New D–A–A-Configured Small-Molecule Donors for High-Efficiency Vacuum-Processed Organic Photovoltaics under Ambient Light

Four new donor–acceptor–acceptor (D–A–A) type molecules (DTCPB, DTCTB, DTCPBO, and DTCTBO), wherein benzothiadiazole or benzoxadiazole serves as the central A bridging triarylamine (D) and cyano group (terminal A), have been synthesized and characterized. The intramolecular charge-transfer character renders these molecules with strong visible light absorption and forms antiparallel dimeric crystal packing with evident π–π intermolecular interactions. The characteristics of the vacuum-processed photovoltaic device with a bulk heterojunction active layer employing these molecules as electronic donors combining C70 as electronic acceptor were examined and a clear structure–property–performance relationship was concluded. Among them, the DTCPB-based device delivers the best power conversion efficiency (PCE) up to 6.55% under AM 1.5 G irradiation. The study of PCE dependence on the light intensity indicates the DTCPB-based device exhibits superior exciton dissociation and less propensity of geminated recombina...