期刊
ADVANCED ENERGY MATERIALS
卷 12, 期 16, 页码 -出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.202103944
关键词
nonradiative recombination; organic solar cells; triplet excitons
类别
资金
- Simons Foundation [601946]
- EPSRC [EP/M01083X/1, EP/M005143/1, EP/P032591/1, EP/L011972/1]
- Strategic University Network to Revolutionize Indian Solar Energy (SUNRISE)
- ERC under the European Union [670405]
- Department of the Navy, Office of Naval Research Award [N00014-21-1-2181]
- Schlumberger foundation
- European Union's Horizon 2020 research and innovation programme under Marie Skodowska Curie [722651]
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) [GRK2112]
- Italian Ministry of Education and Research (MIUR) [2017Z55KCW]
- European Research Council (ERC) [670405] Funding Source: European Research Council (ERC)
This study investigates the formation mechanism of triplet excitons in organic solar cells, revealing differences in triplet formation between fullerene and nonfullerene acceptor systems. Engineering good donor and acceptor domain purity is crucial for suppressing losses via triplet excitons in OSCs.
Organic solar cells (OSCs) have recently shown a rapid improvement in their performance, bringing power conversion efficiencies to above 18%. However, the open-circuit voltage of OSCs remains low relative to their optical gap and this currently limits efficiency. Recombination to spin-triplet excitons is a key contributing factor, and is widely, but not universally, observed in donor-acceptor blends using both fullerene and nonfullerenes as electron acceptors. Here, an experimental framework that combines time-resolved optical and magnetic resonance spectroscopies to detect triplet excitons and identify their formation mechanisms, is reported. The methodology is applied to two well-studied polymer:fullerene systems, PM6:PC60BM and PTB7-Th:PC60BM. In contrast to the more efficient nonfullerene acceptor systems that show only triplet states formed via nongeminate recombination, the fullerene systems also show significant triplet formation via geminate processes. This requires that geminate electron-hole pairs be trapped long enough to allow intersystem crossing. It is proposed that this is a general feature of fullerene acceptor systems, where isolated fullerenes are known to intercalate within the alkyl sidechains of the donor polymers. Thus, the study demonstrates that engineering good donor and acceptor domain purity is key for suppressing losses via triplet excitons in OSCs.
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