本研究主要探討鐵電材料的光伏打特性，有別一般太陽能材料之p-n接面，
只能產生~0.6 V 的光電壓，近來有實驗顯示，鐵電材料BiFeO3 之單晶藉由其
自發極化電場所產生的光電壓可達~20V；但由於鐵電材料普遍皆為絕緣體，電
阻很大(>108 ohm-cm)。本實驗主旨為透過摻雜改善此材料之導電係數，並利用溶膠凝膠法(sol-gel method)易於合成之特性，製備BiFeO3:M 多晶塊材
(BFO:M；M=Ca,Pb,Sr,Ni)，觀察其極化後的光電特性。
經XRD觀察，將無摻雜的BFO與BFO:M(M=Ca,Pb,Sr,Ni)於500~600oC，持溫燒結12小時，可得到具有Rhombohedral結構之純相，但燒結溫度達700oC時會有第二相Bi25FeO40(JCPDS78-1543)出現。BFO:M(M=Ca,Pb,Sr,Ni)在室溫下量測的電阻率，大約為106~107(ohm-cm)，與無摻雜的BFO相比可以降低電阻率約一~二個數量級。將樣品施加電壓，在600oC下進行極化，然後選擇極化效果佳的試片，即d33較大者(包括無摻雜的BFO以及摻雜5,10%Ca和1%Ni的BFO），量測其I-V特性和光伏效應。
經實驗證實，在適當的製程條件下(如合適的燒結溫度、持溫時間、極化溫度、極化時間等)，所得試片可以觀察到開路電壓，照光前後有明顯的電流變化。無摻雜的BFO其開路電壓絕對值最大，約為-1.25(V)，而摻雜鈣與鎳的開路電壓分別是-0.75和-0.2(V)。此外，摻雜Ca和Ni的BFO其光電流增加最大，從光照前的10-9(A)增加到光照後的10-8(A)，而無摻雜的BFO在照光後其電流並無明顯增加，顯示其缺乏可被太陽光激活的電荷載子。

The aim of this study was to search for ferroelectric photovoltaic materials. In contrast to the semiconductor p-n junction, where the photovoltaic voltage is limited to around 0.6 V, the spontaneous polarization in ferroelectric materials can produce a much higher output voltage. Indeed, in a recent work, a large photovoltaic output of over 20 V has been demonstrated with the BiFeO3 single crystals. However, because ferroelectric materials usually have a very high DC resistivity over 108 ohm-cm, there is a need to increase the mobile carrier concentration in these materials. For this purpose, BiFeO3 (BFO) was doped with various ions in the present study. Polycrystalline pellets of BFO:M (M=Ca, Pb, Sr and Ni) were prepared by the sol-gel method. After poling, the photoelectric effects of the samples were studied.
X-ray diffraction showed that after sintering at 500~600oC for 12 hours, undoped BFO and the samples doped with Ca, Pb, Sr and Ni had a pure phase with the well-known rhombohedral structure. If the sintering temperature was raised to 700oC, a second phase of the composition Bi25FeO40 appeared. The resistivities of the BFO samples doped with Ca, Pb, Sr, and Ni doped were measured to be 106~107 ohm-cm, which were1~2 orders lower than that of the undoped BFO. The samples were poled under a high electrical field at 600oC. The degree of the achieved poling was checked by the measured d33 values. I-V curves and photovoltaic effects of the samples with a large d33 were then investigated.
The experiment results showed that under suitable preparation conditions (e.g. sintering temperature and time, degree of achieved poling, etc.), an open-circuit voltage was usually observed in the samples. After the samples were illuminated by the simulated-sunlight, large current increases were observed in the I-V curves. The undoped BFO showed a largest negative open-circuit voltage of -1.25 V, whereas the open-circuit voltages for Ca and Ni doped BFO were -0.75 and -0.2 (V), respectively. On the other hand, The Ca and Ni doped samples showed the largest photocurrents, which were increased from 10-9 A at dark to 10-8 A after the illumination. The undoped BFO showed a trivial photocurrent after illumination, indicating a lack of mobile charge carrier which could be excited by the light.

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