The new heterojunction solar module concept is based on co-extruded EVA/POE/EVA (EPE) encapsulant with UV downshifting (UV-DS) films, which convert harmful UV light into blue light, protecting cells and slightly boosting short-circuit current by 1.5–1.75%.
March 4, 2026
Emiliano Bellini
Researchers at France’s National Solar Energy Institute (INES) – a division of the French Alternative Energies and Atomic Energy Commission (CEA) – and 3SUN, the PV module manufacturing unit of Italian renewable specialist Enel Green Power (Enel Group), have fabricated mini HJT PV panels based on a co-extruded EVA/POE/EVA (EPE) encapsulant containing ultraviolet (UV) downshifting films (UV-DS), which convert harmful UV photons into blue light.
“These encapsulants were conceived as a preventive solution against UV-induced degradation, a critical challenge for advanced photovoltaic technologies such as TOPCon and HJT,” the reseach’s corresponding author, Maxime Babics, told pv magazine. “The sun’s ultraviolet (UV) rays are not only harmful to human skin, they are also harmful to photovoltaic panels, causing power losses and premature deterioration of solar installations.”
The researchers explained that the EPE encapsulant is a co-extruded multilayer EPE film composed of a polyolefin elastomer (POE) core sandwiched between two ethylene vinyl acetate (EVA) layers, with clear interfaces and no intermixing after lamination. It incorporates a benzotriazole-based UV downshifting (UV-DS) additive at 0.5–2 wt%, which absorbs UV photons between 250–400 nm and re-emits visible light from 380–550 nm, with a photoluminescent quantum yield of around 95%.
These properties allow the encapsulant to protect solar cells from UV damage while slightly increasing the short-circuit current by 1.5–1.75% compared to conventional UV-cut films, according to the research team. The EPE structure also provides mechanical robustness, with high adhesion and gel content, remaining intact after damp heat and thermal cycling tests.
The EPE multilayer encapsulant was laminated between glass layers on both front and back sides of mini HJT panels based on half-cut cells.
Mechanically, the modules were found to be robust, showing high adhesion between encapsulant layers, glass, and backsheet, with no delamination observed even after damp heat and thermal cycling. The modules also exhibited power output gains of around 7 W per module compared to those with conventional UV-cut encapsulants, with open-circuit voltage and fill factor remaining largely unchanged.
The outdoor testing also demonstrated that the energy gain is highly dependent on UVA irradiance, reaching 2–2.5 % in summer months and decreasing in winter. Moreover, the modules maintained optical and additive stability, although some high-energy UVB photons still penetrate, and additive migration at edges can occur over time, which is mitigated by proper sealing.
“Short-circuit current gain exceeded 1.5% compared to conventional UV-Cut encapsulants under Standard Test Conditions (STC),” states Babic. “The impact of the light source on the power gain is discussed since different equipment with different light spectra can yield varying results. Outdoor monitoring during several months confirms the energy gain and reveals it is highly dependent on the daily UVA content, with higher gains observed during summer months when UV content in the solar spectrum is at its peak.”
“The study addressed critical reliability and industrial aspects, such as encapsulant adhesion before and after ageing, lamination time and temperature affecting encapsulant gel content and production capacity, and the potential savings from lower EPE prices compared to pure POE,” he went on to say. “Notably, the presence of UV-DS additives did not induce new types of degradation in damp heat up to 3000 hours, and the presence of EVA in the EPE structure in contact with the solar cells did not affect the reliability when compared to pure POE encapsulant.”
The research team is optimistic about the future applications of UV-DS encapsulants, particularly in regions with high UV irradiation, where their benefits are most pronounced. “We are now working on an energy yield model based on local spectral conditions, ensuring accurate predictions of annual outdoor performance gains,” Babic concluded.
The new mini modules were described in “Performance and Reliability of PV Modules Made With Novel Co-Extruded Encapsulant Containing UV Downshifting Compound,” published in Progress in Photovoltaics.
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