Hydrogenation of sputtered ZnO:Al layers for double side poly-Si/SiOx solar cells

Abstract

This work presents the development and the application of innovative and sustainable transparent conductive oxide (TCO) materials for contacting polysilicon (poly-Si) on oxide (SiOx) stacks used as passivating contacts in solar cell devices. Adding hydrogen into ZnO:Al (AZO) layers deposited by magnetron sputtering potentially leads to a twofold positive effect. First, it brings hydrogen atoms into the layers, which can enhance both electrical and optical material properties of the TCO. Second, hydrogen can significantly improve cell performances, by fixing dangling bonds at the SiOx/substrate interface and by passivating bulk defects. In situ and ex situ hydrogenation processes have been compared on those multiple aspects with investigation about anneals at 350 °C. AZO layers have been successfully integrated on the front side of complete solar cells featuring poly-Si/SiOx-based passivating contacts, leading to a record conversion efficiency of 22.4% for a cell with AZO. The results show that using AZO instead of an indium based TCO is suitable for passivated contacts solar cell with high temperature route. Thus, it increases the credibility towards large-scale deployments of TCO-based high efficiency silicon solar cells in terms of cost and resources.