1
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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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2
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Zhang W, Ji W, Yan W, Wang Z, Ling L, Hao X, Guan G. Enhanced electroactivity of BiOCl/PPy hybrid film with anamnestic lattice site for synergistically efficient selective uptake/release of chloride ions. Electrochim Acta 2022. [DOI: 10.1016/j.electacta.2022.140508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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3
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Lukin L. Efficiency of exciton dissociation at the interface between a conjugated polymer and an electron acceptor with consideration for a two-dimensional arrangement of interfacial dipoles. Chem Phys 2021. [DOI: 10.1016/j.chemphys.2021.111327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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4
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Kaiser W, Janković V, Vukmirović N, Gagliardi A. Nonequilibrium Thermodynamics of Charge Separation in Organic Solar Cells. J Phys Chem Lett 2021; 12:6389-6397. [PMID: 34232672 DOI: 10.1021/acs.jpclett.1c01817] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
This work presents a novel theoretical description of the nonequilibrium thermodynamics of charge separation in organic solar cells (OSCs). Using stochastic thermodynamics, we take realistic state populations derived from the phonon-assisted dynamics of electron-hole pairs within photoexcited organic bilayers to connect the kinetics with the free energy profile of charge separation. Hereby, we quantify for the first time the difference between nonequilibrium and equilibrium free energy profile. We analyze the impact of energetic disorder and delocalization on free energy, average energy, and entropy. For a high disorder, the free energy profile is well-described as equilibrated. We observe significant deviations from equilibrium for delocalized electron-hole pairs at a small disorder, implying that charge separation in efficient OSCs proceeds via a cold but nonequilibrated pathway. Both a large Gibbs entropy and large initial electron-hole distance provide an efficient charge separation, while a decrease in the free energy barrier does not necessarily enhance charge separation.
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Affiliation(s)
- Waldemar Kaiser
- Department of Electrical and Computer Engineering, Technical University of Munich, Karlstraße 45, 80333 Munich, Germany
| | - Veljko Janković
- Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia
| | - Nenad Vukmirović
- Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Belgrade, Serbia
| | - Alessio Gagliardi
- Department of Electrical and Computer Engineering, Technical University of Munich, Karlstraße 45, 80333 Munich, Germany
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5
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Hou L, Lv J, Wobben F, Le Corre VM, Tang H, Singh R, Kim M, Wang F, Sun H, Chen W, Xiao Z, Kumar M, Xu T, Zhang W, McCulloch I, Duan T, Xie H, Koster LJA, Lu S, Kan Z. Effects of Fluorination on Fused Ring Electron Acceptor for Active Layer Morphology, Exciton Dissociation, and Charge Recombination in Organic Solar Cells. ACS APPLIED MATERIALS & INTERFACES 2020; 12:56231-56239. [PMID: 33270414 DOI: 10.1021/acsami.0c16411] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Fluorination is one of the effective approaches to alter the organic semiconductor properties that impact the performance of the organic solar cells (OSCs). Positive effects of fluorination are also revealed in the application of fused ring electron acceptors (FREAs). However, in comparison with the efforts allocated to the material designs and power conversion efficiency enhancement, understanding on the excitons and charge carriers' behaviors in high-performing OSCs containing FREAs is limited. Herein, the impact of fluorine substituents on the active layer morphology, and therefore exciton dissociation, charge separation, and charge carriers' recombination processes are examined by fabricating OSCs with PTO2 as the donor and two FREAs, O-IDTT-IC and its fluorinated analogue O-IDTT-4FIC, as the acceptors. With the presence of O-IDTT-4FIC in the devices, it is found that the excitons dissociate more efficiently, and the activation energy required to split the excitons to free charge carriers is much lower; the charge carriers live longer and suffer less extent of trap-assisted recombination; the trap density is 1 order of magnitude lower than that of the nonfluorinated counterpart. Overall, these findings provide information about the complex impacts of FREA fluorination on efficiently performed OSCs.
