期刊
ADVANCED ELECTRONIC MATERIALS
卷 7, 期 5, 页码 -出版社
WILEY
DOI: 10.1002/aelm.202001056
关键词
aggregation; charge recombination; morphology; organic photovoltaics; phase separation
资金
- Research Mobility Programme of Abo Akademi University
- Magnus Ehrnrooth Foundation
- Society of Swedish Literature in Finland
- Jane and Aatos Erkko Foundation through the ASPIRE project
- European Union's Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant [799801]
- Projekt DEAL
- Marie Curie Actions (MSCA) [799801] Funding Source: Marie Curie Actions (MSCA)
Modifying the annealing procedure can lead to different model morphologies with varying phase separation, molecular order, and phase purity, which are crucial for reducing charge recombination rates.
Suppressing charge recombination is key for organic solar cells to become commercial reality. However, there is still no conclusive picture of how recombination losses are influenced by the complex nanoscale morphology. Here, new insight is provided by revisiting the P3HT:PCBM blend, which is still one of the best performers regarding reduced recombination. By changing small details in the annealing procedure, two model morphologies are prepared that vary in phase separation, molecular order, and phase purity, as revealed by electron tomography and optical spectroscopy. Both systems behave very similarly with respect to charge generation and transport, but differ significantly in bimolecular recombination. Only the system containing P3HT aggregates of high crystalline quality and purity is found to achieve exceptionally low recombination rates. The high-quality aggregates support charge delocalization, which assists the re-dissociation of interfacial charge-transfer states formed upon the encounter of free carriers. For devices with the optimized morphology, an exceptional long hole diffusion length is found, which allows them to work as Shockley-type solar cells even in thick junctions of 300 nm. In contrast, the encounter rate and the size of the phase-separated domains appear to be less important.
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