Enhancing kesterite-based thin-film solar cells: A dual-strategy approach utilizing SnS back surface field and eco-friendly ZnSe electron transport layer

• The SnS BSF layer reduced defects and recombination losses, thereby enhancing the power conversion efficiency (PCE). • Replacing the toxic CdS buffer with ZnSe improved efficiency while maintaining environmentally friendly design. • The SnS BSF layer raised the PCE from 1.31 % to 3.47 %, enhancing charge collection and reducing recombination. • The SnS layer improved the PN Mott-Schottky junction, increasing key parameters like J SC , V OC , and FF. • Substituting CdS with ZnSe resulted in a PCE of 7.68 %, improving charge transport and reducing defects. The development of kesterite-based thin-film solar cells (TFSC s ) has faced significant challenges, particularly due to unstable rear contact properties and low power conversion efficiency (PCE). Despite various individual approaches aimed at addressing these issues, progress has remained limited. In this study, a dual strategy is explored to address these problems simultaneously. First, the impact of an SnS intermediate layer at the back surface field in conjunction with an FTO back contact is examined. Second, the introduction of a stable PN Mott-Schottky junction is assessed by utilizing an eco-friendly ZnSe electron transport layer (ETL) as a replacement for the conventional, yet toxic, CdS ETL. The combined application of these strategies produces a synergistic effect, leading to significant improvements in the solar cell’s microstructure and key electrical parameters, including open-circuit voltage (V OC ), short-circuit current density (J SC ), and overall PCE. Additionally, this approach mitigates band-tailing states and reduces deep-level defects often associated with the annealing process. As a result, the power conversion efficiency is significantly enhanced, rising from 1.31 ± 0.13 % to 7.68 ± 0.98 %. This effective dual-strategy offers new insights into overcoming the challenges of unstable rear contact properties and suboptimal device parameters, paving the way for further advancements in the performance of kesterite-based TFSC s .