USA . ; Tel: +1-617-384-8188
| | - Loïc M Roch
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , Massachusetts 02138 , USA . ; Tel: +1-617-384-8188
| | - Alán Aspuru-Guzik
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , Massachusetts 02138 , USA . ; Tel: +1-617-384-8188
- Department of Chemistry and Department of Computer Science , University of Toronto , Toronto , Ontario M5S3H6 , Canada
- Vector Institute for Artificial Intelligence , Toronto , Ontario M5S1M1 , Canada
- Canadian Institute for Advanced Research (CIFAR) Senior Fellow , Toronto , Ontario M5S1M1 , Canada
| |
Collapse
|
113
|
Liu W, Canola S, Köhn A, Engels B, Negri F, Fink RF. A model hamiltonian tuned toward high level ab initio
calculations to describe the character of excitonic states in perylenebisimide aggregates. J Comput Chem 2018; 39:1979-1989. [DOI: 10.1002/jcc.25374] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2018] [Revised: 05/16/2018] [Accepted: 05/18/2018] [Indexed: 01/05/2023]
Affiliation(s)
- Wenlan Liu
- Chongqing Key Laboratory of Green Synthesis and Applications & College of Chemistry; Chongqing Normal University; Chongqing 401331 China
- Institute of Theoretical Chemistry; University of Stuttgart; Pfaffenwaldring 55, 70569 Stuttgart Germany
- Institute of Physical and Theoretical Chemistry, Auf der Morgenstelle 18; University of Tübingen; 72076 Tübingen Germany
| | - Sofia Canola
- Institute of Physical and Theoretical Chemistry, Auf der Morgenstelle 18; University of Tübingen; 72076 Tübingen Germany
- Universitá di Bologna Dipartimento di Chimica 'G. Ciamician'; Via F. Selmi 2, Bologna 40126 Italy
| | - Andreas Köhn
- Institute of Theoretical Chemistry; University of Stuttgart; Pfaffenwaldring 55, 70569 Stuttgart Germany
| | - Bernd Engels
- Institute of Physical and Theoretical Chemistry, Emil-Fischer-Str. 42; University of Würzburg; 97074 Würzburg Germany
| | - Fabrizia Negri
- Universitá di Bologna Dipartimento di Chimica 'G. Ciamician'; Via F. Selmi 2, Bologna 40126 Italy
| | - Reinhold F. Fink
- Institute of Physical and Theoretical Chemistry, Auf der Morgenstelle 18; University of Tübingen; 72076 Tübingen Germany
| |
Collapse
|
114
|
Qian D, Zheng Z, Yao H, Tress W, Hopper TR, Chen S, Li S, Liu J, Chen S, Zhang J, Liu XK, Gao B, Ouyang L, Jin Y, Pozina G, Buyanova IA, Chen WM, Inganäs O, Coropceanu V, Bredas JL, Yan H, Hou J, Zhang F, Bakulin AA, Gao F. Design rules for minimizing voltage losses in high-efficiency organic solar cells. NATURE MATERIALS 2018; 17:703-709. [PMID: 30013057 DOI: 10.1038/s41563-018-0128-z] [Citation(s) in RCA: 289] [Impact Index Per Article: 48.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Accepted: 06/08/2018] [Indexed: 06/08/2023]
Abstract
The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor-acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor-acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
Collapse
Affiliation(s)
- Deping Qian
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Zilong Zheng
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, USA
| | - Huifeng Yao
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
| | - Wolfgang Tress
- Laboratory of Photonics and Interfaces (LPI), Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Thomas R Hopper
- Department of Chemistry, Imperial College London, London, UK
| | - Shula Chen
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Sunsun Li
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
| | - Jing Liu
- Department of Chemistry and Energy Institute, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong
| | - Shangshang Chen
- Department of Chemistry and Energy Institute, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong
| | - Jiangbin Zhang
- Department of Chemistry, Imperial College London, London, UK
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Xiao-Ke Liu
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Bowei Gao
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
| | - Liangqi Ouyang
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Yingzhi Jin
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Galia Pozina
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Irina A Buyanova
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Weimin M Chen
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Olle Inganäs
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Veaceslav Coropceanu
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, USA.
| | - Jean-Luc Bredas
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA, USA
| | - He Yan
- Department of Chemistry and Energy Institute, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong
| | - Jianhui Hou
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
| | - Fengling Zhang
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
| | - Artem A Bakulin
- Department of Chemistry, Imperial College London, London, UK.
| | - Feng Gao
- Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden.
| |
Collapse
|
115
|
Wang JZ, Guo ZQ, Zhou JP, Lei YX. Plasmon-enhanced photocatalytic activity of Na 0.9Mg 0.45Ti 3.55O 8 loaded with noble metals directly observed with scanning Kelvin probe microscopy. NANOTECHNOLOGY 2018; 29:305709. [PMID: 29741495 DOI: 10.1088/1361-6528/aac34a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The noble metals Au, Ag and Pt were loaded onto Na0.9Mg0.45Ti3.55O8 (NMTO) using a chemical bath deposition method devised in our recent work for the first time. The composite photocatalysts exhibit more effective photodegradation of methylene blue, due to the Schottky barrier built between NMTO and noble metal. Hot electrons generated during localized surface plasmon processes in metal nanoparticles transfer to the semiconductor, manifesting as a depression of surface potential directly detectable by scanning Kelvin probe microscopy. The key factor responsible for the improved ability of semiconductor-based photocatalysts is charge separation. The most effective weight concentrations of Au, Ag and Pt loaded onto NMTO were found to be 5.00%, 12.6% and 5.55% respectively. NMTO loaded with noble metals shows good photostability and recyclability for the degradation of methylene blue. A possible mechanism for the photodegradation of methylene blue over NMTO loaded with noble metals is proposed. This work highlights the potential application of NMTO-based photocatalysts, and provides an effective method to detect localized surface plasmons.
Collapse
Affiliation(s)
- Jing-Zhou Wang
- School of Physics and Information Technology, Shaanxi Normal University, Xi'an 710119, People's Republic of China. Ordos Institute of Technology, Ordos 017000, People's Republic of China
| | | | | | | |
Collapse
|
116
|
Ziffer ME, Jo SB, Zhong H, Ye L, Liu H, Lin F, Zhang J, Li X, Ade HW, Jen AKY, Ginger DS. Long-Lived, Non-Geminate, Radiative Recombination of Photogenerated Charges in a Polymer/Small-Molecule Acceptor Photovoltaic Blend. J Am Chem Soc 2018; 140:9996-10008. [PMID: 30008210 DOI: 10.1021/jacs.8b05834] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Minimization of open-circuit-voltage ( VOC) loss is required to transcend the efficiency limitations on the performance of organic photovoltaics (OPV). We study charge recombination in an OPV blend comprising a polymer donor with a small molecule nonfullerene acceptor that exhibits both high photovoltaic internal quantum efficiency and relatively high external electroluminescence quantum efficiency. Notably, this donor/acceptor blend, consisting of the donor polymer commonly referred to as PCE10 with a pseudoplanar small molecule acceptor (referred to as FIDTT-2PDI) exhibits relatively bright delayed photoluminescence on the microsecond time scale beyond that observed in the neat material. We study the photoluminescence decay kinetics of the blend in detail and conclude that this long-lived photoluminescence arises from radiative nongeminate recombination of charge carriers, which we propose occurs via a donor/acceptor CT state located close in energy to the singlet state of the polymer donor. Additionally, crystallographic and spectroscopic studies point toward low subgap disorder, which could be beneficial for low radiative and nonradiative losses. These results provide an important demonstration of photoluminescence due to nongeminate charge recombination in an efficient OPV blend, a key step in identifying new OPV materials and materials-screening criteria if OPV is to approach the theoretical limits to efficiency.
