Triisopropylsilyl‐Substituted Benzo[1,2‐b:4,5‐c′]dithiophene‐4,8‐dione‐Containing Copolymers with More Than 17% Efficiency in Organic Solar Cells

Abstract Considering the special functions of fused‐ring aromatic building blocks and Si‐atom in high‐performance donor–acceptor‐conjugated materials at the same time, herein the synthesis of a novel fused‐ring tricyclic heterocycle, triisopropylsilyl‐substituted benzo[1,2‐b:4,5‐c′]dithiophene‐4,8‐dione (iBDD‐Si), an isomer of well‐known benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione is presented. The iBDD‐Si‐based copolymer series (PM6, PM6‐5Si, PM6‐10Si, and PM6‐15Si) is synthesized via Stille polymerization, revealing fine‐tuned optical and electrochemical properties, and molecular packing with varying iBDD‐Si contents in the backbone. Organic solar cells are fabricated by pairing the copolymer donors with nonfullerene acceptor N3 and characterized. High power conversion efficiency of more than 17% is achieved using the PM6‐5Si‐based solar cell, which is attributed to the balanced charge transport, enhanced charge generation/dissociation kinetics, and minimized total energy and recombination losses. It is demonstrated that iBDD‐Si is a promising backbone toolbox for various high‐performance conjugated materials.