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Chow PCY, Chan CCS, Ma C, Zou X, Yan H, Wong KS. Factors That Prevent Spin-Triplet Recombination in Non-fullerene Organic Photovoltaics. J Phys Chem Lett 2021; 12:5045-5051. [PMID: 34019416 DOI: 10.1021/acs.jpclett.1c01214] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Managing the dynamics of spin-triplet electronic states is crucial for achieving high-performance organic photovoltaics. Here we show that the replacement of fullerene with non-fullerene acceptor (NFA) molecules leads to suppression of triplet recombination and thus more efficient charge generation. This indicates that the relaxation of charges to the local triplet exciton state, although energetically allowed, is outcompeted by the thermally activated separation of interfacial charge-transfer excitons (CTEs) in the NFA-based system. By rationalizing our results with Marcus theory, we propose that triplet recombination in the fullerene system is driven by the small energy difference and strong electronic couplings between the CTE state and the lowest-lying triplet exciton state (T1) of fullerene acceptor molecules. In contrast, the large energy difference and small electronic couplings between these states in the NFA-based blends lead to sufficiently slow triplet relaxation rate compared to the charge separation rate (≪1010 s-1), thus preventing triplet recombination.
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Affiliation(s)
- Philip C Y Chow
- Department of Mechanical Engineering, The University of Hong Kong, Pokfulam, Hong Kong 999077, China
| | - Christopher C S Chan
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China
| | - Chao Ma
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China
| | - Xinhui Zou
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China
- Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China
| | - He Yan
- Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China
| | - Kam Sing Wong
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China
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Analysis of Triplet Exciton Loss Pathways in PTB7:PC71BM Bulk Heterojunction Solar Cells. Sci Rep 2016; 6:29158. [PMID: 27380928 PMCID: PMC4933975 DOI: 10.1038/srep29158] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Accepted: 06/15/2016] [Indexed: 02/03/2023] Open
Abstract
A strategy for increasing the conversion efficiency of organic photovoltaics has been to increase the VOC by tuning the energy levels of donor and acceptor components. However, this opens up a new loss pathway from an interfacial charge transfer state to a triplet exciton (TE) state called electron back transfer (EBT), which is detrimental to device performance. To test this hypothesis, we study triplet formation in the high performing PTB7:PC71BM blend system and determine the impact of the morphology-optimizing additive 1,8-diiodoctane (DIO). Using photoluminescence and spin-sensitive optically detected magnetic resonance (ODMR) measurements at low temperature, we find that TEs form on PC71BM via intersystem crossing from singlet excitons and on PTB7 via EBT mechanism. For DIO blends with smaller fullerene domains, an increased density of PTB7 TEs is observed. The EBT process is found to be significant only at very low temperature. At 300 K, no triplets are detected via ODMR, and electrically detected magnetic resonance on optimized solar cells indicates that TEs are only present on the fullerenes. We conclude that in PTB7:PC71BM devices, TE formation via EBT is impacted by fullerene domain size at low temperature, but at room temperature, EBT does not represent a dominant loss pathway.
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Manninen VM, Heiskanen JP, Pankov D, Kastinen T, Hukka TI, Hormi OEO, Lemmetyinen HJ. The effect of diketopyrrolopyrrole (DPP) group inclusion in p-cyanophenyl end-capped oligothiophene used as a dopant in P3HT:PCBM BHJ solar cells. Photochem Photobiol Sci 2014; 13:1456-68. [DOI: 10.1039/c4pp00207e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Synthesis and properties of DPP-(2TPhCN)2 dopant molecules, which absorb light and transfer energy to PC60BM, increasing the BHJ cell efficiency.
