Asymmetric Π-Bridge Engineering Enables High-Permittivity Benzo[1,2-B:4,5-B']Difuran-Conjugated Polymer for Efficient Organic Solar Cells.

Organic solar cells (OSCs) exhibit complex charge dynamics, which are closely correlated with the dielectric constant (ε r ) of photovoltaic materials. Here we design and synthesize a series of novel conjugated copolymers based on benzo[1,2-b:4,5-b']difuran (BDF) and benzotriazole (BTz), which differ by the nature of π-bridge from one another. The PBDF-TF-BTz with asymmetric furan and thiophene π-bridge demonstrates a larger ε r of 4.22 than PBDF-dT-BTz with symmetric thiophene π-bridge (3.15) and PBDF-dF-BTz with symmetric furan π-bridge (3.90). The PBDF-TF-BTz also offers more favorable molecular packing and appropriate miscibility with non-fullerene acceptor Y6 than its counterparts. The corresponding PBDF-TF-BTz:Y6 OSCs display efficient exciton dissociation, fast charge transport and collection, and reduced charge recombination, eventually leading to a power conversion efficiency of 17.01%. When introducing a fullerene derivative (PCBO-12) as a third component, the PBDF-TF-BTz:Y6:PCBO-12 OSCs yield a remarkable FF of 80.11% with a high efficiency of 18.10%, the highest value among all reported BDF polymer-based OSCs. Our work provides an effective approach to developing high-permittivity photovoltaic materials, showcasing PBDF-TF-BTz as a promising polymer donor for constructing high-performance OSCs. This article is protected by copyright. All rights reserved.