石墨烯/半導體奈米異質結構其界面載子動力學研究

Abstract

由於具有優異的導電性，單層石墨烯(graphene)與半導體奈米晶體結合時能有 效吸引半導體內的光激發電子，進而提升整體結構之載子分離效果，此對光激發電 子的捕捉能力，大大地提昇了graphene 在相關光電轉換用途例如光催化分解水、光 觸媒、與光伏電池等的可應用性。在此研究計畫中，我們提出以水熱反應程序來製 備graphene/半導體之奈米異質結構，經由調整graphene 與半導體之相對能帶關 係，期望進一步提升此異質結構之載子分離效果，使其應用在光電化學系統中作相 關光電轉換用途時，能表現出優異之效能。樣品的製備為利用濕式化學Hummers 法所得的graphene oxide 作為起始物，在水熱反應程序中將graphene oxide 還原 成graphene，同時使半導體奈米晶體成長於其表面，以形成graphene/半導體奈 米異質結構。我們將使用時間解析螢光光譜技術，來對此發生於graphene/半導體 界面間的載子傳輸行為做一定量化描述，藉由改變graphene 的功函數與調控半導體 奈米晶體的能帶結構，可使異質結構表現出具可調性之界面間載子傳輸行為。經比 較此些樣品應用於光催化水分解產生氫氣氧氣之效能，本研究將可建立相對能帶關 係、界面間載子動力學與載子被導出運用效率之間的關連性，此關連性對於發展 graphene/半導體奈米異質結構在光電化學系統中作相關光電轉換用途，可提供十分 有用的資訊。

By virtue of the excellent electrical conductivity, graphene may attract photoexcited electrons of semiconductor nanocrystals to lead to the improvement of overall charge separation efficiency. Such capability of electron trapping for graphene has rendered it promising potential in relevant photoconversion processes such as photocatalytic water splitting, photocatalysis and photovoltaics. This project aims to prepare graphene/semiconductor nanoheterostructures and investigate the interfacial charge carrier dynamics using time-resolved fluorescence spectroscopy. The samples are prepared with a hydrothermal approach by using graphene oxide, which is obtained from Hummers’ method, as the starting material. During the hydrothermal process, reduction of graphene oxide would be accompanied with the growth of semiconductor nanocrystals at the surface of graphene, resulting in the formation of graphene/semiconductor nanoheterostructures. With the adjustment of the work function of graphene as well as the regulation of band structure of semiconductor, the enhanced charge separation efficiency for graphene/semiconductor samples and thus the outstanding performance in photoconversion applications can be achieved. Time-resolved fluorescence spectra will be measured to quantitatively analyze the electron transfer event between semiconductor and graphene for graphene/semiconductor nanoheterostructures and its dependence on modulation of the relative band structures. The performance of the samples in photocatalytic water splitting will also be evaluated and the result will be correlated with that of the charge carrier dynamics measurement, which may provide insightful information when using graphene/semiconductor nanoheterostructures in photoelectrochemical system for photoconversion applications.