1
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Royakkers J, Yang H, Gillett AJ, Eisner F, Ghosh P, Congrave DG, Azzouzi M, Andaji-Garmaroudi Z, Leventis A, Rao A, Frost JM, Nelson J, Bronstein H. Synthesis of model heterojunction interfaces reveals molecular-configuration-dependent photoinduced charge transfer. Nat Chem 2024:10.1038/s41557-024-01578-x. [PMID: 39164580 DOI: 10.1038/s41557-024-01578-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Accepted: 06/12/2024] [Indexed: 08/22/2024]
Abstract
Control of the molecular configuration at the interface of an organic heterojunction is key to the development of efficient optoelectronic devices. Due to the difficulty in characterizing these buried and (probably) disordered heterointerfaces, the interfacial structure in most systems remains a mystery. Here we demonstrate a synthetic strategy to design and control model interfaces, enabling their detailed study in isolation from the bulk material. This is achieved by the synthesis of a polymer in which a non-fullerene acceptor moiety is covalently bonded to a donor polymer backbone using dual alkyl chain links, constraining the acceptor and donor units in a through space co-facial arrangement. The constrained geometry of the acceptor relative to the electron-rich and -poor moieties in the polymer backbone can be tuned to control the kinetics of charge separation and the energy of the resultant charge-transfer state giving insight into factors that govern charge generation at organic heterojunctions.
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Affiliation(s)
- Jeroen Royakkers
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Hanbo Yang
- Department of Physics, Imperial College London, London, UK
| | | | - Flurin Eisner
- Department of Physics, Imperial College London, London, UK.
- School of Materials Science and Engineering, Queen Mary University of London, London, UK.
| | - Pratyush Ghosh
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Daniel G Congrave
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | | | | | - Anastasia Leventis
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Akshay Rao
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Jarvist Moore Frost
- Department of Physics, Imperial College London, London, UK
- Department of Chemistry, Imperial College London, London, UK
| | - Jenny Nelson
- Department of Physics, Imperial College London, London, UK.
| | - Hugo Bronstein
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK.
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.
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2
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Wang C, Wu B, Li Y, Zhou S, Wu C, Dong T, Jiang Y, Hua Z, Song Y, Wen W, Tian J, Chai Y, Wen R, Wang C. Aggregation promotes charge separation in fullerene-indacenodithiophene dyad. Nat Commun 2024; 15:5681. [PMID: 38971813 PMCID: PMC11227505 DOI: 10.1038/s41467-024-50001-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Accepted: 06/25/2024] [Indexed: 07/08/2024] Open
Abstract
Fast photoinduced charge separation (CS) and long-lived charge-separated state (CSS) in small-molecules facilitate light-energy conversion, while simultaneous attainment of both remains challenging. Here we accomplish this through aggregation based on fullerene-indacenodithiophene dyads. Transient absorption spectroscopy reveals that, compared to solution, the CS time in aggregates is accelerated from 41.5 ps to 0.4 ps, and the CSS lifetime is prolonged from 311.4 ps to 40 μs, indicating that aggregation concomitantly promotes fast CS and long-lived CSS. Fast CS arises from the hot charge-transfer states dissociation, opening up additional resonant channels to free carriers (FCs); subsequently, charge recombination into intramolecular triplet CSS becomes favorable mediated by spin-uncorrelated FCs. Different from fullerene/indacenodithiophene blends, the unique CS mechanism in dyad aggregates reduces the long-lived CSS dependence on molecular order, resulting in a CSS lifetime 200 times longer than blends. This endows the dyad aggregates to exhibit both photoelectronic switch properties and superior photocatalytic capabilities.
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Affiliation(s)
- Chong Wang
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Bo Wu
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
- University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Yang Li
- School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing, 100876, China
| | - Shen Zhou
- College of Science, Hunan Key Laboratory of Mechanism and Technology of Quantum Information, National University of Defense Technology, Changsha, 410003, China
| | - Conghui Wu
- Spin-X Institute, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, 511442, China
| | - Tianyang Dong
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
| | - Ying Jiang
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Zihui Hua
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yupeng Song
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
- Key Laboratory of Photochemical Conversion and Optoelectronic Materials and CityU-CAS Joint Laboratory of Functional Materials and Devices, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
| | - Wei Wen
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
| | - Jianxin Tian
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yongqiang Chai
- Department of Chemistry and Pharmacy and Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, 91058, Germany
| | - Rui Wen
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Chunru Wang
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
- University of Chinese Academy of Sciences, Beijing, 100049, China.
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3
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Diaz-Andres A, Tonnelé C, Casanova D. Electronic Couplings for Triplet-Triplet Annihilation Upconversion in Crystal Rubrene. J Chem Theory Comput 2024; 20:4288-4297. [PMID: 38743825 PMCID: PMC11137828 DOI: 10.1021/acs.jctc.4c00185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 05/06/2024] [Accepted: 05/06/2024] [Indexed: 05/16/2024]
Abstract
Triplet-triplet annihilation photon upconversion (TTA-UC) is a process able to repackage two low-frequency photons into light of higher energy. This transformation is typically orchestrated by the electronic degrees of freedom within organic compounds possessing suitable singlet and triplet energies and electronic couplings. In this work, we propose a computational protocol for the assessment of electronic couplings crucial to TTA-UC in molecular materials and apply it to the study of crystal rubrene. Our methodology integrates sophisticated yet computationally affordable approaches to quantify couplings in singlet and triplet energy transfer, the binding of triplet pairs, and the fusion to the singlet exciton. Of particular significance is the role played by charge-transfer states along the b-axis of rubrene crystal, acting as both partial quenchers of singlet energy transfer and mediators of triplet fusion. Our calculations identify the π-stacking direction as holding notable triplet energy transfer couplings, consistent with the experimentally observed anisotropic exciton diffusion. Finally, we have characterized the impact of thermally induced structural distortions, revealing their key role in the viability of triplet fusion and singlet fission. We posit that our approaches are transferable to a broad spectrum of organic molecular materials, offering a feasible means to quantify electronic couplings.
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Affiliation(s)
- Aitor Diaz-Andres
- Donostia
International Physics Center (DIPC), Donostia 20018, Euskadi, Spain
| | - Claire Tonnelé
- Donostia
International Physics Center (DIPC), Donostia 20018, Euskadi, Spain
- IKERBASQUE,
Basque Foundation for Science, Bilbao 48009, Euskadi, Spain
| | - David Casanova
- Donostia
International Physics Center (DIPC), Donostia 20018, Euskadi, Spain
- IKERBASQUE,
Basque Foundation for Science, Bilbao 48009, Euskadi, Spain
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4
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Mei K, Borrelli WR, Vong A, Schwartz BJ. Using Machine Learning to Understand the Causes of Quantum Decoherence in Solution-Phase Bond-Breaking Reactions. J Phys Chem Lett 2024; 15:903-911. [PMID: 38241152 PMCID: PMC10839908 DOI: 10.1021/acs.jpclett.3c03474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2023] [Revised: 01/11/2024] [Accepted: 01/16/2024] [Indexed: 01/21/2024]
Abstract
Decoherence is a fundamental phenomenon that occurs when an entangled quantum state interacts with its environment, leading to collapse of the wave function. The inevitability of decoherence provides one of the most intrinsic limits of quantum computing. However, there has been little study of the precise chemical motions from the environment that cause decoherence. Here, we use quantum molecular dynamics simulations to explore the photodissociation of Na2+ in liquid Ar, in which solvent fluctuations induce decoherence and thus determine the products of chemical bond breaking. We use machine learning to characterize the solute-solvent environment as a high-dimensional feature space that allows us to predict when and onto which photofragment the bonding electron will localize. We find that reaching a requisite photofragment separation and experiencing out-of-phase solvent collisions underlie decoherence during chemical bond breaking. Our work highlights the utility of machine learning for interpreting complex solution-phase chemical processes as well as identifies the molecular underpinnings of decoherence.
