Effect of Interface\nPassivation on the Performance\nof the Cu<sub>2</sub>ZnSnS<sub>4</sub> Solar Cells

This study examines the effect of ultrathin aluminum\noxide (Al<sub>2</sub>O<sub>3</sub>) passivation layer on the performance\nof the\nkesterite Cu<sub>2</sub>ZnSnS<sub>4</sub> (CZTS) solar cells. The\nAl<sub>2</sub>O<sub>3</sub> layer was applied at the back CZTS/Mo\ninterface using atomic layer deposition (ALD). Our findings indicate\nthat the interface passivation with Al<sub>2</sub>O<sub>3</sub> can\nsignificantly enhance the adhesion of CZTS to Mo, preventing delamination\nduring annealing. An optimal Al<sub>2</sub>O<sub>3</sub> thickness\nof 1–2.5 nm yielded a more than 30% increase in efficiency,\nprimarily through enhancements of the open-circuit voltage (<i>V</i><sub>oc</sub>) and short-circuit current (<i>I</i><sub>sc</sub>), which resulted from reduced interface recombination\nand improved charge collection within the CZTS bulk. Furthermore,\nthe Al<sub>2</sub>O<sub>3</sub> layer modified MoS<sub>2</sub> formation\nat the CZTS/Mo back interface, reducing series resistance (<i>R</i><sub>s</sub>). Nevertheless, a thicker Al<sub>2</sub>O<sub>3</sub> layer led to a sharp decrease in efficiency due to increased\nseries resistance and hindered the extraction of holes. Our work reveals\nthat precise control of the Al<sub>2</sub>O<sub>3</sub> layer thickness\nis essential to optimize CZTS solar cell performance by balancing\nthe benefits of passivation with its potential drawbacks.