Studies on up-converting Ho 3+ -Yb 3+ -F − tri-doped TiO 2 nanoparticles for enhancing efficiency of dye-sensitized solar cells

Abstract Titanium dioxide (TiO2) nanoparticles (NPs) tri-doped with different concentrations of Ho3+, Yb3+ and F− ions (abbreviated as UC-F-TiO2 NPs) were synthesized for applications in dye-sensitized solar cells (DSSCs). These UC-F-TiO2 NPs were synthesized using hydrosol−hydrothermal method. The phase structure, morphology and luminescent property of UC-F-TiO2 NPs are characterized using X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy and photoluminescence (PL) spectroscopy. The results indicated that the UC-F-TiO2 NPs are mixed phases of anatase and rutile with approximate sizes in the range from 10 to 15 nm. Photoluminescence (PL) measurements confirmed that the UC-F-TiO2 NPs have a good up-converting (UC) property. The prepared powders were used to make photo-anodes for DSSCs. The DSSCs assembled with a bilayer-structured UP-F-TiO2 NP photo-anode has a 15.2% enhancement in short-circuit current density and a 29.7% enhancement in conversion efficiency comparing with DSSCs assembled with un-doped TiO2 photo-anodes. The photocurrent improvement is due to an increase in the light-harvesting capacity of the photo-anodes attained through the up-converting property of UC-F-TiO2 NPs, which was demonstrated by PL and IPCE measurements. The result suggests that the incorporation of up-converting nanoparticles into photo-anode is an effective approach to improve the photovoltaic characteristics of DSSCs.