Amorphous SnO₂ as Earth-Abundant Stable Transparent Conductive Oxide and Its Application to Si Heterojunction Solar Cells

Transparent conductive oxides that contain indium are widely used in various applications including solar cells. However, In is regarded as one of the critical and economically volatile elements, hindering its massive use in production. Herein, the possibility of using amorphous (a-)SnO2 transparent conductive oxides (TCOs) instead of In2O3-based TCOs in silicon heterojunction (SHJ) solar cells is explored. Reactive plasma deposition is utilized to fabricate a-SnO2 thin films suitable for solar cells, demonstrating good electrical conductivity (>1 x 10(3) S cm(-1)) and high damp heat stability while maintaining high transparency in the visible and near-infrared regions. Furthermore, the a-SnO2 film exhibits a larger optical bandgap than a-In2O3-based TCOs. When the a-SnO2 layer is applied to SHJ solar cells, it is found that the TCO layer shows almost no negative effect on fill factor, open-circuit voltage, and short-circuit current density compared to solar cells with indium tin oxide layers. In-free rear-junction SHJ solar cells with a-SnO2 on both sides of the wafer show an efficiency of 22.2%, suggesting the potential of a-SnO2 as a cost-effective and sustainable substitute for conventional In2O3-based TCOs used in solar cells and other applications.