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Affiliation(s)
- V. M. Manninen
- Department of Chemistry and Bioengineering
- Tampere University of Technology
- Tampere, Finland
| | | | - D. Pankov
- Department of Chemistry
- FI-90014 University of Oulu
- Finland
| | - T. Kastinen
- Department of Chemistry and Bioengineering
- Tampere University of Technology
- Tampere, Finland
| | - T. I. Hukka
- Department of Chemistry and Bioengineering
- Tampere University of Technology
- Tampere, Finland
| | - O. E. O. Hormi
- Department of Chemistry
- FI-90014 University of Oulu
- Finland
| | - H. J. Lemmetyinen
- Department of Chemistry and Bioengineering
- Tampere University of Technology
- Tampere, Finland
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Snedden EW, Monkman AP, Dias FB. Photophysics of the geminate polaron-pair state in copper phthalocyanine organic photovoltaic blends: evidence for enhanced intersystem crossing. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2013; 25:1930-1938. [PMID: 22933249 DOI: 10.1002/adma.201201350] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Revised: 05/15/2012] [Indexed: 06/01/2023]
Abstract
Geminate polaron-pair recombination directly to the triplet state of the small dye molecule copper(II) 1,4,8,11,15,18,22,25-octabutoxy-29H,31H- phthalocyanine (CuPC) and exciton trapping in CuPC domains, combine to reduce the internal quantum efficiency of free polaron formation in the bulk-heterojunction blends of CuPC doped with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor.
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Affiliation(s)
- Edward W Snedden
- Organic Electroactive Materials Group, Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
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Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes. ACTA ACUST UNITED AC 2013. [DOI: 10.1155/2013/670130] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A potential major drawback with organic light-emitting devices, (OLEDs) is the limit of 25% singlet exciton production through spin-dependent charge recombination. Recent device results, however, show that this limit does not hold and far higher efficiencies can be achieved in purely fluorescent-based systems (Wohlgenannt et al. (2001), Dhoot et al. (2002), Lin et al. (2003), Wilson et al. (2001), Cao et al. (1999), Baldo et al. (1999), and Kim et al. (2000)). Thus, the question arises; is recombination spin dependent (Tandon et al. (2003)) or are singlet excitons generated in secondary processes? Direct measurement of the singlet generation rate in working devices of 44% has been shown (Rothe et al. (2006)), which have been verified as being part due to direct singlets formed on recombination and part from triplet fusion, singlets produced during triplet annihilation (Kondakov et al. (2009), King et al. (2011), and Zhang and Forrest (2012)). Here, the various routes by which triplet excitons can generate singlet states are discussed and their relative contributions to the overall electroluminescence yield are given. The materials requirements to obtain maximum singlet production from triplet states are discussed. These triplet contributions can give very high device yields for fluorescent emitters, which in the case of blue devices can be highly advantageous. Further, new devices architectures open up which are simple and have intrinsically low turn on voltages, ideal for large-area OLED lighting applications.
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Jailaubekov AE, Willard AP, Tritsch JR, Chan WL, Sai N, Gearba R, Kaake LG, Williams KJ, Leung K, Rossky PJ, Zhu XY. Hot charge-transfer excitons set the time limit for charge separation at donor/acceptor interfaces in organic photovoltaics. NATURE MATERIALS 2013; 12:66-73. [PMID: 23223125 DOI: 10.1038/nmat3500] [Citation(s) in RCA: 313] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Accepted: 10/24/2012] [Indexed: 05/13/2023]
Abstract
Photocurrent generation in organic photovoltaics (OPVs) relies on the dissociation of excitons into free electrons and holes at donor/acceptor heterointerfaces. The low dielectric constant of organic semiconductors leads to strong Coulomb interactions between electron-hole pairs that should in principle oppose the generation of free charges. The exact mechanism by which electrons and holes overcome this Coulomb trapping is still unsolved, but increasing evidence points to the critical role of hot charge-transfer (CT) excitons in assisting this process. Here we provide a real-time view of hot CT exciton formation and relaxation using femtosecond nonlinear optical spectroscopies and non-adiabatic mixed quantum mechanics/molecular mechanics simulations in the phthalocyanine-fullerene model OPV system. For initial excitation on phthalocyanine, hot CT excitons are formed in 10(-13) s, followed by relaxation to lower energies and shorter electron-hole distances on a 10(-12) s timescale. This hot CT exciton cooling process and collapse of charge separation sets the fundamental time limit for competitive charge separation channels that lead to efficient photocurrent generation.
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Affiliation(s)
- Askat E Jailaubekov
- Energy Frontier Research Center (EFRC: CST), University of Texas, Austin, Texas 78712, USA
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Gélinas S, Kirkpatrick J, Howard IA, Johnson K, Wilson MWB, Pace G, Friend RH, Silva C. Recombination Dynamics of Charge Pairs in a Push–Pull Polyfluorene-Derivative. J Phys Chem B 2012; 117:4649-53. [DOI: 10.1021/jp3089963] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Simon Gélinas
- Département de Physique & Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada
- Cavendish
Laboratory, University of Cambridge, J.J.
