Abstract: In crystalline silicon heterojunction (SHJ) solar cells, although conventional doped amorphous silicon carrier-selective contact layers provide excellent interface passivation, their strong parasitic absorption, high fabrication cost, and use of toxic gases severely limit the further development of SHJ solar cells. ZnO, as a promising wide-bandgap metal-oxide candidate material, has attracted considerable attention due to its superior optoelectronic properties, relatively high safety, and low cost. However, its fixed bandgap and band-edge positions hinder flexible band alignment with c-Si. To address this issue, this work employs an Mg-doping strategy that leverages the highly similar ionic radii of Mg²⁺ and Zn²⁺. While preserving the excellent optoelectronic performance and structural stability of ZnO, Mg doping effectively enhances interfacial band alignment with c-Si. ZnMgO electron transport layers were prepared by radio-frequency magnetron sputtering, and the effects of deposition process parameters on film microstructure, optical transmittance, bandgap, minority carrier lifetime, and contact performance were systematically investigated. The results show that, after optimization, the film exhibits a uniform and dense surface morphology, visible-light transmittance exceeding 80%, an optical bandgap of approximately 3.7 eV, a minority carrier lifetime of 1198 μs, ideal electron-selective band alignment with c-Si, and a reduced specific contact resistivity of 72.37 mΩ·cm². When the optimized ZnMgO layer is integrated into SHJ solar cells, a power conversion efficiency of 21.97% is achieved. This study demonstrates the feasibility of realizing high-performance ZnMgO contacts through precise control of sputtering process parameters and provides a valuable reference for the development of high-performance, low-cost metal-oxide carrier transport layers.