| Summary: | 碩士 === 國立雲林科技大學 === 電子工程系 === 103 === In this study, gold nanoparticles are prepared by photochemical method, and NaOH is added as a dispersing agent to get well-dispersed gold nanoparticles. By changing pH values (pH=5, 7, 10) of HAuCl4 , the color of generated gold nanoparticles are shifted from the blue purple to the red purple along with the increment of the pH value. Gold nanoparticle size will decrease with increasing pH values by the TEM measurement, therefore we can prove that the OH- of NaOH is adsorbed on the surface of gold nanoparticle to cause electrostatic repulsion. The higher the pH values are, the better the dispersion effect is.
Then TiO2-gold nanocomposites are deposited on FTO conductive glass substrate as a photoanode by spin coating method for applying in dye-sensitized solar cell. we investigate the fabrication and the size of gold nanoparticles as well as influences on DSSC using the HAuCl4 with concentration of 0.5 mM, 1 mM, 1.5 mM, 2 mM, respectively. The research points out that the best parameter is the concentration of 1.5mM HAuCl4 with an average nanoparticle size of ~ 15 ± 5nm, where the energy conversion efficiency of DSSC is 4.9%, which is 2.1% higher than those without adding gold nanoparticles. The reason is the gold nanoparticles on the surface of TiO2 form a Schottky barrier which reduce the probability of the electrons back to the dye molecules or electrolyte, therefore Schottky barrier increases the current density (Jsc). The increase of open-circuit voltage (Voc) can be attributed to the adsorption the gold nanoparticles on the surface of TiO2, which raise the Fermi level to make the excited dye molecular injecting an electron with consumed lowest energy into the conduction band of TiO2 thin film. We measure absorbance of the dye sensitized TiO2-gold films by UV-visible. Localized surface plasmon resonance of gold nanoparticle will lead a near-field enhancement of strong electromagnetic fields in the close proximity at the surface of gold nanoparticle. The localized surface plasmon resonance of gold nanoparticle can effectively enhance the absorption coefficient of the dye molecules. By comparing the PV parameters for DSSCs fabricated with the TiO2-gold (1.5 mM, ~15±5 nm) nanocomposite and TiO2 nanoparticles electrodes, the increase for current density is 95%, for open-circuit voltage is 5% and for energy conversion efficiency is 2.1%. Therefore, the gold nanoparticles are manufactured onto the TiO2 as the photoelectrode of DSSC, and then the energy conversion efficiency of DSSC can be significantly increased.
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