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Karuthedath S, Gorenflot J, Melianas A, Kan Z, Kemerink M, Laquai F. Buildup of Triplet-State Population in Operating TQ1:PC 71BM Devices Does Not Limit Their Performance. J Phys Chem Lett 2020; 11:2838-2845. [PMID: 32202789 DOI: 10.1021/acs.jpclett.0c00756] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Triplet generation in organic solar cells has been considered a major loss channel. Determining the density of the triplet-state population in an operating device is challenging. Here, we employ transient absorption (TA) spectroscopy on the quinoxaline-thiophene copolymer TQ1 blended with PC71BM, quantify the transient charge and triplet-state densities, and parametrize their generation and recombination dynamics. The charge recombination parameters reproduce the experimentally measured current-voltage characteristics in charge carrier drift-diffusion simulations, and they yield the steady-state charge densities. We demonstrate that triplets are formed by both geminate and nongeminate recombination of charge carriers and decay primarily by triplet-triplet annihilation. Using the charge densities in the rate equations describing triplet-state dynamics, we find that triplet-state densities in devices are in the range of charge carrier densities. Despite this substantial triplet-state buildup, TQ1:PC71BM devices exhibit only moderate geminate recombination and significantly reduced nongeminate charge recombination, with reduction factors between 10-4 and 10-3 compared to Langevin recombination.
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Affiliation(s)
- Safakath Karuthedath
- Materials Science and Engineering Program (MSE), Physical Sciences and Engineering Division (PSE), KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Julien Gorenflot
- Materials Science and Engineering Program (MSE), Physical Sciences and Engineering Division (PSE), KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Armantas Melianas
- Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics, Center of Organic Electronics (COE), Linköping University, 58183 Linköping, Sweden
| | - Zhipeng Kan
- Materials Science and Engineering Program (MSE), Physical Sciences and Engineering Division (PSE), KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Martijn Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - Frédéric Laquai
- Materials Science and Engineering Program (MSE), Physical Sciences and Engineering Division (PSE), KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
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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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Roland S, Kniepert J, Love JA, Negi V, Liu F, Bobbert P, Melianas A, Kemerink M, Hofacker A, Neher D. Equilibrated Charge Carrier Populations Govern Steady-State Nongeminate Recombination in Disordered Organic Solar Cells. J Phys Chem Lett 2019; 10:1374-1381. [PMID: 30829040 DOI: 10.1021/acs.jpclett.9b00516] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We employed bias-assisted charge extraction techniques to investigate the transient and steady-state recombination of photogenerated charge carriers in complete devices of a disordered polymer-fullerene blend. Charge recombination is shown to be dispersive, with a significant slowdown of the recombination rate over time, consistent with the results from kinetic Monte Carlo simulations. Surprisingly, our experiments reveal little to no contributions from early time recombination of nonequilibrated charge carriers to the steady-state recombination properties. We conclude that energetic relaxation of photogenerated carriers outpaces any significant nongeminate recombination under application-relevant illumination conditions. With equilibrated charges dominating the steady-state recombination, quasi-equilibrium concepts appear suited for describing the open-circuit voltage of organic solar cells despite pronounced energetic disorder.
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Affiliation(s)
- Steffen Roland
- Department of Physics and Astronomy , Universität Potsdam , 14476 Potsdam , Germany
| | - Juliane Kniepert
- Department of Physics and Astronomy , Universität Potsdam , 14476 Potsdam , Germany
| | - John A Love
- Department of Physics and Astronomy , Universität Potsdam , 14476 Potsdam , Germany
| | - Vikas Negi
- Molecular Materials and Nanosystems, Department of Applied Physics , Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven , The Netherlands
| | - Feilong Liu
- Molecular Materials and Nanosystems, Department of Applied Physics , Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven , The Netherlands
| | - Peter Bobbert
- Molecular Materials and Nanosystems, Department of Applied Physics , Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven , The Netherlands
| | - Armantas Melianas
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology , Linköping University , 58183 Linköping , Sweden
| | - Martijn Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology , Linköping University , 58183 Linköping , Sweden
| | - Andreas Hofacker
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , 01187 Dresden , Germany
| | - Dieter Neher
- Department of Physics and Astronomy , Universität Potsdam , 14476 Potsdam , Germany
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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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Wang Z, Zhou Y, Miyadera T, Chikamatsu M, Yoshida Y. Constructing Nanostructured Donor/Acceptor Bulk Heterojunctions via Interfacial Templates for Efficient Organic Photovoltaics. ACS APPLIED MATERIALS & INTERFACES 2017; 9:43893-43901. [PMID: 29172420 DOI: 10.1021/acsami.7b13989] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We demonstrate that a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/diindenoperylene (PEDOT:PSS/DIP) interfacial bilayer could serve as a structural template to enable the morphological control of bulk heterojunctions (BHJs) by co-evaporation of tetraphenyldibenzoperiflanthene:fullerene (DBP:C60), which greatly improves the device performances. Especially, we show that isolated crystalline domains of C60 can be well-controlled at the nanoscale during the co-evaporation. Photoluminescence spectra indicate the realization of DIP/DBP cascade energy architecture, which significantly facilitates both the energy transfer and photocurrent generation. In addition, with bias-dependent external quantum efficiency analysis, we reveal that such a cascade energy device architecture greatly suppresses the energy recombination in both carrier and exciton transfer, resulting in a high open-circuit voltage and a high fill factor. By carefully optimizing the interfacial and BHJ layers, we achieved a high-performance organic photovoltaic cell with a power conversion efficiency of 5.0 ± 0.3%.
