'Li' doping induced physicochemical property modifications of MoO3 thin films

Undoped and lithium (Li) (1-5 wt%) doped MoO3 thin films were deposited over ITO coated glass substrates by spray pyrolysis at a substrate temperature of 325 degrees C. Undoped film was oriented along the < 0 k 0 > direction. The texture coefficient value of the undoped film was higher for the (0 2 0) plane compared to other planes of undoped and 'Li' doped films. The 100% peak (0 2 1) plane of orthorhombic MoO3 and hexagonal phase were induced upon doping with 'Li'. The crystallite size of the undoped film is less compared to the 'Li' doped films. The intense Raman peak at 996 cm(-1) is due to the terminal oxygen (Mo6+ = O stretching mode) in the orthorhombic alpha-MoO3 phase. The characteristic Mo 3d(5/2) and 3d(3/2) doublet caused by spin-orbit coupling are clearly resolved with a splitting of 3.1 eV in the XPS spectra. Scanning electron microscope (SEM) image shows a change in the microstructure, consistent with the change from alpha-MoO3 to mixed alpha and hexagonal phases. Sprout like features were observed in SEM image and rod like features in atomic force microscope (AFM) images. Both direct and indirect band gap showed red shift upon doping with 'Li' compared to undoped film as estimated from the transmittance spectra. Intensity of the green photoluminescence (PL) emission spectra was found to quench with 'Li' concentration. Cyclic voltammetry result shows that the presence of mixed phases in 'Li' doped films decreases the electrochemical performance. Transport study reveals that the carrier concentration and mobility of the 'Li' doped films are lower compared to the undoped film which is due to the evolution of hexagonal phase upon doping with 'Li'. A dye sensitized solar cell (DSSC) was fabricated using undoped MoO3 film as photoanode and its efficiency is calculated. (C) 2013 Elsevier B. V. All rights reserved.