Atomic Layer Deposition-Based Ultrathin SnO_<i>x</i> Buffer for High Passivation Quality in Silicon Heterojunction Solar Cells

Tin oxide (SnOx) layers fabricated via atomic layer deposition (ALD) effectively serve as electron transport or sputter-resistant buffer layers in perovskite, silicon, and tandem solar cells, mitigating the interface defect density induced by transparent conductive oxide (TCO) in heterojunction (HIT) photovoltaic devices. This study introduces a 7 nm SnOx layer between P-doped amorphous Si (n-a-Si:H) and TCO to significantly enhance the minority carrier lifetime (MCLT). The incorporation of SnOx increased the MCLT of silicon wafers by approximately 32.5%, from 1328 to 1760 μs, measured at an excess carrier density of 1.0 × 1015 cm–3. UV–visible spectroscopy analysis determined the SnOx film bandgap to be 3.48 eV, facilitating effective absorption of plasma-induced radiation and substantially reducing damage during TCO deposition. X-ray photoelectron spectroscopy (XPS) reveals that SnOx (x ≈ 1.8) exhibits n-type conductivity, effectively passivating n-a-Si:H and mitigating plasma damage, enhancing MCLT. Consequently, the optimized photovoltaic device achieved superior performance, exhibiting a short-circuit current density (Jsc) of 40.84 mA/cm2, an open-circuit voltage (Voc) of 728 mV, a fill factor (FF) of 80.53%, and an overall power conversion efficiency (PCE) of 23.95%. These findings underscore the potential of ultrathin SnOx layers to enhance both efficiency and durability of advanced silicon-based solar cells.