Direct C–H arylation synthesis of (DD′AD′DA′)-constituted alternating polymers with low bandgaps and their photovoltaic performance

Abstract

A series of new (DD′AD′DA′)-constituted conjugated polymers were synthesized via C–H arylation with the aid of a Pd(OAc)₂/Bu₄NBr catalytic system. The polymers are based on 4,7-bis(4-hexylthiophen-2-yl)-2,1,3-benzothiadiazole (HT.BT.HT), which alternated with 3,4-ethylenedioxythiophene (EDOT) as a second donor and a lactam- and/or imide-containing material as a second acceptor. The synthesis methodology avoided the drawbacks of Stille and Suzuki coupling and obtained high yields. All of the new polymers possessed broader absorption windows with low energy bandgaps (1.34–1.64 eV), as well as low-lying HOMO energy levels. The prescreening of these polymers as an active material in bulk heterojunction solar cells was investigated and a power conversion efficiency of 2.36% was achieved.