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Researchers at the University of New South Wales (UNSW) in Australia have explored the fundamental causes of ultraviolet-induced degradation (UVID) in PERC and TOPCon photovoltaic cells, as detailed in a report released on May 21, 2026.
The investigation revealed that ultraviolet light not only generates additional defects at material interfaces but also modifies their electronic characteristics, rendering them significantly more prone to recombination. This heightened recombination activity drives the observed degradation.
Notably, ultraviolet exposure leads to substantial deterioration on both the front and rear surfaces of PERC cells and on the front side of TOPCon cells. However, the rear side of TOPCon devices remains mostly stable because the polycrystalline silicon layer absorbs the UV radiation. According to corresponding author Bram Hoex, this explains why TOPCon and heterojunction technologies can display greater UV sensitivity compared to traditional PERC designs. He further underscored the importance of interface engineering and hydrogen management for developing future modules that are stable under UV light.
The study, featured in Solar Energy Materials and Solar Cells, emphasizes that the aluminum oxide layer serves as a crucial passivation element in both PERC and TOPCon cells, significantly affecting silicon surface quality and UV resilience. Earlier research indicated that thicker aluminum oxide layers and combinations of aluminum oxide with silicon nitride can mitigate UV-induced degradation by enhancing charge density and surface passivation. While UV exposure alters charge and defect dynamics at interfaces, well-optimized aluminum oxide configurations can markedly boost long-term device stability.
The team examined PERC and TOPCon cells measuring 182 millimeters by 182 millimeters, along with symmetric lifetime test samples made solely of aluminum oxide. The PERC cells feature a p-type gallium-doped silicon base with a phosphorus-doped front emitter, a hydrogenated silicon nitride passivation layer, and silver front contacts. Their rear side comprises an aluminum oxide layer applied via atomic layer deposition and a hydrogenated silicon nitride layer deposited through plasma-enhanced chemical vapor deposition, with aluminum metallization. The TOPCon cells incorporate a boron-doped emitter, an aluminum oxide layer deposited by atomic layer deposition, a silicon dioxide interlayer, and a rear contact stack of phosphorus-doped polycrystalline silicon and silicon nitride, finished with silver grid metallization.
To isolate the mechanisms of UV-induced degradation, the researchers fabricated symmetric lifetime samples using only aluminum oxide on n-type silicon wafers. These samples had aluminum oxide layers approximately 9 to 12 nanometers thick, deposited via atomic layer deposition and fired at 780 degrees Celsius. They were then cut into 40-millimeter by 40-millimeter pieces and exposed to ultraviolet-B radiation at an intensity of roughly 114 watts per square meter and a temperature of 60 degrees Celsius. A control group underwent dark annealing at 60 degrees Celsius to distinguish thermal effects from those caused by light.
Degradation was assessed using photoluminescence imaging, while minority carrier lifetime was measured with the quasi-steady-state photoconductance method under controlled temperature conditions. Interface defect density was determined through corona-oxide characterization of semiconductor measurements. Additionally, photoluminescence intensity was linked to saturation current density and open-circuit voltage using diode and recombination models.
The results indicated that ultraviolet-B irradiation causes severe degradation on both the front and rear sides of PERC cells, whereas dark-annealed samples remained unchanged, confirming that heat alone does not account for the effects. The front side, passivated only by silicon nitride, experienced the most significant deterioration, while the rear side was moderately impacted. For TOPCon cells, ultraviolet-B exposure led to notable degradation on the front surface, but the rear side stayed largely stable due to UV absorption by the polycrystalline silicon layer. Overall, both technologies demonstrate that UV-induced degradation primarily occurs at exposed silicon-dielectric interfaces.
The scientists concluded that UV-induced degradation heavily depends on surface structure and passivation design. The PERC front surface is especially susceptible because of its simpler passivation approach, whereas the TOPCon rear is shielded by UV-absorbing layers. Degradation is linked to the exposure of the crystalline silicon-dielectric interface to ultraviolet radiation.
Hoex remarked that this work helps connect earlier chemical-hydrogen-based UVID models with a more comprehensive electronic-recombination-based understanding of degradation processes in modern silicon solar cells. Prior UNSW research on UVID found that thicker aluminum oxide layers enhance UV resistance by restricting hydrogen movement, providing direction for more durable TOPCon designs. Another study also cautioned about unexpected UV-induced degradation in TOPCon solar cells from invisible light.
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