1
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Nuber M, Spanier LV, Roth S, Vayssilov GN, Kienberger R, Müller-Buschbaum P, Iglev H. Picosecond Charge-Transfer-State Dynamics in Wide Band Gap Polymer-Non-Fullerene Small-Molecule Blend Films Investigated via Transient Infrared Spectroscopy. J Phys Chem Lett 2022; 13:10418-10423. [PMID: 36326207 DOI: 10.1021/acs.jpclett.2c02864] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Organic solar cells based on wide band gap polymers and nonfullerene small-molecule acceptors have demonstrated remarkably good device performances. Nevertheless, a thorough understanding of the charge-transfer process in these materials has not been achieved yet. In this study, we use Fano resonance signals caused by the interaction of broad electronic charge carrier absorption and the molecular vibrations of the electron acceptor molecule to monitor the charge-transfer state dynamics. In our time-resolved infrared spectroscopy experiments, we find that in the small-molecule acceptor, they have additional dynamics on the order of a few picoseconds. A change in the solvent used in thin film deposition, leading to different morphologies, influences this time further. We interpret our findings as the dynamics of the charge-transfer state at the interface of the electron donor and the electron- acceptor. The additional mid-infrared transient signal is generated in this state, as both electron and hole polarons can interact with small-molecule acceptor vibrational modes.
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Affiliation(s)
- Matthias Nuber
- Lehrstuhl für Laser- und Röntgenphysik, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
| | - Lukas V Spanier
- Lehrstuhl für Funktionelle Materialien, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
| | - Sebastian Roth
- Lehrstuhl für Laser- und Röntgenphysik, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
| | - Georgi N Vayssilov
- Faculty of Chemistry and Pharmacy, University of Sofia, Blvd. J. Bauchier 1, 1126 Sofia, Bulgaria
| | - Reinhard Kienberger
- Lehrstuhl für Laser- und Röntgenphysik, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
| | - Peter Müller-Buschbaum
- Lehrstuhl für Funktionelle Materialien, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
- Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Lichtenbergstr. 1, 85748 Garching, Germany
| | - Hristo Iglev
- Lehrstuhl für Laser- und Röntgenphysik, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
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2
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Jemaï G, Chika K, Jemaa Khabthani J, Mayou D. Influence of the electron-vibration coupling on the interfacial charge transfer in organic solar cells: a simple quantum model. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:425001. [PMID: 35926486 DOI: 10.1088/1361-648x/ac8712] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Accepted: 07/27/2022] [Indexed: 06/15/2023]
Abstract
In this paper, we analyze the influence of the electron-vibration interaction on the charge transfer process at the donor-acceptor interface in an organic solar cell. We present an essentially exact numerical analysis for a minimal model with only one vibration mode which is coupled to the charge transfer state. We show that the charge transfer state can be hot or cold depending on the parameters and in particular on the value of the energy of the lowest unoccupied molecular orbital on the donor side. We analyze also different regimes where electron-hole attraction or hybridization effects at the interface can modify the quantum yield of the transfer. We discuss also briefly the possible effects of the other vibration modes that are coupled to the charge either on the donor side or on the acceptor side.
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Affiliation(s)
- Ghassen Jemaï
- Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences de Tunis, Université Tunis El Manar, Campus Universitaire, 1060 Tunis, Tunisia
| | - Khouloud Chika
- Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences de Tunis, Université Tunis El Manar, Campus Universitaire, 1060 Tunis, Tunisia
| | - Jouda Jemaa Khabthani
- Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences de Tunis, Université Tunis El Manar, Campus Universitaire, 1060 Tunis, Tunisia
| | - Didier Mayou
- CNRS, Inst NEEL, F-38042 Grenoble, France
- Université Grenoble Alpes, Inst NEEL, F-38042 Grenoble, France
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3
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Yan Y, Zhang Y, Memon WA, Wang M, Zhang X, Wei Z. The role of entropy gains in the exciton separation in organic solar cells. Macromol Rapid Commun 2022; 43:e2100903. [PMID: 35338684 DOI: 10.1002/marc.202100903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 02/16/2022] [Indexed: 11/06/2022]
Abstract
In organic solar cell (OSC), the lower dielectric constant of organic semiconductor material induces a strong Coulomb attraction between electron-hole pairs, which leads to a low exciton separation efficiency, especially the charge transfer (CT) state. The CT state formed at the electron-donor (D) and electron-acceptor (A) interface is regarded as an unfavorable property of organic photovoltaic devices. Since the OSC works in a nonzero temperature condition, the entropy effect would be one of the main reasons to overcome the Coulomb energy barrier and must be taken into account. In this review, we review the present understanding of the entropy-driven charge separation and describe how factors such as the dimensionality of the organic semiconductor, energy disorder effect, the morphology of the active layer, and the nonequilibrium effect affect the entropy contribution in compensating the Coulomb dissociation barrier for CT exciton separation and charge generation process. We focus on the investigation of the entropy effect on exciton dissociation mechanism from both theoretical and experimental aspects, which provides pathways for understanding the underlying mechanisms of exciton separation and further enhancing the efficiency of OSCs. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Yangjun Yan
- School of Science, Beijing Jiaotong University, Beijing, 100044, China.,CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Yajie Zhang
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Waqar Ali Memon
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Mengni Wang
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Xinghua Zhang
- School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Zhixiang Wei
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
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4
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Wang Y, Kublitski J, Xing S, Dollinger F, Spoltore D, Benduhn J, Leo K. Narrowband organic photodetectors - towards miniaturized, spectroscopic sensing. MATERIALS HORIZONS 2022; 9:220-251. [PMID: 34704585 DOI: 10.1039/d1mh01215k] [Citation(s) in RCA: 41] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Omnipresent quality monitoring in food products, blood-oxygen measurement in lightweight conformal wrist bands, or data-driven automated industrial production: Innovation in many fields is being empowered by sensor technology. Specifically, organic photodetectors (OPDs) promise great advances due to their beneficial properties and low-cost production. Recent research has led to rapid improvement in all performance parameters of OPDs, which are now on-par or better than their inorganic counterparts, such as silicon or indium gallium arsenide photodetectors, in several aspects. In particular, it is possible to directly design OPDs for specific wavelengths. This makes expensive and bulky optical filters obsolete and allows for miniature detector devices. In this review, recent progress of such narrowband OPDs is systematically summarized covering all aspects from narrow-photo-absorbing materials to device architecture engineering. The recent challenges for narrowband OPDs, like achieving high responsivity, low dark current, high response speed, and good dynamic range are carefully addressed. Finally, application demonstrations covering broadband and narrowband OPDs are discussed. Importantly, several exciting research perspectives, which will stimulate further research on organic-semiconductor-based photodetectors, are pointed out at the very end of this review.