Collapse
Affiliation(s)
- Mark E Ziffer
- Department of Chemistry , University of Washington , Seattle , Washington 98195-2120 , United States
| | - Sae Byeok Jo
- Department of Materials Science and Engineering , University of Washington , Seattle , Washington 98195-2120 , United States
| | - Hongliang Zhong
- Department of Materials Science and Engineering , University of Washington , Seattle , Washington 98195-2120 , United States.,School of Chemistry and Chemical Engineering , Shanghai Jiao Tong University , Shanghai 200240 , China
| | - Long Ye
- Department of Physics and Organic and Carbon Electronics Lab (ORaCEL) , North Carolina State University , Raleigh , North Carolina 27695 , United States
| | - Hongbin Liu
- Department of Chemistry , University of Washington , Seattle , Washington 98195-2120 , United States
| | - Francis Lin
- Department of Chemistry , University of Washington , Seattle , Washington 98195-2120 , United States
| | - Jie Zhang
- Department of Chemistry , University of Washington , Seattle , Washington 98195-2120 , United States.,Department of Biology and Chemistry and Department of Physics and Materials Science , City University of Hong Kong , Kowloon , Hong Kong
| | - Xiaosong Li
- Department of Chemistry , University of Washington , Seattle , Washington 98195-2120 , United States
| | - Harald W Ade
- Department of Physics and Organic and Carbon Electronics Lab (ORaCEL) , North Carolina State University , Raleigh , North Carolina 27695 , United States
| | - Alex K-Y Jen
- Department of Materials Science and Engineering , University of Washington , Seattle , Washington 98195-2120 , United States.,Department of Biology and Chemistry and Department of Physics and Materials Science , City University of Hong Kong , Kowloon , Hong Kong
| | - David S Ginger
- Department of Chemistry , University of Washington , Seattle , Washington 98195-2120 , United States
| |
Collapse
|
117
|
Kato A, Ishizaki A. Non-Markovian Quantum-Classical Ratchet for Ultrafast Long-Range Electron-Hole Separation in Condensed Phases. PHYSICAL REVIEW LETTERS 2018; 121:026001. [PMID: 30085757 DOI: 10.1103/physrevlett.121.026001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Indexed: 06/08/2023]
Abstract
In organic photovoltaic systems, a photogenerated molecular exciton in the donor domain dissociates into a hole and an electron at the donor-acceptor heterojunction, and subsequently separates into free charge carriers that can be extracted as photocurrents. The recombination of the once-separated electron and hole is a major loss mechanism in photovoltaic systems, which controls their performance. Hence, efficient photovoltaic systems need built-in ratchet mechanisms, namely, ultrafast charge separation and retarded charge recombination. In order to obtain insight into the internal working of the experimentally observed ultrafast long-range charge separation and protection against charge recombination, we theoretically investigate a potential ratchet mechanism arising from the combination of quantum delocalization and its destruction by performing numerically accurate quantum-dynamics calculations on a model system. We demonstrate that the non-Markovian effect originating from the slow polaron formation strongly suppresses the electron-transfer reaction back to the interfacial charge-transfer state stabilized at the donor-accepter interface and that it plays a critical role in maintaining the long-range electron-hole separation.
Collapse
Affiliation(s)
- Akihito Kato
- Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585, Japan
| | - Akihito Ishizaki
- Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585, Japan
- School of Physical Sciences, The Graduate University for Advanced Studies, Okazaki 444-8585, Japan
| |
Collapse
|
118
|
Sarkar R, Habib M, Pal S, Prezhdo OV. Ultrafast, asymmetric charge transfer and slow charge recombination in porphyrin/CNT composites demonstrated by time-domain atomistic simulation. NANOSCALE 2018; 10:12683-12694. [PMID: 29946626 DOI: 10.1039/c8nr02544d] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The versatile photochemical properties of porphyrin molecules make them excellent candidates for solar energy applications. Carbon nanotubes (CNTs) exhibit superior charge conductivity and have been combined with porphyrins to achieve efficient and ultrafast charge separation. Experiments show that the charge separated state lives less than 10 ps, which is too short for applications. Using real-time time-dependent tight binding density functional theory (DFTB) combined with non-adiabatic molecular dynamics (NAMD), we model photo-induced charge separation and recombination in two porphyrin/CNT composites. Having achieved excellent agreement with the experiment for the electron transfer from the porphyrins to the CNT, we demonstrate that hole transfer can be achieved upon CNT excitation, although in a less efficient way. By exciting the CNT one can extend light harvesting into lower energies of the solar spectrum and increase solar light conversion efficiency. We also show that the charge separated state can live over 1 ns. The two orders of magnitude difference from the experimental lifetime could arise due to the presence of defects or metallic tubes in the samples. The charge separated state is long-lived because the non-adiabatic electron-phonon coupling is very small, less than 1 meV, and the quantum coherence is short, 15-20 fs. The excited states in the isolated porphyrins and CNT live around 100 ps, in agreement with experiments as well. The porphyrin/CNT interaction occurs through the π-electron systems of the two species. The non-radiative relaxation is promoted by both high and low frequency phonons, with higher frequency phonons playing more important roles in electron relaxation than in hole relaxation. Low frequency phonons contribute significantly to the decay of the charge separated state, because they modulate the relative positions of the porphyrins and the CNT. The time-domain atomistic simulations provide a detailed understanding of the charge separation and recombination mechanisms, and generate valuable guidelines for the optimization of photovoltaic efficiency in modern nanoscale materials.
Collapse
Affiliation(s)
- Ritabrata Sarkar
- Department of Chemistry, University of Gour Banga, Malda, 732103, India.
| | | | | | | |
Collapse
|
119
|
Gautam B, Klump E, Yi X, Constantinou I, Shewmon N, Salehi A, Lo CK, Zheng Z, Brédas JL, Gundogdu K, Reynolds JR, So F. Increased Exciton Delocalization of Polymer upon Blending with Fullerene. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1801392. [PMID: 29893011 DOI: 10.1002/adma.201801392] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 05/02/2018] [Indexed: 06/08/2023]
Abstract
Interfaces between donor and acceptor in a polymer solar cell play a crucial role in exciton dissociation and charge photogeneration. While the importance of charge transfer (CT) excitons for free carrier generation is intensively studied, the effect of blending on the nature of the polymer excitons in relation to the blend nanomorphology remains largely unexplored. In this work, electroabsorption (EA) spectroscopy is used to study the excited-state polarizability of polymer excitons in several polymer:fullerene blend systems, and it is found that excited-state polarizability of polymer excitons in the blends is a strong function of blend nanomorphology. The increase in excited-state polarizability with decreased domain size indicates that intermixing of states at the interface between the donor polymers and fullerene increases the exciton delocalization, resulting in an increase in exciton dissociation efficiency. This conclusion is further supported by transient absorption spectroscopy and time-resolved photoluminescence measurements, along with the results from time-dependent density functional theory calculations. These findings indicate that polymer excited-state polarizability is a key parameter for efficient free carrier generation and should be considered in the design and development of high-performance polymer solar cells.
Collapse
Affiliation(s)
- Bhoj Gautam
- Department of Physics, North Carolina State University, Raleigh, NC, 27695, USA
| | - Erik Klump
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Xueping Yi
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Iordania Constantinou
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Nathan Shewmon
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| | - Amin Salehi
- Department of Physics, North Carolina State University, Raleigh, NC, 27695, USA
| | - Chi Kin Lo
- School of Chemistry and Biochemistry, Center for Organic Photonics and Electronics, Georgia Tech Polymer Network, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Zilong Zheng
- School of Chemistry and Biochemistry, Center for Organic Photonics and Electronics, Georgia Tech Polymer Network, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Jean-Luc Brédas
- School of Chemistry and Biochemistry, Center for Organic Photonics and Electronics, Georgia Tech Polymer Network, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Kenan Gundogdu
- Department of Physics, North Carolina State University, Raleigh, NC, 27695, USA
| | - John R Reynolds
- School of Chemistry and Biochemistry, Center for Organic Photonics and Electronics, Georgia Tech Polymer Network, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Franky So
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27695, USA
| |
Collapse
|
120
|
Lee H, Park C, Sin DH, Park JH, Cho K. Recent Advances in Morphology Optimization for Organic Photovoltaics. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1800453. [PMID: 29921007 DOI: 10.1002/adma.201800453] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2018] [Revised: 03/12/2018] [Indexed: 06/08/2023]
Abstract
Organic photovoltaics are an important part of a next-generation energy-harvesting technology that uses a practically infinite pollutant-free energy source. They have the advantages of light weight, solution processability, cheap materials, low production cost, and deformability. However, to date, the moderate photovoltaic efficiencies and poor stabilities of organic photovoltaics impede their use as replacements for inorganic photovoltaics. Recent developments in bulk-heterojunction organic photovoltaics mean that they have almost reached the lower efficiency limit for feasible commercialization. In this review article, the recent understanding of the ideal bulk-heterojunction morphology of the photoactive layer for efficient exciton dissociation and charge transport is described, and recent attempts as well as early-stage trials to realize this ideal morphology are discussed systematically from a morphological viewpoint. The various approaches to optimizing morphologies consisting of an interpenetrating bicontinuous network with appropriate domain sizes and mixed regions are categorized, and in each category, the recent trends in the morphology control on the multilength scale are highlighted and discussed in detail. This review article concludes by identifying the remaining challenges for the control of active layer morphologies and by providing perspectives toward real application and commercialization of organic photovoltaics.
