Thickness dependent optical and eosin-Y sensitized solar cells characteristics of nc-a TiO_2 films

摘要

Herein, we report the thickness dependent optical and eosin-Y dye sensitized solar cell (DSSC) characteristics of nanocrystalline ana-tase (nc-a) TiO_2 films deposited on indium tin oxide (ITO) substrates by using sol-gel dip-coating method with C_(12)H_(28)O_4Ti (TTIP) (0.05 and 0.10 M) as Ti-precursor. The as-deposited films were heated at 400 ℃/2 h in air. The XRD and Raman spectroscopy characterization studies revealed the formation of pure single anatase TiO_2 phase in resultant films. The HRTEM studies reflected uniform size distribution of spherical TiO_2 nanoparticles (average size ～20 nm) with crystalline grains of diameters = 15-20 nm in a structured matrix. This is consistent with XRD results of crystallite size = 10-25 nm. A profound effect of variation of film thickness on optical and eosin-Y sensitized photovoltaic characteristics of nc-a TiO_2 films is observed. With increasing the film thickness, the % optical transmission (T), absorption coefficient (α), refractive index (n) and optical conductivity (σ_(opt)) are found to be decreasing whereas, porosity ratio (% P) and photoconversion efficiency (η) are found to be increasing. The optical indirect band gap is found to be between 3.20 and 3.21 eV. The better photovoltaic performance: open-circuit voltage of 0.554 V, short circuit current of 1.291 mA, fill factor of 41.57% and conversion efficiency (η) of 1.10% is obtained for eosin-Y DSSC using redox polyiodide (1 M KOH + 1 M KI + 0.5 M iodine) electrolyte in actonitrile.