Indium‐Free Silicon Heterojunction Solar Cells: Achieving High Conductivity With Magnetron‐Sputtered SnO ₂

Although magnetron sputtering (MS) is widely used for depositing transparent conducting oxide (TCO) films, achieving highly conductive SnO 2 at low process temperatures (≤ 200°C) remains challenging. This study investigated the effects of substrate temperature, O 2 flow ratio, and residual water vapor on the structural and electrical properties of MS‐deposited SnO 2 , with a focus on amorphization and H incorporation. Under moderately O 2 ‐deficient conditions, SnO 2 films remained mostly amorphous and exhibited high conductivities (resistivity as low as 1.2 × 10 −3 Ωcm) possibly due to the formation of shallow donor states in the disordered network and the reduced contribution of grain boundary scattering in amorphous‐dominant films. H, introduced by residual water vapor in the sputtering atmosphere, may play a secondary and indirect role by relaxing the amorphous network or passivating deep‐level defects, thereby contributing to improved transport properties. Optimized amorphous SnO 2 films were applied to the front and rear electrodes in Si heterojunction solar cells, achieving 21.1% efficiency. In comparison, devices with Sn‐doped In 2 O 3 and reactive plasma‐deposited SnO 2 demonstrated 22.1% and 22.5% efficiencies, respectively. MS‐deposited SnO 2 devices exhibited slightly lower short‐circuit current densities and higher contact resistances at the interface with n ‐type hydrogenated nanocrystalline silicon oxide. The former is attributed to sub‐bandgap and free‐carrier absorption in the MS‐SnO 2 films, while the latter arises from a slightly higher work function of MS‐SnO 2 and process‐induced interfacial degradation during sputtering. These results highlight the need for precise control of structure, H content, and electronic states to advance low‐temperature processed, SnO 2 ‐based TCOs for high‐efficiency photovoltaics.