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Affiliation(s)
- Licheng Hou
- Thin-film Solar Technology Research Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jie Lv
- Thin-film Solar Technology Research Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Friso Wobben
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, Groningen NL-9747AG, The Netherlands
| | - Vincent M Le Corre
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, Groningen NL-9747AG, The Netherlands
| | - Hua Tang
- Thin-film Solar Technology Research Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ranbir Singh
- Department of Energy and Materials Engineering, Dongguk University, Seoul 04620, Korea
| | - Min Kim
- School of Chemical Engineering, Jeonbuk National University, 567 Baekje-daero, Jeonju 54896 Republic of Korea
| | - Fufang Wang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Haitao Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Wenjing Chen
- Department of Physics, CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Zhengguo Xiao
- Department of Physics, CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Manish Kumar
- Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Tongle Xu
- Thin-film Solar Technology Research Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Weimin Zhang
- KAUST Solar Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
| | - Iain McCulloch
- KAUST Solar Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
- Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K
| | - Tainan Duan
- Thin-film Solar Technology Research Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
| | - Huling Xie
- Thin-film Solar Technology Research Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
| | - L Jan Anton Koster
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, Groningen NL-9747AG, The Netherlands
| | - Shirong Lu
- Thin-film Solar Technology Research Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
| | - Zhipeng Kan
- Thin-film Solar Technology Research Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing School, University of Chinese Academy of Sciences, Chongqing 400714, China
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6
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Lukin L. Effect of interfacial dipoles on the attraction energy of geminate electron-hole pairs generated at the donor-acceptor interfaces. Chem Phys Lett 2020. [DOI: 10.1016/j.cplett.2020.137448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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7
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Sousa LE, Coropceanu V, da Silva Filho DA, Sini G. On the Physical Origins of Charge Separation at Donor–Acceptor Interfaces in Organic Solar Cells: Energy Bending versus Energy Disorder. ADVANCED THEORY AND SIMULATIONS 2020. [DOI: 10.1002/adts.201900230] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Leonardo Evaristo Sousa
- Theoretical and Structural Chemistry GroupState University of Goiás 75133‐050 Anápolis Brazil
| | - Veaceslav Coropceanu
- School of Chemistry and Biochemistry and Center for Organic Photonics and ElectronicsGeorgia Institute of Technology Atlanta GA 30332‐0400 USA
| | - Demétrio Antônio da Silva Filho
- Laboratoire de Physicochimie des Polymères et des Interfaces, EA 2528University of Cergy‐Pontoise 5 mail Gay‐Lussac 95031 Cergy‐Pontoise Cedex France
- Institute for Advanced StudiesUniversity of Cergy‐Pontoise 1 rue Descartes 95000 Neuville‐sur‐Oise France
- Institute of PhysicsUniversity of Brasilia 70919‐970 Brasília Brazil
| | - Gjergji Sini
- Laboratoire de Physicochimie des Polymères et des Interfaces, EA 2528University of Cergy‐Pontoise 5 mail Gay‐Lussac 95031 Cergy‐Pontoise Cedex France
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8
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Athanasopoulos S, Bässler H, Köhler A. Disorder vs Delocalization: Which Is More Advantageous for High-Efficiency Organic Solar Cells? J Phys Chem Lett 2019; 10:7107-7112. [PMID: 31661274 DOI: 10.1021/acs.jpclett.9b02866] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We investigate the combined influence of energetic disorder and delocalization on electron-hole charge-transfer state separation efficiency in donor-acceptor organic photovoltaic systems using an analytical hopping model and Monte Carlo calculations, coupled with an effective mass model. Whereas energetic disorder increases the separation yield at intermediate and low electric fields for low-efficiency blends with strongly localized carriers, we find that it reduces dramatically the fill factors and power conversion efficiencies in high-efficiency solar cells that require high carrier delocalization within the conjugated segment and high mobility-lifetime product. We further demonstrate that the initial electron-hole distance and thermalization processes play only a minor role in the separation dynamics.
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Affiliation(s)
- Stavros Athanasopoulos
- Departamento de Física , Universidad Carlos III de Madrid , Avenida Universidad 30 , 28911 Leganés, Madrid , Spain
| | - Heinz Bässler
- Bayreuth Institute of Macromolecular Research (BIMF) and Bavarian Polymer Institute (BPI) , University of Bayreuth , Bayreuth 95440 , Germany
| | - Anna Köhler
- Bayreuth Institute of Macromolecular Research (BIMF) and Bavarian Polymer Institute (BPI) , University of Bayreuth , Bayreuth 95440 , Germany
- Soft Matter Optoelectronics , University of Bayreuth , Bayreuth 95440 , Germany
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9
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Zhao ZW, Duan YC, Pan QQ, Gao Y, Wu Y, Geng Y, Zhao L, Zhang M, Su ZM. A probe into underlying factors affecting utrafast charge transfer at Donor/IDIC interface of all-small-molecule nonfullerene organic solar cells. J Photochem Photobiol A Chem 2019. [DOI: 10.1016/j.jphotochem.2019.02.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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10
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Bombile JH, Janik MJ, Milner ST. Energetics of exciton binding and dissociation in polythiophenes: a tight binding approach. Phys Chem Chem Phys 2019; 21:11999-12011. [DOI: 10.1039/c9cp01116a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A tight-binding exciton model that describes the continuum from the bound exciton to the free hole and electron polarons in conjugated polymer chains is introduced and applied to polythiophenes.
