Silver Surface Treatment of Cu(In,Ga)Se₂(CIGS) Thin Film: A New Passivation Process for the CdS/CIGS Heterojunction Interface

The interface engineering of Cu(In,Ga)Se-2(CIGS)-based solar cells is challenging for high-efficiency devices, especially for the CdS/CIGS heterojunction interface. Recently, post-treatment of the CIGS surface, as an efficient approach to passivate the defects at the CdS/CIGS interface, has attracted widespread attention. Here, a simple Ag surface treatment process is used to realize the passivation of interface defects and the enhancement of the CdS/CIGS heterojunction. This process not only reduces the surface roughness of CIGS films significantly, but also contributes to controlling the Ga composition in the surface layer. Furthermore, characterization techniques reveal that Ag surface treatment can effectively decrease the defect concentrations at the heterojunction interface and enhance the CdS/CIGS heterojunction quality with appropriate Ag deposition duration. Further investigations on the changed defect level caused by the Ag surface treatment indicate that the increased defect level is likely related to the shift of valence band maximum. Eventually, the efficiency of the optimum device has a relative increase of about 18% compared with that of the reference solar cell. This work focuses on revealing the differences of the CIGS surface and CdS/CIGS interface caused by Ag, which provides a new surface processing method for the passivation of the CdS/CIGS heterojunction.