Design and synthesis of carbonyl group modified conjugated polymers for photovoltaic application

Abstract

In this article, a simple and common electron-withdrawing moiety, carbonyl group, is applied in the molecular design of conjugated polymers for high-performance polymer solar cells (PSCs). Two series of donor–acceptor (D–A) copolymers are synthesized through alternating copolymerization of the electron-donating (D) benzodithiophene and dithienopyrrole with various electron-accepting (A) units containing carbonyl groups. The absorption range and the band gap of copolymers can be tuned by changing the molecular structure of A unit and the number of carbonyl groups. Moreover, by introducing the carbonyl group, the highest occupied molecular orbital energy level of the copolymer is lowered efficiently, leading to the improvement of the open-circuit voltage (V OC) of PSCs. The best photovoltaic performance is obtained while poly(benzodithiophene-alt-thiophene-3-carboxylate) is functioned as the electron donor and [6,6]-phenyl-C61-butyric acid methyl ester as electron acceptor in a bulk heterojunction solar cell with a power conversion efficiency of 4.13%, a V OC of 0.80 V, a short-circuit current of 8.19 mA/cm2, and a fill factor of 63.2%.