Thieno[3,2-b]pyrrolo-Fused Pentacyclic Benzotriazole-Based Acceptor for Efficient Organic Photovoltaics

A novel nonfullerene small molecular acceptor (BZIC) based on a ladder-type thieno[3,2-b]pyrrolo-fused pentacyclic benzotriazole core (dithieno[3,2-b]pyrrolobenzotriazole, BZTP) and end-capped with 1,1-dicyanomethylene-3-indanone (INCN) has been first reported in this work. Through introducing multifused benzotriazole and INCN, BZIC could maintain a high lying lowest unoccupied molecular orbital (LUMO) energy level of 3.88 eV. Moreover, BZIC shows a low optical bandgap of 1.45 eV with broad and efficient absorption band from 600 to 850 nm due to increased is, pi-pi interactions by the covalently locking thiophene and benzotriazole units. A power conversion efficiency of 6.30% is delivered using BZIC as nonfullerene acceptor and our recently synthesized hexafluoroquinoxaline-based polymer HFQx-T as donor. This is the first time to synthesize mutifused benzotriazolebased molecules as nonfullerene electron acceptor up to date. The preliminary results demonstrate that the mutifused benzotriazole derivatives hold great potential for efficient photovoltaics.