Light- and Elevated Temperature-Induced Degradation and Recovery from Silicon Wafers by the Impact of Hydrogen Treatment

Abstract

Light- and elevated-temperature-induced degradation (LeTID) affects materials used in solar cell fabrication, especially gallium- and boron-doped p-type, and various n-type silicon wafers. Dark annealing at elevated temperatures promotes hydrogen diffusion into the bulk of silicon wafers. Here, dark-annealing was consistently performed at 200°C for 15 minutes to observe its impact on degradation and recovery. Higher temperatures accelerated LeTID, necessitating rapid annealing for regeneration. The chosen temperature range (75, 120, and 135°C) was selected to simulate real-world solar panel operating conditions and to observe degradation under both moderate and extreme temperatures. Forming-gas annealing increased the carrier lifetime of boron-doped silicon wafers by up to 92.8% and gallium-doped wafers by up to 16.3% from their initial values after degradation. Dark-annealing resulted in 40% and 28% increases in the carrier lifetimes of fully degraded gallium- and boron-doped silicon wafers, respectively. The proposed model explains the behavior related to different diffusivities of hydrogen in gallium- and boron-doped silicon wafers during dark-annealing. The LeTID mechanism involves three stages: generating inactive recombination centers (Di) and H+ ions during manufacturing, converting Di to HDi+1, enhancing carrier recombination, and, during regeneration, the injection of carriers (e-) transitions to a recombination inactive state.