Rapid thermal annealing on ZnMgO window layer for improved performance of CdTe solar cells

Poor qualities of ZnMgO thin films are likely to be obtained at higher Mg content, which can decrease the performance of ZnMgO-based devices. This study focuses on improving the qualities of ZnMgO thin films to increase the performance of CdTe solar cell. It is found that the rapid thermal annealing (RTA) treatment increases the crystallinity, eliminates defects and improves the conductivity of ZnMgO thin films. These are helpful to suppress the recombination caused by bulk and interface defects as well as to reduce the cell's series resistance. The Fermi level moves close to conduction band and both the conduction and valence band energy shift lower relative to band energy of CdSSeTe film after RTA, which could not only increase the built-in voltage but also enhance the electron transport and block the hole recombination. As a result, the efficiency of CdTe solar cells is enhanced when using the RTA-treated ZnMgO, with maxium power conversion efficiency reaching values of 15.7%, which are much higher than those of the cells with the as-grown ZnMgO (11.6%). RTA is proved to be one of the excellent methods to control the properties of ZnMgO for improving the performance of CdTe solar cell.