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Affiliation(s)
- Kenneth
J. Mei
- Department of Chemistry &
Biochemistry, University of California,
Los Angeles, Los Angeles, California 90095-1569, United States
| | - William R. Borrelli
- Department of Chemistry &
Biochemistry, University of California,
Los Angeles, Los Angeles, California 90095-1569, United States
| | - Andy Vong
- Department of Chemistry &
Biochemistry, University of California,
Los Angeles, Los Angeles, California 90095-1569, United States
| | - Benjamin J. Schwartz
- Department of Chemistry &
Biochemistry, University of California,
Los Angeles, Los Angeles, California 90095-1569, United States
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5
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Gómez-Ruiz FJ, Acevedo OL, Rodríguez FJ, Quiroga L, Johnson NF. Energy transfer in N-component nanosystems enhanced by pulse-driven vibronic many-body entanglement. Sci Rep 2023; 13:19790. [PMID: 37968301 PMCID: PMC10651905 DOI: 10.1038/s41598-023-46256-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Accepted: 10/30/2023] [Indexed: 11/17/2023] Open
Abstract
The processing of energy by transfer and redistribution, plays a key role in the evolution of dynamical systems. At the ultrasmall and ultrafast scale of nanosystems, quantum coherence could in principle also play a role and has been reported in many pulse-driven nanosystems (e.g. quantum dots and even the microscopic Light-Harvesting Complex II (LHC-II) aggregate). Typical theoretical analyses cannot easily be scaled to describe these general N-component nanosystems; they do not treat the pulse dynamically; and they approximate memory effects. Here our aim is to shed light on what new physics might arise beyond these approximations. We adopt a purposely minimal model such that the time-dependence of the pulse is included explicitly in the Hamiltonian. This simple model generates complex dynamics: specifically, pulses of intermediate duration generate highly entangled vibronic (i.e. electronic-vibrational) states that spread multiple excitons - and hence energy - maximally within the system. Subsequent pulses can then act on such entangled states to efficiently channel subsequent energy capture. The underlying pulse-generated vibronic entanglement increases in strength and robustness as N increases.
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Affiliation(s)
- Fernando J Gómez-Ruiz
- Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, 47011, Valladolid, Spain
- Instituto de Física Fundamental IFF-CSIC, Calle Serrano 113b, 28006, Madrid, Spain
| | - Oscar L Acevedo
- Escuela de Ciencias Básicas, Institución Universitaria Politécnico Grancolombiano, Bogotá, D.C, 110231, Colombia
| | - Ferney J Rodríguez
- Departamento de Física, Universidad de los Andes, A.A. 4976, Bogotá, D.C, Colombia
| | - Luis Quiroga
- Departamento de Física, Universidad de los Andes, A.A. 4976, Bogotá, D.C, Colombia
| | - Neil F Johnson
- Physics Department, George Washington University, Washington, D.C, 20052, USA.
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6
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Balzer D, Kassal I. Even a little delocalization produces large kinetic enhancements of charge-separation efficiency in organic photovoltaics. SCIENCE ADVANCES 2022; 8:eabl9692. [PMID: 35960797 PMCID: PMC9374333 DOI: 10.1126/sciadv.abl9692] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Accepted: 06/28/2022] [Indexed: 05/25/2023]
Abstract
In organic photovoltaics, charges can separate efficiently even if their Coulomb attraction is an order of magnitude greater than the available thermal energy. Delocalization has been suggested to explain this fact, because it could increase the initial separation of charges in the charge-transfer (CT) state, reducing their attraction. However, understanding the mechanism requires a kinetic model of delocalized charge separation, which has proven difficult because it involves tracking the correlated quantum-mechanical motion of the electron and the hole in large simulation boxes required for disordered materials. Here, we report the first three-dimensional simulations of charge-separation dynamics in the presence of disorder, delocalization, and polaron formation, finding that even slight delocalization, across less than two molecules, can substantially enhance the charge-separation efficiency, even starting with thermalized CT states. Delocalization does not enhance efficiency by reducing the Coulomb attraction; instead, the enhancement is a kinetic effect produced by the increased overlap of electronic states.
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7
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Peng WT, Brey D, Giannini S, Dell’Angelo D, Burghardt I, Blumberger J. Exciton Dissociation in a Model Organic Interface: Excitonic State-Based Surface Hopping versus Multiconfigurational Time-Dependent Hartree. J Phys Chem Lett 2022; 13:7105-7112. [PMID: 35900333 PMCID: PMC9376959 DOI: 10.1021/acs.jpclett.2c01928] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Accepted: 07/19/2022] [Indexed: 05/20/2023]
Abstract
Quantum dynamical simulations are essential for a molecular-level understanding of light-induced processes in optoelectronic materials, but they tend to be computationally demanding. We introduce an efficient mixed quantum-classical nonadiabatic molecular dynamics method termed eXcitonic state-based Surface Hopping (X-SH), which propagates the electronic Schrödinger equation in the space of local excitonic and charge-transfer electronic states, coupled to the thermal motion of the nuclear degrees of freedom. The method is applied to exciton decay in a 1D model of a fullerene-oligothiophene junction, and the results are compared to the ones from a fully quantum dynamical treatment at the level of the Multilayer Multiconfigurational Time-Dependent Hartree (ML-MCTDH) approach. Both methods predict that charge-separated states are formed on the 10-100 fs time scale via multiple "hot-exciton dissociation" pathways. The results demonstrate that X-SH is a promising tool advancing the simulation of photoexcited processes from the molecular to the true nanomaterials scale.
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Affiliation(s)
- Wei-Tao Peng
- Department
of Physics and Astronomy and Thomas Young Centre, University College London, London WC1E 6BT, United Kingdom
| | - Dominik Brey
- Institute
of Physical and Theoretical Chemistry, Goethe
University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany
| | - Samuele Giannini
- Department
of Physics and Astronomy and Thomas Young Centre, University College London, London WC1E 6BT, United Kingdom
| | - David Dell’Angelo
- Department
of Physics and Astronomy and Thomas Young Centre, University College London, London WC1E 6BT, United Kingdom
| | - Irene Burghardt
- Institute
of Physical and Theoretical Chemistry, Goethe
University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany
| | - Jochen Blumberger
- Department
of Physics and Astronomy and Thomas Young Centre, University College London, London WC1E 6BT, United Kingdom
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8
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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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9
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Huang Y, Zhang L, Hao Y. Why ultrafast charge separation occurs in bulk-heterojunction organic solar cells: a multichain tight binding model study. Phys Chem Chem Phys 2021; 23:22685-22691. [PMID: 34604887 DOI: 10.1039/d1cp03686f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Bulk-heterojunction (BHJ) organic solar cells (OSCs) exhibit ultrafast charge separation (UCS) which enables lower geminate charge recombination and high internal quantum efficiency. Unravelling why UCS occurs in BHJ-OSCs is important for the exploration of devices in future, however it is still far from clear. In this work, we build a multichain tight-binding model to study the conditions for realizing UCS. We propose that two conditions are important: (i) the BHJ-OSC has a morphology with donor and acceptor molecules being individually aggregated; (ii) the ratio of the donor/acceptor interfacial coupling to the internal donor/donor and acceptor/acceptor coupling should be smaller than a threshold. In addition, we suggest that increasing the donor/acceptor energetic offset will boost the UCS efficiency. As a fundamental theoretical analysis on the underlying mechanism of UCS, our work provides design rules for optimizing high-performance BHJ OSCs.
