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Song H, Hu D, Lv J, Lu S, Haiyan C, Kan Z. Hybrid Cathode Interlayer Enables 17.4% Efficiency Binary Organic Solar Cells. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2105575. [PMID: 35040581 PMCID: PMC8922103 DOI: 10.1002/advs.202105575] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Indexed: 06/14/2023]
Abstract
With the emergence of fused ring electron acceptors, the power conversion efficiency of organic solar cells reached 19%. In comparison with the electron donor and acceptor materials progress, the development of cathode interlayers lags. As a result, charge extraction barriers, interfacial trap states, and significant transport resistance may be induced due to the unfavorable cathode interlayer, limiting the device performances. Herein, a hybrid cathode interlayer composed of PNDIT-F3N and PDIN is adopted to investigate the interaction between the photoexcited acceptor and cathode interlayer. The state of art acceptor Y6 is chosen and blended with PM6 as the active layer. The device with hybrid interlayer, PNDIT-F3N:PDIN (0.6:0.4, in wt%), attains a power conversion efficiency of 17.4%, outperforming devices with other cathode interlayer such as NDI-M, PDINO, and Phen-DPO. It is resulted from enhanced exciton dissociation, reduced trap-assisted recombination, and smaller transfer resistance. Therefore, the hybrid interlayer strategy is demonstrated as an efficient approach to improve device performance, shedding light on the selection and engineering of cathode interlayers for pairing the increasing number of fused ring electron acceptors.
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Affiliation(s)
- Hang Song
- Chongqing Institute of Green and Intelligent TechnologyChinese Academy of SciencesChongqing400714China
- College of Materials Science and EngineeringChongqing University of TechnologyChongqing400054China
| | - Dingqin Hu
- Chongqing Institute of Green and Intelligent TechnologyChinese Academy of SciencesChongqing400714China
- Chongqing University174 Shazhengjie, ShapingbaChongqing400044China
- Chongqing SchoolUniversity of Chinese Academy of Sciences (UCAS Chongqing)Chongqing400714China
| | - Jie Lv
- Chongqing Institute of Green and Intelligent TechnologyChinese Academy of SciencesChongqing400714China
- Chongqing SchoolUniversity of Chinese Academy of Sciences (UCAS Chongqing)Chongqing400714China
| | - Shirong Lu
- Chongqing Institute of Green and Intelligent TechnologyChinese Academy of SciencesChongqing400714China
- Chongqing SchoolUniversity of Chinese Academy of Sciences (UCAS Chongqing)Chongqing400714China
| | - Chen Haiyan
- Chongqing Institute of Green and Intelligent TechnologyChinese Academy of SciencesChongqing400714China
- Chongqing University174 Shazhengjie, ShapingbaChongqing400044China
- Chongqing SchoolUniversity of Chinese Academy of Sciences (UCAS Chongqing)Chongqing400714China
| | - Zhipeng Kan
- Chongqing Institute of Green and Intelligent TechnologyChinese Academy of SciencesChongqing400714China
- Chongqing SchoolUniversity of Chinese Academy of Sciences (UCAS Chongqing)Chongqing400714China
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Yao J, Qiu B, Zhang ZG, Xue L, Wang R, Zhang C, Chen S, Zhou Q, Sun C, Yang C, Xiao M, Meng L, Li Y. Cathode engineering with perylene-diimide interlayer enabling over 17% efficiency single-junction organic solar cells. Nat Commun 2020; 11:2726. [PMID: 32483159 PMCID: PMC7264349 DOI: 10.1038/s41467-020-16509-w] [Citation(s) in RCA: 178] [Impact Index Per Article: 44.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Accepted: 05/07/2020] [Indexed: 11/09/2022] Open
Abstract
In organic solar cells (OSCs), cathode interfacial materials are generally designed with highly polar groups to increase the capability of lowering the work function of cathode. However, the strong polar group could result in a high surface energy and poor physical contact at the active layer surface, posing a challenge for interlayer engineering to address the trade-off between device stability and efficiency. Herein, we report a hydrogen-bonding interfacial material, aliphatic amine-functionalized perylene-diimide (PDINN), which simultaneously down-shifts the work function of the air stable cathodes (silver and copper), and maintains good interfacial contact with the active layer. The OSCs based on PDINN engineered silver-cathode demonstrate a high power conversion efficiency of 17.23% (certified value 16.77% by NREL) and high stability. Our results indicate that PDINN is an effective cathode interfacial material and interlayer engineering via suitable intermolecular interactions is a feasible approach to improve device performance of OSCs.
