Effect of Cr-doping on the physicochemical properties of blue TiO2 and its application in dye-sensitized solar cells via low-temperature fabrication process

Abstract

Cr-doped blue TiO2 (Cr-BTiO2) nanoparticles were fabricated at room temperature using lithium-ethylenediamine (Li-EDA) as reducing agent. The addition of Li-EDA promotes the selective reduction of the rutile phase of TiO2 into the amorphous phase keeping anatase phase unaltered. Hence, the phase-selective reduction of TiO2 leads to the formation of blue TiO2 nanoparticles. Synthesized samples were characterized by equipment fitted with modern technology. The shifting of (101) peak to a lower angle (2θ) in Cr-BTiO2 in X-ray diffraction (XRD) pattern suggests the successful doping of chromium into TiO2 lattices. In Raman spectra, the shifting of the active Eg peak of Cr-BTiO2 nanoparticles to higher wavenumber also suggests the successful substitution of Ti by Cr. The blue TiO2 and Cr-BTiO2 show increased absorption of light in the visible region compared to TiO2 (P25). The modified TiO2 samples have improved electron-hole separation tendency as predicted by the photoluminescence spectra (PL). Also, doping of Cr- into TiO2 lattice results the formation of oxygen vacancy as detected by X-ray photoelectron spectroscopy (XPS). Among all samples, Cr-BTiO2 demonstrated improvement in Jsc and overall incident photon to current conversion efficiency. Therefore, the synthetic effect is thus responsible for the enhancement in efficiency of Cr-BTiO2 towards the dye-sensitized solar cell (DSSC) by 2.5 and 1.5 times higher than the P25 and blue TiO2, respectively.