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Affiliation(s)
- Yujuan Huang
- College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan, 030024, China.
| | - Longlong Zhang
- College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan, 030024, China.
| | - Yuying Hao
- College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan, 030024, China.
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10
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Balzer D, Smolders TJAM, Blyth D, Hood SN, Kassal I. Delocalised kinetic Monte Carlo for simulating delocalisation-enhanced charge and exciton transport in disordered materials. Chem Sci 2020; 12:2276-2285. [PMID: 34163994 PMCID: PMC8179315 DOI: 10.1039/d0sc04116e] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 12/16/2020] [Indexed: 01/08/2023] Open
Abstract
Charge transport is well understood in both highly ordered materials (band conduction) or highly disordered ones (hopping conduction). In moderately disordered materials-including many organic semiconductors-the approximations valid in either extreme break down, making it difficult to accurately model the conduction. In particular, describing wavefunction delocalisation requires a quantum treatment, which is difficult in disordered materials that lack periodicity. Here, we present the first three-dimensional model of partially delocalised charge and exciton transport in materials in the intermediate disorder regime. Our approach is based on polaron-transformed Redfield theory, but overcomes several computational roadblocks by mapping the quantum-mechanical techniques onto kinetic Monte Carlo. Our theory, delocalised kinetic Monte Carlo (dKMC), shows that the fundamental physics of transport in moderately disordered materials is that of charges hopping between partially delocalised electronic states. Our results reveal why standard kinetic Monte Carlo can dramatically underestimate mobilities even in disordered organic semiconductors, where even a little delocalisation can substantially enhance mobilities, as well as showing that three-dimensional calculations capture important delocalisation effects neglected in lower-dimensional approximations.
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Affiliation(s)
- Daniel Balzer
- School of Chemistry and University of Sydney Nano Institute, University of Sydney NSW 2006 Australia
| | - Thijs J A M Smolders
- School of Chemistry and University of Sydney Nano Institute, University of Sydney NSW 2006 Australia
- Institute for Molecules and Materials, Radboud University 6525 AJ Nijmegen The Netherlands
| | - David Blyth
- School of Mathematics and Physics, University of Queensland St. Lucia QLD 4072 Australia
| | - Samantha N Hood
- School of Mathematics and Physics, University of Queensland St. Lucia QLD 4072 Australia
| | - Ivan Kassal
- School of Chemistry and University of Sydney Nano Institute, University of Sydney NSW 2006 Australia
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11
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Moore GJ, Causa' M, Martinez Hardigree JF, Karuthedath S, Ramirez I, Jungbluth A, Laquai F, Riede M, Banerji N. Ultrafast Charge Dynamics in Dilute-Donor versus Highly Intermixed TAPC:C 60 Organic Solar Cell Blends. J Phys Chem Lett 2020; 11:5610-5617. [PMID: 32564605 DOI: 10.1021/acs.jpclett.0c01495] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Elucidating the interplay between film morphology, photophysics, and device performance of bulk heterojunction (BHJ) organic photovoltaics remains challenging. Here, we use the well-defined morphology of vapor-deposited di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane (TAPC):C60 blends to address charge generation and recombination by transient ultrafast spectroscopy. We gain relevant new insights to the functioning of dilute-donor (5% TAPC) fullerene-based BHJs compared to molecularly intermixed systems (50% TAPC). First, we show that intermolecular charge-transfer (CT) excitons in the C60 clusters of dilute BHJs rapidly localize to Frenkel excitons prior to dissociating at the donor:acceptor interface. Thus, both Frenkel and CT excitons generate photocurrent over the entire fullerene absorption range. Second, we selectively monitor interfacial and bulk C60 clusters via their electro-absorption, demonstrating an energetic gradient that assists free charge generation. Third, we identify a fast (<1 ns) recombination channel, whereby free electrons recombine with trapped holes on isolated TAPC molecules. This can harm the performance of dilute solar cells, unless the electrons are rapidly extracted in efficient devices.
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Affiliation(s)
- Gareth John Moore
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
| | - Martina Causa'
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
| | | | - Safakath Karuthedath
- King Abdullah University of Science and Technology (KAUST), KAUST Solar Center (KSC), Physical Science and Engineering Division (PSE), Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Ivan Ramirez
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, OX1 3PU Oxford, U.K
| | - Anna Jungbluth
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, OX1 3PU Oxford, U.K
| | - Frédéric Laquai
- King Abdullah University of Science and Technology (KAUST), KAUST Solar Center (KSC), Physical Science and Engineering Division (PSE), Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Moritz Riede
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, OX1 3PU Oxford, U.K
| | - Natalie Banerji
- Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
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12
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Nelson TR, White AJ, Bjorgaard JA, Sifain AE, Zhang Y, Nebgen B, Fernandez-Alberti S, Mozyrsky D, Roitberg AE, Tretiak S. Non-adiabatic Excited-State Molecular Dynamics: Theory and Applications for Modeling Photophysics in Extended Molecular Materials. Chem Rev 2020; 120:2215-2287. [PMID: 32040312 DOI: 10.1021/acs.chemrev.9b00447] [Citation(s) in RCA: 213] [Impact Index Per Article: 53.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Optically active molecular materials, such as organic conjugated polymers and biological systems, are characterized by strong coupling between electronic and vibrational degrees of freedom. Typically, simulations must go beyond the Born-Oppenheimer approximation to account for non-adiabatic coupling between excited states. Indeed, non-adiabatic dynamics is commonly associated with exciton dynamics and photophysics involving charge and energy transfer, as well as exciton dissociation and charge recombination. Understanding the photoinduced dynamics in such materials is vital to providing an accurate description of exciton formation, evolution, and decay. This interdisciplinary field has matured significantly over the past decades. Formulation of new theoretical frameworks, development of more efficient and accurate computational algorithms, and evolution of high-performance computer hardware has extended these simulations to very large molecular systems with hundreds of atoms, including numerous studies of organic semiconductors and biomolecules. In this Review, we will describe recent theoretical advances including treatment of electronic decoherence in surface-hopping methods, the role of solvent effects, trivial unavoided crossings, analysis of data based on transition densities, and efficient computational implementations of these numerical methods. We also emphasize newly developed semiclassical approaches, based on the Gaussian approximation, which retain phase and width information to account for significant decoherence and interference effects while maintaining the high efficiency of surface-hopping approaches. The above developments have been employed to successfully describe photophysics in a variety of molecular materials.
