A team led by researchers at Germany-based Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) has developed a parametric predictive model for light and elevated temperature-induced degradation (LeTID) in gallium-doped silicon wafers that includes the kinetics of the temporary recovery effect.
“We specifically investigated the kinetics of temporary recovery in gallium-doped silicon,” the research's corresponding author, Fabian T. Thome, told pv magazine, noting that the group had previously demonstrated and reported in Solar Energy Materials and Solar Cells that temporary recovery can suppress the extent of the LeTID degradation.
Investigating it further, the team developed a model for LeTID in gallium-doped Czochralski silicon wafers, including kinetics at varying temperatures and minority charge carrier densities, and measuring the resulting changes in effective lifetime.
The work resulted in a quantitative description of all relevant subprocesses. “Our new insights into the kinetics enable us to model this suppression precisely,” said Thome.
A challenging aspect was the in situ aspect of the research. “Since temporary recovery rapidly alters the lifetime of the samples, we had to design a specific in-situ experiment. This was necessary to correctly determine the model input parameters,” he explained.
The scientists concluded that temporary recovery is “a multi-step process,” involving at least two distinct sub-reactions.
“By investigating temporary recovery in gallium-doped silicon in isolation from degradation and regeneration, we found that the rate of temporary recovery increases as temperature is reduced. This is quantitatively reflected in a reversed Arrhenius behavior,” said the team.
“This allows to predict the degradation rate and its extent as a function of temperature and minority charge carrier density,” it stated.
“Since temporary recovery (TR) can suppress or revert LeTID, especially in winter periods, quantifying this behavior is key for the complete LeTID model,” Thome said, adding that if TR is not properly included, the degradation caused by LeTID could be heavily overestimated.
The work appears in “Light and elevated temperature induced degradation in gallium-doped silicon: A complete parametric description,” published in Solar Energy Materials and Solar Cells.
The group is now connecting the parametric model with an atomistic one. The preliminary results of which will be presented by research team member Wolfram Kwapil at the European Photovoltaic Solar Energy Conference and Exhibition 2025 (EU PVSEC 2025) in Bilbao, according to Thome. Other members of the research team were from Inatech and the University of Freiburg.
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