Multiple Impacts of the Aluminum Oxide Passivation Layer on the Properties OF Cu(In,Ga)Se2 Solar Cells

In this study, the origins of efficiency gains in Cu(In,Ga)Se₂ (CIGS) solar cells are investigated by introducing an Al₂O₃ passivation layer in terms of the oxidation condition of Mo back contact, alkali-metal diffusion, minority carrier lifetimes (τ), and charge conditions. The study reveals that introduction of an Al₂O₃ back-contact passivation layer into solar cells yields multiple impacts. Al₂O₃ deposition enhances the oxidation of the Mo back contacts, increasing Na solubility in Mo and Na diffusion from Mo into the CIGS layer, thereby modifying the metastable properties of CIGS. The charge condition at the CIGS/Al₂O₃ interface is not fixed negative charge but variable, dependent on whether electrons or holes are supplied. During solar cell operation, the interfacial charge condition is expected to be neutral or positive for Al₂O₃ grown using plasma or thermal atomic layer deposition techniques, respectively. Moreover, the mechanical peeling off of CIGS from Mo back contact enhanced τ in a similar way as with the insertion of Al₂O₃. Based on this study, the enhancement of alkali metal supply and the removal of direct contact of CIGS to the metal contact (Mo) can play crucial roles in improving the performance of CIGS solar cell.