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Affiliation(s)
- Tammie R Nelson
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Alexander J White
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Josiah A Bjorgaard
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Andrew E Sifain
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States.,U.S. Army Research Laboratory , Aberdeen Proving Ground , Maryland 21005 , United States
| | - Yu Zhang
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Benjamin Nebgen
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | | | - Dmitry Mozyrsky
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Adrian E Roitberg
- Department of Chemistry , University of Florida , Gainesville , Florida 32611 , United States
| | - Sergei Tretiak
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
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13
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Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes. Nat Commun 2020; 11:617. [PMID: 32001688 PMCID: PMC6992633 DOI: 10.1038/s41467-020-14476-w] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Accepted: 01/09/2020] [Indexed: 11/24/2022] Open
Abstract
Charge separation dynamics after the absorption of a photon is a fundamental process relevant both for photosynthetic reaction centers and artificial solar conversion devices. It has been proposed that quantum coherence plays a role in the formation of charge carriers in organic photovoltaics, but experimental proofs have been lacking. Here we report experimental evidence of coherence in the charge separation process in organic donor/acceptor heterojunctions, in the form of low frequency oscillatory signature in the kinetics of the transient absorption and nonlinear two-dimensional photocurrent spectroscopy. The coherence plays a decisive role in the initial ~200 femtoseconds as we observe distinct experimental signatures of coherent photocurrent generation. This coherent process breaks the energy barrier limitation for charge formation, thus competing with excitation energy transfer. The physics may inspire the design of new photovoltaic materials with high device performance, which explore the quantum effects in the next-generation optoelectronic applications. Although coherent vibrational motion in donor-acceptor blends may contribute to photogeneration generation in organic solar cells (OSCs), proof of a direct correlation is still lacking. Here, the authors report the role of vibrational coherence on photocurrent generation in ternary OSC blends.
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14
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15
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Kelly A. Exciton dissociation and charge separation at donor–acceptor interfaces from quantum-classical dynamics simulations. Faraday Discuss 2020; 221:547-563. [DOI: 10.1039/c9fd00069k] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Nonadiabatic dynamics simulations based on the quantum-classical Liouville equation are employed to study the real-time dynamics of exciton dissociation and charge separation at a model donor–acceptor interface.
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Affiliation(s)
- Aaron Kelly
- Department of Chemistry
- Dalhousie University
- Halifax
- Canada
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16
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Marmolejo-Valencia AF, Mata-Pinzón Z, Dominguez L, Amador-Bedolla C. Atomistic simulations of bulk heterojunctions to evaluate the structural and packing properties of new predicted donors in OPVs. Phys Chem Chem Phys 2019; 21:20315-20326. [PMID: 31495832 DOI: 10.1039/c9cp04041b] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Organic photovoltaic materials (OPVs), with low cost and structure flexibility, are of great interest and importance for their application in solar cell device development. However, the optimization of new OPV structures and the study of the structure arrangements and packing morphologies when materials are blended takes time and consumes raw materials, thus theoretical models could be of considerable value. In this work, we performed molecular dynamics simulations of present OPVs to understand the morphological packing of the donor-acceptor (DA) phases and DA heterojunction during evaporation and annealing processes, following inter and intramolecular properties like frontier orbitals, π-π stacking, coordination, distances, angles, and aggregation. Our considered donor molecules were selected from already proved experimental studies and also from predicted optimal compounds, designed through high throughput studies. The acceptor molecule employed in all our studied systems was PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). Furthermore, we also analyze the influence of including different lateral aliphatic chains on the structural properties of the resulting DA packing morphologies. Our results can guide the design of new OPVs and subsequent studies applying charge transport and charge separation models.
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Affiliation(s)
- Andrés F Marmolejo-Valencia
- Facultad de Química, Universidad Nacional Autónoma de México, Av. Universidad 3000, Coyoacán, CDMX 04510, Mexico.
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17
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Alvertis AM, Schröder FAYN, Chin AW. Non-equilibrium relaxation of hot states in organic semiconductors: Impact of mode-selective excitation on charge transfer. J Chem Phys 2019; 151:084104. [PMID: 31470711 DOI: 10.1063/1.5115239] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The theoretical study of open quantum systems strongly coupled to a vibrational environment remains computationally challenging due to the strongly non-Markovian characteristics of the dynamics. We study this problem in the case of a molecular dimer of the organic semiconductor tetracene, the exciton states of which are strongly coupled to a few hundreds of molecular vibrations. To do so, we employ a previously developed tensor network approach, based on the formalism of matrix product states. By analyzing the entanglement structure of the system wavefunction, we can expand it in a tree tensor network state, which allows us to perform a fully quantum mechanical time evolution of the exciton-vibrational system, including the effect of 156 molecular vibrations. We simulate the dynamics of hot states, i.e., states resulting from excess energy photoexcitation, by constructing various initial bath states, and show that the exciton system indeed has a memory of those initial configurations. In particular, the specific pathway of vibrational relaxation is shown to strongly affect the quantum coherence between exciton states in time scales relevant for the ultrafast dynamics of application-relevant processes such as charge transfer. The preferential excitation of low-frequency modes leads to a limited number of relaxation pathways, thus "protecting" quantum coherence and leading to a significant increase in the charge transfer yield in the dimer structure.
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Affiliation(s)
- Antonios M Alvertis
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Florian A Y N Schröder
- Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Alex W Chin
- CNRS, Institut des NanoSciences de Paris, Sorbonne Université, 4 place Jussieu boite courrier 840, 75252 Paris Cedex 05, France
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18
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19
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Dimitrov SD, Azzouzi M, Wu J, Yao J, Dong Y, Tuladhar PS, Schroeder BC, Bittner ER, McCulloch I, Nelson J, Durrant JR. Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends. J Am Chem Soc 2019; 141:4634-4643. [PMID: 30807130 PMCID: PMC6429453 DOI: 10.1021/jacs.8b11484] [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] [Indexed: 11/28/2022]
Abstract
![]()
Despite
performance improvements of organic photovoltaics, the
mechanism of photoinduced electron–hole separation at organic
donor–acceptor interfaces remains poorly understood. Inconclusive
experimental and theoretical results have produced contradictory models
for electron–hole separation in which the role of interfacial
charge-transfer (CT) states is unclear, with one model identifying
them as limiting separation and another as readily dissociating. Here,
polymer–fullerene blends with contrasting photocurrent properties
and enthalpic offsets driving separation were studied. By modifying
composition, film structures were varied from consisting of molecularly
mixed polymer–fullerene domains to consisting of both molecularly
mixed and fullerene domains. Transient absorption spectroscopy revealed
that CT state dissociation generating separated electron–hole
pairs is only efficient in the high energy offset blend with fullerene
domains. In all other blends (with low offset or predominantly molecularly
mixed domains), nanosecond geminate electron–hole recombination
is observed revealing the importance of spatially localized electron–hole
pairs (bound CT states) in the electron–hole dynamics. A two-dimensional
lattice exciton model was used to simulate the excited state spectrum
of a model system as a function of microstructure and energy offset.
