Distannylated Bithiophene Imide: Enabling High-Performance n-Type Polymer Semiconductors with an Acceptor-Acceptor Backbone.

A distannylated electron-deficient bithiophene imide (BTI-Tin) monomer was readily synthesized and polymerized with imide-functionalized co-units via Stille coupling to afford homopolymer PBTI and copolymer P(BTI-BTI2), both featuring acceptor-acceptor backbone with high molecular weight. Benefitting from their improved electronic property and increased molecular weight, both polymers exhibited excellent unipolar n-type character in transistors with electron mobility up to 2.60 cm2 V-1 s-1. When applied as acceptor materials in all-polymer solar cells, PBTI and P(BTI-BTI2) achieved high power conversion efficiency (PCE) of 6.67% and 8.61%, respectively. The PCE (6.67%) of polymer PBTI, synthesized from the novel distannylated monomer, is substantially higher than that (0.14%) of the same polymer PBTI*, synthesized from typical dibrominated monomer. The 8.61% PCE of copolymer P(BTI-BTI2) is also substantially higher than those (< 1%) of homopolymers synthesized from dibrominated monomers. The results demonstrate the great success of BTI-Tin for facilely accessing structurally novel n-type polymers with greatly improved device performance.