A solution-processed small molecule with optimal side chains for high efficiency non-fullerene organic solar cells

A novel small molecular electron donor with an optimized side group was synthesized for solution-processed organic solar cells. In order to extend the conjugation length in 2-dimensional structure, 5-alkylthio-thieno[3,2-b]thiophene was attached onto the central benzo[1,2-b:4,5-b']dithiophene unit. The small molecule exhibited an optical energy gap of 1.71 eV, low-lying energy levels, strong intermolecular interaction in solid state, which result in promising power conversion efficiency up to 7.15% with ITIC as a non-fullerene electron acceptor. This work demonstrates the potential of optimal side chain of small molecular donor for high performance of solution-processed non-fullerene organic solar cells.