The results could reproduce the main features of experimental electroluminescence
spectra indicating that electron–hole pairs become less bound
and more spatially separated upon increasing energy offset and fullerene
domain density. Differences between electroluminescence and photoluminescence
spectra could be explained by CT photoluminescence being dominated
by more-bound states, reflecting geminate recombination processes,
while CT electroluminescence preferentially probes less-bound CT states
that escape geminate recombination. These results suggest that apparently
contradictory studies on electron–hole separation can be explained
by the presence of both bound and unbound CT states in the same film,
as a result of a range of interface structures.
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Affiliation(s)
- S D Dimitrov
- SPECIFIC, College of Engineering , Swansea University , Bay Campus , Swansea SA1 8EN , United Kingdom
| | | | | | | | | | | | - B C Schroeder
- Department of Chemistry , University College , London WC1H 0AJ , United Kingdom
| | - E R Bittner
- Department of Chemistry , University of Houston , Houston , Texas 77204 , United States
| | - I McCulloch
- Physical Sciences and Engineering Division, KAUST Solar Center (KSC) , King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900 , Kingdom of Saudi Arabia
| | | | - J R Durrant
- SPECIFIC, College of Engineering , Swansea University , Bay Campus , Swansea SA1 8EN , United Kingdom
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20
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Lankevich V, Bittner ER. Relating free energy and open-circuit voltage to disorder in organic photovoltaic systems. J Chem Phys 2018; 149:244123. [DOI: 10.1063/1.5050506] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Affiliation(s)
- V. Lankevich
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
| | - E. R. Bittner
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
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21
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Dorfman KE, Xu D, Cao J. Efficiency at maximum power of a laser quantum heat engine enhanced by noise-induced coherence. Phys Rev E 2018; 97:042120. [PMID: 29758726 DOI: 10.1103/physreve.97.042120] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2017] [Indexed: 06/08/2023]
Abstract
Quantum coherence has been demonstrated in various systems including organic solar cells and solid state devices. In this article, we report the lower and upper bounds for the performance of quantum heat engines determined by the efficiency at maximum power. Our prediction based on the canonical three-level Scovil and Schulz-Dubois maser model strongly depends on the ratio of system-bath couplings for the hot and cold baths and recovers the theoretical bounds established previously for the Carnot engine. Further, introducing a fourth level to the maser model can enhance the maximal power and its efficiency, thus demonstrating the importance of quantum coherence in the thermodynamics and operation of the heat engines beyond the classical limit.
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Affiliation(s)
- Konstantin E Dorfman
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Dazhi Xu
- Department of Physics and Center for Quantum Technology Research, Beijing Institute of Technology, 5 South Zhongguancun Street, Beijing 100081, China
| | - Jianshu Cao
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA and Beijing Computational Science Research Center, Beijing 100084, China
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22
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Gluchowski A, Gray KLG, Hood SN, Kassal I. Increases in the Charge Separation Barrier in Organic Solar Cells Due to Delocalization. J Phys Chem Lett 2018; 9:1359-1364. [PMID: 29494769 DOI: 10.1021/acs.jpclett.8b00292] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Because of the low dielectric constant, charges in organic solar cells must overcome a strong Coulomb attraction in order to separate. It has been widely argued that intermolecular delocalization would assist charge separation by increasing the effective initial electron-hole separation in a charge-transfer state, thus decreasing their barrier to separation. Here we show that this is not the case: including more than a small amount of delocalization in models of organic solar cells leads to an increase in the free-energy barrier to charge separation. Therefore, if delocalization were to improve the charge separation efficiency, it would have to do so through nonequilibrium kinetic effects that are not captured by a thermodynamic treatment of the barrier height.
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Affiliation(s)
- Adam Gluchowski
- School of Mathematics and Physics and Centre for Engineered Quantum Systems , The University of Queensland , St. Lucia , QLD 4072 , Australia
| | - Katherine L G Gray
- School of Mathematics and Physics and Centre for Engineered Quantum Systems , The University of Queensland , St. Lucia , QLD 4072 , Australia
| | - Samantha N Hood
- School of Mathematics and Physics and Centre for Engineered Quantum Systems , The University of Queensland , St. Lucia , QLD 4072 , Australia
| | - Ivan Kassal
- School of Chemistry and the University of Sydney Nano Institute , The University of Sydney , Sydney , NSW 2006 , Australia
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23
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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
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24
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Nieman R, Tsai H, Nie W, Aquino AJA, Mohite AD, Tretiak S, Li H, Lischka H. The crucial role of a spacer material on the efficiency of charge transfer processes in organic donor-acceptor junction solar cells. NANOSCALE 2017; 10:451-459. [PMID: 29227494 DOI: 10.1039/c7nr07125f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Organic photovoltaic donor-acceptor junction devices composed of π-conjugated polymer electron donors (D) and fullerene electron acceptors (A) show greatly increased performance when a spacer material is inserted between the two layers (W. Y. Nie, G. Gupta, B. K. Crone, F. L. Liu, D. L. Smith, P. P. Ruden, C. Y. Kuo, H. Tsai, H. L. Wang, H. Li, S. Tretiak and A. D. Mohite, Adv. Sci., 2015, 2, 1500024.). For instance, experimental results reveal significant improvement of photocurrent when a terthiophene oligomer derivative is inserted in between π-conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) donor and C60 acceptor. These results indicate favorable charge separation dynamics, which is addressed by our present joint theoretical/experimental study establishing the beneficial alignment of electronic levels due to the specific morphology of the material. Namely, based on the experimental data we have constructed extended structural interface models containing C60 fullerenes and P3HT separated by aligned oligomer chains. Our time-dependent density functional theory (TD-DFT) calculations based on a long-range corrected functional, allowed us to address the energetics of essential electronic states and analyze them in terms of charge transfer (CT) character. Specifically, the simulations reveal the electronic spectra composed of a ladder of excited states evolving excitation toward spatial charge separation: an initial excitonic excitation at P3HT decomposes into charges by sequentially relaxing through bands of C60-centric, oligomer → C60 and P3HT → C60 CT states. Our modeling exposes a critical role of dielectric environment effects and electronic couplings in the self-assembled spacer oligomer layer on the energetics of critical CT states leading to a reduced back-electron transfer, preventing recombination losses, and thus rationalizes physical processes underpinning experimental observations.
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Affiliation(s)
- Reed Nieman
- Department of Chemistry and Biochemistry, Texas Tech University Lubbock, TX 79409-1061, USA.
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25
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Geng Y, Lee MH, Troisi A. Effect of Infrared Pulse Excitation on the Bound Charge-Transfer State of Photovoltaic Interfaces. J Phys Chem Lett 2017; 8:4872-4877. [PMID: 28927273 DOI: 10.1021/acs.jpclett.7b02088] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The nature and dynamics of the bound charge-transfer (CT) state in the exciton dissociation process in organic solar cells are of critical importance for the understanding of these devices. It was recently demonstrated that this state can be probed by a new experiment in which an infrared (IR) push-pulse is used to dissociate charges from the bound excited state. Here we proposed a simple quantum dynamics model to simulate the excitation of the IR pulse on the bound CT state with model parameters extracted from quantum chemical calculations. We show that the pulse dissociates the CT state following two different mechanisms: one, fairly expected, is the direct excitation of higher energy CT states leading to charge separation; the other, proposed here for the first time, is a rebound mechanism in which the negative charge is transferred in the opposite direction to form the neutral Frenkel exciton state from where it dissociates.
