# Luminescence Materials for Dye-Sensitized Solar Cells: Advances and Directions
## 4 Luminescent Materials in DSSCs
### Advances and Research  
It is possible to improve the efficiency of DSSC using luminescent materials [52; 53]. This allows absorbing light in the UV and NIR range, then converting to visible light within the absorption range of the dye sensitizer. Luminescent materials also improve the stability of DSSCs because it prevents the thermal degradation of the dye or the electrolyte due to the energy of the UV light. [PERSON] et al. [54] presented a simple oxalate-assisted hydrothermal method using oxalate assistance to produce nano- and micro-sized \(\beta\)-NaYF\({}_{4}\): Er\({}^{3}\), Yb\({}^{3+}\) (NYEY) powders with diverse morphologies, which can be applied in DSSCs. The hexagonal rod-shaped NYFEY produced good luminescent properties with a photovoltaic efficiency of 7.31%. Hence, the addition of the hexagonal rod-like NYFEY particles to the photo-anode, improved the performance of DSSCs when compared to those made solely with TiO\({}_{2}\) nanoparticles that yielded 5.63% efficiency. This is because the improved photo-anode better absorbs light, therefore increasing the light-harvesting efficiency. Research by [PERSON] et al. [55] demonstrated an efficient spray pyrolysis-assisted gas-phase aerosol technique to synthesize CaAl\({}_{2}\)O\({}_{4}\):Eu\({}^{2+}\), Nd\({}^{3+}\) phosphor particles. They successfully doped the CaAl\({}_{2}\)O\({}_{4}\) matrix particles with Eu\({}^{2+}\) and Nd\({}^{3+}\) after an additional H\({}_{2}\) reduction step. With the prominent emission peak observed at a wavelength of around 440 nm, it was discovered through luminescent emission spectrum measurement that the CaAl\({}_{2}\)O\({}_{4}\):Eu\({}^{2+}\), Nd\({}^{3+}\) phosphor particles created in the study played a crucial role in down-converting the UV radiation into visible blue light. Using DSSC photo-electrodes, they created TiO\({}_{2}\) pastes with different phosphor fractions to study the impact of the CaAl\({}_{2}\)O\({}_{4}\):Eu\({}^{2+}\), Nd\({}^{3+}\) phosphors on photovoltaic performance. With an increase in the CaAl\({}_{2}\)O\({}_{4}\):Eu\({}^{2+}\), Nd\({}^{3+}\) particle contents (\(\leq\)5 wt%) in the TiO\({}_{2}\) matrix, they observed that the \(J_{sc}\) and power conversion efficiency (PCE) of the DSSCs also increased. The photovoltaic performance of the DSSC was shown to be negatively impacted by the addition of an excessive amount of CaAl\({}_{2}\)O\({}_{4}\):Eu\({}^{2+}\), Nd\({}^{3+}\) phosphors (\(>\)5 wt%) to the TiO\({}_{2}\) matrix. The negative impact resulted from the faster recombination of photo-generated electrons with holes and the increase in grains and interfaces brought on by the increased phosphor doping, which further perturbed the charge carrier transport, thereby leading to a decrease in the efficiency. Therefore, based upon their research, it was possible to increase the DSSC PCE to 6.61% by adding 5 wt% of the CaAl\({}_{2}\)O\({}_{4}\):Eu\({}^{2+}\), Nd\({}^{3+}\) phosphors to the TiO\({}_{2}\) matrix, but the concentration of the phosphor beyond 5 wt% yielded a negative impact, which decreased the efficiency of the cell to 5.92% and 4.98% for 10 wt% and 20 wt%, respectively. [PERSON] and [PERSON]. [56] prepared a novel down-converting single-phase white light Pr\({}^{3+}\)-doped BaWO\({}_{4}\) nanophosphor materials for DSSC applications. The material was synthesized by the hydrothermal ultrasonic-assisted method. The X-ray diffraction (XRD) provided a confirmation of the tetragonal phase. A cubic structure measuring 10 nm in average length and 8 nm in average width was revealed by the transmission electron microscope (TEM) measurement. The values of the optical band gap increased as the Pr\({}^{3+}\) ion concentration increased. Three primary emission peaks were observed in the photo-luminescent spectra, which span the white region attributed to the \({}^{3}\)P\({}_{0}\rightarrow\)\({}^{3}\)F\({}_{2}\), \({}^{3}\)P\({}_{1}\rightarrow\)\({}^{3}\)H\({}_{5}\) and \({}^{3}\)P\({}_{0}\rightarrow\)\({}^{3}\)H\({}_{4}\) transitions.