Aluminum‐doped Zn1 − xMgxO as transparent conductive oxide of Cu(In,Ga)(S,Se)2‐based solar cell for minimizing surface carrier recombination

Abstract

AbstractA 19.5%‐efficient Cu(In,Ga)(S,Se)2 (CIGSSe)‐based solar cell is obtained by replacing traditional CdS/ZnO buffer layers with Cd0.75Zn0.25S/Zn0.79Mg0.21O buffer layers for increasing short‐circuit current density because band‐gap energies of Cd0.75Zn0.25S and Zn0.79Mg0.21O are wider than those of CdS and ZnO, respectively. This yields the increase in external quantum efficiency in a short wavelength range of approximately 320 to 550 nm. Moreover, difference of conduction band minimum (EC) between Zn1 − xMgxO:Al (transparent conductive oxide, TCO) layer and CIGSSe absorber is optimized by varying [Mg]/([Mg] + [Zn]), x. It is revealed that Zn1 − xMgxO:Al films with [Mg]/([Mg] + [Zn]) in a range of 0.10 to 0.12, enhancing Eg from 3.72 to 3.76 eV, are appropriate as TCO because of their enhanced mobility and decreased carrier density. Addition of 12% Mg into ZnO:Al to form Zn0.88Mg0.12O:Al as TCO layer effectively decreases surface carrier recombination and improves photovoltaic parameters, especially open‐circuit voltage and fill factor. This is the first experimental proof of the concept for optimizing EC difference between TCO and absorber to minimize surface carrier recombination. Ultimately, conversion efficiency (η) of CIGSSe solar cell with alternative Cd0.75Zn0.25S/Zn0.79Mg0.21O/Zn0.88Mg0.12O:Al (TCO) layers is enhanced to 20.6%, owing to control of total EC alignment, which is higher η up to 12.6% relative as compared with the solar cell with traditional CdS/ZnO/ZnO:Al layers.