Effect of Interface Passivation on the Performance of the Cu₂ZnSnS₄ Solar Cells

This study examines the effect of ultrathin aluminum oxide (Al₂O₃) passivation layer on the performance of the kesterite Cu₂ZnSnS₄ (CZTS) solar cells. The Al₂O₃ layer was applied at the back CZTS/Mo interface using atomic layer deposition (ALD). Our findings indicate that the interface passivation with Al₂O₃ can significantly enhance the adhesion of CZTS to Mo, preventing delamination during annealing. An optimal Al₂O₃ thickness of 1-2.5 nm yielded a more than 30% increase in efficiency, primarily through enhancements of the open-circuit voltage (<i>V</i> _oc) and short-circuit current (<i>I</i> _sc), which resulted from reduced interface recombination and improved charge collection within the CZTS bulk. Furthermore, the Al₂O₃ layer modified MoS₂ formation at the CZTS/Mo back interface, reducing series resistance (<i>R</i> _s). Nevertheless, a thicker Al₂O₃ layer led to a sharp decrease in efficiency due to increased series resistance and hindered the extraction of holes. Our work reveals that precise control of the Al₂O₃ layer thickness is essential to optimize CZTS solar cell performance by balancing the benefits of passivation with its potential drawbacks.