UNSW researchers have investigated the impact of electron irradiation on the performance of PERC and TOPCon solar cells and identified large-scale life degradation as the main cause of power loss. Their work highlights the need to increase radiation tolerance in silicon solar cells in the commercial space.
Scientists from the University of New South Wales (UNSW) in Australia have investigated the impact of electron irradiation on the performance of p-PERC, n-TOPCon and p-TOPCon solar cells and found that this phenomenon can cause ‘severe’ degradation.
“Our work builds on our previous work in modeling solar cells and repairing defects due to hydrogenation, and is intended to guide the future design of radiation-tolerant commercial silicon cells for aerospace applications,” said the study’s corresponding author, Bram Hoex. pv magazine.
Electron radiation degrades the performance of solar cells, especially those used in space, by generating physical defects in the light absorber. In space, high-energy electrons are charged from particle environments solar flares and penetrate the material of the solar cells. This causes damage from electrostatic discharge, which affects the electrical and physical properties of solar cells, which influence parameters such as short-circuit current and no-load voltage.
For their tests, the research team used several types of commercial silicon wafers and cells with a size of 158 mm x 158 mm, where the devices are irradiated with 1 MeV electrons in doses ranging from 1014e/cm2 And 5×1014e/cm2. It also used a Sinton WCT-120 lifetime tester to perform minority carrier lifetime measurements and photoluminescence (PL) images to assess the severity of radiation damage to lifetime wafers.
In addition, there are three types of commercial silicon solar cells, including a 158 mm x 158mm p-PERC cell, a 166mm x 166mm p-TOPCon and six different n-TOPCon solar cells, manufactured by various undisclosed manufacturers between 2021 and 2024, were exposed to 2.16 x 1014e/cm2 of 5 MeV electron irradiation.
“The IV characterization was performed using the PVTools LOANA cell tester for the AM1.5G spectrum and using a Wavelabs SINUS-220 IV tester for the AM0 spectrum,” the scientists explained. “The AM0 IV results were compared with data obtained during the actual space mission. In addition, the external quantum efficiency (EQE) was measured using a PV Measurements QEX7 Spectral Response tool. Quokka 3 was used to simulate optical response, carrier transport and recombination in the silicon solar cells with the drift-diffusion model.”
The analysis showed that both 1 MeV and 5 MeV electron fluxes significantly affected the performance of the silicon bulk in all types of post-irradiated silicon solar cells. The researchers also found that the degradation was particularly pronounced in the p-TOPCon cells, due to the design of the rear p-n junction.
In contrast, in the n-TOPCon cell and p-PERC devices, the losses were mainly attributed to the recombination of photogenerated carriers excited by long-wavelength light. “P-type substrates showed superior radiation tolerance to n-TOPCon, coupled with higher electron mobility and gallium doping,” Brahm explained. “Front-junction architectures outperformed rear-junction p-TOPCon designs, which suffered from short-wavelength EQE losses.”
The research team also found that electron irradiation causes a severe degradation in the lifetime of bulk minority carriers, from about 75 ms to about 0.2 µs at 10¹⁵e cm². “This large loss of life, rather than surface effects, dominates the decline in efficiency,” Brahm said. “Vacancy defects were identified as the most important radiation-induced defects by DPSS/TIDLS analysis, with efficiency dropping to approximately 60% under simulated LEO equivalent irradiation, with n-TOPCon showing the strongest sensitivity.”
The academics presented their findings in the study “Electron radiation-induced degradation of silicon solar cells”, published in Solar energy materials and solar cells.
Previous research by UNSW demonstrated the impact of solder flux on the performance of TOPCon solar cells, that of UV-induced degradation (UVID) in TOPCon cells, degradation mechanisms of industrial TOPCon solar panels encapsulated with ethylene vinyl acetate (EVA) under accelerated moist heat conditionsas well as the vulnerability of TOPCon solar cells to contact corrosion and three types of defects in TOPCon solar modules that have never been detected in PERC panels.
Additionally, UNSW scientists investigated the sodium-induced degradation of TOPCon solar cells under moist heat exposure and the role of ‘hidden contaminants’ in the degradation of both TOPCon and heterojunction devices.
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