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Affiliation(s)
- Yazhong Wang
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
| | - Jonas Kublitski
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
| | - Shen Xing
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
| | - Felix Dollinger
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
| | - Donato Spoltore
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
| | - Johannes Benduhn
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
| | - Karl Leo
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
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5
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Jiao Z, Jiang T, Zhou Z, Qin C, Long J, Liu Y, Jiang Y. Identification of a bridge-specific intramolecular exciton dissociation pathway in donor-π-acceptor alternating conjugated polymers. NANOSCALE RESEARCH LETTERS 2021; 16:51. [PMID: 33745078 PMCID: PMC7981365 DOI: 10.1186/s11671-021-03507-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 03/12/2021] [Indexed: 06/12/2023]
Abstract
Intramolecular exciton dissociation is critical for high efficient mobile charge carrier generations in organic solar cells. Yet despite much attention, the effects of π bridges on exciton dissociation dynamics in donor-π-acceptor (D-π-A) alternating conjugated polymers remain still unclear. Here, using a combination of femtosecond time-resolved transient absorption (TA) spectroscopy and steady-state spectroscopy, we track ultrafast intramolecular exciton relaxation dynamics in three D-π-A alternating conjugated polymers which were synthesized by Qin's group and named HSD-A, HSD-B, HSD-C. It is found that the addition of thiophene unit as π bridges will lead to the red shift of steady-state absorption spectrum. Importantly, we reveal the existence of a new intramolecular exciton dissociation pathway mediated by a bridge-specific charge transfer (CT') state with the TA fingerprint peak at 1200 nm in π-bridged HSD-B and HSD-C. This CT' state results in higher electron capture rates for HSD-B and HSD-C as compared to HSD-A. Depending on the proportion of CT' state and nongeminate recombination are important step for the understanding of high power conversion efficiencies in HSD-B than in HSD-C. We propose that this bridge-specific exciton dissociation pathway plays an important role in ultrafast intramolecular exciton dissociation of organic photovoltaic material D-π-A alternating conjugated polymers.
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Affiliation(s)
- Zhaoyong Jiao
- Henan Key Laboratory of Infrared Materials and Spectrum Measures and Applications, School of Physics, Henan Normal University, Xinxiang, 453007, People's Republic of China
| | - Tingting Jiang
- Henan Key Laboratory of Infrared Materials and Spectrum Measures and Applications, School of Physics, Henan Normal University, Xinxiang, 453007, People's Republic of China
| | - Zhongpo Zhou
- Henan Key Laboratory of Infrared Materials and Spectrum Measures and Applications, School of Physics, Henan Normal University, Xinxiang, 453007, People's Republic of China
| | - Chaochao Qin
- Henan Key Laboratory of Infrared Materials and Spectrum Measures and Applications, School of Physics, Henan Normal University, Xinxiang, 453007, People's Republic of China.
| | - Jinyou Long
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430071, People's Republic of China.
| | - Yufang Liu
- Henan Key Laboratory of Infrared Materials and Spectrum Measures and Applications, School of Physics, Henan Normal University, Xinxiang, 453007, People's Republic of China
| | - Yuhai Jiang
- Henan Key Laboratory of Infrared Materials and Spectrum Measures and Applications, School of Physics, Henan Normal University, Xinxiang, 453007, People's Republic of China.
- Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210, People's Republic of China.
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6
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Abstract
AbstractPhotoinduced charge generation forms the physical basis for energy conversion in organic photovoltaic (OPV) technology. The fundamental initial steps involved are absorption of light by organic semiconductors (generally π-conjugated polymers) to generate photoexcited states (Frenkel excitons) followed by charge transfer and charge separation processes in presence of suitable acceptor. The absorbed photon energy must be utilized completely for achieving maximum device efficiency. However progressive relaxation losses of instantaneously generated high-energy or hot-excited states form major bottleneck for maximum derivable voltage. This efficiency limiting factor has been challenged recently by the role of hot-carriers in efficient generation of charges. Therefore tailoring the dissociation of hot-exciton to be temporally faster than all relaxation processes could minimize the energy loss pathways. Implementation of this concept of hot-carrier photovoltaics demands critical understanding of molecular parameters that circumvent all energy relaxation processes and favor hot-carrier generation. In my dissertation work, I have examined the fate of photo-generated excitons in the context of polymer backbone and morphology, and therefore obtain a fundamental structure-function correlation in organic semiconductors.
