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

Transition metal oxides such as molybdenum oxide (MoO x ) 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 MoO x films. In this study, the effects of oxygen flow rate () on the growth, optical properties, and electrical properties of thermally evaporated MoO x films are investigated. In the Kelvin probe force microscopy results, it is indicated that MoO x thin‐film deposition followed an island‐to‐layer growth model. X‐ray photoelectron spectroscopy shows that MoO x films exhibit stoichiometric composition with fully oxidized Mo 6+ ions, without additional oxygen. Notably, the O 1s orbital peak shifts toward higher binding energy with increased , indicating defect introduction. Consequently, the work function of MoO x films decreases from 5.93 to 5.51 eV as increases from 0 to 8 sccm. The maximum optical bandgap of the MoO x films exceeds 3.60 eV. As a proof of concept, 's impact on MoO x 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 MoO x 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%.