SPIE presents transparent spectral converter to enhance solar cell performance

SPIE, the International Society for Optics and Photonics, has published research on an ultraviolet-wavelength-driven solar spectral converter that can be placed on top of photovoltaic cells to boost their performance.

The converter is based on a GdPO₄ glass-ceramic (GC) material doped with praseodymium (Pr) and europium (Eu) ions. This new material, dubbed GdPO₄-GC:Eu³⁺/Pr³⁺,  can reportedly absorb UV photons from solar radiation and re-emit them as visible (VIS) light.

“This is possible thanks to the efficient energy transfer that happens between the ions in the material,” the researchers said. “When a UV photon hits a Pr³⁺ ion, it generates an excited electronic state. This accumulated energy has a high chance of being transferred to a Gd³⁺ ion, which releases some of it before transferring the rest to a Eu³⁺ ion. As a result, excited electronic states in the Eu³⁺ ion undergo a down transition to lower energy states, emitting visible light.”

The scientists developed a 2 mm thick converter sample synthesized via the melting quenching (MQ) process, a traditional technique of glass making.

They then tested its performance under standard illumination conditions on a solar cell based on amorphous silicon and a perovskite solar cell in an air-conditioned laboratory with a temperature of 20 C to 25 C and a relative humidity level of 30% to 40%. The converter was attached to the cells with index-matching liquid immersion oil to reduce the light loss.

Through these measurements, the academics found that the converter simultaneously absorbs UV solar photons and then emits VIS photons, which they said is in the spectral response (SR) region of the amorphous silicon device. “Incident light harvesting is critical for the efficiency of amorphous silicon solar cells,” they further explained.

The scientists said the converter was able to increase the cells' short-circuit current compared to reference devices without cover or UV filters, and added the efficiency of both cells was “effectively” improved thanks to the optimized spectral distribution. They also explained that the novel converter may be used as a protective layer in solar cells that can keep high thermal and chemical stabilities in space.

The converter was introduced in the paper “Ultraviolet-wavelength driven solar spectral converter for photovoltaic cell application,” in Journal of Photonics for Energy.

“More studies will be needed to further improve the efficiency of solar cells using doped GC materials as spectral converters,” the research team concluded. “Future work could focus on improving cost-effectiveness by adjusting doping concentrations and optimizing the thickness of the protective layer.”