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

Si/Cu2O Schottky‐junction photovoltaic devices are fabricated by the thermal deposition of a Cu2O thin film on a silicon surface that has been passivated with methyl (CH3) groups. X‐ray photoelectron spectroscopy shows that the methyl‐group passivation is efficient for suppressing the oxidation of silicon and the formation of CuxO species. The thermally deposited Cu2O presents a pure phase with a valance band edge at (EF – 0.97) eV, where EF 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–CH3/Cu2O junction deviates from the thermionic emission diode model because part of the applied voltage drops at the depletion layer as a result of the CH3 passivation. This explains the higher short‐circuit current density (JSC) and open‐circuit voltage (VOC) and the lower fill factor (FF) of the Si–CH3/Cu2O device relative to a device with H passivation. These findings provide insight into strategies for further improving the photovoltaic performance of the Si/Cu2O heterojunction.