Collapse
Affiliation(s)
- Hansol Lee
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 37673, South Korea
| | - Chaneui Park
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 37673, South Korea
| | - Dong Hun Sin
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 37673, South Korea
| | - Jong Hwan Park
- Nano Hybrid Technology Research Center, Creative and Fundamental Research Division, Korea Electrotechnology Research Institute (KERI), Changwon, 51543, South Korea
| | - Kilwon Cho
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 37673, South Korea
| |
Collapse
|
121
|
Ahmed B, Jo H, Oh SJ, Ok KM. Variable Asymmetric Chains in Transition Metal Oxyfluorides: Structure-Second-Harmonic-Generation Property Relationships. Inorg Chem 2018; 57:6702-6709. [PMID: 29763308 DOI: 10.1021/acs.inorgchem.8b00903] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Four novel transition metal oxyfluorides, [Zn(pz)3][MoO2F4]·0.1H2O (1), [Zn(pz)2F2][Zn(pz)3]2[WO2F4]2 (2), [Cd(pz)4][Cd(pz)4(H2O)][MoO2F4]2·0.625H2O (3), and [Zn(mpz)3]2[MoO2F4]2 (4) (pz = pyrazole; mpz = 3-methyl pyrazole) have been synthesized. Compounds 1 and 4 contain helical chains. Compound 2 accommodates zigzag chains, and compound 3 has quasi-one-dimensional linear chains. The variable chain structures are found to be attributable to the different structure-directing anionic groups and hydrogen bonding interactions. Compound 4 crystallized in the noncentrosymmetric (NCS) polar space group, Pna21, is nonphase-matchable (Type I), and reveals a moderate second-harmonic-generation (SHG) efficiency (10 × α-SiO2). The observed SHG efficiency of compound 4 is due to the small net polarization occurring from the arrangement of ZnN3F2 trigonal bipyramids. Spectroscopic and thermal characterizations along with calculations for the title materials are reported.
Collapse
Affiliation(s)
- Belal Ahmed
- Department of Chemistry , Chung-Ang University , 84 Heukseok-ro, Dongjak-gu , Seoul 06974 , Republic of Korea
| | - Hongil Jo
- Department of Chemistry , Chung-Ang University , 84 Heukseok-ro, Dongjak-gu , Seoul 06974 , Republic of Korea
| | - Seung-Jin Oh
- Department of Chemistry , Chung-Ang University , 84 Heukseok-ro, Dongjak-gu , Seoul 06974 , Republic of Korea
| | - Kang Min Ok
- Department of Chemistry , Chung-Ang University , 84 Heukseok-ro, Dongjak-gu , Seoul 06974 , Republic of Korea
| |
Collapse
|
122
|
Zhong C, Sangwan VK, Wang C, Bergeron H, Hersam MC, Weiss EA. Mechanisms of Ultrafast Charge Separation in a PTB7/Monolayer MoS 2 van der Waals Heterojunction. J Phys Chem Lett 2018; 9:2484-2491. [PMID: 29688016 DOI: 10.1021/acs.jpclett.8b00628] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Mixed-dimensional van der Waals heterojunctions comprising polymer and two-dimensional (2D) semiconductors have many characteristics of an ideal charge separation interface for optoelectronic and photonic applications. However, the photoelectron dynamics at polymer-2D semiconductor heterojunction interfaces are currently not sufficiently understood to guide the optimization of devices for these applications. This Letter reports a systematic exploration of the time-dependent photophysical processes that occur upon photoexcitation of a type-II heterojunction between the polymer PTB7 and monolayer MoS2. In particular, photoinduced electron transfer from PTB7 to electronically hot states of MoS2 occurs in less than 250 fs. This process is followed by a 1-5 ps exciton diffusion-limited electron transfer from PTB7 to MoS2 and a sub-3 ps photoinduced hole transfer from MoS2 to PTB7. The equilibrium between excitons and polaron pairs in PTB7 determines the charge separation yield, whereas the 3-4 ns lifetime of photogenerated carriers is probably limited by MoS2 defects.
Collapse
Affiliation(s)
- Chengmei Zhong
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208-3113 , United States
- Department of Materials Science and Engineering , Northwestern University , Evanston , Illinois 60208-3108 , United States
| | - Vinod K Sangwan
- Department of Materials Science and Engineering , Northwestern University , Evanston , Illinois 60208-3108 , United States
| | - Chen Wang
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208-3113 , United States
| | - Hadallia Bergeron
- Department of Materials Science and Engineering , Northwestern University , Evanston , Illinois 60208-3108 , United States
| | - Mark C Hersam
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208-3113 , United States
- Department of Materials Science and Engineering , Northwestern University , Evanston , Illinois 60208-3108 , United States
- Department of Electrical Engineering and Computer Science , Northwestern University , Evanston , Illinois 60208-3108 , United States
| | - Emily A Weiss
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208-3113 , United States
- Department of Materials Science and Engineering , Northwestern University , Evanston , Illinois 60208-3108 , United States
| |
Collapse
|
123
|
Jang H, Dhakal KP, Joo KI, Yun WS, Shinde SM, Chen X, Jeong SM, Lee SW, Lee Z, Lee J, Ahn JH, Kim H. Transient SHG Imaging on Ultrafast Carrier Dynamics of MoS 2 Nanosheets. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1705190. [PMID: 29436068 DOI: 10.1002/adma.201705190] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2017] [Revised: 12/10/2017] [Indexed: 05/17/2023]
Abstract
Understanding the collaborative behaviors of the excitons and phonons that result from light-matter interactions is important for interpreting and optimizing the underlying fundamental physics at work in devices made from atomically thin materials. In this study, the generation of exciton-coupled phonon vibration from molybdenum disulfide (MoS2 ) nanosheets in a pre-excitonic resonance condition is reported. A strong rise-to-decay profile for the transient second-harmonic generation (TSHG) of the probe pulse is achieved by applying substantial (20%) beam polarization normal to the nanosheet plane, and tuning the wavelength of the pump beam to the absorption of the A-exciton. The time-dependent TSHG signals clearly exhibit acoustic phonon generation at vibration modes below 10 cm-1 (close to the Γ point) after the photoinduced energy is transferred from exciton to phonon in a nonradiative fashion. Interestingly, by observing the TSHG signal oscillation period from MoS2 samples of varying thicknesses, the speed of the supersonic waves generated in the out-of-plane direction (Mach 8.6) is generated. Additionally, TSHG microscopy reveals critical information about the phase and amplitude of the acoustic phonons from different edge chiralities (armchair and zigzag) of the MoS2 monolayers. This suggests that the technique could be used more broadly to study ultrafast physics and chemistry in low-dimensional materials and their hybrids with ultrahigh fidelity.
Collapse
Affiliation(s)
- Houk Jang
- School of Electrical and Electronic Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Krishna P Dhakal
- School of Electrical and Electronic Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Kyung-Il Joo
- School of Electronics and Engineering, Kyungpook National University, Daegu, 41566, Republic of Korea
| | - Won Seok Yun
- Department of Emerging Materials Science, DGIST, Daegu, 42988, Republic of Korea
| | - Sachin M Shinde
- School of Electrical and Electronic Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Xiang Chen
- School of Electrical and Electronic Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Soon Moon Jeong
- Smart Textile Convergence Research Group, DGIST, Daegu, 42988, Republic of Korea
| | - Suk Woo Lee
- School of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Zonghoon Lee
- School of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - JaeDong Lee
- Department of Emerging Materials Science, DGIST, Daegu, 42988, Republic of Korea
| | - Jong-Hyun Ahn
- School of Electrical and Electronic Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Hyunmin Kim
- Companion Diagnostics and Medical Technology Research Group, DGIST, Daegu, 42988, Republic of Korea
| |
Collapse
|
124
|
Tan S, Dai Y, Zhang S, Liu L, Zhao J, Petek H. Coherent Electron Transfer at the Ag/Graphite Heterojunction Interface. PHYSICAL REVIEW LETTERS 2018; 120:126801. [PMID: 29694071 DOI: 10.1103/physrevlett.120.126801] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2017] [Indexed: 06/08/2023]
Abstract
Charge transfer in transduction of light to electrical or chemical energy at heterojunctions of metals with semiconductors or semimetals is believed to occur by photogenerated hot electrons in metal undergoing incoherent internal photoemission through the heterojunction interface. Charge transfer, however, can also occur coherently by dipole coupling of electronic bands at the heterojunction interface. Microscopic physical insights into how transfer occurs can be elucidated by following the coherent polarization of the donor and acceptor states on the time scale of electronic dephasing. By time-resolved multiphoton photoemission spectroscopy (MPP), we investigate the coherent electron transfer from an interface state that forms upon chemisorption of Ag nanoclusters onto graphite to a σ symmetry interlayer band of graphite. Multidimensional MPP spectroscopy reveals a resonant two-photon transition, which dephases within 10 fs completing the coherent transfer.