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Affiliation(s)
- Jia Yao
- State Key Laboratory of Organic/Inorganic Composites, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China
| | - Beibei Qiu
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
| | - Zhi-Guo Zhang
- State Key Laboratory of Organic/Inorganic Composites, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China.
| | - Lingwei Xue
- State Key Laboratory of Organic/Inorganic Composites, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China
| | - Rui Wang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
| | - Chunfeng Zhang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
| | - Shanshan Chen
- Department of Energy Engineering, School of Energy and Chemical Engineering, Low Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, South Korea
- MOE Key Laboratory of Low-grade Energy Utilization Technologies and Systems, CQU-NUS Renewable Energy Materials & Devices Joint Laboratory, School of Energy & Power Engineering, Chongqing University, Chongqing, 400044, China
| | - Qiuju Zhou
- Analysis & Testing Center, Xinyang Normal University, Xinyang, Henan, 464000, China
| | - Chenkai Sun
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
- School of Chemical Science, University of Chinese Academy of Sciences, Beijing, 100049, China
- College of Chemistry and Molecular Engineering, Zhengzhou University, Henan, 450001, China
| | - Changduk Yang
- Department of Energy Engineering, School of Energy and Chemical Engineering, Low Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, South Korea
| | - Min Xiao
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
| | - Lei Meng
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
| | - Yongfang Li
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
- School of Chemical Science, University of Chinese Academy of Sciences, Beijing, 100049, China.
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3
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Melianas A, Kemerink M. Photogenerated Charge Transport in Organic Electronic Materials: Experiments Confirmed by Simulations. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1806004. [PMID: 30719756 DOI: 10.1002/adma.201806004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2018] [Revised: 10/29/2018] [Indexed: 06/09/2023]
Abstract
The performance of organic optoelectronic devices, such as organic photovoltaic (OPV) cells, is to a large extent dictated by their ability to transport the photogenerated charge, with relevant processes spanning a wide temporal (fs-µs) and spatial (1-100 nm) range. However, time-resolved techniques can access only a limited temporal window, and often contradict steady-state measurements. Here, commonly employed steady-state and time-resolved techniques are unified over an exceptionally wide temporal range (fs-µs) in a consistent physical picture. Experimental evidence confirmed by numerical simulations shows that, although various techniques probe different time scales, they are mutually consistent as they probe the same physical mechanisms governing charge motion in disordered media-carrier hopping and thermalization in a disorder-broadened density of states (DOS). The generality of this framework is highlighted by time-resolved experimental data obtained on polymer:fullerene, polymer:polymer, and small-molecule blends with varying morphology, including recent experiments revealing that low donor content OPV devices operate by long-range hole tunneling between non-nearest-neighbor molecules. The importance of nonequilibrium processes in organic electronic materials is reviewed, with a particular focus on experimental data and understanding charge transport physics in terms of material DOS.
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Affiliation(s)
- Armantas Melianas
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA
| | - Martijn Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183, Linköping, Sweden
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Lee JH, Do JY, Park NK, Seo MW, Ryu HJ, Hong JP, Kim YS, Kim SK, Kang M. Cost-effective and dynamic carbon dioxide conversion into methane using a CaTiO3@Ni-Pt catalyst in a photo-thermal hybrid system. J Photochem Photobiol A Chem 2018. [DOI: 10.1016/j.jphotochem.2018.05.045] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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5
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Inganäs O. Organic Photovoltaics over Three Decades. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1800388. [PMID: 29938847 DOI: 10.1002/adma.201800388] [Citation(s) in RCA: 235] [Impact Index Per Article: 39.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 03/20/2018] [Indexed: 05/20/2023]
Abstract
The development of organic semiconductors for photovoltaic devices, over the last three decades, has led to unexpected performance for an alternative choice of materials to convert sunlight to electricity. New materials and developed concepts have improved the photovoltage in organic photovoltaic devices, where records are now found above 13% power conversion efficiency in sunlight. The author has stayed with the topic of organic materials for energy conversion and energy storage during these three decades, and makes use of the Hall of Fame now built by Advanced Materials, to present his view of the path travelled over this time, including motivations, personalities, and ambitions.
