Impact of titanium dioxide nanofiber on performance of dye sensitized.

摘要

As the third generation solar cell, dye sensitized solar cells (DSSCs), which have the advantage of low cost, have attracted much attention since they were invented by Grätzel in 1991. However, DSSCs have modest efficiency due to slow electron transport in the TiO2 nanoparticle photoanode, and potential leakage and contamination issues due to the liquid iodide/triiodide electrolyte, which is popularly used in current high-efficiency of DSSCs. The excessive loss of voltage during the dye-regeneration reaction by iodide/triiodide electrolyte in DSSCs limits the attainable open-circuit voltage to 0.7∼0.8V, and is thus a critical drawback of current DSSCs. One dimensional (1D) TiO 2 nanofiber has great potential as the new photoanode of DSSCs, because it might improve electron transport efficiency and provide the opportunity to develop a redox mediators exhibiting higher reduction potentials than that of iodine electrolyte to increase voltage output.;In this dissertation, the impact of electron transport and optical absorption on the performance of the DSSCs based on TiO2 nanofiber was studied. The results were applied to develop solid state DSSCs based on TiO2 nanofiber. At first, TiO2 nanofiber was prepared by electrospinning and annealing processes and DSSCs based on nanofiber were fabricated. The electron diffusion length of TiO2 nanofiber based DSSCs was measured. It was shown that the electron diffusion length of TiO2 nanofiber-based DSSCs doubled that of nanoparticle-based DSSCs, which indicated that TiO2 nanofiber-based DSSCs have better electron collection efficiency. Secondly, to improve the light-harvesting efficiency of TiO 2 nanofiber based DSSCs, the TiO2 nanofibers used in the DSSCs were doped with Ag nanoparticles. It was found the optical absorption and electron collection was improved when the TiO2 nanofibers were doped. DSSCs based on the Ag nanoparticle doped TiO2 nanofibers had a significantly increased photocurrent density resulting in 25% improved power conversion efficiency. Thirdly, typical DSSCs use liquid electrolyte, which has potential leakage and corrosion problems. To address this issue, nanofiber-based solid state DSSCs using poly (3-hexylthiophene) (P3HT) as hole transport material were developed. The nanofiber based solid state DSSCs with blocking layer prepared by spin coating and atomic layer deposition (ALD) method were investigated. The nanofiber solid state DSSCs with the ALD TiO 2 blocking layer displayed a significantly increased open circuit voltage and photocurrent output compared with the control devices in which the TiO 2 blocking layers were prepared by spin coating method. Finally, solid state DSSCs based on TiO2 nanoparticle-nanofiber composite photoanode with optimized TiO2 blocking layer prepared by ALD method were developed, which take advantage of the large surface area of nanoparticles and the efficient charge transport from 1D nanostructures. It was found that TiO2 nanofiber could improve open circuit voltage of solid state DSSC because of efficient charge transport of TiO2 nanofiber and the current density was related to the percentage of the nanofiber. By optimizing the percentage of TiO2 nanofiber amount to trade off the optical absorption and electron transport in solid state DSSCs, the efficiency was increased to 1.63%.