Collapse
Affiliation(s)
- Shijing Tan
- Department of Physics and Astronomy and Pittsburgh Quantum Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
- Hefei National Laboratory for Physical Sciences at the Microscale, and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yanan Dai
- Department of Physics and Astronomy and Pittsburgh Quantum Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
| | - Shengmin Zhang
- Department of Physics and Astronomy and Pittsburgh Quantum Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
| | - Liming Liu
- ICQD/Hefei National Laboratory for Physical Sciences at the Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jin Zhao
- Department of Physics and Astronomy and Pittsburgh Quantum Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
- ICQD/Hefei National Laboratory for Physical Sciences at the Microscale, and Key Laboratory of Strongly-Coupled Quantum Matter Physics, Chinese Academy of Sciences, and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Hrvoje Petek
- Department of Physics and Astronomy and Pittsburgh Quantum Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
| |
Collapse
|
125
|
Zhang G, Zhao J, Chow PCY, Jiang K, Zhang J, Zhu Z, Zhang J, Huang F, Yan H. Nonfullerene Acceptor Molecules for Bulk Heterojunction Organic Solar Cells. Chem Rev 2018; 118:3447-3507. [PMID: 29557657 DOI: 10.1021/acs.chemrev.7b00535] [Citation(s) in RCA: 586] [Impact Index Per Article: 97.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The bulk-heterojunction blend of an electron donor and an electron acceptor material is the key component in a solution-processed organic photovoltaic device. In the past decades, a p-type conjugated polymer and an n-type fullerene derivative have been the most commonly used electron donor and electron acceptor, respectively. While most advances of the device performance come from the design of new polymer donors, fullerene derivatives have almost been exclusively used as electron acceptors in organic photovoltaics. Recently, nonfullerene acceptor materials, particularly small molecules and oligomers, have emerged as a promising alternative to replace fullerene derivatives. Compared to fullerenes, these new acceptors are generally synthesized from diversified, low-cost routes based on building block materials with extraordinary chemical, thermal, and photostability. The facile functionalization of these molecules affords excellent tunability to their optoelectronic and electrochemical properties. Within the past five years, there have been over 100 nonfullerene acceptor molecules synthesized, and the power conversion efficiency of nonfullerene organic solar cells has increased dramatically, from ∼2% in 2012 to >13% in 2017. This review summarizes this progress, aiming to describe the molecular design strategy, to provide insight into the structure-property relationship, and to highlight the challenges the field is facing, with emphasis placed on most recent nonfullerene acceptors that demonstrated top-of-the-line photovoltaic performances. We also provide perspectives from a device point of view, wherein topics including ternary blend device, multijunction device, device stability, active layer morphology, and device physics are discussed.
Collapse
Affiliation(s)
- Guangye Zhang
- Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration & Reconstruction , Hong Kong University of Science and Technology (HKUST) , Clear Water Bay , Kowloon, Hong Kong , China.,HKUST-Shenzhen Research Institute , No. 9 Yuexing first RD, Hi-tech Park , Nanshan, Shenzhen 518057 , China
| | - Jingbo Zhao
- Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration & Reconstruction , Hong Kong University of Science and Technology (HKUST) , Clear Water Bay , Kowloon, Hong Kong , China
| | - Philip C Y Chow
- Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration & Reconstruction , Hong Kong University of Science and Technology (HKUST) , Clear Water Bay , Kowloon, Hong Kong , China.,HKUST-Shenzhen Research Institute , No. 9 Yuexing first RD, Hi-tech Park , Nanshan, Shenzhen 518057 , China
| | - Kui Jiang
- Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration & Reconstruction , Hong Kong University of Science and Technology (HKUST) , Clear Water Bay , Kowloon, Hong Kong , China.,HKUST-Shenzhen Research Institute , No. 9 Yuexing first RD, Hi-tech Park , Nanshan, Shenzhen 518057 , China
| | - Jianquan Zhang
- Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration & Reconstruction , Hong Kong University of Science and Technology (HKUST) , Clear Water Bay , Kowloon, Hong Kong , China.,HKUST-Shenzhen Research Institute , No. 9 Yuexing first RD, Hi-tech Park , Nanshan, Shenzhen 518057 , China
| | - Zonglong Zhu
- Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration & Reconstruction , Hong Kong University of Science and Technology (HKUST) , Clear Water Bay , Kowloon, Hong Kong , China
| | - Jie Zhang
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices , South China University of Technology , Guangzhou 510640 , P. R. China
| | - Fei Huang
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices , South China University of Technology , Guangzhou 510640 , P. R. China
| | - He Yan
- Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration & Reconstruction , Hong Kong University of Science and Technology (HKUST) , Clear Water Bay , Kowloon, Hong Kong , China.,HKUST-Shenzhen Research Institute , No. 9 Yuexing first RD, Hi-tech Park , Nanshan, Shenzhen 518057 , China.,Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices , South China University of Technology , Guangzhou 510640 , P. R. China
| |
Collapse
|
126
|
Yan Y, Song L, Shi Q. Understanding the free energy barrier and multiple timescale dynamics of charge separation in organic photovoltaic cells. J Chem Phys 2018; 148:084109. [DOI: 10.1063/1.5017866] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Affiliation(s)
- Yaming Yan
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190, China and University of Chinese Academy of Sciences, Beijing 100049, China
| | - Linze Song
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190, China and University of Chinese Academy of Sciences, Beijing 100049, China
| | - Qiang Shi
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190, China and University of Chinese Academy of Sciences, Beijing 100049, China
| |
Collapse
|
127
|
Mandal A, Yamijala SSRKC, Huo P. Quasi-Diabatic Representation for Nonadiabatic Dynamics Propagation. J Chem Theory Comput 2018; 14:1828-1840. [DOI: 10.1021/acs.jctc.7b01178] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Arkajit Mandal
- Department of Chemistry, University of Rochester, 120 Trustee Road, Rochester, New York 14627, United States
| | - Sharma SRKC Yamijala
- Department of Chemistry, University of Rochester, 120 Trustee Road, Rochester, New York 14627, United States
| | - Pengfei Huo
- Department of Chemistry, University of Rochester, 120 Trustee Road, Rochester, New York 14627, United States
| |
Collapse
|
128
|
Sun J, Li X, Yang J. The roles of buckled geometry and water environment in the excitonic properties of graphitic C 3N 4. NANOSCALE 2018; 10:3738-3743. [PMID: 29411812 DOI: 10.1039/c7nr08541a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The exciton plays a crucial role in two-dimensional materials involved in photocatalytic water splitting, where its properties are determined not only by the material itself, but also by the surrounding water environment. By the framework of many-body perturbation theory, we investigated the excitonic effects in pure and water-adsorbed g-C3N4. It is shown that the excitonic properties are very sensitive to the geometry of g-C3N4 and the adsorption of water molecules. Firstly, the optical band gap, i.e. the first bright excitonic energy of pure g-C3N4 decreases remarkably from a high symmetry planar structure (3.8 eV) to a P1 buckled configuration (2.7 eV). Secondly, the hydrogen bonds between water and g-C3N4 induce the generation of interface excitons. With a reduced binding energy (at least 0.2 eV), interface excitons can contribute to a more efficient separation of electrons and holes. Our work provides an insight into the excitation mechanism of 2D photocatalysts in a real environment.
