近年來，鐵電光伏材料的研究越來越多，尤其以鐵酸鉍為最熱門的研究材料之一，但所有鐵電材料都具有相當大的電阻，若要應用於鐵電光伏上，首先需要提高其導電度，本研究的主要研究目標即是透過摻雜來增加鐵酸鉍的導電度。在本實驗中，以水熱法成功製備出鎳摻雜鐵酸鉍純相，並在鈮(Nb)摻雜之鈦酸鍶基板(NSTO)上成長鎳摻雜鐵酸鉍磊晶薄膜，比較冷壓塊材與磊晶薄膜間電性的差異。首先，本研究針對不同的水熱條件，包含水熱溫度、礦化劑KOH(Mineralizer)濃度等，尋找最適合鐵酸鉍成長的環境，發現在溫度200oC、KOH濃度為9M為最佳的鐵酸鉍成相條件，並摻雜少量的鎳離子(3%)，經由TOPAS精修軟體進行擬合後，發現鎳摻雜鐵酸鉍的晶格體積增加，符合預期，而拉曼光譜的結果發現，鎳摻雜鐵酸鉍試片在高頻區段的鐵離子振動模式皆往低頻位置位移，亦可證實鎳離子有取代鐵離子；而透過電性的量測，發現鎳摻雜確實有助於鐵酸鉍電導率的提升，3%鎳摻雜可提升鐵酸鉍電導率兩個數量級，經由阿瑞尼斯方程式的擬合，未摻雜鐵酸鉍活化能約為0.95 eV，經過3%鎳摻雜鐵酸鉍活化能為0.8 eV，鎳摻雜降低了鐵酸鉍的電阻活化能，但皆屬於氧空缺的活化能範圍內(0.8-1.2 eV)。XPS結果說明了鎳摻雜後鐵酸鉍中Fe3+轉變為Fe2+，未摻雜的Fe2+/Fe3+為15.8/84.2，而3%鎳摻雜鐵酸鉍Fe2+/Fe3+為23.9/76.1，Fe2+的含量增加，為了維持整體晶格電中性，氧空缺濃度需增加以進行電荷補償，所以鐵酸鉍的導電機制源自於氧空缺；最後，我們量測鎳摻雜鐵酸鉍的光電性質，發現鎳摻雜使鐵酸鉍的電阻下降後，有利於整體光載子的提取，成功證實降低電阻確實有助於光電流的增加，未摻雜鐵酸鉍光電流約為0.92 uA/cm2，3%鎳摻雜鐵酸鉍光電流則為3.40 uA/cm2；此外，本實驗亦利用水熱法在NSTO基板上成長鐵酸鉍薄膜，因NSTO與鐵酸鉍的晶格匹配，能夠成長良好的磊晶薄膜，其照光的電流行為表現出類似p-n二極體的整流行為，且鎳摻雜對於其光電流的提升更加明顯，未摻雜鐵酸鉍光電流為12 uA/cm2，3%摻雜鐵酸鉍光電流則可達369.2 uA/cm2，但無論是在塊材或薄膜，均未觀察到明顯的開路電壓，僅照光後光電流提升，詳細機制尚待進一步探討

SUMMARY
The anomalous photovoltaic (PV) effect in BiFeO3 (BFO), which results in an open-circuit voltage that is considerably larger than the bandgap of the material, has recently received attention in the field of photoferroelectrics. For solar power applications, in addition to open-circuit voltage, electric current is important. In this study, we dope nickel into BFO to increase the carrier concentration and thus PV current. This doping is expected to increase the PV current by several-fold due to the introduction of extra carriers. Ni-doped BFO powder and epitaxy films are prepared via the hydrothermal method. The effects of nickel doping on the crystal structure, microstructure, chemical bonding, electrical resistance, and PV properties are investigated. The results show that BFO doped with 0-3% Ni has a perovskite structure. The addition of nickel effectively decreases the electrical resistance of BFO because it increases the oxygen vacancy concentration. The illumination current of Ni-doped BFO increases with increasing nickel content, which can be explained by the decrease in electrical resistance. The Ni-doped BFO films show rectifying characteristics similar to those of a diode. The current density-electric field behavior of the films differs from that of the bulk. The illumination current increases dramatically when the Ni-doped BFO films are illuminated.

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