Synergistic effect of fluorination on both donor and acceptor materials for high performance non-fullerene polymer solar cells with 13.5% efficiency

Abstract

A high performance polymer solar cells (PSCs) based on polymer donor PM6 containing fluorinated thienyl benzodithiophene unit and n -type organic semiconductor acceptor IT-4F containing fluorinated end-groups were developed. In addition to complementary absorption spectra ( 300–830 nm) with IT-4F, the PM6 also has a deep HOMO (the highest occupied molecular) level (−5.50 eV), which will lower the open-circuit voltage ( V oc) sacrifice and reduce the E loss of the IT-4F-based PSCs. Moreover, the strong crystallinity of PM6 is beneficial to form favorable blend morphology and hence to suppress recombination. As a result, in comparison with the PSCs based on a non-fluorinated D/A pair of PBDB-T:ITIC with a medium PCE of 11.2%, the PM6:IT-4F-based PSCs yielded an impressive PCE of 13.5% due to the synergistic effect of fluorination on both donor and acceptor, which is among the highest values recorded in the literatures for PSCs to date. Furthermore, a PCE of 12.2% was remained with the active layer thickness of up to 285 nm and a high PCE of 11.4% was also obtained with a large device area of 1 cm2. In addition, the devices also showed good storage, thermal and illumination stabilities with respect to the efficiency. These results indicate that fluorination is an effective strategy to improve the photovoltaic performance of materials, as well as the both fluorinated donor and acceptor pair-PM6:IT-4F is an ideal candidate for the large scale roll-to-roll production of efficient PSCs in the future.