Optimization of Sn-alloyed BaZrS3 chalcogenide perovskite solar cells via charge transport layer engineering

Despite the promising thermal stability and non-toxic nature of chalcogenide perovskites such as BaZrS 3 , device-level optimization that accounts for both absorber composition and charge transport layer selection remains largely unexplored. Here we develop a composition-resolved optimization framework for BaZr 1−x Sn x S 3 (x = 0, 0.125, 0.25) solar cells using SCAPS-1D, evaluating 504 device configurations across 12 electron transport layers (ETLs) and 14 hole transport layers (HTLs). Sn alloying at x = 0.125 reduces the bandgap to 1.48 eV and increases the short-circuit current density (J SC ), whereas increasing the Sn content to x = 0.25 degrades the junction quality and reduces the built-in potential from 1.00 V to 0.52 V. Critically, we find that the optimal ETL/HTL combination depends strongly on the Sn composition. For unalloyed BaZrS 3 (x = 0), WO 3 provides a favorable conduction band offset of approximately + 0.2 eV and together with FeS 2 as HTL yields a maximum power conversion efficiency of 20.02%. Temperature-dependent analysis (300–400 K) reveals a V OC temperature coefficient of − 1.40 mV K − 1 , indicating good thermal stability with interface-limited recombination. Analysis of activation energy and Mott–Schottky characteristics shows that recombination is predominantly governed by interface-related processes, with well-defined junction properties observed for x = 0 and x = 0.125, while significant deviation from ideal behavior occurs at x = 0.25. The novelty of this work lies in the simultaneous optimization of Sn alloying and transport layer selection, demonstrating that a performance gain from bandgap tuning can be negated by unfavorable interface alignment if the transport layers are not re-optimized accordingly. These results provide a clear, evidence-based guideline for designing high-efficiency, lead-free chalcogenide perovskite solar cells.