D. Beena

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

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 f...

Transparent and low resistive nanostructured laser ablated tungsten oxide thin films by nitrogen doping: II. Substrate temperature

Nitrogen incorporated tungsten oxide thin films are deposited onto fused quartz substrates at various substrate temperatures (Ts) in nitrogen ambient (pN2) of 12 Pa by pulsed laser deposition. The structural, optical and electrical properties of the deposited films are found to depend on the substrate temperature/nitrogen doping concentration. Compositional analysis by energy dispersive x-ray spectra confirms the incorporation of nitrogen into the films, with maximum nitrogen incorporation for films deposited at Ts = 973 K. X-ray diffraction analysis reveals an orthorhombic crystalline phase for the WO3 : N films deposited at Ts = 300, 873 and 973 K, with a nanocrystalline structure for the films prepared at intermediate growth temperatures. Morphology investigation of WO3 : N films in relation to substrate temperature/nitrogen doping is done by scanning electron microscopy and atomic force microscopy. Vibrational properties of the WO3 : N films are measured using micro-Raman spectroscopy. Bandgap of WO3 : N films decreases from 3.31 ± 0.04 to 2.85 ± 0.03 eV and room temperature resistivity decreases from 1.77 × 103 to 4.3 × 10−2 Ω m with change in substrate temperature/nitrogen content. Analysis of optical and electrical properties reveals that the incorporated nitrogen acts as an electronic dopant in WO3. Narrow bandgap, low dc resistivity at room temperature and average transmittance in the visible range, observed for the films deposited at higher substrate temperatures (873 and 973 K), make very interesting prospects for technological transfer, especially as novel solar cell materials.