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Affiliation(s)
- Palas Roy
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai-400005, India
- School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK
| | - Jyotishman Dasgupta
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai-400005, India
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7
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Tu Z, Han G, Yi Y. Barrier-Free Charge Separation Enabled by Electronic Polarization in High-Efficiency Non-fullerene Organic Solar Cells. J Phys Chem Lett 2020; 11:2585-2591. [PMID: 32163716 DOI: 10.1021/acs.jpclett.0c00405] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The separation of charge-transfer states into free charges at the donor/acceptor (D/A) interfaces plays a central role in organic solar cells (OSCs). Because of strong Coulomb attraction, the separation mechanisms are elusive, particularly for the high-efficiency non-fullerene (NF) OSCs with low exciton-dissociation driving forces. Here, we demonstrate that the Coulomb barriers can be substantially overcome by electronic polarization for OSCs based on a series of A-D-A acceptors (ITIC, IT-4F, and Y6). In contrast to fullerene-based D/A heterojunctions, the polarization energies for both donor holes and acceptor electrons are remarkably increased from the interfaces to pure regions in the NF heterojunctions because of strong stabilization on electrons but destabilization on holes by electrostatic interactions in the A-D-A acceptors. In particular, upon incorporation of fluorine substituents and electron-poor cores into ITIC, the increased polarization energies can completely compensate for the Coulomb attraction in the IT-4F- and Y6-based heterojunctions, leading to barrierless charge separation.
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Affiliation(s)
- Zeyi Tu
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy Sciences, Beijing 100049, China
| | - Guangchao Han
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Yuanping Yi
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy Sciences, Beijing 100049, China
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8
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Jiang B, Tang Q, Zhao W, Sun J, An R, Niu T, Fuchs H, Ji Q. Tailoring structural features and functions of fullerene rod crystals by a ferrocene-modified fullerene derivative. CrystEngComm 2020. [DOI: 10.1039/d0ce01019g] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Effective functional intercalation and facile structural manipulation of fullerene crystals could be achieved by ferrocene-modified fullerene based on the liquid–liquid interfacial precipitation process.
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Affiliation(s)
- Bohong Jiang
- Herbert Gleiter Institute of Nanoscience
- Nanjing University of Science & Technology
- Nanjing 210094
- China
| | - Qin Tang
- Herbert Gleiter Institute of Nanoscience
- Nanjing University of Science & Technology
- Nanjing 210094
- China
| | - Wenli Zhao
- Herbert Gleiter Institute of Nanoscience
- Nanjing University of Science & Technology
- Nanjing 210094
- China
| | - Jiao Sun
- Herbert Gleiter Institute of Nanoscience
- Nanjing University of Science & Technology
- Nanjing 210094
- China
| | - Rong An
- Herbert Gleiter Institute of Nanoscience
- Nanjing University of Science & Technology
- Nanjing 210094
- China
| | - Tianchao Niu
- Herbert Gleiter Institute of Nanoscience
- Nanjing University of Science & Technology
- Nanjing 210094
- China
| | - Harald Fuchs
- Herbert Gleiter Institute of Nanoscience
- Nanjing University of Science & Technology
- Nanjing 210094
- China
- Center for Nanotechnology
| | - Qingmin Ji
- Herbert Gleiter Institute of Nanoscience
- Nanjing University of Science & Technology
- Nanjing 210094
- China
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9
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Niu MS, Wang KW, Yang XY, Bi PQ, Zhang KN, Feng XJ, Chen F, Qin W, Xia JL, Hao XT. Hole Transfer Originating from Weakly Bound Exciton Dissociation in Acceptor-Donor-Acceptor Nonfullerene Organic Solar Cells. J Phys Chem Lett 2019; 10:7100-7106. [PMID: 31682127 DOI: 10.1021/acs.jpclett.9b02837] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The underlying hole-transfer mechanism in high-efficiency OSC bulk heterojunctions based on acceptor-donor-acceptor (A-D-A) nonfullerene acceptors (NFAs) remains unclear. Herein, we study the hole-transfer process between copolymer donor J91 and five A-D-A NFAs with different highest occupied molecular orbital energy offsets (ΔEH) (0.05-0.42 eV) via ultrafast optical spectroscopies. Transient absorption spectra reveal a rapid hole-transfer rate with small ΔEH, suggesting that a large energy offset is not required to overcome the exciton binding energy. Capacitance-frequency spectra and time-resolved photoluminescence spectra confirm the delocalization of an A-D-A-structured acceptor exciton with weak binding energy. Relative to the hole-transfer rate, hole-transfer efficiency is the key factor affecting device performance. We propose that holes primarily stem from weakly bound acceptor exciton dissociation, revealing a new insight into the hole-transfer process in A-D-A NFA-based OSCs.
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Affiliation(s)
- Meng-Si Niu
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Kang-Wei Wang
- School of Chemistry, Chemical Engineering and Life Science, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing , Wuhan University of Technology , 430070 Wuhan , Hubei , China
| | - Xiao-Yu Yang
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Peng-Qing Bi
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Kang-Ning Zhang
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Xian-Jin Feng
- School of Microelectronics , Shandong University , 250100 Jinan , Shandong , China
| | - Fei Chen
- Department of Mechanical, Materials and Manufacturing Engineering , The University of Nottingham Ningbo China , Ningbo 315100 , P.R. China
| | - Wei Qin
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Jian-Long Xia
- School of Chemistry, Chemical Engineering and Life Science, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing , Wuhan University of Technology , 430070 Wuhan , Hubei , China
| | - Xiao-Tao Hao
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
- ARC Centre of Excellence in Exciton Science, School of Chemistry , The University of Melbourne , Parkville , Victoria 3010 , Australia
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10
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Wang Y, Ke Y, Zhao Y. The hierarchical and perturbative forms of stochastic Schrödinger equations and their applications to carrier dynamics in organic materials. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2018. [DOI: 10.1002/wcms.1375] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Yu‐Chen Wang
- State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
| | - Yaling Ke
- State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
| | - Yi Zhao
- State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
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11
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Teuscher J, Brauer JC, Stepanov A, Solano A, Boziki A, Chergui M, Wolf JP, Rothlisberger U, Banerji N, Moser JE. Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2017; 4:061503. [PMID: 29308415 PMCID: PMC5736396 DOI: 10.1063/1.4996409] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 11/13/2017] [Indexed: 05/16/2023]
Abstract
Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation), which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research "Molecular Ultrafast Science and Technology," a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here.