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Affiliation(s)
- Zhiping Wang
- Research Center for Photovoltaic Technologies and ‡Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) , AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba, Japan
| | - Ying Zhou
- Research Center for Photovoltaic Technologies and ‡Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) , AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba, Japan
| | - Tetsuhiko Miyadera
- Research Center for Photovoltaic Technologies and ‡Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) , AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba, Japan
| | - Masayuki Chikamatsu
- Research Center for Photovoltaic Technologies and ‡Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) , AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba, Japan
| | - Yuji Yoshida
- Research Center for Photovoltaic Technologies and ‡Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) , AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba, Japan
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Kurpiers J, Neher D. Dispersive Non-Geminate Recombination in an Amorphous Polymer:Fullerene Blend. Sci Rep 2016; 6:26832. [PMID: 27225584 PMCID: PMC4881019 DOI: 10.1038/srep26832] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Accepted: 05/10/2016] [Indexed: 11/16/2022] Open
Abstract
Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer:fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions.
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Affiliation(s)
- Jona Kurpiers
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, D-14476 Potsdam, Germany
| | - Dieter Neher
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, D-14476 Potsdam, Germany
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Melianas A, Etzold F, Savenije TJ, Laquai F, Inganäs O, Kemerink M. Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells. Nat Commun 2015; 6:8778. [PMID: 26537357 PMCID: PMC4659933 DOI: 10.1038/ncomms9778] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Accepted: 10/01/2015] [Indexed: 11/23/2022] Open
Abstract
In photovoltaic devices, the photo-generated charge carriers are typically assumed to be in thermal equilibrium with the lattice. In conventional materials, this assumption is experimentally justified as carrier thermalization completes before any significant carrier transport has occurred. Here, we demonstrate by unifying time-resolved optical and electrical experiments and Monte Carlo simulations over an exceptionally wide dynamic range that in the case of organic photovoltaic devices, this assumption is invalid. As the photo-generated carriers are transported to the electrodes, a substantial amount of their energy is lost by continuous thermalization in the disorder broadened density of states. Since thermalization occurs downward in energy, carrier motion is boosted by this process, leading to a time-dependent carrier mobility as confirmed by direct experiments. We identify the time and distance scales relevant for carrier extraction and show that the photo-generated carriers are extracted from the operating device before reaching thermal equilibrium.
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Affiliation(s)
- Armantas Melianas
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - Fabian Etzold
- Max Planck Research Group for Organic Optoelectronics, Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany
| | - Tom J. Savenije
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, 2628 BL Delft, The Netherlands
| | - Frédéric Laquai
- Max Planck Research Group for Organic Optoelectronics, Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany
- Physical Sciences and Engineering Division, Material Science and Engineering, Solar and Photovoltaics Engineering Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Olle Inganäs
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - Martijn Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
- Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
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8
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Gao F, Inganäs O. Charge generation in polymer-fullerene bulk-heterojunction solar cells. Phys Chem Chem Phys 2014; 16:20291-304. [PMID: 24994122 DOI: 10.1039/c4cp01814a] [Citation(s) in RCA: 169] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Charge generation in organic solar cells is a fundamental yet heavily debated issue. This article gives a balanced review of different mechanisms proposed to explain efficient charge generation in polymer-fullerene bulk-heterojunction solar cells. We discuss the effect of charge-transfer states, excess energy, external electric field, temperature, disorder of the materials, and delocalisation of the charge carriers on charge generation. Although a general consensus has not been reached yet, recent findings, based on both steady-state and transient measurements, have significantly advanced our understanding of this process.
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Affiliation(s)
- Feng Gao
- Biomolecular and Organic Electronics, IFM and Center of Organic Electronics, Linköping University, Linköping SE-581 83, Sweden.
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