Enhanced light harvesting in dye‐sensitized solar cells enabled by TiO 2 :Er 3+ , Yb 3+ upconversion phosphor particles as solar spectral converter and light scattering medium

Abstract

To improve the light-harvesting properties of dye-sensitized solar cells (DSSCs), light from the ultraviolet (UV), visible, and infrared (IR) regions of the solar energy should be effectively harvested. Ru(II)-based dyes play a key role in harvesting energy from parts of the UV and visible regions but cannot absorb IR light. A strategy for improving the DSSC efficiency is to employ upconversion phosphors (UCPs) that can convert IR into visible light. In this study, using TiO2:Er3+, Yb3+ UCPs fabricated via a simple aerosol process and calcination, we examine the effects of upconversion and light scattering of UCPs added into the TiO2 thin-film-based photoelectrode on DSSC efficiency. Under IR irradiation, the fabricated TiO2:Er3+, Yb3+ UCPs emit visible light with emission peaks at 529, 550, and 650 nm. The power conversion efficiency (PCE) of the DSSCs is significantly improved by adding the optimized amount of UCPs with the average size of 500 nm in the TiO2 nanoparticles (NPs) matrix with the average size of 25 nm due to light upconversion and scattering effects. However, the addition of excess UCPs deteriorates the DSSCs efficiency owing to the rapid recombination between photogenerated electrons and holes and the increased interfaces between UCPs and TiO2. These results suggest that the light-harvesting efficiency of DSSCs in the IR region can be enhanced by employing the optimal amount of large-sized UCPs as light upconversion and scattering medium in the TiO2 thin-film-based photoelectrode.