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Affiliation(s)
| | - Jan C Brauer
- FemtoMat Group, Department of Chemistry, Université de Fribourg, 1700 Fribourg, Switzerland
| | - Andrey Stepanov
- GAP-Biophotonics Group, Department of Applied Physics, Université de Genève, 1205 Geneva, Switzerland
| | | | | | | | - Jean-Pierre Wolf
- GAP-Biophotonics Group, Department of Applied Physics, Université de Genève, 1205 Geneva, Switzerland
| | | | - Natalie Banerji
- FemtoMat Group, Department of Chemistry, Université de Fribourg, 1700 Fribourg, Switzerland
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12
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Zhang Y, Chen W, Lin Z, Li S, George TF. Ultrafast optical pulse convertor caused by oscillations of the energy level structure in the conjugated polymer poly(p-phenylenevinylene). OPTICS EXPRESS 2017; 25:20233-20242. [PMID: 29041706 DOI: 10.1364/oe.25.020233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Accepted: 05/19/2017] [Indexed: 06/07/2023]
Abstract
For a conjugated polymer irradiated by two optical pulses, the whole process of excitation, involving lattice oscillations, oscillations of the energy level structure, and evolution of the electron cloud, is investigated. Localization of the electron cloud appears in the first 100 fs of irradiation, which in turn induces vibrations of lattice of the polymer chain as well as oscillations of the band gap. These oscillations filter the absorption of the external optical field inversely and convert the original optical field to an ultrafast light field whose intensity varies with a certain period. Based on the mechanism, oscillations of the energy level structure, induced by the external excitation, can be designed as an ultrafast response optical convertor that is able to change the external optical pulse into a new effective light field with a certain oscillation period. This helps provide new insight into designing nanostructures for polymeric optoelectronics.
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13
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Ke Y, Zhao Y. Hierarchy of stochastic Schrödinger equation towards the calculation of absorption and circular dichroism spectra. J Chem Phys 2017; 146:174105. [DOI: 10.1063/1.4982230] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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14
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Yang F, Qian D, Balawi AH, Wu Y, Ma W, Laquai F, Tang Z, Zhang F, Li W. Performance limitations in thieno[3,4-c]pyrrole-4,6-dione-based polymer:ITIC solar cells. Phys Chem Chem Phys 2017; 19:23990-23998. [DOI: 10.1039/c7cp04780k] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Three thieno[3,4-c]pyrrole-4,6-dione-based conjugated polymers were applied in non-fullerene solar cells, in which the polymer PTPDBDT provided a high photovoltage but a low quantum efficiency. This was caused by the large phase separation in the bulk-heterojunction as confirmed by systematic studies.
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Affiliation(s)
- Fan Yang
- Beijing National Laboratory for Molecular Sciences
- Key Laboratory of Organic Solids
- Institute of Chemistry
- Chinese Academy of Sciences
- Beijing 100190
| | - Deping Qian
- Biomolecular and Organic Electronics
- Department of Physics
- Chemistry and Biology
- Linköping University
- SE-581 83
| | - Ahmed Hesham Balawi
- King Abdullah University of Science and Technology (KAUST)
- KAUST Solar Center (KSC)
- Physical Sciences and Engineering Division (PSE)
- Material Science and Engineering Program (MSE)
- Thuwal 23955-6900
| | - Yang Wu
- State Key Laboratory for Mechanical Behavior of Materials
- Xi'an Jiaotong University
- Xi'an 710049
- P. R. China
| | - Wei Ma
- State Key Laboratory for Mechanical Behavior of Materials
- Xi'an Jiaotong University
- Xi'an 710049
- P. R. China
| | - Frédéric Laquai
- King Abdullah University of Science and Technology (KAUST)
- KAUST Solar Center (KSC)
- Physical Sciences and Engineering Division (PSE)
- Material Science and Engineering Program (MSE)
- Thuwal 23955-6900
| | - Zheng Tang
- Institut für Angewandte Photophysik
- Technische Universität Dresden
- George-Bähr-Straße 1
- Dresden
- Germany
| | - Fengling Zhang
- Biomolecular and Organic Electronics
- Department of Physics
- Chemistry and Biology
- Linköping University
- SE-581 83
| | - Weiwei Li
- Beijing National Laboratory for Molecular Sciences
- Key Laboratory of Organic Solids
- Institute of Chemistry
- Chinese Academy of Sciences
- Beijing 100190
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15
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Chen W, Jiang D, Chen R, Li S, George TF. Intrinsic Delocalization during the Decay of Excitons in Polymeric Solar Cells. Polymers (Basel) 2016; 8:E414. [PMID: 30974693 PMCID: PMC6431987 DOI: 10.3390/polym8120414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 11/24/2016] [Accepted: 11/24/2016] [Indexed: 12/04/2022] Open
Abstract
In bulk heterojunction polymer solar cells, external photoexcitation results in localized excitons in the polymer chain. After hot exciton formation and subsequent relaxation, the dipole moment drives the electron to partially transfer to extended orbitals from the original localized ones, leading to self-delocalization. Based on the dynamic fluorescence spectra, the delocalization of excitons is revealed to be an intrinsic property dominated by exciton decay, acting as a bridge for the exciton to diffuse in the polymeric solar cell. The modification of the dipole moment enhances the efficiency of polymer solar cells.
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Affiliation(s)
- Weikang Chen
- Department of Physics, Zhejiang Normal University, Jinhua 321004, Zhejiang, China.
| | - Deyao Jiang
- Department of Physics, Zhejiang Normal University, Jinhua 321004, Zhejiang, China.
- Department of Physics, Fudan University, Shanghai 200433, China.
| | - Renai Chen
- Department of Physics, Zhejiang Normal University, Jinhua 321004, Zhejiang, China.
- Department of Physics, Fudan University, Shanghai 200433, China.
| | - Sheng Li
- Department of Physics, Zhejiang Normal University, Jinhua 321004, Zhejiang, China.
- Department of Physics, Fudan University, Shanghai 200433, China.
