Numerical investigation of Sn-based chalcogenide thin-film solar cells: dominant role of absorber thickness and contact engineering

This study presents a numerical investigation of SnSe 1−x S x (x = 0, 0.4, 1) chalcogenide thin-film solar cells using the SCAPS-1D simulator, to better understand the key device parameters that influence photovoltaic performance. While SnSe and SnS based absorbers have been studied individually, a direct, structurally-controlled comparison across the full SnSe 1−x S x compositional range within an identical device architecture remains limited, motivating the present study. The device structure FTO/ZnSe/SnSe 1−x S x /P3HT/Au was examined by systematically varying seven parameters; absorber thickness (0.05–0.30 μm), back-contact work function (4.2–5.9 eV), series resistances R S (1–10 Ω cm 2 ), shunt resistance, R Sh (10 2 -10 5 Ω cm²), operating temperature (300–600 K), bulk defect density N t, bulk (10 12 -10 15 cm -3 ), and interface-defect-density N t, int (10 10 –10 17 cm − 2 ). Absorber thickness and defect density emerged as the most critical factors. At 0.25–0.30 μm thickness, power conversion efficiencies (PCE) of 24.13% for SnSe, 23.92% for SnSe0.6S0.4, and 23.75% for SnS were achieved under realistic defect conditions. Temperature-dependent analysis determined that short-circuit current density (J SC ) remains largely stable across the 300–600 K range, suggesting good thermal robustness. In terms of back-contact engineering, work functions exceeding 4.65 eV enabled quasi-ohmic hole extraction and efficiency saturation. In addition, the External Quantum Efficiency (EQE) spectra for all three compositions exceed 95% across most of the visible range, with simulated band edges consistent within 1–2 nm of the corresponding absorber bandgaps, confirming the consistency of the optical and electronic parameters used throughout this study. Finally, interface defect-density range (10 10 –10 17 cm − 2 ) showed a strong threshold behavior, with negligible performance loss below ≈ 10 14 cm − 2 followed by a sharp decline. Overall, device engineering parameters have a greater influence on efficiency than compositional variation, offering practical guidance for designing high-efficiency, lead-free, and earth-abundant thin-film photovoltaic devices.