The role of hydrogen for crystalline silicon solar cells

Hydrogen plays a significant role in the hydrogenation and hydrogen-induced degradation (HID) of crystalline silicon solar cells. In solar cells, the main hydrogen source was contributed from hydrogenated silicon nitride (SiNx: H) to enhance the surface and bulk passivation. This paper depicts a review of the current investigations on mechanisms of hydrogen in the silicon bulk and the defects passivation through manipulating the charge states of hydrogens. Based on the passivation mechanism, we introduced four convertible states of boron-oxygen (BO) related defects in help of understanding the degradation suppression of P-type crystalline silicon. It explains the mechanism of light-induced degradation (LID) because most industrial solar cells are based on boron-doped silicon wafers. Also, we introduced new light sources of laser and light-emitting diodes (LEDs) in the application of hydrogenation. We also explained an efficiency loss that emerged in hydrogenation processes which is considered to be related to the injection of excess hydrogens, similar to the HID of light and elevated temperature induced degradation (LeTID). In the conclusion, optimized methods and conditions of advanced hydrogenation for silicon solar cells are proposed, which can further improve the electrical performance and enhance the stability of silicon solar cells.