High open-circuit voltage organic solar cells enabled by a difluorobenzoxadiazole-based conjugated polymer donor

A new polymer donor based on 3,3′-difluoro-2,2′-bithiophene (2F2T) and difluorobenzoxadiazole (ffBX), named 2F2T-ffBX, is designed and synthesized. The organic solar cell (OSC) based on 2F2T-ffBX donor and [6,6]-phenyl-C60-butyl acid methyl ester ([60]PCBM) acceptor exhibits a high efficiency of 7.3% with a high open-circuit voltage (Voc) of 1.03 V. When blended with perylenediimide-based acceptor (PDI6), the corresponding OSC shows a higher Voc of 1.19 V with a low energy loss of 0.50 eV but a much lower efficiency of 2.0%. The detailed analyses including charge generation, transport, recombination properties, and morphology were performed to understand the performance of corresponding devices.