Journal
NATURE ENERGY
Volume 7, Issue 11, Pages 1076-1086Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41560-022-01138-y
Keywords
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Funding
- City University of Hong Kong [9380086]
- Innovation and Technology Commission of Hong Kong [GHP/018/20SZ, MRP/040/21X]
- Environment and Ecology Bureau of Hong Kong under the Green Tech Fund [202020164]
- US Office of Naval Research [N00014-20-1-2191, N000141712204, N000142012155]
- Research Grants Council of Hong Kong [11307621, 11316422, C6023-19GF]
- Hong Kong Postdoctoral Fellowship Scheme
- Guangdong Major Project of Basic and Applied Basic Research [2019B030302007]
- Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials [2019B121205002]
- National Key R&D Program of China [2017YFA0303703, 2018YFA0209100]
- Fundamental Research Funds for the Central Universities [0204-14380177]
- National Natural Science Foundation of China [22225305, 21922302, 21873047, 52002393, 51873160]
- Hong Kong Baptist University
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Researchers have discovered that using donor and acceptor materials with intrinsically weaker exciton binding strengths in sequentially processed planar-mixed heterojunction devices can alleviate photocurrent loss caused by triplet states and achieve higher power conversion efficiencies.
At present, high-performance organic photovoltaics mostly adopt a bulk-heterojunction architecture, in which exciton dissociation is facilitated by charge-transfer states formed at numerous donor-acceptor (D-A) heterojunctions. However, the spin character of charge-transfer states originated from recombination of photocarriers allows relaxation to the lowest-energy triplet exciton (T-1) at these heterojunctions, causing photocurrent loss. Here we find that this loss pathway can be alleviated in sequentially processed planar-mixed heterojunction (PMHJ) devices, employing donor and acceptor with intrinsically weaker exciton binding strengths. The reduced D-A intermixing in PMHJ alleviates non-geminate recombination at D-A contacts, limiting the chance of relaxation, thus suppressing T-1 formation without sacrificing exciton dissociation efficiency. This resulted in devices with high power conversion efficiencies of >19%. We elucidate the working mechanisms for PMHJs and discuss the implications for material design, device engineering and photophysics, thus providing a comprehensive grounding for future organic photovoltaics to reach their full promise. Organic solar cells with a bulk-heterojunction architecture suffer from photocurrent loss driven by triplet states. Now, Jiang et al. show that sequentially deposited donor-acceptor planar-mixed heterojunctions suppress triplet formation, enabling efficiencies over 19%.
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