Sulfur-enhanced surface passivation for hole-selective contacts in crystalline silicon solar cells

<h2>Summary</h2> Effective surface passivation is pivotal for achieving high performance in crystalline silicon (<i>c</i>-Si) solar cells. However, many passivation techniques in solar cells involve high temperatures and cost. Here, we report a low-cost and easy-to-implement sulfurization treatment as a surface passivation strategy. By treating <i>p</i>-type <i>c</i>-Si (<i>p</i>-Si) wafers with (NH₄)₂S solution, sulfur can be introduced onto the surface and passivate the dangling bonds by forming an Si–S bond. Sulfurization also contributes to a higher negative fixed charge at the <i>p</i>-Si/Al₂O₃ interface and, thus, better field-effect passivation. Due to the improved passivation, sulfurization effectively enhances hole selectivity, evidenced by the substantially improved open-circuit voltage and efficiency of solar cells. Eventually, by employing sulfurization in hole-selective contacts, remarkable efficiencies of 19.85% and 22.01% are attained for NiO_x- and MoO_x-based passivating contact <i>c</i>-Si solar cells, respectively. Our work highlights a promising sulfurization strategy to enhance surface passivation and hole selectivity for dopant-free <i>c</i>-Si solar cells.