Undoped and nitrogen-doped titanium dioxide (TiO2) thin films of 400 nm thick deposited by spray pyrolysis were structurally and optically characterized. The effect of substrate temperature on the optical properties of the films was also investigated. Structural studies of the films were undertaken by X-ray diffraction (XRD). Energy dispersive X-ray (EDX) spectrum analysis was used to confirm the presence of nitrogen atoms in the film after doping. The optical properties such as refractive index (n), energy band gap (Eg) and Urbach energy (Eu) were determined from spectrophotometric measurements of reflectance and transmittance for both undoped and doped films. The Undoped films had an energy band gap of 3.25 eV while the doped films had band gap of 2.90 eV. The Urbach energy increased from 1.00 eV for undoped films to 1.04 eV for the nitrogen-doped films. The reduction in energy band gap and increase in Urbach energy was attributed to the introduction of nitrogen impurity tail states on either the conduction band or the valence band of the titanium dioxide.
A new highly structured system based on TiO 2 /In(OH) x S y /PbS/PEDOT:PSS/Au has been developed for photovoltaic applications. In this device, TiO 2 , In(OH) x S y , PbS and PEDOT:PSS serve as electron conductor, buffer layer, absorber and hole conductor, respectively. Both buffer and absorber layers have been prepared by chemical bath deposition. For annealed In(OH) x S y , an optical band gap of 2.2 eV has been obtained and for PbS the bulk value is widened to about 0.85 eV due to the presence of oxide in the film composition. At present stage, solar cells with such configuration have reached up to about 1% efficiency with J sc = 8 mA/cm 2 and V oc = 0.3 V.
Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique. Optimization has been done by doping SnO2 with palladium at varying levels of concentration and then recording sheet resistance. The sheet resistivity has been observed to decrease gradually as at% Pd concentration is increased; an optimum sheet resistivity value of 2.71 × 10 −2 Ω cm has been recorded. The decrease in sheet resistivity has been attributed to presence of Pd ions which contribute in increment of charge carrier density. Using the optimum value of at% Pd doping, the same procedure has been repeated to study the effect of fluorine on Pd:SnO2; an optimum value of 1.64 × 10 Ω cm which is attributed to effects resulting from annealing the samples in nitrogen gas atmosphere.
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