紫質分子在TiO2奈米薄膜上的能量與電子轉移動力學研究

Abstract

本論文研究之紫質的分子結構與自然界中參與光合作用的葉綠素相近，其衍生物具有相當優異的光電轉換特性，因此近年來人工紫質在染料敏化太陽能電池(DSSC)的研究中扮演重要的角色。由於紫質分子間作用力強，在奈米二氧化鈦薄膜上容易聚集形成雙體或多體，而使得分子間能量轉移變的非常有效，導致其激發態能量焠滅，使其激發態的電子轉移到二氧化鈦的效率大幅衰減進而影響了DSSC的整體效能。為了解決紫質分子堆疊(aggregation)的問題，我們設計了ZnCAPETPP(ZnP1)以及t-butyl ZnCAPETPP(ZnP2)兩種紫質分子，將無共軛性且具立體障礙的四丁基(tert-Butyl)導入後者，而使後者的分子間能量轉移速率降低，並使得更多在激發態的光電子有效地注入二氧化鈦。我們利用飛秒螢光上轉移(femtosecond fluorescence up-conversion)的技術去研究以上二者在溶液與TiO2奈米薄膜上的動力行為，並比較其製成元件後之光電轉換效率差異，為未來染料分子設計提供一個新的方向。

In TiO2-based dye-sensitized nanocrystalline solar cells, efficiencies of up to 11% have been obtained using Ru dyes, but the limited availability of these dyes together with their undesirable environmental impact have led to the search for cheaper and safer Porphyrin dyes. We aim to investigate the effect of adding t-butyl groups substituents to unsymmetrical Zn-Porphyrins used for the preparation of dye sensitised solar cells (DSSC). We have used two different unsymmetrical meso-tetraphenyl substituted Zn-Porphyrins attending to two objectives: (1) to observe how the substitution of three para positions of the meso-phenyl groups adding t-butyl groups substituents influences the formation of molecular aggregates onto the semiconductor nanoparticles (2) To deduce the influence that the substitution the electron transfer processes that take place at the different interfaces of the photovoltaic device using, steady-state and time resolved spectroscopic techniques. The electron transfer reaction between the photoinjected electrons in the nanocrystalline TiO2 mesoporous sensitized films and the oxidized electrolyte in dye sensitized solar cells _DSSC_ plays a major role on the device efficiency. In this article we show that, although the presence of molecular aggregates on the Zn- porphyrin DSSC we measurement the device photocurrent then use femtosecond fluorescence up-conversion tech to understand electron injection kinetics and intra-molecular energy-transfer rate .Therefore, their drawback can be overcome by designing dyes with peripheral moieties that prevent the formation of the aggregates and are able to achieve efficiencies as high as 1% under A.M 1.5 sun.