Researchers at the University of South New Wales (USNW) in Australia have investigated the physical origin of ultraviolet-induced degradation (UVID) in PERC and TOPCon solar cell technologies and have found that UV exposure not only creates additional interface defects, but also alters their electronic activity, making them substantially more recombination-active.
One of the key findings of the research is that UV exposure induces pronounced degradation on both the front and rear surfaces of PERC solar cells, as well as on the front surface of TOPCon cells, while the rear side of TOPCon remains largely unaffected due to UV absorption in the poly-Si layer. “This explains why TOPCon and heterojunction (HJT) technologies can exhibit stronger UV sensitivity than conventional PERC architectures,” corresponding author Bram Hoex told pv magazine. “It also highlights the critical role of interface engineering and hydrogen management for future UV-stable high-efficiency modules.”
In the study “Energy-dependent increase in Dit and larger capture cross sections drive UV-induced degradation,” published in Solar Energy Materials and Solar Cells, Hoex and his colleagues explained that in PERC and TOPCon solar cells, the aluminum oxide (AlOx) layer is a key passivation component that strongly influences silicon surface quality and UV stability. Previous studies show that thicker AlOx layers and AlOx/silicon nitride (SiNx) stacks can reduce UV-induced degradation by improving charge density and surface passivation. Overall, UV exposure changes charge and defect behavior at material interfaces, but well-optimized AlOx structures can significantly improve long-term device stability.
The team investigated PERC and TOPCon cells with dimensions of 182 mm × 182 mm, along with AlOx symmetric lifetime test samples. The PERC cells use a p-type gallium-doped silicon substrate with a phosphorus-doped front emitter, a hydrogenated silicon nitride (SiNx:H) passivation layer, and silver front contacts, while the rear side consists of an aluminum oxide layer deposited by atomic layer deposition and a hydrogenated silicon nitride layer deposited by plasma-enhanced chemical vapor deposition, with aluminum metallization.
The TOPCon cells include a boron-doped emitter, an aluminum oxide layer deposited by atomic layer deposition, a silicon dioxide interlayer, and a phosphorus-doped polycrystalline silicon/SiNx rear contact stack with silver grid metallization.
To isolate ultraviolet-induced degradation mechanisms, aluminum oxide-only symmetric lifetime samples were fabricated on n-type silicon wafers, featuring approximately 9–12 nm aluminum oxide layers deposited by atomic layer deposition and fired at 780 C. The samples were divided into groups, cut into 40 mm × 40 mm pieces, and subjected to ultraviolet-B (UV-B) irradiation at an intensity of about 114 W/m² and a temperature of 60 C. A dark-annealing group at 60 C was used as a control to separate thermal effects from light-induced effects.
Photoluminescence (PL) imaging was used to evaluate degradation behavior, and photoluminescence ratio maps were generated to visualize changes before and after UV exposure. Minority carrier lifetime was measured using the quasi-steady-state photoconductance method under controlled temperature conditions, while interface defect density was extracted using corona-oxide characterization of semiconductor measurements, which provide non-contact capacitance–voltage profiling. In addition, PL intensity was correlated with saturation current density and open-circuit voltage using diode and recombination models, enabling quantitative comparison of recombination changes under UV stress.
The analysis showed that ultraviolet-B (UVB) irradiation causes strong degradation on both the front and rear sides of the PERC cells, while dark-annealed samples remain stable, confirming that temperature alone is not responsible for the observed effects. The front side, passivated only by SiNx, exhibits the most severe degradation, while the rear side is moderately affected. As for the TOPCon cells, UVB exposure leads to pronounced degradation on the front surface, whereas the rear side remains largely stable due to UV absorption by the polycrystalline silicon layer. Overall, both technologies show that UV-induced degradation occurs primarily at exposed silicon–dielectric interfaces.
The scientists said these results highlight that UV-induced degradation is strongly dependent on surface structure and passivation design. The PERC front surface is particularly vulnerable due to its simpler passivation scheme, whereas the TOPCon rear is protected by UV-absorbing layers. Overall, degradation correlates with exposure of the crystalline silicon–dielectric interface to UV radiation.
“We believe this work helps bridge the gap between earlier chemical-hydrogen-based UVID models and a more complete electronic-recombination-based understanding of degradation mechanisms in modern silicon solar cells,” Hoex concluded.
Previous research on UVID degradation by UNSW showed that thicker AlOx layers significantly improve UV resilience by limiting hydrogen migration, offering clear guidance for more robust TOPCon designs. Another work also warned of unexpected UV-induced degradation in TOPCon solar cells from invisible light.
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