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Affiliation(s)
- Olle Inganäs
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology (IFM), Linköping University, S-581 83, Linköping, Sweden
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6
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Noriega R. Efficient Charge Transport in Disordered Conjugated Polymer Microstructures. Macromol Rapid Commun 2018; 39:e1800096. [DOI: 10.1002/marc.201800096] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 03/12/2018] [Indexed: 11/09/2022]
Affiliation(s)
- Rodrigo Noriega
- Chemistry Department; University of Utah; 315 S 1400 E Salt Lake City UT 84112 USA
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7
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Analysis of collision-controlled time dependence of diffusion coefficient of polaron pairs from transient absorption spectra of conducting polymers. CHEMICAL PAPERS 2018. [DOI: 10.1007/s11696-018-0439-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Abstract
![]()
The field of organic
photovoltaics has developed rapidly over the
last 2 decades, and small solar cells with power conversion efficiencies
of 13% have been demonstrated. Light absorbed in the organic layers
forms tightly bound excitons that are split into free electrons and
holes using heterojunctions of electron donor and acceptor materials,
which are then extracted at electrodes to give useful electrical power.
This review gives a concise description of the fundamental processes
in photovoltaic devices, with the main emphasis on the characterization
of energy transfer and its role in dictating device architecture,
including multilayer planar heterojunctions, and on the factors that
impact free carrier generation from dissociated excitons. We briefly
discuss harvesting of triplet excitons, which now attracts substantial
interest when used in conjunction with singlet fission. Finally, we
introduce the techniques used by researchers for characterization
and engineering of bulk heterojunctions to realize large photocurrents,
and examine the formed morphology in three prototypical blends.
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Affiliation(s)
- Gordon J Hedley
- Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews , North Haugh, St Andrews, Fife KY16 9SS, U.K
| | - Arvydas Ruseckas
- Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews , North Haugh, St Andrews, Fife KY16 9SS, U.K
| | - Ifor D W Samuel
- Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews , North Haugh, St Andrews, Fife KY16 9SS, U.K
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9
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Role of coherence and delocalization in photo-induced electron transfer at organic interfaces. Sci Rep 2016; 6:32914. [PMID: 27605035 PMCID: PMC5015064 DOI: 10.1038/srep32914] [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: 04/25/2016] [Accepted: 07/28/2016] [Indexed: 11/08/2022] Open
Abstract
Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces.
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10
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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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11
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Pranculis V, Ruseckas A, Vithanage D, Hedley GJ, Samuel IDW, Gulbinas V. Influence of Blend Ratio and Processing Additive on Free Carrier Yield and Mobility in PTB7:PC 71BM Photovoltaic Solar Cells. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2016; 120:9588-9594. [PMID: 27293495 PMCID: PMC4897731 DOI: 10.1021/acs.jpcc.6b01548] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 04/21/2016] [Indexed: 06/06/2023]
Abstract
Charge separation and extraction dynamics were investigated in high-performance bulk heterojunction solar cells made from the polymer PTB7 and the soluble fullerene PC71BM on a broad time scale from subpicosecond to microseconds using ultrafast optical probing of carrier drift and the integral-mode photocurrent measurements. We show that the short circuit current is determined by the separation of charge pairs into free carriers, which is strongly influenced by blend composition. This separation is found to be efficient in fullerene-rich blends where a high electron mobility of >0.1 cm2 V-1 s-1 is observed in the first 10 ps after excitation. Morphology optimization using the solvent additive 1,8-diiodooctane (DIO) doubles the charge pair separation efficiency and the short-circuit current. Carrier extraction at low internal electric field is slightly faster from the cells prepared with DIO, which can reduce recombination losses and enhance a fill factor.
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Affiliation(s)
- Vytenis Pranculis
- Center
for Physical Sciences and Technology, Savanoriu Ave 231, 02300 Vilnius, Lithuania
| | - Arvydas Ruseckas
- Organic
Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - Dimali
A. Vithanage
- Organic
Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - Gordon J. Hedley
- Organic
Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - Ifor D. W. Samuel
- Organic
Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - Vidmantas Gulbinas
- Center
for Physical Sciences and Technology, Savanoriu Ave 231, 02300 Vilnius, Lithuania
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Zhang W, Pan X, Feng X, Wang CH, Yang YW, Ju H, Zhu J. Interface properties between a low band gap conjugated polymer and a calcium metal electrode. Phys Chem Chem Phys 2016; 18:9446-52. [PMID: 26979721 DOI: 10.1039/c5cp08066e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Interfaces between metal electrodes and π-conjugated polymers play an important role in the organic optoelectronic devices. In this paper, the molecular orientation of the pristine poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (APFO3) films, chemical reactions and the electronic structure during the interface formation of Ca/APFO3 have been investigated in detail using synchrotron radiation photoemission spectroscopy (SRPES), X-ray photoemission spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. It is shown that the APFO3 film has a high degree of orientational ordering with its aromatic ring tilted at an angle of 43° from the substrate, and the 9,9-dioctyl fluorene unit (F8) is almost in the same plane as the benzothiazole unit (BT). Upon vapor-deposition of Ca onto APFO3 at room temperature, Ca dopes electrons into APFO3 and induces the downward band bending of APFO3. Moreover, Ca can diffuse into the APFO3 subsurface and react with N, S and C atoms of APFO3. Finally, the barrier of electron injection at the Ca/APFO3 interface is derived by the energy level alignment diagram. These results enable us to gain comprehensive insights into APFO3 and will facilitate the reasonable design of high performance devices based on APFO3.