Collapse
Affiliation(s)
- Jiuyu Sun
- Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
| | | | | |
Collapse
|
129
|
Boström EV, Mikkelsen A, Verdozzi C, Perfetto E, Stefanucci G. Charge Separation in Donor-C 60 Complexes with Real-Time Green Functions: The Importance of Nonlocal Correlations. NANO LETTERS 2018; 18:785-792. [PMID: 29266952 DOI: 10.1021/acs.nanolett.7b03995] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We use the nonequilibrium Green function (NEGF) method to perform real-time simulations of the ultrafast electron dynamics of photoexcited donor-C60 complexes modeled by a Pariser-Parr-Pople Hamiltonian. The NEGF results are compared to mean-field Hartree-Fock (HF) calculations to disentangle the role of correlations. Initial benchmarking against numerically highly accurate time-dependent density matrix renormalization group calculations verifies the accuracy of NEGF. We then find that charge-transfer (CT) excitons partially decay into charge separated (CS) states if dynamical nonlocal correlation corrections are included. This CS process occurs in ∼10 fs after photoexcitation. In contrast, the probability of exciton recombination is almost 100% in HF simulations. These results are largely unaffected by nuclear vibrations; the latter become however essential whenever level misalignment hinders the CT process. The robust nature of our findings indicates that ultrafast CS driven by correlation-induced decoherence may occur in many organic nanoscale systems, but it will only be correctly predicted by theoretical treatments that include time-nonlocal correlations.
Collapse
Affiliation(s)
- Emil Viñas Boström
- Lund University , Department of Physics and European Theoretical Spectroscopy Facility (ETSF), P.O. Box 118, 221 00 Lund, Sweden
| | - Anders Mikkelsen
- Lund University , Department of Physics and NanoLund, P.O. Box 118, 221 00 Lund, Sweden
| | - Claudio Verdozzi
- Lund University , Department of Physics and European Theoretical Spectroscopy Facility (ETSF), P.O. Box 118, 221 00 Lund, Sweden
| | - Enrico Perfetto
- CNR-ISM , Division of Ultrafast Processes in Materials (FLASHit), Area della Ricerca di Roma 1, Via Salaria Km 29.3, I-00016 Monterotondo Scalo, Italy
- Dipartimento di Fisica and European Theoretical Spectroscopy Facility (ETSF), Università di Roma Tor Vergata , Via della Ricerca Scientifica 1, 00133 Rome, Italy
| | - Gianluca Stefanucci
- Dipartimento di Fisica and European Theoretical Spectroscopy Facility (ETSF), Università di Roma Tor Vergata , Via della Ricerca Scientifica 1, 00133 Rome, Italy
- INFN, Sezione di Roma Tor Vergata , Via della Ricerca Scientifica 1, 00133 Rome, Italy
| |
Collapse
|
130
|
Hou J, Inganäs O, Friend RH, Gao F. Organic solar cells based on non-fullerene acceptors. NATURE MATERIALS 2018; 17:119-128. [PMID: 29358765 DOI: 10.1038/nmat5063] [Citation(s) in RCA: 879] [Impact Index Per Article: 146.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Accepted: 12/06/2017] [Indexed: 05/19/2023]
Abstract
Organic solar cells (OSCs) have been dominated by donor:acceptor blends based on fullerene acceptors for over two decades. This situation has changed recently, with non-fullerene (NF) OSCs developing very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 13%, which is higher than the best fullerene-based OSCs. NF acceptors show great tunability in absorption spectra and electron energy levels, providing a wide range of new opportunities. The coexistence of low voltage losses and high current generation indicates that new regimes of device physics and photophysics are reached in these systems. This Review highlights these opportunities made possible by NF acceptors, and also discuss the challenges facing the development of NF OSCs for practical applications.
Collapse
Affiliation(s)
- Jianhui Hou
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Olle Inganäs
- Biomolecular and organic electronics, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping SE-58183, Sweden
| | | | - Feng Gao
- Biomolecular and organic electronics, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping SE-58183, Sweden
| |
Collapse
|
131
|
Order enables efficient electron-hole separation at an organic heterojunction with a small energy loss. Nat Commun 2018; 9:277. [PMID: 29348491 PMCID: PMC5773693 DOI: 10.1038/s41467-017-02457-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 12/03/2017] [Indexed: 11/08/2022] Open
Abstract
Donor-acceptor organic solar cells often show low open-circuit voltages (V OC) relative to their optical energy gap (E g) that limit power conversion efficiencies to ~12%. This energy loss is partly attributed to the offset between E g and that of intermolecular charge transfer (CT) states at the donor-acceptor interface. Here we study charge generation occurring in PIPCP:PC61BM, a system with a very low driving energy for initial charge separation (E g-E CT ~ 50 meV) and a high internal quantum efficiency (η IQE ~ 80%). We track the strength of the electric field generated between the separating electron-hole pair by following the transient electroabsorption optical response, and find that while localised CT states are formed rapidly (<100 fs) after photoexcitation, free charges are not generated until 5 ps after photogeneration. In PIPCP:PC61BM, electronic disorder is low (Urbach energy <27 meV) and we consider that free charge separation is able to outcompete trap-assisted non-radiative recombination of the CT state.
Collapse
|
132
|
Rozzi CA, Troiani F, Tavernelli I. Quantum modeling of ultrafast photoinduced charge separation. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:013002. [PMID: 29047450 DOI: 10.1088/1361-648x/aa948a] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Phenomena involving electron transfer are ubiquitous in nature, photosynthesis and enzymes or protein activity being prominent examples. Their deep understanding thus represents a mandatory scientific goal. Moreover, controlling the separation of photogenerated charges is a crucial prerequisite in many applicative contexts, including quantum electronics, photo-electrochemical water splitting, photocatalytic dye degradation, and energy conversion. In particular, photoinduced charge separation is the pivotal step driving the storage of sun light into electrical or chemical energy. If properly mastered, these processes may also allow us to achieve a better command of information storage at the nanoscale, as required for the development of molecular electronics, optical switching, or quantum technologies, amongst others. In this Topical Review we survey recent progress in the understanding of ultrafast charge separation from photoexcited states. We report the state-of-the-art of the observation and theoretical description of charge separation phenomena in the ultrafast regime mainly focusing on molecular- and nano-sized solar energy conversion systems. In particular, we examine different proposed mechanisms driving ultrafast charge dynamics, with particular regard to the role of quantum coherence and electron-nuclear coupling, and link experimental observations to theoretical approaches based either on model Hamiltonians or on first principles simulations.
Collapse
|
133
|
Sosorev AY, Godovsky DY, Paraschuk DY. Hot kinetic model as a guide to improve organic photovoltaic materials. Phys Chem Chem Phys 2018; 20:3658-3671. [DOI: 10.1039/c7cp06158g] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The model yields that the most promising ways to increase the OSC performance are decreasing the reorganization energy, increasing the dielectric permittivity and enhancing the charge delocalization.
Collapse
Affiliation(s)
- Andrey Yu. Sosorev
- Faculty of Physics and International Laser Center
- M.V. Lomonosov Moscow State University
- Moscow 119991
- Russia
| | - Dmitry Yu. Godovsky
- Institute of Elementoorganic Compounds
- Russian Academy of Science
- Moscow
- Russia
| | - Dmitry Yu. Paraschuk
- Faculty of Physics and International Laser Center
- M.V. Lomonosov Moscow State University
- Moscow 119991
- Russia
- Enikolopov Institute of Synthetic Polymeric Materials
| |
Collapse
|
134
|
Kan B, Zhang J, Liu F, Wan X, Li C, Ke X, Wang Y, Feng H, Zhang Y, Long G, Friend RH, Bakulin AA, Chen Y. Fine-Tuning the Energy Levels of a Nonfullerene Small-Molecule Acceptor to Achieve a High Short-Circuit Current and a Power Conversion Efficiency over 12% in Organic Solar Cells. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:1704904. [PMID: 29205535 DOI: 10.1002/adma.201704904] [Citation(s) in RCA: 78] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2017] [Revised: 10/23/2017] [Indexed: 05/20/2023]
Abstract
Organic solar cell optimization requires careful balancing of current-voltage output of the materials system. Here, such optimization using ultrafast spectroscopy as a tool to optimize the material bandgap without altering ultrafast photophysics is reported. A new acceptor-donor-acceptor (A-D-A)-type small-molecule acceptor NCBDT is designed by modification of the D and A units of NFBDT. Compared to NFBDT, NCBDT exhibits upshifted highest occupied molecular orbital (HOMO) energy level mainly due to the additional octyl on the D unit and downshifted lowest unoccupied molecular orbital (LUMO) energy level due to the fluorination of A units. NCBDT has a low optical bandgap of 1.45 eV which extends the absorption range toward near-IR region, down to ≈860 nm. However, the 60 meV lowered LUMO level of NCBDT hardly changes the Voc level, and the elevation of the NCBDT HOMO does not have a substantial influence on the photophysics of the materials. Thus, for both NCBDT- and NFBDT-based systems, an unusually slow (≈400 ps) but ultimately efficient charge generation mediated by interfacial charge-pair states is observed, followed by effective charge extraction. As a result, the PBDB-T:NCBDT devices demonstrate an impressive power conversion efficiency over 12%-among the best for solution-processed organic solar cells.
