EFFECTS OF TiO2 FILM THICKNESS AND ELECTROLYTE CONCENTRATION ON PHOTOVOLTAIC PERFORMANCE OF DYE-SENSITIZED SOLAR CELL

Effects of film thickness and electrolyte concentration on the photovoltaic performance of TiO2-based dye-sensitized solar cell (DSSC) were studied. Nanocrystalline anatase TiO2 thin films with varying thicknesses (3.2-18.9 mu m) have been deposited on FTO/glass substrates by screen printing method as work electrodes for DSSC. The prepared samples were characterized by UV-Vis spectroscopy, Atomic Force Microscopy/Scanning Tunneling Microscopy (AFM/STM) and X-ray diffraction (XRD). The optimal thickness of the TiO2 photoanode is 13.5 mu m. Short-circuit photocurrent density (J(sc)) increases with film thickness due to enlargement of surface area whereas opencircuit voltage decreases with increase in thickness due to increase in electron diffusion length to the electrode. However, the J(sc) and V-oc of DSSC with a film thickness of 18.9 mu m (7.5 mA/cm(2) and 0.687 V) are smaller than those of DSSC with a TiO2 film thickness of 13.5 mu m (9.9mA/cm(2) and 0.734 V). This is because the increased thickness of TiO2 thin film resulted in the decrease in the transmittance of TiO2 thin films hence reducing the incident light intensity on the N719 dye. Photovoltaic performance also depends greatly on the redox couple concentration in iodide\triiodide. Jsc decreases as the redox concentration increases as a result of increased viscosity of the solution which lowers ion mobility. Similarly, V-oc decreases as the electrolyte concentration increases due to enhanced back electron transfer reaction. An optimum power conversion efficiency of 4.3% was obtained in a DSSC with the TiO2 film thickness of 13.5 mu m and redox concentration of 0.03 mol dm(-3) under AM 1.5G illumination at 100mW/cm(2).