Dual-Functional ITO Interlayer for Effective Defect Passivation and Cationic Composition Engineering in Kesterite...

Excessive back interface interdiffusion and absorber defects are the primary limitations to the performance of Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. In this study, we address these limiting factors by introducing an ITO interlayer at the back interface. During the initial stage of selenization, the ITO functions as a diffusion barrier, effectively suppressing the migration of metal elements toward the Mo electrode and thereby mitigating elemental loss. In the middle and final stages of selenization, the ITO acts as a self-sacrificing layer, supplying Sn and In elements to compensate for the absorber layer. The dual-functional ITO interlayer facilitates the redistribution of elemental composition within the absorber layer. It reduces Sn-related vacancy defects through supplemental Sn supply and alleviates Sn-related substitutional defects via trace In doping. Through the optimization in this work, the defects in the absorber layer were effectively reduced. The reverse saturation current density decreased from 4.14 × 10^-7 to 2.67 × 10^-8 A/cm², indicating effective suppression of carrier recombination. Finally, the ITO-10 sample achieved a photoelectric conversion efficiency of 13.11%. This work presents a new interlayer material that reveals the synergistic mechanism of bulk doping and defect regulation in transparent conductive oxide ITO for CZTSSe.