Collapse
Affiliation(s)
- Bin Kan
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Jiangbin Zhang
- Department of Chemistry, Imperial College London, London, SW7 2AZ, UK
- Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge, CB3 0HE, UK
| | - Feng Liu
- Department of Physics and Astronomy, Shanghai Jiaotong University, Shanghai, 200240, China
| | - Xiangjian Wan
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Chenxi Li
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Xin Ke
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Yunchuang Wang
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Huanran Feng
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Yamin Zhang
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Guankui Long
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| | - Richard H Friend
- Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge, CB3 0HE, UK
| | - Artem A Bakulin
- Department of Chemistry, Imperial College London, London, SW7 2AZ, UK
| | - Yongsheng Chen
- State Key Laboratory and Institute of Elemento-Organic Chemistry, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
| |
Collapse
|
135
|
Shimazaki T, Tashiro M, Nakajima T. Theoretical study on mesoscopic-size impurity effects in the charge separation process of organic photocells. Phys Chem Chem Phys 2018; 20:14846-14854. [DOI: 10.1039/c7cp08125a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A bulk-heterojunction structure is often employed to develop high-performance organic photocells, in which the donor and acceptor regions are complexly intertwined.
Collapse
Affiliation(s)
- Tomomi Shimazaki
- Kobe University
- Graduate School of System Informatics
- Kobe 657-8501
- Japan
- RIKEN
| | | | | |
Collapse
|
136
|
Zhu T, Yuan L, Zhao Y, Zhou M, Wan Y, Mei J, Huang L. Highly mobile charge-transfer excitons in two-dimensional WS 2/tetracene heterostructures. SCIENCE ADVANCES 2018; 4:eaao3104. [PMID: 29340303 PMCID: PMC5766329 DOI: 10.1126/sciadv.aao3104] [Citation(s) in RCA: 93] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 12/01/2017] [Indexed: 05/22/2023]
Abstract
Charge-transfer (CT) excitons at heterointerfaces play a critical role in light to electricity conversion using organic and nanostructured materials. However, how CT excitons migrate at these interfaces is poorly understood. We investigate the formation and transport of CT excitons in two-dimensional WS2/tetracene van der Waals heterostructures. Electron and hole transfer occurs on the time scale of a few picoseconds, and emission of interlayer CT excitons with a binding energy of ~0.3 eV has been observed. Transport of the CT excitons is directly measured by transient absorption microscopy, revealing coexistence of delocalized and localized states. Trapping-detrapping dynamics between the delocalized and localized states leads to stretched-exponential photoluminescence decay with an average lifetime of ~2 ns. The delocalized CT excitons are remarkably mobile with a diffusion constant of ~1 cm2 s-1. These highly mobile CT excitons could have important implications in achieving efficient charge separation.
Collapse
|
137
|
Shi L, Lee CK, Willard AP. The Enhancement of Interfacial Exciton Dissociation by Energetic Disorder Is a Nonequilibrium Effect. ACS CENTRAL SCIENCE 2017; 3:1262-1270. [PMID: 29296666 PMCID: PMC5746863 DOI: 10.1021/acscentsci.7b00404] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Indexed: 05/29/2023]
Abstract
The dissociation of excited electron-hole pairs is a microscopic process that is fundamental to the performance of photovoltaic systems. For this process to be successful, the oppositely charged electron and hole must overcome an electrostatic binding energy before they undergo ground state recombination. It has been observed previously that the presence of energetic disorder can lead to a reduction in recombination losses. Here we investigate this effect using a simple model of charge dynamics at a donor-acceptor interface. We consider the effect of spatial variations in electronic energy levels, such as those that arise in disordered molecular systems, on dissociation yield and demonstrate that it is maximized with a finite amount of disorder. We demonstrate that this is a nonequilibrium effect that is mediated by the dissipation driven formation of partially dissociated intermediate states that are long-lived because they cannot easily recombine. We present a kinetic model that incorporates these states and show that it is capable of reproducing similar behavior when it is parametrized with nonequilibrium rates.
Collapse
Affiliation(s)
- Liang Shi
- Chemistry and Chemical Biology, University of California, Merced, California 95343, United States
| | - Chee Kong Lee
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Adam P Willard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| |
Collapse
|
138
|
Miao G, Dou W, Subotnik J. Vibrational relaxation at a metal surface: Electronic friction versus classical master equations. J Chem Phys 2017; 147:224105. [DOI: 10.1063/1.5000237] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Gaohan Miao
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Wenjie Dou
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Joseph Subotnik
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| |
Collapse
|
139
|
Rinn A, Breuer T, Wiegand J, Beck M, Hübner J, Döring RC, Oestreich M, Heimbrodt W, Witte G, Chatterjee S. Interfacial Molecular Packing Determines Exciton Dynamics in Molecular Heterostructures: The Case of Pentacene-Perfluoropentacene. ACS APPLIED MATERIALS & INTERFACES 2017; 9:42020-42028. [PMID: 29135216 DOI: 10.1021/acsami.7b11118] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The great majority of electronic and optoelectronic devices depend on interfaces between p-type and n-type semiconductors. Finding matching donor-acceptor systems in molecular semiconductors remains a challenging endeavor because structurally compatible molecules may not necessarily be suitable with respect to their optical and electronic properties, and the large exciton binding energy in these materials may favor bound electron-hole pairs rather than free carriers or charge transfer at an interface. Regardless, interfacial charge-transfer exciton states are commonly considered as an intermediate step to achieve exciton dissociation. The formation efficiency and decay dynamics of such states will strongly depend on the molecular makeup of the interface, especially the relative alignment of donor and acceptor molecules. Structurally well-defined pentacene-perfluoropentacene heterostructures of different molecular orientations are virtually ideal model systems to study the interrelation between molecular packing motifs at the interface and their electronic properties. Comparing the emission dynamics of the heterosystems and the corresponding unitary films enables accurate assignment of every observable emission signal in the heterosystems. These heterosystems feature two characteristic interface-specific luminescence channels at around 1.4 and 1.5 eV that are not observed in the unitary samples. Their emission strength strongly depends on the molecular alignment of the respective donor and acceptor molecules, emphasizing the importance of structural control for device construction.
Collapse
Affiliation(s)
- Andre Rinn
- Faculty of Physics & Materials Sciences Centre, Philipps-Universität Marburg , Renthof 5, 35032 Marburg, Germany
| | - Tobias Breuer
- Faculty of Physics & Materials Sciences Centre, Philipps-Universität Marburg , Renthof 5, 35032 Marburg, Germany
| | - Julia Wiegand
- Institut für Festkörperphysik, Leibniz Universität Hannover , Appelstrasse 2, D-30167 Hannover, Germany
| | - Michael Beck
- Institut für Festkörperphysik, Leibniz Universität Hannover , Appelstrasse 2, D-30167 Hannover, Germany
| | - Jens Hübner
- Institut für Festkörperphysik, Leibniz Universität Hannover , Appelstrasse 2, D-30167 Hannover, Germany
| | - Robin C Döring
- Faculty of Physics & Materials Sciences Centre, Philipps-Universität Marburg , Renthof 5, 35032 Marburg, Germany
| | - Michael Oestreich
- Institut für Festkörperphysik, Leibniz Universität Hannover , Appelstrasse 2, D-30167 Hannover, Germany
| | - Wolfram Heimbrodt
- Faculty of Physics & Materials Sciences Centre, Philipps-Universität Marburg , Renthof 5, 35032 Marburg, Germany
| | - Gregor Witte
- Faculty of Physics & Materials Sciences Centre, Philipps-Universität Marburg , Renthof 5, 35032 Marburg, Germany
| | - Sangam Chatterjee
- Faculty of Physics & Materials Sciences Centre, Philipps-Universität Marburg , Renthof 5, 35032 Marburg, Germany
- Institute of Experimental Physics I, Justus-Liebig-University Giessen , Heinrich-Buff-Ring 16, D-35392 Giessen, Germany
| |
Collapse
|
140
|
Häse F, Kreisbeck C, Aspuru-Guzik A. Machine learning for quantum dynamics: deep learning of excitation energy transfer properties. Chem Sci 2017; 8:8419-8426. [PMID: 29619189 PMCID: PMC5863613 DOI: 10.1039/c7sc03542j] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Accepted: 10/23/2017] [Indexed: 12/20/2022] Open
Abstract
Understanding the relationship between the structure of light-harvesting systems and their excitation energy transfer properties is of fundamental importance in many applications including the development of next generation photovoltaics. Natural light harvesting in photosynthesis shows remarkable excitation energy transfer properties, which suggests that pigment-protein complexes could serve as blueprints for the design of nature inspired devices. Mechanistic insights into energy transport dynamics can be gained by leveraging numerically involved propagation schemes such as the hierarchical equations of motion (HEOM). Solving these equations, however, is computationally costly due to the adverse scaling with the number of pigments. Therefore virtual high-throughput screening, which has become a powerful tool in material discovery, is less readily applicable for the search of novel excitonic devices. We propose the use of artificial neural networks to bypass the computational limitations of established techniques for exploring the structure-dynamics relation in excitonic systems. Once trained, our neural networks reduce computational costs by several orders of magnitudes. Our predicted transfer times and transfer efficiencies exhibit similar or even higher accuracies than frequently used approximate methods such as secular Redfield theory.