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Affiliation(s)
- Yun Geng
- Department of Chemistry, University of Warwick , Coventry CV4 7AL, U.K
- Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University , Changchun 130024, P.R. China
| | - Myeong H Lee
- Department of Chemistry, University of Warwick , Coventry CV4 7AL, U.K
- Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, U.K
| | - Alessandro Troisi
- Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, U.K
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26
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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.
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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
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27
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Ponseca CS, Chábera P, Uhlig J, Persson P, Sundström V. Ultrafast Electron Dynamics in Solar Energy Conversion. Chem Rev 2017; 117:10940-11024. [DOI: 10.1021/acs.chemrev.6b00807] [Citation(s) in RCA: 211] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Carlito S. Ponseca
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Pavel Chábera
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Jens Uhlig
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Petter Persson
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Villy Sundström
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
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28
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Athanasopoulos S, Tscheuschner S, Bässler H, Köhler A. Efficient Charge Separation of Cold Charge-Transfer States in Organic Solar Cells Through Incoherent Hopping. J Phys Chem Lett 2017; 8:2093-2098. [PMID: 28436660 DOI: 10.1021/acs.jpclett.7b00595] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We demonstrate that efficient and nearly field-independent charge separation of electron-hole pairs in organic planar heterojunction solar cells can be described by an incoherent hopping mechanism. Using kinetic Monte Carlo simulations that include the effect of on-chain delocalization as well as entropic contributions, we simulate the dissociation of the charge-transfer state in polymer-fullerene bilayer solar cells. The model further explains experimental results of almost field independent charge separation in bilayers of molecular systems with fullerenes and provides important guidelines at the molecular level for maximizing the efficiencies of organic solar cells. Thus, utilizing coherent phenomena is not necessarily required for highly efficient charge separation in organic solar cells.
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Affiliation(s)
- Stavros Athanasopoulos
- Departamento de Física, Universidad Carlos III de Madrid , Avenida Universidad 30, Leganés 28911, Madrid, Spain
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29
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Simine L, Rossky PJ. Relating Chromophoric and Structural Disorder in Conjugated Polymers. J Phys Chem Lett 2017; 8:1752-1756. [PMID: 28350467 DOI: 10.1021/acs.jpclett.7b00290] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The optoelectronic properties of amorphous conjugated polymers are sensitive to the details of the conformational disorder, and spectroscopy provides the means for structural characterization of the fragments of the chain that interact with light-"chromophores". A faithful interpretation of spectroscopic conformational signatures, however, presents a theoretical challenge. Here we investigate the relationship between the ground-state optical gaps, the properties of the excited states, and the structural features of chromophores of a single molecule poly(3-hexyl)-thiophene (P3HT) using quantum-classical atomistic simulations. Our results demonstrate that chromophoric disorder arises through the interplay between excited-state delocalization and electron-hole polarization, controlled by the torsional disorder introduced by side chains. Within this conceptual framework, we predict and explain the counterintuitive spectral behavior of P3HT, a red-shifted absorption, despite shortening of chromophores, with increasing temperature. This discussion introduces the concept of disorder-induced separation of charges in amorphous conjugated polymers.
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Affiliation(s)
- Lena Simine
- Department of Chemistry, Rice University , Houston, Texas 77005, United States
| | - Peter J Rossky
- Department of Chemistry, Rice University , Houston, Texas 77005, United States
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30
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Using coherence to enhance function in chemical and biophysical systems. Nature 2017; 543:647-656. [DOI: 10.1038/nature21425] [Citation(s) in RCA: 398] [Impact Index Per Article: 56.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2016] [Accepted: 12/07/2016] [Indexed: 12/23/2022]
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31
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Yang X, Keane T, Delor M, Meijer AJHM, Weinstein J, Bittner ER. Identifying electron transfer coordinates in donor-bridge-acceptor systems using mode projection analysis. Nat Commun 2017; 8:14554. [PMID: 28233775 PMCID: PMC5333094 DOI: 10.1038/ncomms14554] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Accepted: 01/10/2017] [Indexed: 11/13/2022] Open
Abstract
We report upon an analysis of the vibrational modes that couple and drive the state-to-state electronic transfer branching ratios in a model donor-bridge-acceptor system consisting of a phenothiazine-based donor linked to a naphthalene-monoimide acceptor via a platinum-acetylide bridging unit. Our analysis is based upon an iterative Lanczos search algorithm that finds superpositions of vibronic modes that optimize the electron/nuclear coupling using input from excited-state quantum chemical methods. Our results indicate that the electron transfer reaction coordinates between a triplet charge-transfer state and lower lying charge-separated and localized excitonic states are dominated by asymmetric and symmetric modes of the acetylene groups on either side of the central atom in this system. In particular, we find that while a nearly symmetric mode couples both the charge-separation and charge-recombination transitions more or less equally, the coupling along an asymmetric mode is far greater suggesting that IR excitation of the acetylene modes preferentially enhances charge-recombination transition relative to charge-separation. Manipulating chemical reactions using laser pulses to control electron transfer is an attractive goal, however much of the underlying physics remains unexplored. Here the authors analyse and explain the intramolecular electronic transfer occurring during charge-separation in acetylene, a model donor-bridge-acceptor molecule.
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Affiliation(s)
- Xunmo Yang
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
| | - Theo Keane
- Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
| | - Milan Delor
- Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
| | | | - Julia Weinstein
- Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
| | - Eric R Bittner
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA.,Department of Physics, University of Houston, Houston, Texas 77204, USA
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32
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Xie X, Ma H. Opposite Anisotropy Effects of Singlet and Triplet Exciton Diffusion in Tetracene Crystal. ChemistryOpen 2016; 5:201-205. [PMID: 27933226 PMCID: PMC5126140 DOI: 10.1002/open.201500214] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Indexed: 11/10/2022] Open
Abstract
We observe the diffusion anisotropy difference between singlet and triplet excitons in organic crystals; that is, singlet and triplet excitons may have completely different spatial direction preference for diffusion. This phenomenon can be ascribed to the distinct dependence of different excitonic couplings (Coulomb Förster vs. exchange Dexter) existing in singlet and triplet excitons on their intermolecular distance and intermolecular orientation. Such a discovery provides insights for understanding the fundamental photophysical process in a vast range of organic condensed-phase systems and optimizing the efficiency of organic optoelectronic materials.