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11
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Yang W, Yao Y, Guo P, Sun H, Luo Y. Optimum driving energy for achieving balanced open-circuit voltage and short-circuit current density in organic bulk heterojunction solar cells. Phys Chem Chem Phys 2018; 20:29866-29875. [PMID: 30468215 DOI: 10.1039/c8cp05145c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Organic bulk heterojunction solar cells generally suffer from a trade-off between the open circuit voltage (Voc) and the short circuit current density (Jsc) under a given donor/acceptor (D/A) interfacial energetic offset (or the so-called driving force). Here we theoretically investigate the optimum driving energy required for achieving the balanced Jsc and Voc simultaneously. To this end, the Jscversus the driving force ΔE curves are calculated under two different charge separation mechanisms by employing the drift-diffusion method. For the Marcus incoherent mechanism, the curve features a high plateau in a broad range of ΔE starting from 0.2 eV, which is due to the accumulation of undissociated excitons within their lifetime and signifies the possibility of obtaining a sizable Jsc under a ΔE value much smaller than the reorganization energy. After incorporating both the electron and hole transfer pathways into the device model, the calculated J-V curves are comparable to experimentally measured ones foractual blended systems of different driving forces. For the coherent mechanism, it is demonstrated that the maximum Jsc can also be achieved under the ΔE of 0.2 eV if a large proportion of the high-lying delocalized states are harvested through tuning the density of states for the charge transfer excitons to reduce the sub-gap states. This theoretical work revealed quantitatively the relationship between the interfacial energy offsets and device performance, and also provides some guidelines for identifying the macroscopic features of the actual charge separation mechanisms in bulk heterojunction solar cells.
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Affiliation(s)
- Wenchao Yang
- Key Laboratory of Microelectronics and Energy of Henan, School of Physics and Electronic Engineering, Xinyang Normal University, Xinyang, 464000, China.
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12
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Brédas J, Li Y, Sun H, Zhong C. Why Can High Charge‐Carrier Mobilities be Achieved Along π‐Conjugated Polymer Chains with Alternating Donor–Acceptor Moieties? ADVANCED THEORY AND SIMULATIONS 2018. [DOI: 10.1002/adts.201800016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Jean‐Luc Brédas
- School of Chemistry and Biochemistry Georgia Institute of Technology Atlanta GA 30332‐0400 USA
- Center for Organic Photonics and Electronics Georgia Institute of Technology Atlanta GA 30332‐0400 USA
- Laboratory for Computational and Theoretical Chemistry of Advanced Materials King Abdullah University of Science and Technology Thuwal 23955‐6900 Kingdom of Saudi Arabia
| | - Yuan Li
- School of Information Science and Engineering Shandong University Qingdao 266237 P. R. China
- State Key Laboratory of Precision Spectroscopy School of Physics and Materials Science East China Normal University Shanghai 200062 P. R. China
| | - Haitao Sun
- Laboratory for Computational and Theoretical Chemistry of Advanced Materials King Abdullah University of Science and Technology Thuwal 23955‐6900 Kingdom of Saudi Arabia
- State Key Laboratory of Precision Spectroscopy School of Physics and Materials Science East China Normal University Shanghai 200062 P. R. China
| | - Cheng Zhong
- Laboratory for Computational and Theoretical Chemistry of Advanced Materials King Abdullah University of Science and Technology Thuwal 23955‐6900 Kingdom of Saudi Arabia
- Department of Chemistry Wuhan University Wuhan 430072 P. R. China
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13
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Kurpiers J, Ferron T, Roland S, Jakoby M, Thiede T, Jaiser F, Albrecht S, Janietz S, Collins BA, Howard IA, Neher D. Probing the pathways of free charge generation in organic bulk heterojunction solar cells. Nat Commun 2018; 9:2038. [PMID: 29795114 PMCID: PMC5966440 DOI: 10.1038/s41467-018-04386-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 04/24/2018] [Indexed: 11/30/2022] Open
Abstract
The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges. Contradictory models are being debated on the dominant pathways of charge generation in organic solar cells. Here Kurpiers et al. determine the activation energy for this fundamental process and reveal that the main channel is via thermalized charge transfer states instead of hot exciton dissociation.
