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Indium-Free Silicon Heterojunction Solar Cells: Achieving High Conductivity With Magnetron-Sputtered SnO2

delete2026-07-29
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T
Takashi Koida *
T
Takuya Matsui
H
Hitoshi Sai
DOI:10.1002/pip.70134delete
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Abstract

Abstract

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Although magnetron sputtering (MS) is widely used for depositing transparent conducting oxide (TCO) films, achieving highly conductive SnO2 at low process temperatures (≤ 200°C) remains challenging. This study investigated the effects of substrate temperature, O2 flow ratio, and residual water vapor on the structural and electrical properties of MS-deposited SnO2, with a focus on amorphization and H incorporation. Under moderately O2-deficient conditions, SnO2 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 SnO2 films were applied to the front and rear electrodes in Si heterojunction solar cells, achieving 21.1% efficiency. In comparison, devices with Sn-doped In2O3 and reactive plasma-deposited SnO2 demonstrated 22.1% and 22.5% efficiencies, respectively. MS-deposited SnO2 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-SnO2 films, while the latter arises from a slightly higher work function of MS-SnO2 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, SnO2-based TCOs for high-efficiency photovoltaics.
Keywords:
amorphous
contact resistivity
hydrogen
indium
magnetron sputtering
reactive plasma deposition
silicon heterojunction solar cell
tin oxide
transparent conductive oxide
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Progress in Photovoltaics
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