電鍍氧化亞銅經退火處理於光解水製氫應用之探討

Abstract

本研究利用電化學沉積法沉積氧化亞銅薄膜，由控制鍍液酸鹼值、沉積時間及過電位大小來控制氧化亞銅薄膜的成長。在pH值為9的鍍液中能得到擇優方向以(200)方向為主的結構，pH值為11的鍍液中則能得到擇優方向為(111)方向的結構。取其中以pH值為9的鍍液，過電位為-0.3 V，電鍍時間為100 分鐘的薄膜，以及pH值為11的鍍液，過電位為-0.3 V，電鍍時間為60 分鐘的薄膜作為研究其退火影響的對象。 退火溫度為150、200、250、300、350 ℃等五個溫度，持溫時間分別為10、30及60 分鐘。兩種不同擇優方向的薄膜在其樣貌形狀上皆產生了晶粒變小的變化，但其電阻值則呈現兩種相反的趨勢。在擇優方向為(200)方向的薄膜，其電阻值隨著溫度的上升及持溫時間的延長，皆有下降的趨勢。相反的，在擇優方向為(111)方向的薄膜，其電阻值隨著溫度的上升及持溫時間的延長，皆有些微增加的趨勢。再經由350 ℃ 退火30 分鐘的處理後，擇優方向為(200)方向的薄膜其電阻值由1.602 Ω㎝大幅下降至3.96E-4 Ω㎝。 最後分別研究不同退火條件對於氧化亞銅薄膜的光電性質的影響，以Photoelectrochemical solar cell (PEC)量測其光電流造氫的表現。結果兩種擇優方向的膜薄都以在350 ℃ 退火60 分鐘的處理後，能有最佳的光電轉換造氫效率。擇優方向為(200)方向的薄膜，其最佳光電流表現為-141 μA㎝-2；擇優方向為(111)方向的薄膜，其最佳光電流表現為-119 μA㎝-2。退火對其光電轉換造氫效率的影響，主要反映出退火處理後其導電度的變化，結果證明退火處理能增進半導體薄膜的結晶性與導電度，而能得到較好的光電表現。

The Cu2O films were electrodeposited in two different pH values of plating bath. We controlled the deposition times and overpotentials to study the growth of Cu2O films. The film deposited in pH 9 bath demonstrated a preferred orientation in (200) plane, and in pH 11 bath revealed a preferred orientation of (111). The film deposited in pH 9 bath under -0.3 V for 100 min and the film deposited in pH 11 bath under -0.3 V for 60 min were used to study the annealing effect. The annealing temperatures were 150, 200, 250, 300, and 350 ℃, and the annealing times were 10, 30, and 60 min. The grain sizes for these two films were both decreased after annealing. However, their resistivity exhibited an opposite direction. The pH 9 films after annealing revealed a reduced resistivity as the temperature and annealing time were increased. On the other hand, the pH 11 films after annealing showed increased as the temperature and annealing time were increased. The pH 9 film after annealing at 350 ℃ for 30 min demonstrated a stable resistivity reduction decreased from 1.602 to 3.96E-4 Ω㎝. We studied the photoelectrochemical properties of Cu2O film for H2 generation before and after annealing process. The photocurrents were collected to explore the effect of annealing. The results indicated that both films had best performance at 350 ℃ annealing for 60 min. The photocurrent of pH 9 film annealed at 350 ℃ for 60 min was -141 μA㎝-2, and the pH 11 film annealed at 350 ℃ for 60 min was -119 μA㎝-2. The photocurrents revealed the resistivity transition of Cu2O films which was affected by the annealing process. The results exhibited that the annealing process could improve the crystallinity and was greatly enhanced conductivity of Cu2O film. As a result, enhanced the photoelectrochemical performance.