Oxalate-assisted morphological effect of NaYF4:Yb3+,Er3+ on photoelectrochemical performance for dye-sensitized solar cells

Abstract

In this study, we have employed a facile oxalate-assisted hydrothermal approach to tailor the morphology of β-NaYF4:Er3+,Yb3+ (NYFEY) powders through the variation of the molar ratio of oxalate ions (Oxa2−) and rare earth ions (RE3+) in the range of 0.5:1, 1:1, 2:1, 5:1, and 10:1. The obtained results show that the crystallinity, particle size and upconversion luminescence intensity of the as-synthesized NYFEY particles are gradually decreased as the Oxa2−:RE3+ molar ratio increases from 0.5:1 to 10:1. For the purpose of photoelectrochemical performance evaluation, the as-synthesized NYFEY particles with different morphologies are incorporated into the nanocrystalline TiO2 films to form the multifunctional nano- and sub-micrometer composite photoanodes of dye-sensitized solar cells (DSSCs). A short-circuit current density (JSC) of 14.26 mA/cm2 and power conversion efficiency (PCE) of 7.31% are obtained for DSSCs prepared with hexagonal rod-like NYFEY crystals, evidencing an increase of 29.8% compared with DSSCs prepared with only TiO2 nanoparticles. The demonstrated synthesis approach for tailoring the morphology and size of NYFEY particles and enhancing the performance of DSSCs can also be applied for other types of solar cells.