Comparative study of Cd-free Cu(In,Ga)Se₂ solar cells with amorphous In₂O₃:H and ZnO:Al front contact layers

Abstract Cu(In,Ga)Se₂ (CIGSe) thin-film solar cells are known to be a promising solution for the current energy challenge. However, the environmental and health concerns associated with the conventional use of toxic CdS buffer layers, along with the limitations posed by the conductivity of commonly used ZnO:Al (AZO), require further innovation for new alternatives. It was shown independently that both layers can be replaced by non-toxic and highly conductive layers, such as zinc-tin oxide (Zn_1−x Sn _x O _y , ZTO) and hydrogen-doped indium oxide (In₂O₃:H, IOH), respectively. Thus, this study presents a strategic modification by replacing the CdS buffer layer with ZTO, deposited by chemical bath deposition, and the AZO front contact with highly conductive IOH. Our IOH-based solar cells display higher fill factor and open-circuit voltage (V _oc), though lower short-circuit current compared to AZO-based devices. Notably, the ZTO/IOH-based solar cell achieved a maximum power conversion efficiency (PCE) of 11.5%, with a V _oc of 607 mV, while the best device for the CdS/IOH-based solar cell reached a PCE of 13.5%, with a V _oc of 633 mV. Therefore, we demonstrate the viability of scalable and cost-effective deposition methods for both buffer and front contact layers in CIGSe solar cells, offering comparable performance to conventional layers reported in the literature.