Influences of Mg concentration in ZnMgO film on energy band alignment at CIGSSe/Zn1-xMgxO interface and performances of CIGSSe solar cells

Zn1-xMgxO buffered CdS free CIGSSe solar cell has been believed to be a new simplified structure solar cell with great potential. ZnMgO film plays an important role. To obtain a high quality Zn1-xMgxO thin film becomes a key issue. In this work, Zn1-xMgxO films with different Mg concentrations were prepared by magnetron co-sputtering, and physical performances of Zn1-xMgxO films were investigated. Meanwhile, CdS free CIGSSe solar cells were prepared based on Zn1-xMgxO buffer layers. The effects of Mg concentration in Zn1-xMgxO buffer layers on device performances, energy band alignment, and interface recombination of CIGSSe solar cells were studied. The results show that although the doping of Mg reduces the crystallinity of Zn1-xMgxO films, it increases the band gap by increasing the conduction band minimum. In Zn1-xMgxO buffered CdS free CIGSSe solar cells by all-sputtering process, the photoelectric conversion efficiency increases first and then decreases with the increase of Mg concentration in the x range from 0 to 0.3, which is mainly attributed to the changes of FF and VOC. Meanwhile, the change of Mg concentration affects the energy band alignment at the CIGSSe/Zn1-xMgxO interfaces. The highest efficiency of 15.2 % of Zn0.8Mg0.2O buffered CdS free CIGSSe solar cell with the energy band difference of 0.27 eV was obtained in this work.