High-performance wide-bandgap copolymers based on indacenodithiophene and indacenodithieno[3,2-b]thiophene units

Abstract

In this work, we demonstrated the synthesis and characterization of two novel donor–acceptor type conjugated polymers, IDT-T1 and IDTT-T1, which consist of indacenodithiophene (IDT) and indacenodithieno[3,2-b]thiophene (IDTT) donor and 1,3-bis(5-bromothiophen-2-yl)-5,7-bis(2-ethylhexyl)-4H,8H-benzo[1,2-c:4,5-c]dithiophene-4,8-dione (T1) acceptor building blocks. The resulting copolymers exhibited a wide bandgap of about 1.90 eV with a comparatively low-lying highest occupied molecular orbital (HOMO) energy level. However, IDTT-T1 with an extended fused-ring unit was found to have better coplanarity and higher carrier mobility (0.11 cm² V⁻¹ s⁻¹). As a consequence, organic solar cells employing IDTT-T1 as the donor material afforded a power conversion efficiency (PCE) of 6.58%, while IDT-T1-based devices yielded a relatively lower PCE of 6.26%.