Effect of Temperature on Optical and Photovoltaic Properties of nc-TiO2 Thin Films for Dye Sensitized Solar Cell

In this investigation, anatase nanocrystalline TiO2 (nc-TiO2) films are deposited by using sol-gel dip coating method on ITO substrates followed by annealing at 200, 300, 400 and 500 °C / 2 hr in air. To examine the structure and morphology of films, XRD, Raman spectroscopy, SEM and HRTEM techniques are used. The XRD studies showed the evolution of pure anatase TiO2 phase with average crystallite size = 12-15 nm in resultant films. The morphological studies using SEM and HRTEM indicated ~ uniform size distribution of spherical agglomerates in films and nanocrystalline state of films (average particle size ~ 20 nm) respectively. The optical properties calculated from UV-Visible transmission spectra are found to be indirect band gap energy = 3.20 eV, absorbance coefficient = 9.2 x 104 cm-1, transmittance = 88.5 %, refractive index = 2.12 and porosity ratio = 36.6 % for the 400 °C annealed film. The better photovoltaic performance: JSC = 2.34 mA/cm2, VOC = 0.562V, FF = 35.23 % & η = 0.46 % is obtained for eosin-Y dye sensitized solar cell made with 400 °C annealed film.