Investigation of Cu(In,Ga)S ₂ Thin Films–Based Solar Cells Deposited on In ₂ O ₃ : Sn Transparent Back Contacts for Rear‐Side Illumination Applications

This study investigates the optoelectronic characteristics of solar cells based on wide bandgap Cu(In,Ga)S 2 (CIGS) absorbers, co‐evaporated onto glass substrates covered with 100 nm‐thick indium tin oxide (ITO) back contact. Devices based on absorbers with different thicknesses (ranging from 320 to 1580 nm) were investigated. Structural characterizations confirmed that all of the films were made of large grains, crystallized in the chalcopyrite structure with no secondary phases. It has been observed that the performance of the cells with front‐side illumination improves with increasing CIGS thickness, mainly because of increased short‐circuit current ( J SC ). In contrast, the opposite trend is observed for rear‐side illumination, further suggesting a hindered collection of carriers generated close to the ITO/CIGS interface. The modelling of quantum efficiency using e‐ARC tool and Gartner theory suggests that all absorbers, independently of their thickness, are nearly fully depleted. In addition, they all exhibit a region with a low collection of photogenerated carriers at the vicinity of the ITO/CIGS interface. It is proposed that this area results from the consumption of gallium during gallium oxide formation at the ITO/CIGS interface.