Studies on the Langmuir-Blodgett thin film of ZnTPP and its photoelectric effect
| Autor: | Wen-feng Huang, 黃文峰 |
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| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 This thesis consists of two parts. In part one, we studied the process of deposition of Zn tetraphenylporphrin (ZnTPP) thin films onto the ITO substrates by Langmuir-Blodgett technique. In part two, we studied the photoelectrochemical cell based on the ZnTPP thin films; the cosensitization of a mixed film of ZnTPP and a substituted copper phthalocyanine (4-cum)CuPc ) was also studied. The ZnTPP molecule is not amphiphilic, thus its π-A isotherm does not show clear phase transitions. The molecular cross section measurements indicate aggregation of ZnTPP, probably due to π-πor metal-π interactions. The Z-type transfer was observed for ZnTPP onto ITO, i.e. the positive transfer ratio was observed during the lifting of the ITO substrate from the water surface. The UV-Visible spectrum of the LB film shows the typical Soret band at 425 nm and the Q band at 550 nm. The absorbances were found to increase linearly with the number of layers, up to n=9. Photoelectric effects were observed for the photoelectrochemical cell (ITO/ZnTPP/electrolyte). We discovered that both the open-circuit voltage (Voc) and the short-circuit current (Isc) increase with the number of layers, up to n=9, and decrease with the surface pressure used to deposit the ZnTPP films. Two electrolyte systems, HQ/BQ and ascorbic acid, were used. For the HQ/BQ electrolyte, both Voc and Isc increase linearly with log([BQ]/[HQ]), the slopes are 33.6mV and 2.45μA, respectively. For the ascorbic acid electrolyte, both Voc and Isc decrease with log [ascorbic acid], the slopes are -145mV and 8.2μA, respectively. We also found that Voc decreases as pH increases, due to the shift of flatband potential of ZnTPP. The slopes are -26mV/pH and -22mV/pH, for HQ/BQ and ascorbic acid solutions, respectively. A mixed film of ZnTPP and CuPc were also used. The quantum efficiency measurements show that IPCE of the mixed film is 40% at ??? nm, while that of the pure ZnTPP is 15%, and the IPCE of the mixed film is 10% at ??? nm, while that of the pure CuPc is 1%. The enhancement of quantum efficiency due to cosensitization can be explained by the hetroaggregation in the mixed film. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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