Investigation of GaOx formation at the (Ag,Cu)(In,Ga)Se 2 /In 2 O 3 :Sn interface with STEM and XPS techniques

This study investigates the interface between (Ag,Cu)(In,Ga)Se 2 (ACIGS) and In 2 O 3 :Sn (ITO) in bifacial solar cells with X-ray Photoelectron Spectroscopy (XPS), Scanning Transmission Electron Microscopy (STEM) and Energy-dispersive X-ray Spectroscopy (STEM-EDS). The aim is to characterize the GaO x layer forming at the rear interface in solar cell samples with varying NaF precursor layer, maximum deposition temperature, deposition time, and Ga-concentration. The GaO x layer is present in all samples, even when no NaF is added. Temperature and excess NaF appear to increase the thickness or roughness of the GaO x layer, yet a continuous layer of < 3 nm is found at the ACIGS/ITO interface in all samples. Good performance could be reached, with FF∽72-76% even with a GaO x layer present. Considering the limited thickness of the GaO x layer measured in this study, it does not block the current flow and could have a degree of passivation on the rear interface of the solar cells, leading to the high FF.