電化學法製備氧化亞銅薄膜並探討其光電化學特性

Study of Photoelectrochemistry of Cu2O Thin Films Prepared by Electrodeposition

本研究嘗試於含乳酸之硫酸銅鍍浴中，直接以電化學法在純銅陰極板上成長氧化亞銅（Cu2O）薄膜，鍍浴控制在35、50及65℃等三個溫度為變數，探討其對生成之薄膜微結構、光學及光電化學特性之影響。結果顯示：掃描式電子顯微鏡（FE-SEM）觀察所得薄膜形貌，於35℃低溫下所得薄膜由奈米椎體晶粒所構成，隨著溫度上升至50及65℃，構成薄膜之錐體晶粒尺寸逐漸增大，經拉曼光譜（Raman spectra）鑑定，三種溫度成長之薄膜均屬於氧化亞銅，並未出現雜相訊號。由拉曼光譜顯示：在35℃下成長之薄膜，其氧空缺訊號（150 cm-1）較強，經由電化學進行Mott-Schottky scan確定這些氧化亞銅薄膜均為p-type半導體，計算其載子濃度顯示在35℃成長之薄膜為4.16×1016 cm-3，比65℃成長之氧化亞銅高約10倍（6.01×1015 cm-3 ）。採用氙燈（強度在100 mW/cm2），搭配AM 1.5濾光片模擬太陽光通過大氣層（吸收紫外線），照射地球表面以測試光電化學，顯示在35℃成長之氧化亞銅薄膜之光電流密度最強（偏壓-0.4 V vs. SCE時為-0.22 mA/cm2）約為65℃成薄膜之1.4倍，推測低溫成長之氧化亞銅薄膜晶粒較細，氧空缺較多，導電率與其光電性質較佳。

In this study, we attempted to quantitatively interpret the effect of electrodeposition temperature on Cu2O film's microstructure, optical and photoelectrochemical properties. Three deposit temperatures (35, 50, and 65 ℃) were taken into consideration. Based upon our observations, a general trend was concluded. That is, Cu2O films deposited at lower temperature (35 ℃) always possessed a smaller pyramidal-like crystal size, high photolumminance and a higher carrier concentration. These properties made Cu2O films deposited at 35 ℃ a better photoelectrochemical performance with photocurrent density of -0.22 mA/cm2 (at -0.4 V vs. SCE). This value is about 35% higher than those Cu2O films deposited at higher temperatures. Observed higher photocurrent density is likely due to the intrinsic of a higher charge carrier concentration analyzed by Mott-Schottky plot.