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Affiliation(s)
- Xiaoyu Xie
- Key Laboratory of Mesoscopic Chemistry of the Ministry of Education (MOE) Collaborative Innovation Centre of Chemistry for Life Sciences School of Chemistry and Chemical Engineering Nanjing University Nanjing 210093 P. R. China
| | - Haibo Ma
- Key Laboratory of Mesoscopic Chemistry of the Ministry of Education (MOE) Collaborative Innovation Centre of Chemistry for Life Sciences School of Chemistry and Chemical Engineering Nanjing University Nanjing 210093 P. R. China
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33
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Determining the spatial coherence of excitons from the photoluminescence spectrum in charge-transfer J-aggregates. Chem Phys 2016. [DOI: 10.1016/j.chemphys.2016.06.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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34
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Li H, Gauthier-Houle A, Grégoire P, Vella E, Silva-Acuña C, Bittner ER. Probing polaron excitation spectra in organic semiconductors by photoinduced-absorption-detected two-dimensional coherent spectroscopy. Chem Phys 2016. [DOI: 10.1016/j.chemphys.2016.07.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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35
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Yao Y, Xie X, Ma H. Ultrafast Long-Range Charge Separation in Organic Photovoltaics: Promotion by Off-Diagonal Vibronic Couplings and Entropy Increase. J Phys Chem Lett 2016; 7:4830-4835. [PMID: 27934051 DOI: 10.1021/acs.jpclett.6b02400] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The exciton dissociation in a model donor/acceptor heterojunction with electron-phonon couplings is simulated by a full quantum dynamical method, in which ultrafast long-range charge separation is observed. Such a novel scenario does not undergo short-range interfacial (pinned) charge transfer states, but can be mainly ascribed to the quantum resonance between local Frenkel excited states and a broad array of long-range charge transfer (LRCT) states assisted by the moderate off-diagonal vibronic couplings. The entropy-increasing effect associated with the very dense density of states for LRCT states is also found to be beneficial for lowering the free energy barrier for charge generation in organic solar cells.
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Affiliation(s)
- Yao Yao
- Department of Physics, South China University of Technology , Guangzhou 510640, China
| | - Xiaoyu Xie
- Key Laboratory of Mesoscopic Chemistry of MOE, Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University , Nanjing 210023, China
| | - Haibo Ma
- Key Laboratory of Mesoscopic Chemistry of MOE, Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University , Nanjing 210023, China
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36
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Hood SN, Kassal I. Entropy and Disorder Enable Charge Separation in Organic Solar Cells. J Phys Chem Lett 2016; 7:4495-4500. [PMID: 27783509 DOI: 10.1021/acs.jpclett.6b02178] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Although organic heterojunctions can separate charges with near-unity efficiency and on a subpicosecond time scale, the full details of the charge-separation process remain unclear. In typical models, the Coulomb binding between the electron and the hole can exceed the thermal energy kBT by an order of magnitude, suggesting that it is impossible for the charges to separate before recombining. Here, we consider the entropic contribution to charge separation in the presence of disorder and find that even modest amounts of disorder have a decisive effect, reducing the charge-separation barrier to about kBT or eliminating it altogether. Therefore, the charges are usually not thermodynamically bound at all and could separate spontaneously if the kinetics otherwise allowed it. Our conclusion holds despite the worst-case assumption of localized, thermalized carriers and is only strengthened if mechanisms like delocalization or "hot" states are also present.
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Affiliation(s)
- Samantha N Hood
- Centre for Engineered Quantum Systems, Centre for Organic Photonics and Electronics and School of Mathematics and Physics, The University of Queensland , Brisbane, Queensland 4072, Australia
| | - Ivan Kassal
- Centre for Engineered Quantum Systems, Centre for Organic Photonics and Electronics and School of Mathematics and Physics, The University of Queensland , Brisbane, Queensland 4072, Australia
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37
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Johnson AS, Miseikis L, Wood DA, Austin DR, Brahms C, Jarosch S, Strüber CS, Ye P, Marangos JP. Measurement of sulfur L 2,3 and carbon K edge XANES in a polythiophene film using a high harmonic supercontinuum. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2016; 3:062603. [PMID: 27822487 PMCID: PMC5074992 DOI: 10.1063/1.4964821] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 09/30/2016] [Indexed: 05/19/2023]
Abstract
We use a high harmonic generated supercontinuum in the soft X-ray region to measure X-ray absorption near edge structure (XANES) spectra in polythiophene (poly(3-hexylthiophene)) films at multiple absorption edges. A few-cycle carrier-envelope phase-stable laser pulse centered at 1800 nm was used to generate a stable soft X-ray supercontinuum, with amplitude gating limiting the generated pulse duration to a single optical half-cycle. We report a quantitative transmission measurement of the sulfur L2,3 edge over the range 160-200 eV and the carbon K edge from 280 to 330 eV. These spectra show all the features previously reported in the XANES spectra of polythiophene, but for the first time they are measured with a source that has an approximately 1 fs pulse duration. This study opens the door to measurements that can fully time-resolve the photoexcited electronic dynamics in these systems.
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Affiliation(s)
- A S Johnson
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
| | - L Miseikis
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
| | - D A Wood
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
| | - D R Austin
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
| | - C Brahms
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
| | - S Jarosch
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
| | - C S Strüber
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
| | - P Ye
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
| | - J P Marangos
- Blackett Laboratory, Imperial College London , Prince Consort Road, London SW7 2AZ, United Kingdom
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38
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Does organic/organic interface mimic band bending by deforming structure? J Photochem Photobiol A Chem 2016. [DOI: 10.1016/j.jphotochem.2016.08.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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39
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Dutta R, Bagchi B. Effects of dynamic disorder on exciton migration: Quantum diffusion, coherences, and energy transfer. J Chem Phys 2016; 145:164907. [DOI: 10.1063/1.4966035] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Rajesh Dutta
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
| | - Biman Bagchi
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
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40
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Abstract
Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjugated polymers are considered, and their applications in organic solar cells, photodetectors, and photorefractive devices are discussed.
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Affiliation(s)
- Oksana Ostroverkhova
- Department of Physics, Oregon State University , Corvallis, Oregon 97331, United States
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41
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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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42
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Wang L, Jakowski J, Garashchuk S, Sumpter BG. Understanding How Isotopes Affect Charge Transfer in P3HT/PCBM: A Quantum Trajectory-Electronic Structure Study with Nonlinear Quantum Corrections. J Chem Theory Comput 2016; 12:4487-500. [DOI: 10.1021/acs.jctc.6b00126] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Lei Wang
- Department
of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Jacek Jakowski
- Center
for Nanophase Materials Sciences and Computer Science and Mathematics
Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Sophya Garashchuk
- Department
of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Bobby G. Sumpter
- Center
for Nanophase Materials Sciences and Computer Science and Mathematics
Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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43
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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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44
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Vella E, Li H, Grégoire P, Tuladhar SM, Vezie MS, Few S, Bazán CM, Nelson J, Silva-Acuña C, Bittner ER. Ultrafast decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells. Sci Rep 2016; 6:29437. [PMID: 27412119 PMCID: PMC4944175 DOI: 10.1038/srep29437] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 06/17/2016] [Indexed: 11/23/2022] Open
Abstract
All-organic-based photovoltaic solar cells have attracted considerable attention because of their low-cost processing and short energy payback time. In such systems the primary dissociation of an optical excitation into a pair of photocarriers has been recently shown to be extremely rapid and efficient, but the physical reason for this remains unclear. Here, two-dimensional photocurrent excitation spectroscopy, a novel non-linear optical spectroscopy, is used to probe the ultrafast coherent decay of photoexcitations into charge-producing states in a polymer:fullerene based solar cell. The two-dimensional photocurrent spectra are interpreted by introducing a theoretical model for the description of the coupling of the electronic states of the system to an external environment and to the applied laser fields. The experimental data show no cross-peaks in the twodimensional photocurrent spectra, as predicted by the model for coherence times between the exciton and the photocurrent producing states of 20 fs or less.
