Effect of fluorine-doped TiO_2 photoanode on electron transport, recombination dynamics and improved DSSC efficiency

摘要

Fluorine doped TiO2 (F-TiO2) nanocuboids were synthesized using a simple template-free hydrothermal method and the XRD studies confirms that the nanoparticles are crystallized in anatase phase. Both HRSEM and HRTEM examinations reveal the formation of nanocuboids with nanovoids/pores morphology by corrosive fluorine action in hydrothermal container and such porous morphological feature can increase the surface area for high level dye adsorption. BET studies confirm the F-TiO2 exhibits a higher surface area than that of pure TiO2. The dye adsorption-desorption study confirms high dye-loading capacity in F-TiO2. XPS result confirms the existence of Ti3+ trap states and Ti-F bonding is evidenced from FTIR results. The absorption spectra of pure and F-TiO2 shows a broad absorption in ultraviolet range and increase in band gap energy with F doping is determined using Kubelka-Munk function. Raman analysis shows the increase in percentage of exposed high reactive (0 0 1) facet with increasing the fluorine doping concentration. A high carrier concentration by F doping is found to promote fast electron hopping and increase the electrical conductivity, verified using ac impedance spectroscopy and photoconductivity measurements. The interfacial charge transfer kinetics such as charge transfer resistance, chemical capacitance, diffusion length, electron recombination lifetime and charge collection efficiency of fabricated DSSCs are calculated using EIS measurements. Enhanced power conversion efficiency of 7.46% was achieved in F-TiO2 photoanode based DSSC by using AAA solar simulator under standard test condition (lsun intensity; 100 mW/cm(2) with AM 1.5G filter).