Non‐Fullerene Organic Solar Cells Based on Benzo[1,2‐b:4,5‐b′]difuran‐Conjugated Polymer with 14% Efficiency

Abstract The development of high‐performance donor polymers is important for obtaining high power conversion efficiencies (PCEs) of non‐fullerene polymer solar cells (PSCs). Currently, most high‐efficiency PSCs are fabricated with benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based conjugated polymers. The photovoltaic performance of benzo[1,2‐b:4,5‐b′]difuran (BDF)‐based copolymers has lagged far behind that of BDT‐based counterparts. In this study, a novel BDF‐based copolymer L2 is designed and synthesized, in which BDF and benzotriazole (BTz) building blocks have been used as the electron‐sufficient and deficient units, respectively. When blending with a non‐fullerene small molecule acceptor (SMA), TTPT‐T‐4F, the L2‐based device exhibits a remarkably high PCE of 14.0%, which is higher than that of the device fabricated by its analogue BDT copolymer (12.72%). Moreover, PSCs based on the L2:TTPT‐T‐4F blend demonstrate excellent ambient stability with 92% of its original PCE remaining after storage in air for 1800 h. Thus, BDF is a promising electron‐donating unit, and the BDF‐based copolymers can be competitive or even surpass the performance of BDT‐based counterparts.