- Office of the Chancellor and Center for Nanoscience, Departments of Chemistry & Biochemistry and Physics & Astronomy, University of Missouri⁻St. Louis, St. Louis, MO 63121, USA.
| | - Thomas F George
- Office of the Chancellor and Center for Nanoscience, Departments of Chemistry & Biochemistry and Physics & Astronomy, University of Missouri⁻St. Louis, St. Louis, MO 63121, USA.
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16
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Bragg AE, Yu W, Zhou J, Magnanelli T. Ultrafast Raman Spectroscopy as a Probe of Local Structure and Dynamics in Photoexcited Conjugated Materials. J Phys Chem Lett 2016; 7:3990-4000. [PMID: 27681200 DOI: 10.1021/acs.jpclett.6b01060] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
An important challenge in the study of conjugated organic materials is to relate the properties of transient states underlying macroscopic material responses directly with intra- and intermolecular structure. We discuss recent efforts using the vibrational sensitivity of time-resolved Raman spectroscopy to interrogate structural properties of transient excited and charge-separated states in conjugated oligomers and polymers in order to relate them to molecular conformations and material microstructures. We focus on recent work with excited-state Raman spectroscopy that provides mode-specific signatures of structural relaxation in oligo- and polythiophenes, examination of structural heterogeneities associated with exciton localization in different structural motifs of amorphous polymers, and interrogation of correlations between microstructure and properties and dynamics of charge-separated states within polymer aggregates. On the basis of these recent efforts, we provide an outlook for further applying this method to elucidate relationships between the structure and properties of transient states and the photoresponses of conjugated materials.
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Affiliation(s)
- Arthur E Bragg
- Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Wenjian Yu
- Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Jiawang Zhou
- Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Timothy Magnanelli
- Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States
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17
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The fate of electron-hole pairs in polymer:fullerene blends for organic photovoltaics. Nat Commun 2016; 7:12556. [PMID: 27586309 PMCID: PMC5025766 DOI: 10.1038/ncomms12556] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 07/14/2016] [Indexed: 12/26/2022] Open
Abstract
There has been long-standing debate on how free charges are generated in donor:acceptor blends that are used in organic solar cells, and which are generally comprised of a complex phase morphology, where intermixed and neat phases of the donor and acceptor material co-exist. Here we resolve this question, basing our conclusions on Stark effect spectroscopy data obtained in the absence and presence of externally applied electric fields. Reconciling opposing views found in literature, we unambiguously demonstrate that the fate of photogenerated electron–hole pairs—whether they will dissociate to free charges or geminately recombine—is determined at ultrafast times, despite the fact that their actual spatial separation can be much slower. Our insights are important to further develop rational approaches towards material design and processing of organic solar cells, assisting to realize their purported promise as lead-free, third-generation energy technology that can reach efficiencies over 10%. Charge generation and transport are crucial to the performance of organic solar cells, but the mechanism remains controversial. Causa' et al. show that the phase morphology of polymer:fullerene blends determines the exciton dissociation at femtoseconds, although the spatial separation can occur at picoseconds.
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18
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Zarrabi N, Burn PL, Meredith P, Shaw PE. Acceptor and Excitation Density Dependence of the Ultrafast Polaron Absorption Signal in Donor-Acceptor Organic Solar Cell Blends. J Phys Chem Lett 2016; 7:2640-2646. [PMID: 27355877 DOI: 10.1021/acs.jpclett.6b00806] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Transient absorption spectroscopy on organic semiconductor blends for solar cells typically shows efficient charge generation within ∼100 fs, accounting for the majority of the charge carriers. In this Letter, we show using transient absorption spectroscopy on blends containing a broad range of acceptor content (0.01-50% by weight) that the rise of the polaron signal is dependent on the acceptor concentration. For low acceptor content (<10% by weight), the polaron signal rises gradually over ∼1 ps with most polarons generated after 200 fs, while for higher acceptor concentrations (>10%) most polarons are generated within 200 fs. The rise time in blends with low acceptor content was also found to be sensitive to the pump fluence, decreasing with increasing excitation density. These results indicate that the sub-100 fs rise of the polaron signal is a natural consequence of both the high acceptor concentrations in many donor-acceptor blends and the high excitation densities needed for transient absorption spectroscopy, which results in a short average distance between the exciton and the donor-acceptor interface.
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Affiliation(s)
- Nasim Zarrabi
- Centre for Organic Photonics & Electronics, School of Mathematics & Physics, and School of Chemistry and Molecular Biosciences, The University of Queensland , Brisbane, Queensland 4072, Australia
| | - Paul L Burn
- Centre for Organic Photonics & Electronics, School of Mathematics & Physics, and School of Chemistry and Molecular Biosciences, The University of Queensland , Brisbane, Queensland 4072, Australia
| | - Paul Meredith
- Centre for Organic Photonics & Electronics, School of Mathematics & Physics, and School of Chemistry and Molecular Biosciences, The University of Queensland , Brisbane, Queensland 4072, Australia
| | - Paul E Shaw
- Centre for Organic Photonics & Electronics, School of Mathematics & Physics, and School of Chemistry and Molecular Biosciences, The University of Queensland , Brisbane, Queensland 4072, Australia
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19
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Shen X, Han G, Yi Y. The nature of excited states in dipolar donor/fullerene complexes for organic solar cells: evolution with the donor stack size. Phys Chem Chem Phys 2016; 18:15955-63. [PMID: 27241621 DOI: 10.1039/c6cp02296k] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electronic delocalization at donor/acceptor (D/A) interfaces can play an important role in photocurrent generation for organic solar cells. Here, we have investigated the nature of local excited and interfacial charge transfer (CT) states in model complexes including one to four anti-parallel stacking dipolar donor (DTDCTB) molecules and one fullerene (C60) molecule by means of density functional theory (DFT) and time-dependent DFT (TDDFT). For all the donor-to-acceptor CT states, despite the number of DTDCTB molecules in the complexes, the hole is mainly localized on a single DTDCTB, and moves farther away from C60 for the energy higher level. However, the highest occupied molecular orbitals (HOMOs) and the excitonic states (EX) including the bright and dark EX are delocalized over the whole donor stacks in the complexes. This implies that the formation of ordered DTDCTB arrangements can substantially shorten the exciton diffusion process and facilitate ultrafast charge generation. Interestingly, owing to strong intermolecular Coulomb attraction, the donor-to-donor CT states are situated below the local excited states, but can approach the donor-to-acceptor CT states, indicating a weak role as charge traps. Our work would be helpful for understanding the electronic delocalization effects in organic solar cells.
