Thin-film Cu(In,Ga)(Se,S)2-based solar cell with (Cd,Zn)S buffer layer and Zn1-xMgxO window layer

(Cd,Zn)S buffer layer and Zn1-xMgxO window layer were investigated to replace the traditional CdS buffer layer and ZnO window layer in Cu(In,Ga)(Se,S)(2) (CIGSSe)-based solar cell. (Cd,Zn)S with band-gap energy (E-g) of approximately 2.6eV was prepared by chemical bath deposition, and Zn1-xMgxO films with different [Mg]/([Mg]+[Zn]) ratios, x, were deposited by radio frequency magnetron co-sputtering of ZnO and MgO. The estimated optical E-g of Zn1-xMgxO films is linearly enhanced from 3.3eV for pure ZnO (x=0) to 4.1eV for Zn0.6Mg0.4O (x=0.4). The quality of the Zn1-xMgxO films, implied by Urbach energy, is severely deteriorated when x is above 0.211. Moreover, the temperature-dependent current density-voltage characteristics of the CIGSSe solar cells were conducted for the investigation of the heterointerface recombination mechanism. The external quantum efficiency of the CIGSSe solar cell with the (Cd,Zn)S buffer layer/Zn1-xMgxO window layer is improved in the wavelength range of 320-520nm. Therefore, a gain in short-circuit current density up to about 5.7% was obtained, which is higher conversion efficiency of up to around 5.4% relative as compared with the solar cell with the traditional CdS buffer layer/ZnO window layer. The peak efficiency of 19.6% was demonstrated in CIGSSe solar cell with (Cd,Zn)S buffer layer and Zn1-xMgxO window layer, where x is optimized at 0.211. Copyright (c) 2017 John Wiley & Sons, Ltd.