Highly Efficient Non-Fullerene Organic Solar Cells Using 4,8-Bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-Based Polymers as Additives

Electron acceptor units play an important role in the design of donor–acceptor (D–A) type polymers for efficient organic solar cells (OSCs). In this report, with the oxidation of the thiophene moiety, the electron-rich 4,8-bis((2-ethylhexyl)oxy)benzo[1,2- b:4,5- b ′]dithiophene (BDT) unit was tuned into electron-deficient 4,8-bis((2-ethylhexyl)oxy)benzo[1,2- b:4,5- b ′]dithiophene 1,1,5,5-tetraoxide (BDTO) unit. Two novel polymers of PBDTO and PBDTO-T based on BDTO unit were synthesized and employed as additives in efficient non-fullerene OSCs with the active layer consist of PBDB-T and IT-M. With doping 1% PBDTO or PBDTO-T, the power conversion efficiency (PCE) of the prepared OSCs increased from 10.31% to 11.47% or 11.12%, respectively. These two polymers can afford cascaded energy levels and smooth the surface of the active layer, which are beneficial for better carrier transportation and separation. Our results open a new avenue to construct electron acceptor backbone in the design of D–A type polymers for OSCs.