Ultraviolet (UV) radiation can affect the long-term reliability of TOPCon solar cells and module materials. Prolonged exposure can also cause yellowing and make polymer encapsulants brittle. Conventional UV-absorbing encapsulants help protect these components, but they also prevent some of the absorbed light from contributing to electricity generation.
Researchers from the University of Ljubljana, École Polytechnique Fédérale de Lausanne (EPFL), and CSEM in Switzerland have studied an alternative approach using UV down-shifting (UVDS) layers that convert absorbed UV radiation into longer-wavelength light. Published in Solar Energy Materials and Solar Cells, the study titled Optical Modelling and Energy-Yield Assessment of UV Down-Shifting Layers for High-Efficiency TOPCon Solar Modules examines how these layers affect the performance of TOPCon solar cells and modules.
For the study, the team prepared encapsulation films by mixing light-converting dyes into polyolefin elastomer (POE). They measured how the films absorb and emit light to understand their optical properties.
The team then used an optical simulation tool called CROWM (Combined Ray Optics/Wave Optics Model) to study how light travels through the encapsulation layers and solar cells. They extended the model to account for UV absorption, light emission, and the possibility of emitted light being absorbed again. The simulation results agreed well with measurements from TOPCon mini-modules.
Lower Photocurrent Losses With UVDS
The simulations showed that UVDS layers capable of absorbing around 90% of incident UV radiation could limit photocurrent losses to below 1%. In one comparison, a comparable UV-blocking layer without light re-emission reduced the short-circuit current density by 1.77%, while a UVDS layer with similar UV absorption limited the loss to 0.20%. The researchers also found that UVDS layers could provide photocurrent gains of more than 2% compared with conventional UV-blocking materials offering similar protection.
Potential Long-Term Energy Benefits
The team also examined how these layers could affect electricity generation over 10 years, using simulations for Minneapolis and Phoenix in the US. The calculations assumed that an unprotected solar cell would experience a 6% voltage loss over 10 years due to UV-induced degradation (UVID), while cells with UVDS layers would remain fully protected. Under these conditions, the initial performance loss of around 1% could be offset by more than 4% additional cumulative energy production over the simulated period.
The study also considered practical module features, including busbars and gaps between cells. The results indicated that some UV light absorbed above these areas could be converted into longer-wavelength light and redirected towards active cell regions. This could help recover a small amount of light that would otherwise be lost.
The 10-year energy-yield calculations were based on simulated degradation rather than field measurements. The researchers also considered how UVDS layer performance might change as the light-converting dyes age. Their analysis showed that reduced light-conversion efficiency could lower the energy benefits over time.