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Affiliation(s)
- Xingxing Shen
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
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20
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Affiliation(s)
- Koen Vandewal
- Institut für Angewandte Photophysik, Technische Universität Dresden, 01062, Dresden, Germany;
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21
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Fazzi D, Barbatti M, Thiel W. Unveiling the Role of Hot Charge-Transfer States in Molecular Aggregates via Nonadiabatic Dynamics. J Am Chem Soc 2016; 138:4502-11. [DOI: 10.1021/jacs.5b13210] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Daniele Fazzi
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Mario Barbatti
- Aix Marseille Université, CNRS, ICR UMR7273, 13397 Marseille, France
| | - Walter Thiel
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
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22
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Roy P, Jha A, Dasgupta J. Photoinduced charge generation rates in soluble P3HT : PCBM nano-aggregates predict the solvent-dependent film morphology. NANOSCALE 2016; 8:2768-2777. [PMID: 26763690 DOI: 10.1039/c5nr06445g] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The device efficiency of bulk heterojunction (BHJ) solar cells is critically dependent on the nano-morphology of the solution-processed polymer : fullerene blend. Active control on blend morphology can only emanate from a detailed understanding of solution structures during the film casting process. Here we use photoinduced charge transfer (CT) rates to probe the effective length scale of the pre-formed solution structures and their energy disorder arising from a mixture of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in three different organic solvents. The observed solvent-dependent ultrafast biphasic rise of the transient polaron state in solution along with changes detected in the C=C stretching frequency of bound PCBM provides direct evidence for film-like P3HT : PCBM interfaces in solution. Using the diffusive component of the charge transfer rate, we deduce ∼3-times larger functional nano-domain size in toluene than in chlorobenzene thereby correctly predicting the relative polymer nanofiber widths observed in annealed films. We thus provide first experimental evidence for the postulated polymer : fullerene : solvent ternary phase that seeds the eventual morphology in spin-cast films. Our work motivates the design of new chemical additives to tune the grain size of the evolving polymer : fullerene domains within the solution phase.
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Affiliation(s)
- Palas Roy
- Department of Chemical Sciences, 1 Homi Bhabha Road, Tata Institute of Fundamental Research, Mumbai 400005, India.
| | - Ajay Jha
- Department of Chemical Sciences, 1 Homi Bhabha Road, Tata Institute of Fundamental Research, Mumbai 400005, India.
| | - Jyotishman Dasgupta
- Department of Chemical Sciences, 1 Homi Bhabha Road, Tata Institute of Fundamental Research, Mumbai 400005, India.
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23
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Constantinou I, Lai TH, Klump ED, Goswami S, Schanze KS, So F. Effect of Polymer Side Chains on Charge Generation and Disorder in PBDTTPD Solar Cells. ACS APPLIED MATERIALS & INTERFACES 2015; 7:26999-27005. [PMID: 26575214 DOI: 10.1021/acsami.5b09497] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The effect of polymer side chains on device performance was investigated for PBDT(EtHex)-TPD(Oct):PC70BM and PBDT(EtHex)-TPD(EtHex):PC70BM BHJ solar cells. Going from a linear side chain on the polymer's acceptor moiety to a branched side chain was determined to have a negative impact on the overall device efficiency, because of significantly reduced short-circuit current (J(sc)) and fill factor (FF) values. Sub-bandgap external quantum efficiency (EQE) and transient photoluminescence (PL) measurements showed more-efficient carrier generation for the polymer with linear side chains, because of a higher degree of charge-transfer (CT) state delocalization, leading to more-efficient exciton dissociation. Furthermore, the increase in π-π stacking distance and disorder for the bulkier ethylhexyl side chain were shown to result in a lower hole mobility, a higher bimolecular recombination, and a higher energetic disorder. The use of linear side chains on the polymer's acceptor moiety was shown to promote photogeneration, because of more-effective CT states and favorable carrier transport resulting in improved solar cell performance.