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Affiliation(s)
- Wei Zhang
- National Synchrotron Radiation Laboratory and Collaborative Innovation Center of Suzhou Nano Science and Technology, University of Science and Technology of China, Hefei, Anhui 230029, China. and Hefei Science Center, Chinese Academy of Sciences, China
| | - Xiao Pan
- National Synchrotron Radiation Laboratory and Collaborative Innovation Center of Suzhou Nano Science and Technology, University of Science and Technology of China, Hefei, Anhui 230029, China.
| | - Xuefei Feng
- National Synchrotron Radiation Laboratory and Collaborative Innovation Center of Suzhou Nano Science and Technology, University of Science and Technology of China, Hefei, Anhui 230029, China.
| | - Chia-Hsin Wang
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Yaw-Wen Yang
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Huanxin Ju
- National Synchrotron Radiation Laboratory and Collaborative Innovation Center of Suzhou Nano Science and Technology, University of Science and Technology of China, Hefei, Anhui 230029, China. and Hefei Science Center, Chinese Academy of Sciences, China
| | - Junfa Zhu
- National Synchrotron Radiation Laboratory and Collaborative Innovation Center of Suzhou Nano Science and Technology, University of Science and Technology of China, Hefei, Anhui 230029, China. and Hefei Science Center, Chinese Academy of Sciences, China
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Ponseca CS, Tian Y, Sundström V, Scheblykin IG. Excited state and charge-carrier dynamics in perovskite solar cell materials. NANOTECHNOLOGY 2016; 27:082001. [PMID: 26820442 DOI: 10.1088/0957-4484/27/8/082001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technology. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved conductivity, transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research.
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14
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Devižis A, De Jonghe-Risse J, Hany R, Nüesch F, Jenatsch S, Gulbinas V, Moser JE. Dissociation of Charge Transfer States and Carrier Separation in Bilayer Organic Solar Cells: A Time-Resolved Electroabsorption Spectroscopy Study. J Am Chem Soc 2015; 137:8192-8. [PMID: 26037526 DOI: 10.1021/jacs.5b03682] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ultrafast optical probing of the electric field by means of Stark effect in planar heterojunction cyanine dye/fullerene organic solar cells enables one to directly monitor the dynamics of free electron formation during the dissociation of interfacial charge transfer (CT) states. Motions of electrons and holes is scrutinized separately by selectively probing the Stark shift dynamics at selected wavelengths. It is shown that only charge pairs with an effective electron-hole separation distance of less than 4 nm are created during the dissociation of Frenkel excitons. Dissociation of the coulombically bound charge pairs is identified as the major rate-limiting step for charge carriers' generation. Interfacial CT states split into free charges on the time-scale of tens to hundreds of picoseconds, mainly by electron escape from the Coulomb potential over a barrier that is lowered by the electric field. The motion of holes in the small molecule donor material during the charge separation time is found to be insignificant.
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Affiliation(s)
- Andrius Devižis
- ∥Center for Physical Sciences and Technology, Savanoriu 231, LT-02300 Vilnius, Lithuania
| | | | - Roland Hany
- §Laboratory for Functional Polymers, EMPA, Swiss Federal Laboratories for Materials Science and Technology, CH-8600, Dübendorf, Switzerland
| | - Frank Nüesch
- §Laboratory for Functional Polymers, EMPA, Swiss Federal Laboratories for Materials Science and Technology, CH-8600, Dübendorf, Switzerland
| | - Sandra Jenatsch
- §Laboratory for Functional Polymers, EMPA, Swiss Federal Laboratories for Materials Science and Technology, CH-8600, Dübendorf, Switzerland
| | - Vidmantas Gulbinas
- ∥Center for Physical Sciences and Technology, Savanoriu 231, LT-02300 Vilnius, Lithuania
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