Created by E.Ö., SUPSI, on 27.11.2025
Photovoltaic (PV) modules are exposed to various environmental stressors throughout their lifetime, as highlighted in Alpine PV Stressors, among which ultraviolet (UV) radiation is one of the most critical. High levels of both total irradiance and UV irradiance are typical at elevated altitudes. With increasing altitude, not only does the overall irradiance rise, but the UV portion of sunlight also becomes more significant. In addition, snow surfaces strongly reflect UV radiation, further intensifying exposure.
Consequently, PV modules operating at high altitudes, particularly in snowy environments, are subjected to substantial UV stress. Prolonged exposure to UV radiation can cause long-term degradation of both the module materials and the solar cells. Over time, this UV-induced degradation can reduce system efficiency, compromise material integrity, and ultimately affect both performance and long-term reliability.
The UV-induced degradation occurs at the PV module material and PV cell levels, as explained in more detail below.
UV-Induced Degradation of PV Materials
The materials used in the construction of PV modules, particularly the polymer-based materials such as encapsulants and backsheets, can be vulnerable to UV radiation. These materials serve critical functions, including the protecting the solar cells and ensuring their durability. UV degradation primarily occurs due to absorption of UV light, leading to chemical reactions that alter the structure of these materials.
UV radiation can break down the polymer chains within encapsulant material, resulting in their deterioration. This degradation may lead to yellowing, which in turn reduces the material’s transparency (Figure 1). This can also compromise the structural integrity of the whole PV module, potentially leading to accelerated delamination, which is often followed by moisture ingress and corrosion. Depending on the encapsulant type, degradation byproducts such as acetic acid may be produced during encapsulation degradation, which can oxidize the metallic contact of the solar cell, increasing series resistance and further degradation in performance.
Figure 1: (left) Slightly browned EVA in the centre of the cell with photobleaching at the edges. (right) Encapsulant delamination near cell edges in combination with cell browning [1].
Prolonged exposure to UV light can lead to the degradation of the backsheets, resulting in yellowing and delamination, which diminishes its protective qualities (Figure 2). Additionally, this degradation can cause the backsheet to become brittle and the formation of microcracks, compromising the overall structural integrity of the module.
Figure 2: (left) Discolouration of the backsheet and front delamination. (right) Delamination of the top layer of the backsheet [1].
UV-Induced Degradation of Solar Cells
In addition to the degradation of module materials, UV radiation can also impact the solar cells, affecting their electrical performance and long-term efficiency. Most PV modules use crystalline silicon (c-Si) solar cells. Apart from Al-BSF, the most common types of c-Si solar cells – such as passivated emitter and rear contact (PERC), tunnel oxide passivating contact (TOPCon), heterojunction (HJT), interdigitated back contact (IBC), and passivated emitter rear totally diffused (PERT) solar cells – are vulnerable to UV-induced damage to varying extents [2,3,4] (Figure 3 and Figure 4). Moreover, the rear sides of bifacial cells have been found to be more susceptible to UV-induced degradation than the front sides, likely due to differences in the surface field and passivation techniques applied on the front and rear sides.
High-energy UV photons can degrade solar cells through several mechanisms. They can directly break Si–H bonds that initially passivated the cell surface, leading to the formation of recombination-active dangling bonds [5,6]. Sinha et al. observed an increased concentration of hydrogen (H) near the passivation/Si interface and within the Si bulk [2]. This occurs due to the breaking of hydrogen bonds that initially passivated the cell surface, leading to the formation of excess hydrogen atom clusters. These clusters facilitate carrier recombination, which ultimately deteriorates the cell’s performance.
Figure 3: Final change in I–V parameters of test cells after 2000 hours of UV exposure testing, partitioned by cell technology and cell type. The data corresponding to rear-side exposure of bifacial cells is indexed as +. The same side of the cell was illuminated during the I–V measurements as it was facing the UV lamps in the screen test. This shows the UV sensitivity of the front and rear sides of the bifacial cell. As a guide to the eye, a 0% change is indicated by a red dotted line. The 25%–75% confidence intervals are denoted by boxes, and the mean and median are indicated by a square and crossbar, respectively [2].
Figure 4: Loss in implied maximum power point voltage iVmpp due to front UV exposure as a function of the dose for the best- and worst-performing groups of each cell technology. The top axis shows the equivalent outdoor exposure time for modules stationed in the Negev desert [3].
UV induced degradation of junction box and cables
Over time, prolonged UV radiation can cause junction boxes, its adhesives used and cable insulation to degrade, embrittle, crack, or discolour. This can expose internal conductors, reduce insulation resistance, and increase the risk of moisture ingress, electrical leakage, and connector failure. Junction box adhesives and seals can also lose flexibility or detach under strong UV exposure, leading to detachment or water penetration.