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Affiliation(s)
- Jona Kurpiers
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany
| | - Thomas Ferron
- Department of Physics and Astronomy, Washington State University, 100 Dairy Road, Pullman, WA, 99164, USA
| | - Steffen Roland
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany
| | - Marius Jakoby
- Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology (IMT), Hermann-von-Helmholtz Platz-1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Tobias Thiede
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany
| | - Frank Jaiser
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany
| | - Steve Albrecht
- Helmholtz-Zentrum Berlin für Materialien und Energie, Nachwuchsgruppe Perowskit Tandemsolarzellen, Kekuléstraße 5, 12489, Berlin, Germany
| | - Silvia Janietz
- Fraunhofer IAP, Polymere und Elektronik, Geiselbergstraße 69, 14476, Potsdam-Golm, Germany
| | - Brian A Collins
- Department of Physics and Astronomy, Washington State University, 100 Dairy Road, Pullman, WA, 99164, USA
| | - Ian A Howard
- Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology (IMT), Hermann-von-Helmholtz Platz-1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Dieter Neher
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
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14
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Shi L, Lee CK, Willard AP. The Enhancement of Interfacial Exciton Dissociation by Energetic Disorder Is a Nonequilibrium Effect. ACS CENTRAL SCIENCE 2017; 3:1262-1270. [PMID: 29296666 PMCID: PMC5746863 DOI: 10.1021/acscentsci.7b00404] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Indexed: 05/29/2023]
Abstract
The dissociation of excited electron-hole pairs is a microscopic process that is fundamental to the performance of photovoltaic systems. For this process to be successful, the oppositely charged electron and hole must overcome an electrostatic binding energy before they undergo ground state recombination. It has been observed previously that the presence of energetic disorder can lead to a reduction in recombination losses. Here we investigate this effect using a simple model of charge dynamics at a donor-acceptor interface. We consider the effect of spatial variations in electronic energy levels, such as those that arise in disordered molecular systems, on dissociation yield and demonstrate that it is maximized with a finite amount of disorder. We demonstrate that this is a nonequilibrium effect that is mediated by the dissipation driven formation of partially dissociated intermediate states that are long-lived because they cannot easily recombine. We present a kinetic model that incorporates these states and show that it is capable of reproducing similar behavior when it is parametrized with nonequilibrium rates.
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Affiliation(s)
- Liang Shi
- Chemistry and Chemical Biology, University of California, Merced, California 95343, United States
| | - Chee Kong Lee
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Adam P Willard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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15
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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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16
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Nakano K, Tajima K. Organic Planar Heterojunctions: From Models for Interfaces in Bulk Heterojunctions to High-Performance Solar Cells. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29:1603269. [PMID: 27885716 DOI: 10.1002/adma.201603269] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Revised: 08/30/2016] [Indexed: 05/28/2023]
Abstract
Recent progress regarding planar heterojunctions (PHJs) is reviewed, with respect to the fundamental understanding of the photophysical processes at the donor/acceptor interfaces in organic photovoltaic devices (OPVs). The current state of OPV research is summarized and the advantages of PHJs as models for exploring the relationship between organic interfaces and device characteristics described. The preparation methods and the characterization of PHJ structures to provide key points for the appropriate handling of PHJs. Next, we describe the effects of the donor/acceptor interface on each photoelectric conversion process are reviewed by examining various PHJ systems to clarify what is currently known and not known. Finally, it is discussed how we the knowledge obtained by studies of PHJs can be used to overcome the current limits of OPV efficiency.