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Affiliation(s)
- Iordania Constantinou
- Department of Materials Science and Engineering, University of Florida , Gainesville, Florida 32611, United States
| | - Tzung-Han Lai
- Department of Materials Science and Engineering, University of Florida , Gainesville, Florida 32611, United States
| | - Erik D Klump
- Department of Materials Science and Engineering, University of Florida , Gainesville, Florida 32611, United States
| | - Subhadip Goswami
- Department of Chemistry, University of Florida , Gainesville, Florida 32611, United States
| | - Kirk S Schanze
- Department of Chemistry, University of Florida , Gainesville, Florida 32611, United States
| | - Franky So
- Department of Materials Science and Engineering, University of Florida , Gainesville, Florida 32611, United States
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24
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25
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Li Y, Zhou M, Niu Y, Guo Q, Xia A. Solvent-dependent intramolecular charge transfer delocalization/localization in multibranched push-pull chromophores. J Chem Phys 2015. [DOI: 10.1063/1.4926998] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Yang Li
- Beijing National Laboratory for Molecular Sciences (BNLMS) and Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Meng Zhou
- Beijing National Laboratory for Molecular Sciences (BNLMS) and Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Yingli Niu
- Beijing National Laboratory for Molecular Sciences (BNLMS) and Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Qianjin Guo
- Beijing National Laboratory for Molecular Sciences (BNLMS) and Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Andong Xia
- Beijing National Laboratory for Molecular Sciences (BNLMS) and Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
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26
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Long R, Prezhdo OV. Time-Domain Ab Initio Analysis of Excitation Dynamics in a Quantum Dot/Polymer Hybrid: Atomistic Description Rationalizes Experiment. NANO LETTERS 2015; 15:4274-4281. [PMID: 26061416 DOI: 10.1021/nl5046268] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Hybrid organic/inorganic polymer/quantum dot (QD) solar cells are an attractive alternative to the traditional cells. The original, simple models postulate that one-dimensional polymers have continuous energy levels, while zero-dimensional QDs exhibit atom-like electronic structure. A realistic, atomistic viewpoint provides an alternative description. Electronic states in polymers are molecule-like: finite in size and discrete in energy. QDs are composed of many atoms and have high, bulk-like densities of states. We employ ab initio time-domain simulation to model the experimentally observed ultrafast photoinduced dynamics in a QD/polymer hybrid and show that an atomistic description is essential for understanding the time-resolved experimental data. Both electron and hole transfers across the interface exhibit subpicosecond time scales. The interfacial processes are fast due to strong electronic donor-acceptor, as evidenced by the densities of the photoexcited states which are delocalized between the donor and the acceptor. The nonadiabatic charge-phonon coupling is also strong, especially in the polymer, resulting in rapid energy losses. The electron transfer from the polymer is notably faster than the hole transfer from the QD, due to a significantly higher density of acceptor states. The stronger molecule-like electronic and charge-phonon coupling in the polymer rationalizes why the electron-hole recombination inside the polymer is several orders of magnitude faster than in the QD. As a result, experiments exhibit multiple transfer times for the long-lived hole inside the QD, ranging from subpicoseconds to nanoseconds. In contrast, transfer of the short-lived electron inside the polymer does not occur beyond the first picosecond. The energy lost by the hole on its transit into the polymer is accommodated by polymer's high-frequency vibrations. The energy lost by the electron injected into the QD is accommodated primarily by much lower-frequency collective and QD modes. The electron dynamics is exponential, whereas evolution of the injected hole through the low density manifold of states of the polymer is highly nonexponential. The time scale of the electron-hole recombination at the interface is intermediate between those in pristine polymer and QD and is closer to that in the polymer. The detailed atomistic insights into the photoinduced charge and energy dynamics at the polymer/QD interface provide valuable guidelines for optimization of solar light harvesting and photovoltaic efficiency in modern nanoscale materials.
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Affiliation(s)
| | - Oleg V Prezhdo
- §Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
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27
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Yan H, Song Y, McKeown GR, Scholes GD, Seferos DS. Adding Amorphous Content to Highly Crystalline Polymer Nanowire Solar Cells Increases Performance. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2015; 27:3484-3491. [PMID: 25940102 DOI: 10.1002/adma.201501065] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 04/02/2015] [Indexed: 06/04/2023]
Abstract
Polymer solar cells are fabricated with systematic variation of the phase purity. Photovoltaic tests demonstrate that devices with ca. 10% of mixed phases outperform pure-phase devices. Photophysical studies reveal the effects of mixed phase on charge generation and recombination. These results show a promising strategy for the optimization of organic electronic materials.
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Affiliation(s)
- Han Yan
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada
| | - Yin Song
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada
| | - George R McKeown
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada
| | - Gregory D Scholes
- Department of Chemistry, Princeton University, Washington Road, Princeton, NJ, 08544, USA
| | - Dwight S Seferos
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada
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28
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Ke Y, Liu Y, Zhao Y. Visualization of Hot Exciton Energy Relaxation from Coherent to Diffusive Regimes in Conjugated Polymers: A Theoretical Analysis. J Phys Chem Lett 2015; 6:1741-1747. [PMID: 26263343 DOI: 10.1021/acs.jpclett.5b00490] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The unified coherent-to-diffusive energy relaxation of hot exciton in organic aggregates or polymers, which still remains largely unclear and is also a great challenge theoretically, is investigated from a time-dependent wavepacket diffusive approach. The results demonstrate that in the multiple time scale energy relaxation dynamics, the fast relaxation time essentially corresponds to the dephasing time of excitonic coherence motion, whereas the slow time is related to a hopping migration, and a suggested kinetic model successfully connects these two processes. The dependencies of those times on the initial energy and delocalization of exciton wavepacket as well as exciton-phonon interactions are further analyzed. The proposed method together with quantum chemistry calculations has explained an experimental observation of hot exciton energy relaxation in the low-bandgap copolymer PBDTTPD.
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Affiliation(s)
- Yaling Ke
- State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Yuxiu Liu
- State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Yi Zhao
- State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
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29
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Scarongella M, De Jonghe-Risse J, Buchaca-Domingo E, Causa' M, Fei Z, Heeney M, Moser JE, Stingelin N, Banerji N. A close look at charge generation in polymer:fullerene blends with microstructure control. J Am Chem Soc 2015; 137:2908-18. [PMID: 25650696 DOI: 10.1021/ja510032x] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We reveal some of the key mechanisms during charge generation in polymer:fullerene blends exploiting our well-defined understanding of the microstructures obtained in pBTTT:PCBM systems via processing with fatty acid methyl ester additives. Based on ultrafast transient absorption, electro-absorption, and fluorescence up-conversion spectroscopy, we find that exciton diffusion through relatively phase-pure polymer or fullerene domains limits the rate of electron and hole transfer, while prompt charge separation occurs in regions where the polymer and fullerene are molecularly intermixed (such as the co-crystal phase where fullerenes intercalate between polymer chains in pBTTT:PCBM). We moreover confirm the importance of neat domains, which are essential to prevent geminate recombination of bound electron-hole pairs. Most interestingly, using an electro-absorption (Stark effect) signature, we directly visualize the migration of holes from intermixed to neat regions, which occurs on the subpicosecond time scale. This ultrafast transport is likely sustained by high local mobility (possibly along chains extending from the co-crystal phase to neat regions) and by an energy cascade driving the holes toward the neat domains.
