Improving the Quality of the Si/Cu2O Interface by Methyl‐Group Passivation and Its Application in Photovoltaic Devices

Si/Cu 2 O Schottky‐junction photovoltaic devices are fabricated by the thermal deposition of a Cu 2 O thin film on a silicon surface that has been passivated with methyl (CH 3 ) groups. X‐ray photoelectron spectroscopy shows that the methyl‐group passivation is efficient for suppressing the oxidation of silicon and the formation of Cu x O species. The thermally deposited Cu 2 O presents a pure phase with a valance band edge at ( E F – 0.97) eV, where E F is the Fermi level. By optimizing the nanostructure of the silicon surface, air‐stable devices with a maximum power conversion efficiency of 6.02% are achieved. Analysis of the dark current density as a function of voltage ( J–V curves) shows that the carrier transport through the Si–CH 3 /Cu 2 O junction deviates from the thermionic emission diode model because part of the applied voltage drops at the depletion layer as a result of the CH 3 passivation. This explains the higher short‐circuit current density ( J SC ) and open‐circuit voltage ( V OC ) and the lower fill factor (FF) of the Si–CH 3 /Cu 2 O device relative to a device with H passivation. These findings provide insight into strategies for further improving the photovoltaic performance of the Si/Cu 2 O heterojunction.