Seed-layer-assisted crystallization engineering of CdS for high-performance CdS/SnS heterojunction solar cells

Tin(II) sulfide (SnS) has exhibited promising characteristics for photovoltaic applications, yet the efficiency of SnS thin-film photovoltaics is still constrained by carrier transport bottlenecks at interfaces and defect-mediated recombination near the buffer/absorber heterojunction. This study systematically investigates the influence of seed-layer-induced crystallization engineering on the CdS buffer layer to optimize SnS device performance. XRD and cross-sectional TEM confirm the transition to a polycrystalline CdS structure, while TPV and EIS analyses reveal a significant enhancement in recombination resistance and carrier lifetime. Moreover, the seed-layer-induced crystallization leads to a favorable downshift of the CdS conduction band minimum, facilitating electron injection from SnS into CdS and thereby improving charge collection. As a result, the optimized FTO/CdS/SnS/Ag solar cells achieve a notable 83% increase in PCE (from 1.16% to 2.12%), underscoring the critical importance of crystallinity control and interface engineering in developing high-performance SnS-based photovoltaics.