Stable small-molecule organic solar cells with 1,3,5-tris(2-N-phenylbenzimidazolyl) benzene as an organic buffer

We demonstrate in this paper that crystallization of bathocuproine (BCP) is the main reason for the instability of fullerene-based devices with BCP buffer by in-situ measurement of current degradation in oxygen and by polarized light microscopy. In order to improve the performance of organic solar cells, 1,3,5-tris(2-N-phenylbenzimidazolyl) benzene (TPBI) takes the place of BCP. Organic solar cells with power conversion efficiency 2.32% under 75 mW/cm2 AM1.5G simulated illumination and shelf-lifetime over 1800 min in atmosphere without encapsulation are achieved. The improved performance is ascribed to the better stability and higher electron mobility of TPBI than that of BCP.