Band Offset Engineering at the CuO/BaZrS₃ Interface for High-Efficiency Lead-Free Perovskite Solar Cells

Chalcogenide perovskite solar cells based on BaZrS₃ have recently emerged as promising lead-free alternatives to conventional halide perovskites, thanks to their high absorption coefficient, thermal stability and non-toxicity. In the present work, the performance of a  BaZrS₃-based perovskite solar cell with the structure FTO/TiO₂/BaZrS₃/CuO was investigated through one-dimensional numerical simulations using the SCAPS-1D software. A CuO hole transport layer (HTL) was introduced between the perovskite absorber and the back contact to improve hole extraction and minimize carrier recombination at the rear interface. The study focuses on the influence of the conduction band offset (CBO) and valence band offset (VBO) at the HTL/perovskite interface. These band alignments play a key role in charge transport by affecting the extraction and recombination of photogenerated carriers. An unfavorable energy band alignment creates potential barriers for electrons or holes, leading to increased carrier recombination and transport losses, resulting in a pronounced degradation in both the fill factor (FF) and the open-circuit voltage (Voc). To identify the most favorable interface configuration, the band offsets (ΔEc and ΔEv) were systematically optimized through numerical simulations. The optimized solar cell parameters yielded a power conversion efficiency (PCE) of 16.94%, with an open-circuit voltage (Voc) of 0.78 V, a short-circuit current density (Jsc) of 27.57 mA/cm², and a fill factor (FF) of 78.62%. These results confirm that manipulating interface bands at the HTL/perovskite junction is an effective strategy for improving the performance of  BaZrS₃-based solar cells and provide practical recommendations for the design of future lead-free perovskite photovoltaic devices.