Delicate Energy-Level Adjustment and Interfacial Defect Passivation of ZnO Electron Transport Layers in Organic Solar Cells by Constructing ZnO/In Nanojunctions

N-type metal oxides are popular electron transport materials and are always deposited onto the indium tin oxide electrode as the interfacial layer in bulk-heterojunction solar cells because of their excellent optical and electrical properties. Conventional metal oxides such as ZnO, however, not only suffer from the high work function (WF) which does not match the energy level of the acceptor component in the blend active layer but also introduce trap states as charge carrier recombination centers. To solve these disadvantages, the ZnO/In nanojunction was introduced as the interfacial modification layer, and by carefully controlling the thickness of the indium (In) film, we successfully suppressed carrier recombination by filling the trap states, facilitated carrier transport by decreasing the contact barrier potential, and maintained good carrier extraction at the electrodes. In addition, we also found In2O3 in the surface of the In metal, which participates in the charge transfer process by forming energy cascade because of its lower WF. Using this approach, solar cells exhibit better charge transport/recombination properties and enhanced carrier extraction abilities. The resulting device exhibits improved power conversion efficiencies of 9.84% than that of the control one (8.13%), which attributed to the improvement of interfacial properties, and demonstrates a feasible approach to increase the efficiency of organic photovoltaics.