The Energy Band Structures of Cd1-xZnx Te Polycrystalline Thin films and their Applications for Photovoltaic Devices

ABSTRACTIn the paper, Cd1-xZnxTe polycrystalline films have been prepared by co-evaporation, which can control the zinc content, using CdTe and ZnTe as the evaporation sources. The cubic phase in these films as-deposited and annealed has been demonstrated by XRD. The XRD peaks of Cd1-xZnxTe films are always between the corresponding peaks of CdTe and ZnTe. According to Vegard Formula, x values of Cd1-xZnxTe films have been confirmed from XRD data, which shows that both the calculated and experimental x values are almost identical. The optical transmission of Cd1-xZnxTe films has been measured, and the optical energy gaps have been calculated from the transmission. The band gaps vary in a quadratic way with x values, and increase with annealing temperatures. When application of Cd1-xZnxTe film as a buffer of around 80nm thick in CdS/CdTe solar cells, the structure of the cells becomes CdS/CdTe / Cd1-xZnxTe / ZnTe:Cu and their average conversion efficiency is improved by 40% where x is in the range of 0.55 to 0.65. The mentioned above results are discussed.