Collapse
Affiliation(s)
- Florian Häse
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , 02138 , USA . ; ; Tel: +1-617-384-8188
| | - Christoph Kreisbeck
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , 02138 , USA . ; ; Tel: +1-617-384-8188
| | - Alán Aspuru-Guzik
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , 02138 , USA . ; ; Tel: +1-617-384-8188
| |
Collapse
|
141
|
Roy P, Jha A, Yasarapudi VB, Ram T, Puttaraju B, Patil S, Dasgupta J. Ultrafast bridge planarization in donor-π-acceptor copolymers drives intramolecular charge transfer. Nat Commun 2017; 8:1716. [PMID: 29170455 PMCID: PMC5700982 DOI: 10.1038/s41467-017-01928-z] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2017] [Accepted: 10/24/2017] [Indexed: 11/09/2022] Open
Abstract
Donor-π-acceptor conjugated polymers form the material basis for high power conversion efficiencies in organic solar cells. Large dipole moment change upon photoexcitation via intramolecular charge transfer in donor-π-acceptor backbone is conjectured to facilitate efficient charge-carrier generation. However, the primary structural changes that drive ultrafast charge transfer step have remained elusive thereby limiting a rational structure-function correlation for such copolymers. Here we use structure-sensitive femtosecond stimulated Raman spectroscopy to demonstrate that π-bridge torsion forms the primary reaction coordinate for intramolecular charge transfer in donor-π-acceptor copolymers. Resonance-selective Raman snapshots of exciton relaxation reveal rich vibrational dynamics of the bridge modes associated with backbone planarization within 400 fs, leading to hot intramolecular charge transfer state formation while subsequent cooling dynamics of backbone-centric modes probe the charge transfer relaxation. Our work establishes a phenomenological gating role of bridge torsions in determining the fundamental timescale and energy of photogenerated carriers, and therefore opens up dynamics-based guidelines for fabricating energy-efficient organic photovoltaics.
Collapse
Affiliation(s)
- Palas Roy
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Ajay Jha
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Vineeth B Yasarapudi
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Thulasi Ram
- Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Boregowda Puttaraju
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, 560012, India
| | - Satish Patil
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, 560012, India
| | - Jyotishman Dasgupta
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India.
| |
Collapse
|
142
|
Ullbrich S, Siegmund B, Mischok A, Hofacker A, Benduhn J, Spoltore D, Vandewal K. Fast Organic Near-Infrared Photodetectors Based on Charge-Transfer Absorption. J Phys Chem Lett 2017; 8:5621-5625. [PMID: 29095624 DOI: 10.1021/acs.jpclett.7b02571] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
We present organic near-infrared photodetectors based on the absorption of charge-transfer (CT) states at the zinc-phthalocyanine-C60 interface. By using a resonant optical cavity device architecture, we achieve a narrowband detection, centered around 1060 nm and well below (>200 nm) the optical gap of the neat materials. We measure transient photocurrent responses at wavelengths of 532 and 1064 nm, exciting dominantly the neat materials or the CT state, respectively, and obtain rise and fall times of a few nanoseconds at short circuit, independent of the excitation wavelength. The current transients are modeled with time-dependent drift-diffusion simulations of electrons and holes which reconstruct the photocurrent signal, including capacitance and series resistance effects. The hole mobility of the donor material is identified as the limiting factor for the high-frequency response. With this knowledge, we demonstrate a new device concept, which balances hole and electron extraction times and achieves a cutoff frequency of 68 MHz upon 1064 nm CT excitation.
Collapse
Affiliation(s)
- Sascha Ullbrich
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Phyics, Technische Universität Dresden , Nöthnitzer Straße 61, 01187 Dresden, Germany
| | - Bernhard Siegmund
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Phyics, Technische Universität Dresden , Nöthnitzer Straße 61, 01187 Dresden, Germany
| | - Andreas Mischok
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Phyics, Technische Universität Dresden , Nöthnitzer Straße 61, 01187 Dresden, Germany
| | - Andreas Hofacker
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Phyics, Technische Universität Dresden , Nöthnitzer Straße 61, 01187 Dresden, Germany
| | - Johannes Benduhn
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Phyics, Technische Universität Dresden , Nöthnitzer Straße 61, 01187 Dresden, Germany
| | - Donato Spoltore
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Phyics, Technische Universität Dresden , Nöthnitzer Straße 61, 01187 Dresden, Germany
| | - Koen Vandewal
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Phyics, Technische Universität Dresden , Nöthnitzer Straße 61, 01187 Dresden, Germany
| |
Collapse
|
143
|
Penwell SB, Ginsberg LDS, Noriega R, Ginsberg NS. Resolving ultrafast exciton migration in organic solids at the nanoscale. NATURE MATERIALS 2017; 16:1136-1141. [PMID: 28920937 DOI: 10.1038/nmat4975] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2016] [Accepted: 07/25/2017] [Indexed: 05/16/2023]
Abstract
Effectiveness of molecular-based light harvesting relies on transport of excitons to charge-transfer sites. Measuring exciton migration, however, has been challenging because of the mismatch between nanoscale migration lengths and the diffraction limit. Instead of using bulk substrate quenching methods, here we define quenching boundaries all-optically with sub-diffraction resolution, thus characterizing spatiotemporal exciton migration on its native nanometre and picosecond scales. By transforming stimulated emission depletion microscopy into a time-resolved ultrafast approach, we measure a 16-nm migration length in poly(2,5-di(hexyloxy)cyanoterephthalylidene) conjugated polymer films. Combined with Monte Carlo exciton hopping simulations, we show that migration in these films is essentially diffusive because intrinsic chromophore energetic disorder is comparable to chromophore inhomogeneous broadening. Our approach will enable previously unattainable correlation of local material structure to exciton migration character, applicable not only to photovoltaic or display-destined organic semiconductors but also to explaining the quintessential exciton migration exhibited in photosynthesis.
Collapse
Affiliation(s)
- Samuel B Penwell
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Lucas D S Ginsberg
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Rodrigo Noriega
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Naomi S Ginsberg
- Department of Chemistry, University of California, Berkeley, California 94720, USA
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Kavli Energy NanoScience Institute, Berkeley, California 94720, USA
- Department of Physics, University of California, Berkeley, California 94720, USA
| |
Collapse
|
144
|
Xiang B, Li Y, Pham CH, Paesani F, Xiong W. Ultrafast direct electron transfer at organic semiconductor and metal interfaces. SCIENCE ADVANCES 2017; 3:e1701508. [PMID: 29159282 PMCID: PMC5694661 DOI: 10.1126/sciadv.1701508] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Accepted: 10/19/2017] [Indexed: 06/01/2023]
Abstract
The ability to control direct electron transfer can facilitate the development of new molecular electronics, light-harvesting materials, and photocatalysis. However, control of direct electron transfer has been rarely reported, and the molecular conformation-electron dynamics relationships remain unclear. We describe direct electron transfer at buried interfaces between an organic polymer semiconductor film and a gold substrate by observing the first dynamical electric field-induced vibrational sum frequency generation (VSFG). In transient electric field-induced VSFG measurements on this system, we observe dynamical responses (<150 fs) that depend on photon energy and polarization, demonstrating that electrons are directly transferred from the Fermi level of gold to the lowest unoccupied molecular orbital of organic semiconductor. Transient spectra further reveal that, although the interfaces are prepared without deliberate alignment control, a subensemble of surface molecules can adopt conformations for direct electron transfer. Density functional theory calculations support the experimental results and ascribe the observed electron transfer to a flat-lying polymer configuration in which electronic orbitals are found to be delocalized across the interface. The present observation of direct electron transfer at complex interfaces and the insights gained into the relationship between molecular conformations and electron dynamics will have implications for implementing novel direct electron transfer in energy materials.