Thompson Avenue, Cambridge
CB3 0HE, United Kingdom
| | - James Kirkpatrick
- Oxford
Martin School, University of Oxford, Oxford
OX1 2JD, United Kingdom
| | - Ian A. Howard
- Max Planck Institute for Polymer Research, D-55128 Mainz, Germany
| | - Kerr Johnson
- Cavendish
Laboratory, University of Cambridge, J.J.
Thompson Avenue, Cambridge
CB3 0HE, United Kingdom
| | - Mark W. B. Wilson
- Cavendish
Laboratory, University of Cambridge, J.J.
Thompson Avenue, Cambridge
CB3 0HE, United Kingdom
| | - Giuseppina Pace
- Cavendish
Laboratory, University of Cambridge, J.J.
Thompson Avenue, Cambridge
CB3 0HE, United Kingdom
| | - Richard H. Friend
- Cavendish
Laboratory, University of Cambridge, J.J.
Thompson Avenue, Cambridge
CB3 0HE, United Kingdom
| | - Carlos Silva
- Département de Physique & Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada
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Thompson BC, Khlyabich PP, Burkhart B, Aviles AE, Rudenko A, Shultz GV, Ng CF, Mangubat LB. Polymer-Based Solar Cells: State-of-the-Art Principles for the Design of Active Layer Components. ACTA ACUST UNITED AC 2011. [DOI: 10.1515/green.2011.002] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractThe vision of organic photovoltaics is that of a low cost solar energy conversion platform that provides lightweight, flexible solar cells that are easily incorporated into existing infrastructure with minimal impact on land usage. Polymer solar cells have been a subject of growing research interest over the past quarter century, and are now developed to the point where they are on the verge of introduction into the market. Towards the goal of continuing to improve the performance of polymer solar cells, a number of avenues are being explored. Here, the focus is on optimization of device performance via the development of a more fundamental understanding of device parameters. The fundamental operating principle of an organic solar cell is based on the cooperative interaction of molecular or polymeric electron donors and acceptors. Here the state-of-the-art in understanding of the physical and electronic interactions between donor and acceptor components is examined, as is important for understanding future avenues of research and the ultimate potential of this technology.
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Eng MP, Shoaee S, Molina-Ontoria A, Gouloumis A, Martín N, Durrant JR. Impact of concentration self-quenching on the charge generation yield of fullerene based donor–bridge–acceptor compounds in the solid state. Phys Chem Chem Phys 2011; 13:3721-9. [DOI: 10.1039/c0cp02107e] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Deibel C, Strobel T, Dyakonov V. Role of the charge transfer state in organic donor-acceptor solar cells. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2010; 22:4097-111. [PMID: 20803527 DOI: 10.1002/adma.201000376] [Citation(s) in RCA: 298] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Charge transfer complexes are interfacial charge pairs residing at the donor-acceptor heterointerface in organic solar cell. Experimental evidence shows that it is crucial for the photovoltaic performance, as both photocurrent and open circuit voltage directly depend on it. For charge photogeneration, charge transfer complexes represent the intermediate but essential step between exciton dissotiation and charge extraction. Recombination of free charges to the ground state is via the bound charge transfer state before being lost to the ground state. In terms of the open circuit voltage, its maximum achievable value is determined by the energy of the charge transfer state. An important question is whether or not maximum photocurrent and maximum open circuit voltage can be achieved simultaneously. The impact of increasing the CT energy-in order to raise the open circuit voltage, but lowering the kinetic excess energy of the CT complexes at the same time-on the charge photogeneration will accordingly be discussed. Clearly, the fundamental understanding of the processes involving the charge transfer state is essential for an optimisation of the performance of organic solar cells.
