Effects of annealing temperature and atmosphere on performances of Zn0.9Mg0.1O buffer layers for CIGS solar cell

Abstract

Zn 0.9 Mg 0.1 O (ZMO) thin films were fabricated by magnetron co-sputtering without substrates heating. Annealing process was introduced to reduce the defect density and improve the photoelectric performances. The effects of annealing temperature and atmosphere on the crystallization, defect density, and photoelectric performances of ZMO films were investigated. The variation mechanisms for intrinsic point defects in ZMO films during the annealing process were discussed. The results show that annealing reduces the defect-bound emission and improves the crystallization. And annealing promotes the desorption of adsorbed oxygen and the diffusion of oxygen in air. Besides, the near-band-edge emission peak shifts to shorter wavelengths and the band gap ( E g) increases, which should be attributed to the changes in the position of Mg atoms. And the common increase of the Hall mobility and carrier concentration of the ZMO films, which leads to a decrease in the resistivity. Finally, after annealing in air and Ar atmosphere, the resistivity of ZMO films is 63.8 and 2.2 Ω.cm, and the value of E g is 3.42 and 3.39 eV, respectively. And based on the performance optimization of ZMO films, the efficiency of CIGS solar cells with ZMO buffer layers reaches up to 12.9%. These results are helpful for the application of ZMO buffer layers on CIGS solar cells to improve cell efficiency.