Extensive enhancement in power conversion efficiency of dye-sensitized solar cell by using Al-doped TiO2 photoanode

In this work, we have prepared Al-doped TiO2 nanoparticles via a hydrothermal method and used it for making photoanode in dye-sensitized solar cell (DSSC). Material characterizations were done using XRD, AFM, SEM, TEM and EDAX. XPS results reveal that Al is introduced successfully into the structure of TiO2 creating new impurity energy levels in the forbidden gap. This resulted in tuning of the conduction band of TiO2 and reduced charge recombination which led to better current conversion efficiency of DSSC. Greater dye loading and enhanced surface area was obtained for Al-doped TiO2 compared to un-doped TiO2. I-V analysis, EIS and Bode plots are employed to evaluate photovoltaic performance. The short-circuit current density (J (sc)) and efficiency (eta) of cell employing Al-doped TiO2 photoanode were extensively enhanced compared to the cell using un-doped TiO2. The optical band gap (E (g)) for Al-doped and un-doped TiO2 was obtained as 2.8 and 3.2 eV, respectively. J (sc) and eta were 13.39 mAcm(-2) and 4.27%, respectively, under illumination of 100 mWcm(-2) light intensity when thin films of 1% Al-doped TiO2 was employed as photoanode in DSSC using N719 as the sensitizer dye. With the use of un-doped TiO2 as photoanode under similar conditions, J (sc) 5.12 mAcm(-2) and eta 1.06% only could be obtained. The maximum IPCE% obtained with Al-doped TiO2 and un-doped TiO2 was 67 and 38% respectively at the characteristic wavelength of dye (lambda (max) = 540 nm). The EIS analyses revealed resistive and capacitive elements that provided an insight into various interfacial processes in terms of the charge transport. It was observed that Al-doping reduced the interfacial resistance leading to better charge transport which has improved both photocurrent density and conversion efficiency. Higher electron mobility and fast diffusion resulting in greater charge collection efficiency was obtained for Al-doped TiO2 compared to the un-doped TiO2. Using the Mott-Schottky plot, the donor density was calculated for un-doped and Al-doped TiO2. The work demonstrated that the Al-doped TiO2 is potential photoanode material for low-cost and high-efficiency DSSC.