Simple benzothiadiazole-based small molecules as additives for efficient organic solar cells

Multiple strategies have been developed to improve the photovoltaic performance of organic solar cells (OSCs) by fine-tuning the morphology of the active layers, such as introducing functional third components, taking post-treatments and so on. In this work, a series of non-volatile solid additives BT, BTOR, BT2F, BTNO2(2 + 6), and BTNO2(6) were synthesized, by introducing substituent groups into benzothiadiazole units, and the thermal stability, optical and electrochemical properties were systematically studied. These additives were applied to further investigate the effect on the photovoltaic performance of OSCs. The results show that these additives could effectively promote exciton dissociation and charge transfer, reduce bimolecular recombination, and optimize the morphology of the active layer. Significantly, the PBDB-T:ITIC-based devices processed with BT achieved a power conversion efficiency (PCE) of 11.57%, increased by 17% compared to the as-cast devices due to the high and balanced carrier mobility. Enhancement of PCE proved the feasibility of the application of non-volatile solid additives in the non-fullerene-based binary system.