Long-Term Effects and Performance Loss
The cumulative effect of UV degradation on PV modules is a gradual decline in performance. As the materials in the module degrade, the overall efficiency of the system decreases, which can shorten the operational lifetime of the PV module. The combination of material degradation (such as yellowing of the encapsulant or cracking of the backsheet) and solar cell degradation (such as increased recombination) leads to increased performance losses over time.
UV-induced degradation is not uniform across all regions of the world, as modules in locations with high UV exposure, such as areas closer to the equator or high-altitude regions, may experience faster degradation than those in areas with less UV exposure. This variability means that the design of PV modules must take into account regional UV exposure to enhance long-term durability. Although module temperature do not directly influence UV-induced degradation of solar cells, higher temperatures do accelerate the UV-induced degradation of module materials.
Mitigation Strategies
- High UV resistant encapsulants: Develop and use encapsulant materials with enhanced UV stability to resist discoloration and degradation.
- More durable backsheets or Glass/Glass modules: Select backsheet materials that are less susceptible to UV-induced cracking, chalking, or embrittlement. Another possibility is using Glass/Glass modules instead of Glass/Backsheet modules.
- UV filtering through module components: Since UV photons must reach the c-Si surface to cause cell-level damage, mitigation can involve increasing UV absorption or reflection within the module BOM, such as the module glass, encapsulant, or coatings.
- Encapsulant with UV photon downshifting: An alternative approach is to convert (downshift) UV photons into visible light, which both protects the underlying materials and may improve overall module performance
- Consideration of material trade-offs: Increasing UV absorption within the BOM can shift degradation to these materials, so the balance between protection and material stability must be considered [7].
- UV-resistant cables: Use UV-resistant cable jackets certified for long-term outdoor exposure.
- UV-stabilized junction boxes: Select junction boxes made from UV-stabilized polymer materials suitable for high-irradiance environments.
- UV-rated connectors: Ensure that connector housings and seals are also UV-rated, not just the cables.
- Cable routing: Avoid routing cables in locations where they are directly exposed to sunlight over long distances; instead, use cable trays or place cables in shaded areas behind modules whenever possible.
- Mechanical protection: Provide proper strain relief and avoid tight bends so that any embrittled insulation does not crack under tension over time.
- Durable adhesives and potting compounds: Verify that adhesives and potting materials used in junction boxes are certified for UV and temperature cycling stability.
References
[1] IEA PVPS Task 13, Photovoltaic Failure Fact Sheets (PVFS), 2025, doi: 10.69766/CKCD1805
[2] Sinha A, Qian J, Moffitt SL, et al. UV-induced degradation of high-efficiency silicon PV modules with different cell architectures. Prog Photovolt Res Appl. 2023; 31(1): 36-51. doi:10.1002/pip.3606
[3] Thome, F.T., Meßmer, P., Mack, S., Schnabel, E., Schindler, F., Kwapil, W. and Schubert, M.C. (2024), UV-Induced Degradation of Industrial PERC, TOPCon, and HJT Solar Cells: The Next Big Reliability Challenge?. Sol. RRL, 8: 2400628. https://doi.org/10.1002/solr.202400628
[4] P. Gebhardt, E. Fokuhl, S. S. Mujumdar, H. Frey, A. Beinert, A. Stöhr, M. Kaiser and I. Hädrich, “Stabilization Procedures for TOPCon PV Modules after UV‑Induced Degradation,” Solar Energy Materials & Solar Cells, vol. 294, art. no. 113885, 2026. doi: 10.1016/j.solmat.2025.113885.
[5] Ye, H., Huang, S., Qian, C., Sun, Z., Chen, Y., Song, X., Zhang, Y., Wang, N., Hu, Y., Yang, Y., Li, L., Ma, Z., Chen, T., Liu, W. and Yu, J. (2023), Short Wavelength Photons Destroying Si–H Bonds and Its Influence on High-Efficiency Silicon Solar Cells and Modules. Sol. RRL, 7: 2300334. https://doi-org.proxy2.biblio.supsi.ch/10.1002/solr.202300334
[6] T. Kamioka, D. Takai, T. Tachibana, T. Kojima and Y. Ohshita, «Plasma damage effect on ultraviolet-induced degradation of PECVD SiNx:H passivation,» 2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), New Orleans, LA, USA, 2015, pp. 1-3, doi: 10.1109/PVSC.2015.7356326.
[7] Pinochet N, Couderc R, Therias S. Solar cell UV-induced degradation or module discolouration: Between the devil and the deep yellow sea. Prog Photovolt Res Appl. 2023; 31(11): 1091-1100. doi:10.1002/pip.3725
