Scientists have found that UVB causes more degradation in TOPCON cells than UVA.

The research group led by Bram Hoex at the University of New South Wales, Australia, in collaboration with Artes, studied the ultraviolet-induced degradation (UVID) of TOPCON cells. They found that UVB and UVA cause UVID through the same mechanism, but the effect of UVB is more than 100 times stronger than that of the same dose of UVA. Therefore, UVB is recommended as the light source for accelerated UVID aging tests.

The figure below shows the AM0 and AM1.5G solar spectra, as well as the spectra of the UVB and UVA ultraviolet light sources used in the paper.

Source: M. U. Khan et al.,   Solar Energy Materials & Solar Cells 294 (2026) 113895 The samples were divided into three groups: Group B samples before and after UVB irradiation, Group C samples before and after UVA irradiation, and Group A as the control group, all subjected to 60°C dark annealing (DA). During the experiment, the quasi-steady-state photoconductance decay method (QSSPC) was used to measure minority carrier lifetime, calculate normalized defect density, and the Kane-Swanson method was used to obtain the emitter saturation current density J₀ₑ. ₀ₑ From the J₀ₑ results of Group B samples, ₀ₑ it can be seen that the front surface recombination of TOPCON cells significantly increased after UVB irradiation, while the rear surface showed no similar change after UVB exposure. Researchers attributed this to the absorption of ultraviolet light by the polycrystalline silicon layer on the back of the TOPCON cells.

Source: M. U. Khan et al.,   Solar Energy Materials & Solar Cells 294 (2026) 113895 A and B, C group samples' J₀ₑ ₀ₑ data are summarized in the figure below. Data from Group A indicate that surface recombination remains unchanged without ultraviolet exposure (no UVID). Comparing results from Groups B and C, a UVB dose of 0.72 kWh/m² causes a J₀ₑ increase greater than that caused by a 49 kWh/m² UVA dose, ² indicating that the UVID effect caused by the same dose of UVB is much higher than that caused by UVA. ₀ₑ dose UVB causes a J₀ₑ increase greater than 49 kWh/m² ² dose UVA causes a J₀ₑ increase, ₀ₑ indicating that the UVID effect produced by the same dose of UVB is far greater than that of UVA.

Source: M. U. Khan et al.,   Solar Energy Materials & Solar Cells 294 (2026) 113895 To investigate the UVID degradation mechanism, the research team used Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) to analyze the samples and found that the hydrogen concentration near the aluminum oxide (AlOₓ) layer on the front surface increased after UVID. ₓ They explained this by stating that the energy from ultraviolet light breaks Si-H bonds in the sample, causing hydrogen to diffuse outward from inside the cell and accumulate at the interface of the AlOₓ layer, leading to increased interface recombination. Meanwhile, the reduction of hydrogen concentration inside the cell after UV exposure can also explain the observed weakening of the LeTID effect after UV exposure. ₓ (Reference article Hydrogen in Crystalline Silicon Solar Cells: Sources, Concentration Control, and Its Impact on Cell Degradation )

Source: M. U. Khan et al.,   Solar Energy Materials & Solar Cells 294 (2026) 113895