應用於太陽能轉換之量子點敏化InN/TiO2奈米粒子薄膜研發（第三年）

Abstract

本計劃擬繼續分三部份進行量子點增益的InN/TiO2奈米粒子薄膜研發：A. InN//InP Q-dots//TiO2薄膜的製備－InP量子點可以利用有機金屬化學蒸鍍法(OMCVD)，將TMIn 和PH3沈積在TiO2奈米粒子薄膜上產生InP。InP與TiO2的鍵結強化可以利用預先將TiO2羥基化後再與In(CH3)3反應形成一層TiO-In(CH3)2。根據我們最近所進行的量子化學計算結果顯示此TiO-In之鍵結應該相當強。InP量子點也可以利用如Nozik所使用之濕式化學反應來合成。但因Nozik的造作方法不易產生良好的InP量子點，並且重要的磷原料有劇毒，吾人將以一種新的製造程序將TiO2奈米薄膜浸入P(OH)3高濃渡溶液，乾燥後在400-500K與In(CH3)3反應。此法可能可以製造穩固接連在TiO2之InP量子點。B. InN//Si Q-dots//TiO2薄膜的製備－藉由電漿沈積法，使用適當的矽元素之化學蒸鍍前驅物，如SiH4或Si2H6，則可以很有效率地在TiO2奈米粒子薄膜上生長矽量子點或矽奈米粒子。我們預期矽元素經電漿化學蒸鍍在Ti(O-SiXn), X=H, Cl的吸附層上，視化學蒸鍍的時間而定，可在TiO2奈米粒子薄膜上形成矽量子點或矽奈米粒子。接著，我們可利用有機金屬化學蒸鍍法，以InN或InGaN(以In(Ga)N代表之)包覆那些附著於TiO2上的Si量子點。此In(Ga)N不僅具有光學活性，且很穩定在光電轉換應用中保護矽量子點使之不與空氣起化學反應，或者在分解水的應用中不與電解液溶液反應。倘若In(Ga)N//Si Q-dots//TiO2系統被證實在光電轉換中極有效率，則此體系可能是一個極具經濟效益的系統，因為相較之下，多晶形矽系統需要極大量的高品質之矽。此系統的研製已與核能所的科學家共同合作，目前，初步結果已顯示光電效用，將來的計畫在於如何增進此效率。在本計畫中，所有研製出來的薄膜都將利用薄膜的光電流量測以分析其電子轉移的效率，並利用紫外/可見光及紅外光區的飛秒雷射系統以泵-探（pump-probe）技術研究其電子轉移的動態學。此外，我們亦將利用相關設施進行薄膜表面的特性分析，如：X光光電子譜(XPS)、紫外光光電子譜(UPS)及X光繞射。C. 在In(Ga)N及TiO2中間加入半導體和金及其他金屬量子點以促進太陽能轉換效率，其中包含InSx、InTex等量子點。

This proposal will investigate quantum-dot enhanced InN/ TiO2 nanoparticle films for solar energy conversion application. A. Preparation of InN//InP Q-dots//TiO2 films: InP Q-dots may be generated by OMCVD on TiO2 nanoparticle films, similar to the preparation of InN by using TMIn and PH3 as the P-precursor. The bonding of InP to the TiO2 nanoparticle substrate can be enhanced by pre-treating the hydroxylated TiO2 (i.e., a layer of Ti(OH)x formed by TiO2 reaction with H2O or Ti(OH)4) with In(CH3)3 forming a layer of TiO-In(CH3)2 with a very strong TiO-In bond as suggested by the result of our recent quantum chemical calculations. InP Q-dots can also be synthesized by wet-chemistry as demonstrated by Nozik et al.5 As the processor of P for InP QD-preparation are extremely toxic and compounds such as P(OCH3)3 are unavailable commercially, we plan to employ a high concentration of P(OH)3 solution. After dipping TiO2 nanoparticle films in P(OH)3, dry the film and react it with In(CH3)3 at 400-500K to convert P(OH)3 layers to InP QD’s. This process may be workable. B. Preparation of InN//Si Q-dots//TiO2 films: Si Q-dots or nanoparticles may be grown quite efficiently on TiO2 nanoparticle films by plasma deposition using appropriate Si-CVD sources such as silane or disilane. The bonding between Si and TiO2 may be significantly strengthened by the siloxylation of the hydroxylated TiO2 or Ti(OH)4 film using SiCl4. Reaction of the hydroxylated TiO2 with the vapor of SiCl4can readily form Ti(OSiXn) (X=H, Cl) with a very strong TiO-Si bond. The plasma CVD of Si over the ad-layer of the Ti(O-SiXn) is expected to form Si Q-dots or nanoparticles on TiO2 nanoparticle films, depending on the duration of the CVD process. Over the Si Q-dots strongly anchored on TiO2, we can then carry out OMCVD to encapsulate them with InN and/or InGaN, to be denoted as In(Ga)N, which is not only photo-active but also physically strong to protect Si from chemical reactions with air in the photovoltaic application or with electrolyte solutions in the H2O-splitting application. The In(Ga)N//Si Q-dots//TiO2 system, if it is proved to be efficient, may be an economically very viable device comparing with the polycrystalline Si system which requires a much larger amount of high quality Si. The fabrication of this system has been carried out collaboratively with scientists at INER. Preliminary results have clearly shown photocurrents from the SiC/Si-QD/TiO2 system. Our future objective lies in the continual improvement of conversion efficiency. All deposited films will be analyzed for their electron transfer efficiencies by photo-current measurements as well as by fs-laser pump/probe spectroscopic studies on their electron-transfer dynamics with both UV/visible and IR fs-lasers available at the Center for Interdisciplinary Molecular Science (CIMS), NCTU. Surface electronic properties of the films will also be analyzed by XPS, UPS and X-ray diffraction using the advanced light source at the National Synchrotron Radiation Center. C. Incapsulation of gold or other metal quantum dots as well as semiconductor quantum dots between In(Ga)N and TiO2 to enhance solar energy conversion efficiencies. These QD’s include InSx, InTex, etc.