Collapse
Affiliation(s)
- Bo Xiang
- Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093–0418, USA
| | - Yingmin Li
- Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093–0418, USA
| | - C. Huy Pham
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093–0358, USA
| | - Francesco Paesani
- Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093–0418, USA
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093–0358, USA
| | - Wei Xiong
- Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093–0418, USA
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093–0358, USA
| |
Collapse
|
145
|
Ohta K, Tokonami S, Takahashi K, Tamura Y, Yamada H, Tominaga K. Probing Charge Carrier Dynamics in Porphyrin-Based Organic Semiconductor Thin Films by Time-Resolved THz Spectroscopy. J Phys Chem B 2017; 121:10157-10165. [DOI: 10.1021/acs.jpcb.7b07025] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Kaoru Ohta
- Molecular
Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
- Graduate
School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| | - Shunrou Tokonami
- Graduate
School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| | - Kotaro Takahashi
- Graduate
School of Materials Science, Nara Institute of Science and Technology, 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Yuto Tamura
- Graduate
School of Materials Science, Nara Institute of Science and Technology, 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Hiroko Yamada
- Graduate
School of Materials Science, Nara Institute of Science and Technology, 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Keisuke Tominaga
- Molecular
Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
- Graduate
School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| |
Collapse
|
146
|
Ferron T, Pope M, Collins BA. Spectral Analysis for Resonant Soft X-Ray Scattering Enables Measurement of Interfacial Width in 3D Organic Nanostructures. PHYSICAL REVIEW LETTERS 2017; 119:167801. [PMID: 29099210 DOI: 10.1103/physrevlett.119.167801] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Indexed: 06/07/2023]
Abstract
Interfaces are of critical importance to many materials and phenomena yet are difficult to probe. This difficulty is compounded in three-dimensional nanostructures and with delicate organic materials. Here we demonstrate a quantitative spectral analysis of resonant soft x-ray scattering that can accurately measure properties of buried nonplanar interfaces within polymeric systems. We measure the scattering invariant on an absolute scale to quantify the interfacial volume and width involved in mixing at the interface of block copolymer nanostructures. Using continuous contrast tuning, this spectral analysis enables the separation and identification of any number of unique scatterers in complex nanostructures.
Collapse
Affiliation(s)
- Thomas Ferron
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, USA
| | - Michael Pope
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, USA
| | - Brian A Collins
- Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, USA
| |
Collapse
|
147
|
Joseph S, Ravva MK, Bredas JL. Charge-Transfer Dynamics in the Lowest Excited State of a Pentacene-Fullerene Complex: Implications for Organic Solar Cells. J Phys Chem Lett 2017; 8:5171-5176. [PMID: 28968105 DOI: 10.1021/acs.jpclett.7b02049] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We characterize the dynamic nature of the lowest excited state in a pentacene/C60 complex on the femtosecond time scale, via a combination of ab initio molecular dynamics and time-dependent density functional theory. We analyze the correlations between the molecular vibrations of the complex and the oscillations in the electron-transfer character of its lowest excited state, which point to vibration-induced coherences between the (pentacene-based) local-excitation (LE) state and the complex charge-transfer (CT) state. We discuss the implications of our results on this model system for the exciton-dissociation process in organic solar cells.
Collapse
Affiliation(s)
- Saju Joseph
- KAUST Solar Center, Physical Science and Engineering Division, King Abdullah University of Science and Technology , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Mahesh Kumar Ravva
- KAUST Solar Center, Physical Science and Engineering Division, King Abdullah University of Science and Technology , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Jean-Luc Bredas
- KAUST Solar Center, Physical Science and Engineering Division, King Abdullah University of Science and Technology , Thuwal 23955-6900, Kingdom of Saudi Arabia
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States
| |
Collapse
|
148
|
Popescu A, Younts RA, Hoffman B, McAfee T, Dougherty DB, Ade HW, Gundogdu K, Bondarev IV. Monitoring Charge Separation Processes in Quasi-One-Dimensional Organic Crystalline Structures. NANO LETTERS 2017; 17:6056-6061. [PMID: 28873308 DOI: 10.1021/acs.nanolett.7b02471] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We perform the transient absorption spectroscopy experiments to investigate the dynamics of the low-energy collective electron-hole excitations in α-copper phthalocyanine thin films. The results are interpreted in terms of the third-order nonlinear polarization response function. It is found that, initially excited in the molecular plane, the intramolecular Frenkel exciton polarization reorients with time to align along the molecular chain direction to form coupled Frenkel-charge-transfer exciton states, the eigenstates of the one-dimensional periodic molecular lattice. The process pinpoints the direction of the charge separation in α-copper phthalocyanine and similar organic molecular structures. Being able to observe and monitor such processes is important both for understanding the physical principles of organic thin film solar energy conversion device operation and for the development of organic optoelectronics in general.
Collapse
Affiliation(s)
- Adrian Popescu
- Department of Math and Physics, North Carolina Central University , Durham, North Carolina 27707, United States
| | | | | | - Terry McAfee
- Department of Physics and Engineering Physics, Tulane University , New Orleans, Louisiana 70118, United States
| | | | | | | | - Igor V Bondarev
- Department of Math and Physics, North Carolina Central University , Durham, North Carolina 27707, United States
| |
Collapse
|
149
|
Gerbert D, Tegeder P. Molecular Ion Formation by Photoinduced Electron Transfer at the Tetracyanoquinodimethane/Au(111) Interface. J Phys Chem Lett 2017; 8:4685-4690. [PMID: 28899087 DOI: 10.1021/acs.jpclett.7b01897] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Optically induced processes in organic materials are essential for light harvesting, switching, and sensor technologies. Here we studied the electronic properties of the tetracyanoquinodimethane(TCNQ)/Au(111) interface by using two-photon photoemission spectroscopy. For this interface we demonstrated the lack of charge-transfer interactions, but we found a significant increase in the sample work function due to UV-light illumination, while the electronic structure of the TCNQ-derived states remain unaffected. Thereby the work function of the interface can be tuned over a wide range via the photon dose. We assigned this to a photoinduced metal-to-molecule electron transfer creating negative ions. The electrons are bound by a small potential barrier. Thus thermal activation reverses the process resulting in the original work function value. The presented photoinduced charge transfer at the TCNQ/Au(111) interface can be used for continuous work function tuning across the substrate's work function, which can be applied in device-adapted hole-injection layers or organic UV-light sensors.
Collapse
Affiliation(s)
- David Gerbert
- Ruprecht-Karls-Universität Heidelberg , Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany
| | - Petra Tegeder
- Ruprecht-Karls-Universität Heidelberg , Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany
| |
Collapse
|
150
|
Fazzi D, Barbatti M, Thiel W. Hot and Cold Charge-Transfer Mechanisms in Organic Photovoltaics: Insights into the Excited States of Donor/Acceptor Interfaces. J Phys Chem Lett 2017; 8:4727-4734. [PMID: 28903560 DOI: 10.1021/acs.jpclett.7b02144] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The evolution of the excited-state manifold in organic D/A aggregates (e.g., the prototypical P3HT/PCBM) is investigated through a bottom-up approach via first-principles calculations. We show how the excited-state energies, the charge transfer (CT) states, and the electron-hole density distributions are strongly influenced by the size, the orientation, and the position (i.e., on-top versus on-edge phases) of P3HT/PCBM domains. We discuss how the structural order influences the excited-state electronic structure, providing an atomistic interpretation of the photophysics of organic blends. We show how the simultaneous presence of on-top and on-edge phases does not alter the optical absorption spectrum of the blend but does affect the photophysics. Photovoltaic processes such as (i) the simultaneous charge generation obtained from hot and cold excitations, (ii) the instantaneous and delayed charge separation, and (iii) the pump-push-probe charge generation can be interpreted based on our study.
Collapse
Affiliation(s)
- Daniele Fazzi
- Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | | | - Walter Thiel
- Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| |
Collapse
|