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Affiliation(s)
- Eleonora Vella
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
| | - Hao Li
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
| | - Pascal Grégoire
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
| | - Sachetan M. Tuladhar
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Michelle S. Vezie
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Sheridan Few
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Claudia M. Bazán
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
| | - Jenny Nelson
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Carlos Silva-Acuña
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Eric R. Bittner
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
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45
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Fujii M, Shin W, Yasuda T, Yamashita K. Photon-absorbing charge-bridging states in organic bulk heterojunctions consisting of diketopyrrolopyrrole derivatives and PCBM. Phys Chem Chem Phys 2016; 18:9514-23. [PMID: 26984809 DOI: 10.1039/c5cp06183k] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
We have investigated the photo- and electrochemical properties of five diketopyrrolopyrrole (DPP) derivatives both experimentally and theoretically. In the experimental study, we found that a blend of a DPP derivative named D2 and phenyl-C61-butyric acid methyl ester (PCBM) exhibits the highest internal quantum efficiency (IQE) and power convergence efficiency (PCE) among the five derivatives investigated. In the theoretical study, we found that the open-circuit voltage can be estimated from the difference between the energy gap of frontier orbitals and the voltage loss and that the latter is suppressed when the IQE is large. Then, to investigate the factors that influence the IQE, investigations on charge recombination, hole transfer, and charge transfer induced by photoabsorption were conducted for the complexes of each DPP derivative and PCBM. It was found that D2/PCBM exhibits the largest charge-bridging upon photoabsorption, which leads to the highest IQE and PCE among the five DPP derivatives.
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Affiliation(s)
- Mikiya Fujii
- Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Tokyo, 113-8656, Japan.
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46
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D'Avino G, Muccioli L, Olivier Y, Beljonne D. Charge Separation and Recombination at Polymer-Fullerene Heterojunctions: Delocalization and Hybridization Effects. J Phys Chem Lett 2016; 7:536-40. [PMID: 26785294 DOI: 10.1021/acs.jpclett.5b02680] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We address charge separation and recombination in polymer/fullerene solar cells with a multiscale modeling built from accurate atomistic inputs and accounting for disorder, interface electrostatics and genuine quantum effects on equal footings. Our results show that bound localized charge transfer states at the interface coexist with a large majority of thermally accessible delocalized space-separated states that can be also reached by direct photoexcitation, thanks to their strong hybridization with singlet polymer excitons. These findings reconcile the recent experimental reports of ultrafast exciton separation ("hot" process) with the evidence that high quantum yields do not require excess electronic or vibrational energy ("cold" process), and show that delocalization, by shifting the density of charge transfer states toward larger effective electron-hole radii, may reduce energy losses through charge recombination.
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Affiliation(s)
- Gabriele D'Avino
- Laboratory for Chemistry of Novel Materials, University of Mons , 7000 Mons, Belgium
| | - Luca Muccioli
- Laboratoire de Chimie des Polymères Organiques, UMR 5629, University of Bordeaux , 33607 Pessac, France
| | - Yoann Olivier
- Laboratory for Chemistry of Novel Materials, University of Mons , 7000 Mons, Belgium
| | - David Beljonne
- Laboratory for Chemistry of Novel Materials, University of Mons , 7000 Mons, Belgium
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47
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Bittner ER, Kelley A. The role of structural fluctuations and environmental noise in the electron/hole separation kinetics at organic polymer bulk-heterojunction interfaces. Phys Chem Chem Phys 2016; 17:28853-9. [PMID: 26449151 DOI: 10.1039/c5cp05037e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
We investigate the electronic dynamics of a model organic photovoltaic (OPV) system consisting of polyphenylene vinylene (PPV) oligomers and a [6,6]-phenyl C61-butyric acid methylester (PCBM) blend using a mixed molecular mechanics/quantum mechanics (MM/QM) approach. Using a heuristic model that connects energy gap fluctuations to the average electronic couplings and decoherence times, we provide an estimate of the state-to-state internal conversion rates within the manifold of the lowest few electronic excitations. We find that the lowest few excited states of a model interface are rapidly mixed by C[double bond, length as m-dash]C bond fluctuations such that the system can sample both intermolecular charge-transfer and charge-separated electronic configurations on a time scale of 20 fs. Our simulations support an emerging picture of carrier generation in OPV systems in which interfacial electronic states can rapidly decay into charge-separated and current producing states via coupling to vibronic degrees of freedom.
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Affiliation(s)
- Eric R Bittner
- Department of Chemistry and Centre for Quantum Engineering, University of Houston, Houston, TX 77204, USA.
| | - Allen Kelley
- Department of Chemistry and Centre for Quantum Engineering, University of Houston, Houston, TX 77204, USA.
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48
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Competition between diagonal and off-diagonal coupling gives rise to charge-transfer states in polymeric solar cells. Sci Rep 2015; 5:14555. [PMID: 26412693 PMCID: PMC4585960 DOI: 10.1038/srep14555] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 08/19/2015] [Indexed: 11/24/2022] Open
Abstract
It has long been a puzzle on what drives charge separation in artificial polymeric solar cells as a consensus has yet to emerge among rivaling theories based upon electronic localization and delocalization pictures. Here we propose an alternative using the two-bath spin-boson model with simultaneous diagonal and off-diagonal coupling: the critical phase, which is born out of the competition of the two coupling types, and is neither localized nor delocalized. The decoherence-free feature of the critical phase also helps explain sustained coherence of the charge-transfer state. Exploiting Hamiltonian symmetries in an enhanced algorithm of density-matrix renormalization group, we map out boundaries of the critical phase to a precision previously unattainable, and determine the bath spectral densities inducive to the existence of the charge-transfer state.
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49
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Lee Y, Gomez ED. Challenges and Opportunities in the Development of Conjugated Block Copolymers for Photovoltaics. Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b00112] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Youngmin Lee
- Department of Chemical Engineering and ‡Materials Research
Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Enrique D. Gomez
- Department of Chemical Engineering and ‡Materials Research
Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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50
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Yang X, Bittner ER. Computing intramolecular charge and energy transfer rates using optimal modes. J Chem Phys 2015; 142:244114. [PMID: 26133417 DOI: 10.1063/1.4923191] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In our recent work [X. Yang and E. R. Bittner, J. Phys. Chem. A 118, 5196 (2014)], we showed how to construct a reduced set of nuclear motions that capture the coupling between electronic and nuclear degrees of freedom over the course of an electronic transition. We construct these modes, referred to as "Lanczos modes," by applying a search algorithm to find linear combinations of vibrational normal modes that optimize the electronic/nuclear coupling operator. Here, we analyze the irreducible representations of the dominant contributions of these modes and find that for the cases considered here, these belong to totally symmetric irreducible representations of the donor and acceptor moieties. Upon investigating the molecular geometry changes following the transition, we propose that the electronic transition process can be broken into two steps, in the agreement of Born-Oppenheimer approximation: a fast excitation transfer occurs, facilitated by the "primary Lanczos mode," followed by slow nuclear relaxation on the final electronic diabatic surface.
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Affiliation(s)
- Xunmo Yang
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
| | - Eric R Bittner
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
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