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 ( i BDD‐Si), an isomer of well‐known benzo[1,2‐ c :4,5‐ c ′]dithiophene‐4,8‐dione is presented. The i BDD‐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 i BDD‐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 i BDD‐Si is a promising backbone toolbox for various high‐performance conjugated materials.