Cu2ZnSn(S, Se)4 (CZTSSe) device is fabricated with Zn1−xSnxO (ZTO) buffer layer deposited by atomic layer deposited (ALD). The ALD process results in a precise control of thickness and Sn/(Sn+Zn) ratio of the buffer layer. The performance of the CZTSSe device with ZTO buffer layer has been enhanced by adjusting proper Zn and Sn ratio during the ALD process. The optimized Sn/(Sn+Zn) pulse ratio is found to be around 0.167, with a thickness of around 50 nm. The champion device with a ZTO buffer layer has an efficiency of 8.60% (active area efficiency 9.20%) compared with 8.14% (active area efficiency 8.70%) of the reference solar cell with chemical bath deposited CdS buffer layer. The optimum device performance is a result of optimized band alignment between CZTSSe absorber and the ALD ZTO buffer as shown by ultraviolet photoelectron spectroscopy (UPS).
X. Li, Su, Z., Venkataraj, S., Batabyal Sudip Kumar, and Wong, L. Helena, “8.6% Efficiency CZTSSe solar cell with atomic layer deposited Zn-Sn-O buffer layer”, Solar Energy Materials and Solar Cells, vol. 157, pp. 101–107, 2016.