Efficient as-cast thick film small-molecule organic solar cell with less fluorination on the donor†
Herein, two donor materials based on fluorine substituted isatin units (DI3T-1F, DI3T-2F) were designed and synthesized for thick-film small molecule solar cells. The devices based on DI3T-1F demonstrate balanced charge transport and less trap-assisted recombination, leading to higher power conversion efficiency (PCE) of 8.33% with a thickness ca. 150 nm compared to DI3F-2F (PCE of 7.32% with thick film at ca. 160 nm) without additives, solvent or thermal annealing treatments. More interestingly, the device based on DI3T-1F small molecules demonstrates good tolerance to active layer thickness from 150 to 300 nm with device performance over 5%. Our results indicate that less fluorine atoms on the donor units can optimize the charge transport, and phase-segregated morphology in small molecule solar cells without the need for post-treatment.