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Affiliation(s)
- Mariateresa Scarongella
- Institute of Chemical Sciences & Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL) , SB ISIC GR-MO, Station 6, CH-1015 Lausanne, Switzerland
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30
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Barker AJ, Chen K, Hodgkiss JM. Distance distributions of photogenerated charge pairs in organic photovoltaic cells. J Am Chem Soc 2014; 136:12018-26. [PMID: 25102389 DOI: 10.1021/ja505380j] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Strong Coulomb interactions in organic photovoltaic cells dictate that charges must separate over relatively long distances in order to circumvent geminate recombination and produce photocurrent. In this article, we measure the distance distributions of thermalized charge pairs by accessing a regime at low temperature where charge pairs are frozen out following the primary charge separation step and recombine monomolecularly via tunneling. The exponential attenuation of tunneling rate with distance provides a sensitive probe of the distance distribution of primary charge pairs, reminiscent of electron transfer studies in proteins. By fitting recombination dynamics to distributions of recombination rates, we identified populations of charge-transfer states and well-separated charge pairs. For the wide range of materials we studied, the yield of separated charges in the tunneling regime is strongly correlated with the yield of free charges measured via their intensity-dependent bimolecular recombination dynamics at room temperature. We therefore conclude that populations of free charges are established via long-range charge separation within the thermalization time scale, thus invoking early branching between free and bound charges across an energetic barrier. Subject to assumed values of the electron tunneling attenuation constant, we estimate critical charge separation distances of ∼3-4 nm in all materials. In some blends, large fullerene crystals can enhance charge separation yields; however, the important role of the polymers is also highlighted in blends that achieved significant charge separation with minimal fullerene concentration. We expect that our approach of isolating the intrinsic properties of primary charge pairs will be of considerable value in guiding new material development and testing the validity of proposed mechanisms for long-range charge separation.
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Affiliation(s)
- Alex J Barker
- The MacDiarmid Institute for Advanced Materials and Nanotechnology , Wellington 6140, New Zealand
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31
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Guo Z, Lee D, Schaller RD, Zuo X, Lee B, Luo T, Gao H, Huang L. Relationship between Interchain Interaction, Exciton Delocalization, and Charge Separation in Low-Bandgap Copolymer Blends. J Am Chem Soc 2014; 136:10024-32. [DOI: 10.1021/ja503465s] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
| | | | - Richard D. Schaller
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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32
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Tamai Y, Tsuda K, Ohkita H, Benten H, Ito S. Charge-carrier generation in organic solar cells using crystalline donor polymers. Phys Chem Chem Phys 2014; 16:20338-46. [PMID: 24980903 DOI: 10.1039/c4cp01820f] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Charge generation and recombination dynamics in a blend film of a crystalline low-bandgap polymer, poly[(4,4-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-4,7-diyl] (PSBTBT), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were studied by transient absorption spectroscopy. Upon photoexcitation of the PSBTBT absorption band at 800 nm, singlet excitons were promptly generated, and then rapidly converted into polarons in a few picoseconds. We found that there are two different polarons in PSBTBT: one is ascribed to polarons generated in the disorder phase and the other is ascribed to polarons in the crystalline phase. On a time scale of nanoseconds, ∼50% of polarons in the disorder phase recombined geminately to the ground state. On the other hand, such geminate recombination was negligible for polarons in the crystalline phase. As a result, the overall charge dissociation efficiency is as high as ∼75% for PSBTBT/PCBM blend films. On the basis of these analyses, we discuss the role of polymer crystallinity in the charge-carrier generation in organic solar cells.
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Affiliation(s)
- Yasunari Tamai
- Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510, Japan.
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Albrecht S, Tumbleston JR, Janietz S, Dumsch I, Allard S, Scherf U, Ade H, Neher D. Quantifying Charge Extraction in Organic Solar Cells: The Case of Fluorinated PCPDTBT. J Phys Chem Lett 2014; 5:1131-1138. [PMID: 26274460 DOI: 10.1021/jz500457b] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We introduce a new and simple method to quantify the effective extraction mobility in organic solar cells at low electric fields and charge carrier densities comparable to operation conditions under one sun illumination. By comparing steady-state carrier densities at constant illumination intensity and under open-circuit conditions, the gradient of the quasi-Fermi potential driving the current is estimated as a function of external bias and charge density. These properties are then related to the respective steady-state current to determine the effective extraction mobility. The new technique is applied to different derivatives of the well-known low-band-gap polymer PCPDTBT blended with PC70BM. We show that the slower average extraction due to lower mobility accounts for the moderate fill factor when solar cells are fabricated with mono- or difluorinated PCPDTBT. This lower extraction competes with improved generation and reduced nongeminate recombination, rendering the monofluorinated derivative the most efficient donor polymer.
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Affiliation(s)
- Steve Albrecht
- †Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
| | - John R Tumbleston
- ‡Department of Physics, North Carolina State University, 421 Riddick Hall, Raleigh, North Carolina 27695-8202, United States
| | - Silvia Janietz
- §Fraunhofer Institut für Angewandte Polymerforschung, Geiselbergstr. 69, 14476 Potsdam, Germany
| | - Ines Dumsch
- ∥Bergische Universität Wuppertal, Institut für Polymertechnologie, Gauss-Str. 20, 42097 Wuppertal, Germany
| | - Sybille Allard
- ∥Bergische Universität Wuppertal, Institut für Polymertechnologie, Gauss-Str. 20, 42097 Wuppertal, Germany
| | - Ullrich Scherf
- ∥Bergische Universität Wuppertal, Institut für Polymertechnologie, Gauss-Str. 20, 42097 Wuppertal, Germany
| | - Harald Ade
- ‡Department of Physics, North Carolina State University, 421 Riddick Hall, Raleigh, North Carolina 27695-8202, United States
| | - Dieter Neher
- †Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
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