Donor-acceptor polymers based on 5,6-difluoro-benzo[1,2,5]thiadiazole for high performance solar cells

•The effect of DIO on the photovoltaic performance of polymer/PC71BM blends is studied.•The addition of DIO can optimize the morphology of the active layer and enhance hole and electron mobilities.•The impact of chalcogen atom on the intrinsic properties of donor materials has been studied.

Two donor-acceptor polymers P8 and P9 based on 5,6-difluoro-benzo[1,2,5]thiadiazole unit have been prepared and applied as the donor materials in polymer solar cells. Due to the slight difference between electronic structures of thiophene and selenophene, P8 and P9 show similar absorption spectra and similar frontier energy levels. However, the pristine P8:PC71BM and P9:PC71BM blend films display distinct morphologies as revealed by AFM measurement. After the addition of DIO, both blend films feature a nanoscale interconnected-network structure, which leads to the enhancement in solar cells performance with PCE up to 6.73% and 6.84% for P8 and P9, respectively. Alternating current impedance spectrometry measurements revealed that high surface roughness could improve the PCE of P8-based PSCs, while in P9-based PSCs DIO can enhance hole and electron mobilities of the active layer.

Graphical abstractTwo donor-acceptor polymers based on 5,6-difluoro-benzo[1,2,5]thiadiazole have been prepared as donor materials for high efficiency polymer solar cells.Figure optionsDownload full-size imageDownload as PowerPoint slide