High light intensity effects on nanoscale open-circuit voltage for three common donor materials in bulk heterojunction solar cells

Abstract

White light photoconductive atomic force microscopy (pc-AFM) was employed to evaluate nanoscale open circuit (V_oc) at high light intensities (up to 200 sun) of three donor:acceptor blends comprising two widely studied polymers and one small molecule donor material. By varying the work function of electron extraction contacts, the V_oc observed in nanoscale measurements reveals a unified dependence on the electrode work functions regardless of the blend materials; in line with earlier macroscopic measurements at 1 sun. At high light intensities, an agreement between the nanoscale and bulk V_oc is observed. Nonetheless, light intensity dependent V_oc measurements suggest that under high light intensities, the V_oc obtained by pc-AFM exhibits contact-limited behavior.