Graded bandgap optimization for high-efficiency BaZrTiS3 chalcogenide perovskite solar cells with theoretical efficiency exceeding 22 %

This study investigates an optimized design of BaZr1-xTixS3-based perovskite solar cells (PSCs) via a graded bandgap engineering and various electron transport layers (ETLs) evaluation. The graded bandgap in BaZr1-xTixS3 is achieved by varying the zirconium (Zr) and titanium (Ti) content, which significantly affects light absorption and carrier transport. Three ETLs, MoS2, SnS2, and WS2 are tested, with WS2 and SnS2 showing superior performance compared to MoS2, particularly in terms of open-circuit voltage (VOC), short-circuit current density (JSC), and power conversion efficiency (PCE). The study highlights the impact of energy level alignment between the ETL and the absorber, with WS2 showing the best alignment, leading to enhanced charge extraction and reduced recombination losses. Further optimization of the absorber's thickness and defect density also contributes to improved device performance. A linear graded bandgap configuration is found to be optimal for enhancing light absorption, while a moderate band offset ensures efficient hole extraction, reducing recombination and improving device efficiency. The study concludes that the optimized WS2-based PSC, with a graded bandgap, achieves a PCE of 22.35 %, demonstrating the critical role of absorber engineering and ETL selection in optimizing PSC performance.