New developments in non-fullerene small molecule acceptors for polymer solar cells
During the past two years, non-fullerene electron acceptors for organic solar cells have attracted considerable attention. Significant progress has been made in that the power conversion efficiency of polymer solar cells based on non-fullerene small molecule acceptors now exceeds 12%, exhibiting many advantages over their fullerene counterparts. One of the greatest strengths for NFAs is their tunability via chemical modulation to fine-tune their absorption, energy level and electronic mobility, which is difficult to achieve with fullerene derivatives. This review describes very recent developments of polymer donor:small molecular non-fullerene acceptors in several systems since 2015, including rylene imide, indacenodithiophene and diketopyrrolopyrrole-based small molecular acceptors. Molecular design considerations and structure–property relationships are also discussed.