Fluorescent Pigments for Application in Downshifting Ultraviolet Light

Although silicon and perovskite solar cells have achieved efficiency surpassing 26 %, several factors still limit achieving higher efficiency. One proposed mechanism to circumvent this limitation is using wavelength shifter materials to use ultraviolet light better. Here we investigate the properties of thin film of low-cost photoluminescent pigment currently used in coatings, graphic arts, cosmetics and adhesives. The aim was to evaluate the capability of shifting the ultraviolet light to the wavelength where silicon solar cells are more efficient (around 600 nm). Precursor solutions were prepared by dissolving the pigments in ethanol. Thin film deposition was performed by spin-coating technique with good uniformity. After each deposition, the substrates were placed on a heating plate to evaporate the solvent. The pigments were characterized by X-ray diffraction, AFM, UV-Vis transmittance, and photoluminescence. The XRD diffractograms are compatible with the expected structure of organic pigments. Photoluminescence measurements show the PL emission covers a range of 500 – 650 nm, which is in the region of the highest efficiency of silicon solar cells. UV-Vis spectra show absorption bands related to specific pigment structures. The absorption occurs in the wavelength range from 300 to 700 nm, being more intense in the UV range. This absorption corresponds to the one associated with converting UV light to visible light. The PL emission, on the other hand, is shifted to the 550 to 700 nm range. This result shows that the film made of pigment, deposited by spin coating, works as a wavelength shifter.