Enhanced performance of organic photovoltaics by TiO2-interlayer with precisely controlled thickness between ZnO electron collecting and active layers

Abstract

Organic photovoltaics (OPVs) consisting of ZnO ripple structures used as electron-collecting layer were fabricated without and with additional TiO2 layers prepared by atomic layer deposition (ALD). We show that TiO2 layer with a thickness of less than 1nm can enhance OPV performance, since additional TiO2 can heal surface defects of ZnO, which can act as recombination center of electron and hole created in the active layer by photon-absorption. In contrast, a thicker TiO2 film (>2nm) showed a lower OPV performance than that of bare sample without TiO2, most likely due to a lower conductivity of TiO2 than that of ZnO. We show that precise control of oxide thin layer using ALD can be beneficial for fabricating high-performing OPV.