Small molecular donor materials based on electron withdrawing benzobisthiazole core unit enable an efficiency of 11.8% for organic solar cells

All-small-molecule (ASM) organic solar cells (OSCs) are in advantage of their defined molecular structures and good reproducibility. However, the state-of-art donor molecules are usually based on benzodithiophene (BDT) as the core unit, which limits the modulation of energy levels, optical absorption, and opto-electronic properties. In this research, we designed and synthesized two small molecular donors (BBTSM-1 and BBTSM-2) with electron withdrawing benzobisthiazole (BBT) as the core unit, developing a type of A-π-A'-π-A conjugated system. The molecules exhibit reduced energy levels, high charge carrier mobilities, and ordered edge-on molecular packing in thin films. High power conversion efficiency of 11.8% was achieved in solar cells based on BBTSM-1:Y6, which indicating that small molecular donors based on the weak electron withdrawing BBT unit would be promising candidates for high-performance organic solar cells.