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Affiliation(s)
- Kyohei Nakano
- RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
| | - Keisuke Tajima
- RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan
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17
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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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18
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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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Tress W, Beyer B, Ashari Astani N, Gao F, Meloni S, Rothlisberger U. Extended Intermolecular Interactions Governing Photocurrent-Voltage Relations in Ternary Organic Solar Cells. J Phys Chem Lett 2016; 7:3936-3944. [PMID: 27673686 DOI: 10.1021/acs.jpclett.6b01962] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Efficient organic solar cells are based on (electron) donor-acceptor heterojunctions. An optically generated excited molecular state (exciton) is dissociated at this junction, forming a charge-transfer (CT) state in an intermediate step before the electron and hole are completely separated. The observed highly efficient dissociation of this Coulombically bound state raises the question on the dissociation mechanism. Here, we show that the observed high quantum yields of charge carrier generation and CT state dissociation are due to extended (and consequently weakly bound) CT states visible in absorption and emission spectra and first-principles calculations. Identifying a new geminate-pair loss mechanism via donor excimers, we find that the hole on the small-molecule donor is not localized on a single molecule and charge separation is correlated with the energetic offset between excimer and CT states. Thus, the charges upon interface charge transfer and even in the case of back-transfer and recombination are less localized than commonly assumed.
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Affiliation(s)
- Wolfgang Tress
- Biomolecular and Organic Electronics, IFM, Linköping University , 58183 Linköping, Sweden
| | - Beatrice Beyer
- Fraunhofer Institute for Electron Beam, Plasma Technology and COMEDD (FEP) , Maria-Reiche-Strasse 2, 01109 Dresden, Germany
| | - Negar Ashari Astani
- Laboratoire de chimie et biochimie computationnelles, ISIC, FSB-BCH, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland
| | - Feng Gao
- Biomolecular and Organic Electronics, IFM, Linköping University , 58183 Linköping, Sweden
| | - Simone Meloni
- Laboratoire de chimie et biochimie computationnelles, ISIC, FSB-BCH, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland
| | - Ursula Rothlisberger
- Laboratoire de chimie et biochimie computationnelles, ISIC, FSB-BCH, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland
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de Gier HD, Jahani F, Broer R, Hummelen JC, Havenith RWA. Promising Strategy To Improve Charge Separation in Organic Photovoltaics: Installing Permanent Dipoles in PCBM Analogues. J Phys Chem A 2015; 120:4664-71. [PMID: 26478954 DOI: 10.1021/acs.jpca.5b09279] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A multidisciplinary approach involving organic synthesis and theoretical chemistry was applied to investigate a promising strategy to improve charge separation in organic photovoltaics: installing permanent dipoles in fullerene derivatives. First, a PCBM analogue with a permanent dipole in the side chain (PCBDN) and its reference analogue without a permanent dipole (PCBBz) were successfully synthesized and characterized. Second, a multiscale modeling approach was applied to investigate if a PCBDN environment around a central donor-acceptor complex indeed facilitates charge separation. Alignment of the embedding dipoles in response to charges present on the central donor-acceptor complex enhances charge separation. The good correspondence between experimentally and theoretically determined electronic and optical properties of PCBDN, PCBBz, and PCBM indicates that the theoretical analysis of the embedding effects of these molecules gives a reliable expectation for their influence on the charge separation process at a microscopic scale in a real device. This work suggests the following strategies to improve charge separation in organic photovoltaics: installing permanent dipoles in PCBM analogues and tuning the concentration of these molecules in an organic donor/acceptor blend.
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Affiliation(s)
- Hilde D de Gier
- Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Fatemeh Jahani
- Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.,Stratingh Institute for Chemistry, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Ria Broer
- Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Jan C Hummelen
- Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.,Stratingh Institute for Chemistry, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Remco W A Havenith
- Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.,Stratingh Institute for Chemistry, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.,Ghent Quantum Chemistry Group, Department of Inorganic and Physical Chemistry, Ghent University , Krijgslaan 281 (S3), B-9000 Gent, Belgium
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Bässler H, Köhler A. “Hot or cold”: how do charge transfer states at the donor–acceptor interface of an organic solar cell dissociate? Phys Chem Chem Phys 2015; 17:28451-62. [DOI: 10.1039/c5cp04110d] [Citation(s) in RCA: 104] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This perspective discusses concepts to understand efficient photogeneration of charges in organic semiconductors, with particular emphasis on the role of excess energy.
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Affiliation(s)
- Heinz Bässler
- Bayreuth Institute of Macromolecular Research
- Universität Bayreuth
- 95440 Bayreuth
- Germany
| | - Anna Köhler
- Bayreuth Institute of Macromolecular Research
- Universität Bayreuth
- 95440 Bayreuth
- Germany
- Experimentalphysik II (Organic Semiconductors)
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