From Event: SPIE Organic Photonics + Electronics, 2015
Electron back transfer (EBT), potentially occurring after electron transfer from donor to acceptor may populate the lower lying donor or acceptor triplet state and serve as recombination channel. Here we report on studies of charge transfer and triplet states in blends of highly efficient benzodithiophene PTB7 polymer in combination with the fullerene-derivative PC71BM using the spin sensitive optically detected magnetic resonance (ODMR) technique and compare the results with those obtained in P3HT (poly(3- hexylthiophene):PC61BM blends. Although PTB7:PC71BM absorbers yield much higher power conversion efficiencies in solar cells exceeding 7%, we found a significant increase of triplet exciton generation, which was absent in the P3HT based blends. We discuss this observation within the EBT scenario with the emphasis on the influence of morphology, fullerene load, HOMO/LUMO energy and presence of additives (DIO). Suppressing the EBT process by morphology and/or energetics of polymer and molecules is important to achieve the full potential of highly efficient OPV materials.  M. Liedtke, et al., JACS 133, 9088 (2011).
Vladimir Dyakonov, "Charge transfer and triplet states in OPV materials and devices (Presentation Recording)," Proc. SPIE 9567, Organic Photovoltaics XVI, 95670O (Presented at SPIE Organic Photonics + Electronics: August 12, 2015; Published: 5 October 2015); https://doi.org/10.1117/12.2189230.4519371825001.
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