Direct Deposition of Sb₂S₃ Thin Films via the Hydrothermal Method on Si Substrates for Fabricating Tandem Photovoltaics

Recently, the emerging Sb2S3 thin film material has attracted considerable research interest as a potential candidate to fabricate top/outer subcells for high-performance crystalline-Si-based tandem solar cells, with a calculated power conversion efficiency (PCE) value exceeding 40% for Si-based tandem solar cells, overcoming the Shockley–Queisser limit (∼33%). Although much effort has been spent on Sb2S3 thin film solar cells, they are still in an early stage toward practical applications, let alone being compatible with Si substrates. In this work, a modified hydrothermal deposition method using NH4F as an additive has been investigated to develop a functional strategy for directly growing high-quality Sb2S3 thin films onto the surface of c-Si substrates. By adding a proper concentration of NH4F to the precursor, the nucleation and growth of Sb2S3 thin films can be modulated, as well as reducing the defect states and improving the crystallinity of the annealed ones. These results can pave a promising way to directly fabricate Sb2S3/Si tandem photovoltaic devices using a simple and low-cost method to seek a higher performance and a more market-competitive levelized cost of electricity (LCOE).