| Summary: | 博士 === 國立臺灣科技大學 === 化學工程系 === 104 === In this study, the growth mechanism of ZnO nanowire arrays (ZnO-NWAs) via chemical solution method under different additives, such as: polyethylenimine (PEI) and ammonia (NH3), has been investigated. By using photoluminescence spectroscopy (PL) and X-ray absorption spectroscopy (XAS), the relation between PL emissions, interstitial zinc defects (Zni) interstitial oxygen defects (Oi) has been investigated. To further improve the quality of ZnO-NWAs, unlike the conventional batch process, a facile continuous flow injection (CFI) process has been conducted to synthesize high-quality ZnO-NAWs. According to the study, the concentration of zinc precursor can be maintained at a constant level in CFI process to provide a steady-state growth environment. High quality and long length ZnO-NWAs can be obtained from CFI process to be the photoanode of ZnO based dye-sensitized solar cells (DSSCs). From the results, the increment of length of ZnO-NWAs could effectively improve the dye absorption amount; however, it also influenced the electron collection efficiency (ηCC). To effectively increase the power conversion efficiency (PCE) of DSSCs with long ZnO-NWAs, the diffusion coefficient (Dn) need to improve simultaneously. In this study, NH3 was added into the chemical solution process and it could effectively reduce the surface defects and increase the diffusion coefficient achieved 1.2x10-2 cm2s-1, which was investigated by Raman spectroscopy and electrochemical impedance spectroscopy (EIS) techniques. ZnO-NWAs with length of 55 μm was synthesized via NH3-assised CFI process to use as photoanode of DSSCs and the PCE achieved 3.92 %. To improve the performance of ZnO-based DSSCs furthermore, a low temperature chemical bath deposition (CBD) was employed to decorate ZnO nanoparticles (ZnO-NPs) on the surfaces of ZnO-NWAs photoanodes for increasing dye loading amount. The PCE of ZnO-NWAs/NPs composite DSSC could achieve 5.25 % under the thickness of 13.5 μm. When the thickness of ZnO-NWAs/NPs composite photoanode increased to 26.2 %, the PCE could achieve 7.53 %, which is the highest value in this study. Finally, we also studied the influence of photoanode surface treatment on the performance of DSSCs. In this study, 4-tert-butylpyridine (t-BP) and water vapor were employed as surface modifier. According to the results, the excess dye molecules could be removed by t-BP treatment to avoid the multilayer adsorption and the carrier transport/transfer properties could effectively be improved by water vapor. The PCE could enhanced from 5.25 % to 6.59% via t-BP and water vapor treatment under the photoanode thickness of 13.5 μm.
|
|---|
