Nanoscale Rear-Interface Passivation in Cu₂ZnSn(S,Se)₄ Solar Cells through the CuAlO₂ Intermediate Layer

The present work demonstrates that the addition of p-type CuAlO2 (CAO) as an intermediate layer between molybdenum (Mo) and the absorber rear interface efficiently improves the Cu2ZnSn(S,Se)4 (CZTSSe) device performance. The efficacy of the intermediate layer is analyzed through sputtering the CAO nanolayer at different deposition times on top of the Mo layer. The addition of an ultrathin CAO nanolayer improved the absorber bulk quality with the formation of compact and larger crystalline grains. Furthermore, the CZTSSe device with an optimum deposition time (154 s) of the CAO nanolayer successfully reduced the Mo(S,Se)2 layer thickness from ∼50 to ∼25 nm. This reduced Mo(S,Se)2 layer thickness results in the reduced series resistance (Rs) in the device providing improvement in the overall device performance. The short-circuit current density (JSC) and the power conversion efficiency of the device with the CAO nanolayer increased from 33.48 to 35.40 mA/cm2 and from 9.61 to 10.54%, respectively, compared to a reference device.