Contamination control

Abstract

The tunnel oxide passivated contact (TOPCon) silicon solar cell is a technology that is gaining traction in the photovoltaic industry due to high performance and competitive manufacturing costs. Yet given the relatively recent development of the technology, its reliability under operational conditions is not yet fully understood. In particular, TOPCon solar cells have been reported to be susceptible to contaminants originating from manufacturing or environmental stress. For example, sodium, which diffuses from the glass substrate, has been shown to degrade the front metal contact. In an academic–industry collaboration, Hongbo Tong, Xinyuan Wu, Zhenguo Li, Bram Hoex and colleagues across China and Australia demonstrate that the device’s rear side is also vulnerable to sodium corrosion and diffusion into the silicon layer.

To simulate contamination, the researchers spray a solution containing sodium salts at the front and at the back of TOPCon solar cells under accelerated testing conditions, that is 85 °C and 85% relative humidity. While degradation is observed on both sides, elemental changes and chemical reactions at the surface are more pronounced on the rear side, as it lacks the robust chemical passivation layers present on the front side. The reactions lead to the formation of defects and the diffusion of sodium ions into the solar cell.