Degradation of MoOx Thin‐Films Properties in Excessive Oxygen Environments and Its Influence on Dopant‐Free Silicon Solar Cells

Transition metal oxides such as molybdenum oxide (MoOx) demonstrate significant potential as efficient hole‐selective passivating contacts in silicon heterojunction solar cells. Achieving efficient hole collection necessitates precise control over the optical and electrical properties of MoOx films. In this study, the effects of oxygen flow rate (FO2$F_{O_{2}} $) on the growth, optical properties, and electrical properties of thermally evaporated MoOx films are investigated. In the Kelvin probe force microscopy results, it is indicated that MoOx thin‐film deposition followed an island‐to‐layer growth model. X‐ray photoelectron spectroscopy shows that MoOx films exhibit stoichiometric composition with fully oxidized Mo6+ ions, without additional oxygen. Notably, the O 1s orbital peak shifts toward higher binding energy with increased FO2$F_{O_{2}} $, indicating defect introduction. Consequently, the work function of MoOx films decreases from 5.93 to 5.51 eV as FO2$F_{O_{2}} $ increases from 0 to 8 sccm. The maximum optical bandgap of the MoOx films exceeds 3.60 eV. As a proof of concept, FO2$F_{O_{2}} $'s impact on MoOx as a front buffer layer for dopant‐free silicon solar cells is analyzed. An efficiency of 20.8% was achieved for dopant‐free silicon solar cells after optimized MoOx film deposition, with an open‐circuit voltage of 713.7 mV, short‐circuit current density of 39.1 mA cm−2, and fill factor of 74.6%. This study investigates how oxygen flow rate (FO2$F_{O_{2}} $) affects MoOx thin film growth and properties. It finds that high‐quality stoichiometric MoO3 films can be produced without additional oxygen. Analyzing FO2$F_{O_{2}} $'s impact on device performance, it achieves 20.8% efficiency in dopant‐free silicon solar cells using optimized MoOx films, offering guidelines for efficient photoelectric devices with transition metal oxides.