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Lupton JM, McCamey DR, Boehme C. Coherent Spin Manipulation in Molecular Semiconductors: Getting a Handle on Organic Spintronics. Chemphyschem 2010; 11:3040-58. [DOI: 10.1002/cphc.201000186] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Affiliation(s)
- Tracey M Clarke
- Centre for Plastic Electronics, Department of Chemistry, Imperial College London, London, SW7 2AZ, United Kingdom
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Karsten BP, Bouwer RKM, Hummelen JC, Williams RM, Janssen RAJ. Charge separation and (triplet) recombination in diketopyrrolopyrrole–fullerene triads. Photochem Photobiol Sci 2010; 9:1055-65. [DOI: 10.1039/c0pp00098a] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Karsten BP, Bouwer RKM, Hummelen JC, Williams RM, Janssen RAJ. Charge separation and recombination in small band gap oligomer-fullerene triads. J Phys Chem B 2009; 114:14149-56. [PMID: 19817359 DOI: 10.1021/jp906973d] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Synthesis and photophysics of a series of thiophene-thienopyrazine small band gap oligomers, end-capped at both ends with C(60), are presented. In these triads, a photoinduced electron transfer reaction occurs between the oligomer as a donor and the fullerene as an acceptor. Femtosecond photoinduced absorption has been used to determine the rates for charge separation and recombination. It was found that charge separation takes place within approximately 10 ps, and is situated close to the Marcus optimal region. Charge recombination is faster in o-dichlorobenzene (ODCB) (15-45 ps) than in toluene (90-730 ps), because in ODCB charge recombination takes place close to the optimal region. In toluene, the recombination is situated in the inverted region, with a much higher activation barrier. No signs of recombination into a triplet state were observed.
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Affiliation(s)
- Bram P Karsten
- Molecular Materials and Nanosystems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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Karsten BP, Bijleveld JC, Viani L, Cornil J, Gierschner J, Janssen RAJ. Electronic structure of small band gap oligomers based on cyclopentadithiophenes and acceptor units. ACTA ACUST UNITED AC 2009. [DOI: 10.1039/b901374a] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Westenhoff S, Howard IA, Hodgkiss JM, Kirov KR, Bronstein HA, Williams CK, Greenham NC, Friend RH. Charge Recombination in Organic Photovoltaic Devices with High Open-Circuit Voltages. J Am Chem Soc 2008; 130:13653-8. [DOI: 10.1021/ja803054g] [Citation(s) in RCA: 201] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sebastian Westenhoff
- OE-Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, U.K., Department of Chemistry, Biochemistry & Biophysics, University of Gothenburg, Box 462, 40530 Gothenburg, Sweden, and Department of Chemistry, Imperial College London, London SW7 2AZ, U.K
| | - Ian A. Howard
- OE-Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, U.K., Department of Chemistry, Biochemistry & Biophysics, University of Gothenburg, Box 462, 40530 Gothenburg, Sweden, and Department of Chemistry, Imperial College London, London SW7 2AZ, U.K
| | - Justin M. Hodgkiss
- OE-Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, U.K., Department of Chemistry, Biochemistry & Biophysics, University of Gothenburg, Box 462, 40530 Gothenburg, Sweden, and Department of Chemistry, Imperial College London, London SW7 2AZ, U.K
| | - Kiril R. Kirov
- OE-Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, U.K., Department of Chemistry, Biochemistry & Biophysics, University of Gothenburg, Box 462, 40530 Gothenburg, Sweden, and Department of Chemistry, Imperial College London, London SW7 2AZ, U.K
| | - Hugo A. Bronstein
- OE-Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, U.K., Department of Chemistry, Biochemistry & Biophysics, University of Gothenburg, Box 462, 40530 Gothenburg, Sweden, and Department of Chemistry, Imperial College London, London SW7 2AZ, U.K
| | - Charlotte K. Williams
- OE-Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, U.K., Department of Chemistry, Biochemistry & Biophysics, University of Gothenburg, Box 462, 40530 Gothenburg, Sweden, and Department of Chemistry, Imperial College London, London SW7 2AZ, U.K
| | - Neil C. Greenham
- OE-Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, U.K., Department of Chemistry, Biochemistry & Biophysics, University of Gothenburg, Box 462, 40530 Gothenburg, Sweden, and Department of Chemistry, Imperial College London, London SW7 2AZ, U.K
| | - Richard H. Friend
- OE-Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, U.K., Department of Chemistry, Biochemistry & Biophysics, University of Gothenburg, Box 462, 40530 Gothenburg, Sweden, and Department of Chemistry, Imperial College London, London SW7 2AZ, U.K
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