Bandgap renormalization in titania modified nanostructured tungsten oxide thin films prepared by pulsed laser deposition technique for solar cell applications

Abstract

Pure and titania modified WO3 films are prepared using pulsed laser ablation technique in an oxygen ambient of 0.12mbar at a substrate temperature of 873K. Titania incorporation effects on the microstructure, optical, and electrical properties on the tungsten oxide films are systematically investigated using techniques such as x-ray diffraction, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, micro-Raman spectroscopy, and UV-visible absorption spectroscopy measurements. The resistivity measurements of the pure and titania modified WO3 films are done at room temperature. The variation of resistivity with temperature for the range of 170–450K is also investigated. The microstructural analysis indicates that titania addition strongly perturbs the tungsten oxide lattice and suppresses the grain growth. Optical measurements revealed a bandgap renormalization in tungsten oxide films for higher titania concentrations. Bandgap values of the films decrease from 3.17eV for pure WO3 to 2.7eV for 10wt% TiO2 modified WO3 films. The shifting of photoresponse of WO3 films to visible range by titania incorporation throw light on the feasibility of their application in visible-light-driven photocatalysis and in solar cells. All the films show semiconducting behavior in their temperature dependence of resistivity.