為減緩持續惡化之全球暖化危機，人類正積極尋找石化燃料以外之乾淨、可永續利用之能源。光電催化(PEC)電解槽可透過水分解產生氫氣，或還原二氧化碳成可利用之碳氫化合物。在光電催化領域中氧化亞銅(Cu2O)為眾所注目之光陰極材料，其在可見光波段之高吸收係數、低成本、無毒與好合成等優點，使其成為主要之研究對象。然而高電子-電洞再結合率與在液相溶液中之不穩定特性阻礙其實際應用，因此對於Cu2O之研究多為降低載子再結合率以提升光電流表現，與披覆保護層阻絕與溶液之直接接觸以提高穩定性。文獻上大都以異質界面結構方式，在Cu2O電極外側披覆保護層，以兩材料能帶排列之電場效應分離光激發載子，提高光電性質表現。
本實驗以低成本之電鍍沉積法，在相同電鍍溶液條件下，以不同電鍍電流密度於FTO導電玻璃上電鍍Cu2O薄膜，成功鍍製以不同優選方向成長之Cu2O薄膜，並選擇以光電性質較佳之(111)優選方向進行性質優化，在載子擴散距離與光穿透深度間取得最佳值，發現在膜厚為0.66 μm時可得最大光電流值2.9 mA/cm2，高於文獻平均2 mA/cm2許多。接著同樣以能帶結構排列之概念，在FTO基板與Cu2O薄膜間引入該領域未被使用過之Cu2Te，作為電洞傳輸層，提高載子分離效率以提升光電流。結果證實引入Cu2Te後，Cu2O薄膜之光電流值由2.9 提升至4.9 mA/cm2，效果相當顯著，且光激發螢光光譜(PL)之結果證實Cu2Te能降低Cu2O中之載子再結合率，顯示Cu2Te能透過能帶結構排列產生之電場效應提升Cu2O光電流表現。最後則針對Cu2O薄膜中空位缺陷進行分析，發現氧空位缺陷僅分佈於薄膜表面，且電鍍於FTO上或Cu2Te上之分佈沒有差異，氧空位缺陷能提高載子生命週期，降低再結合率，提高光電流。而銅空位缺陷能提高Cu2O之主要載子濃度，提高電荷傳輸效率，提升Cu2O薄膜光電性能。

A clean and sustainable energy source other than fossil fuel is highly desired to avoid the continuous deterioration of global warming crisis. A photoelectrochemical (PEC) cell can be used to produce hydrogen fuel and hydrocarbon derivatives through water splitting and reduction of carbon dioxide gas, respectively. Cuprous oxide (Cu2O) is a well-known photocathode material in a PEC cell owing to its advantages of high absorption coefficient in visible light range, low-cost, non-toxicity and ease of fabrication. However, the chemical instability in aqueous solution and high electron-hole recombination rate have prevented the Cu2O from practical PEC applications. Some research indicated that the photoelectrochemical performance of Cu2O can be enhanced through heterogeneous junction structure. By depositing a protection layer on the Cu2O film, photoexcited carriers can be separated by the electric field established at the junction, leading to improved photoelectric properties.
In this study, a low-cost electrodeposition method is used to deposit Cu2O thin film on the fluorine-doped tin oxide (FTO) glass substrate with different electrodeposition current density. The Cu2O thin films were grown with different preferred orientations by adjusting the applied current density. Further optimizations including Cu2O film thickness adjustments and insertion of Cu2Te were done on the well performed (111) oriented Cu2O films. We found that the 0.66 μm-thick Cu2O film shows the maximum photocurrent density of 2.9 mA/cm2, which is much higher than the reported value around 2 mA/cm2 in the literature. Next, we introduced a copper(Ⅰ) telluride (Cu2Te) as hole transmission layer between Cu2O film and the FTO substrate. The Cu2Te insertion layer can enhance the separation efficiency of photocarriers and increase the output photocurrent of Cu2O. The results showed that after the introduction of Cu2Te, the photocurrent of Cu2O thin film significantly increased from 2.9 to 4.9 mA/cm2. The photoluminescence (PL) results confirmed that Cu2Te can reduce the carrier recombination rate of Cu2O. Finally, the vacancy defects in the Cu2O thin film were analyzed. It is found that the oxygen vacancy defects are mainly located on the surface of the Cu2O film regardless the presence of Cu2Te insertion layer. Oxygen vacancy defects can increase the carrier life time, reduce the recombination rate, and increase the photocurrent. Copper vacancy defects can increase the majority carrier concentration of Cu2O film, improve the charge transfer efficiency, and improve the photoelectric performance of Cu2O thin films.

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