As the solar industry accelerates toward higher efficiency and longer operational lifespans, heterojunction (HJT) solar technology has emerged as a leading candidate for next-generation photovoltaic systems. However, a persistent technical hurdle-ultraviolet (UV)-induced degradation-has limited the real-world durability of HJT modules. Now, a new wave of innovations centered on UV downshifting and UV blocking is poised to overcome this bottleneck, unlocking the full potential of HJT cells for mass deployment.
Heterojunction solar panels consist of crystalline silicon paired with thin layers of amorphous (non-crystalline) silicon. As a result, these panels have a high efficiency gain/loss and improved temperature characteristics more than traditional PERC panels (passivated emitter, rear cell) solar panels. Still, the HJT's (heterojunction) UV sensitivities are still an issue HJT cells and their sensitive interface layers (e.g., TCO - transparent conducting oxide) are both affected by accelerated aging when exposed to high-energy UV photons. In addition, the HJT cell's charge carriers may have less charge collected by the HJT cells with the increased loss of charge carriers and/or an increase in charge carrier recombination rates will cause a decrease of power output from those HJT cells.
Establishing solutions for mitigating the UV radiation damage to the HJT panel structure, researchers and manufacturers have worked together on two separate strategies for improving the HJT panel's optical performance, which will help to mitigate the UV damage to the HJT panel structure. The strategies are complementary to the other, in terms of how each one prevents the ultraviolet light from causing damage to the HJT panel's structure.
UV Downshifting: Converting Harmful Rays into Useful Light
UV downshifting involves integrating specialized luminescent materials-often rare-earth-based phosphors or advanced quantum dots-into the encapsulant or front encapsulant layer of the module. These materials absorb high-energy UV photons (typically 280–400 nm) and re-emit them as lower-energy, visible light (usually green, yellow, or red), which HJT cells can efficiently convert into electricity.
According to Dr. Elena Marchetti, a senior photovoltaics researcher at the European Solar Innovation Center, "Downshifting effectively turns a parasitic degradation pathway into a performance asset. Instead of letting UV photons damage the TCO or a-Si:H layers, we convert them into useful photons that contribute to current generation." Early field tests have shown that modules with optimized downshifting encapsulants can reduce UV-induced degradation by up to 65% while gaining 1.5–2.8% in short-circuit current due to the additional converted visible light.
Recent breakthroughs include the use of europium-doped organometallic frameworks and lead-free perovskite quantum dots that offer high photoluminescence quantum yields and excellent long-term stability. These downshifting layers are being integrated into both ethylene-vinyl acetate (EVA) and polyolefin elastomer (POE) encapsulants, without compromising optical clarity or adhesion.
UV Blocking: A Selective Barrier Approach
UV blocking is done by keeping the UV photons from ever reaching the sensitive cell layers of the module, making it a more direct way to achieve this goal but simply using standard UV absorber is not adequate. Conventional blockers typically reduce solar resource for power generation by cutting out part of the blue-violet spectrum area (less than 450 nm).
Next-generation UV-blocking films use multilayer interference coatings or hybrid organic-inorganic barriers that selectively reflect or absorb UV light (280 nm to 380 nm), while allowing >95% of visible and near infrared light (400 nm to 1200 nm) to pass. These films can be added to the front glass of the solar module or as an independent interlayer.
An example of this technology is the UV-blocking coated front glass developed jointly between Fraunhofer Institute for Solar Energy Systems and a large glass manufacturer. This UV blocking coated front glass reduces UV transmission to <3% of the total incident light while maintaining 96% of the visible light transmission. Accelerated aging tests (IEC 61215) using HJT modules with UV-blocking front glass show that the retained power after 2,000 hours of UV exposure is 94% as compared with only 79% for control modules with standard glass.
Synergy and Commercial Outlook
The latest developments in UV protection technology indicate that a combined approach involving both UV blocking films and downshifting encapsulants offers the best solution for maximizing the useful life and total energy yield of solar photovoltaic (PV) modules. The first level of protection is achieved by placing UV-blocking film on the surface of the PV module, which will eliminate most of the UV photons from entering through this layer. Any UV light that does penetrate through this barrier will be captured and converted to harmless visible light using a downshifting encapsulant. This two-layered design provides maximum protection to the PV module, resulting in both longer module life and increased total energy yield.
The following major manufacturers of PV equipment have begun pilot production of HJT modules with UV protection techniques: Various manufacturers in Europe and various manufacturers in China. According to early projections, the added material cost for these two UV protection techniques will be about $1.20 to $1.80 per HJT module; this extra material cost is expected to be compensated for by the increase in efficiency achieved by 0.8% to 1.5% and by extending the useful lifetimes of the modules from 25 years to 30 years or more. Thus, the use of HJT modules will reduce the levelized cost of electricity (LCOE) and provide a greater return on investment for utility-scale projects.
"UV downshifting and blocking are not just academic exercises anymore," says Mark Chen, product director at a leading Chinese HJT module maker. "They are mature enough for commercialization. We expect that by 2028, over half of all premium HJT modules will ship with some form of UV management technology."
Conclusion
As the solar energy sector strives to achieve 30% efficiency and 40-year module lifetimes, finding solutions to UV exposure deteriorating heterojunction modules is imperative. Dual progressions in downshifting luminescent materials along with more precise UV-Blocking coatings create a very clear and functional pathway to achieve this. By protecting the sensitive interfaces of HJT modules, these technologies help allow the next generation of solar farms, both in terms of longevity and energy output as well as providing cleaner electricity at lower costs. The time has come for True Durable Heterojunction Photovoltaics!
