A versatile small molecular electron donor with 2-dimensional conjugation structure for efficient organic solar cells compatible with both fullerene and non-fullerene electron acceptors

We herein report design, synthesis and photovoltaic properties of a small molecular donor composed of bithienyl-substituted benzo [1,2-b:4,5-b′]dithiophene flanked with diketopyrrolopyrrole. For constructing the 2-dimensional conjugated architecture, it is functionalized with bithienyl side chains onto the benzo [1,2-b:4,5-b′]dithiophene, resulting in intense absorption in UV-Vis region, a low optical band gap, low-lying energy levels and high crystallinity of the resulting donor molecule. These affirmative properties for photovoltaic applications affords the power conversion efficiency of 5.35% with a fullerene acceptor, while even higher efficiency of 5.95% was achieved using a non-fullerene acceptor. This work suggests a design strategy of 2-dimensional conjugation of small molecular donor for efficient organic solar cells compatible with multiple electron acceptors.