Preparation Of Bismuth Ferrite Thin Films And Its Photovoltaic Effect

Bismuth ferrite（BiFeO₃, BFO） is a kind of multiferroic materials. It has ferroelectricity and antiferromagnetism at room temperature, which makes it the research hotspot of multiferroic materials, and has attracted much attention. Researches shows that BFO has a good performance in ferroelectricity, ferromagnetism and photoelectricity, and a very broad application prospects in terms of nonvolatile store, dynamic random access memory, spintronic devices and sensors. Recently, the photovoltaic effect of the ferroelectric materials has aroused the interest of scientists. BFO is a rare kind of ferroelectric with a narrow bandgap. Besides the unique spontaneous polarization of ferroelectric materials, it also has a band gap which can match with the wavelength of visible light. Photo device with BFO thin films has exhibited strong photovoltaic effect, it can produce an open circuit voltage which is much larger than the material band gap. It has overcome the problem that the traditional semiconductor solar cell’s open circuit voltage is limited by the absorption material layer’s band gap, and also provides an alternative way for the development of new type efficient and stable solar cells and photo device in the future.The emphasis of this paper is to prepare BFO thin films doped with dysprosium（Dy） on the FTO transparent conductive glass by magnetron sputtering deposition and to observe its micro structural characterization and photovoltaic property. The main contents and results are as follows:（1） With X-ray diffraction, Raman scattering, we have respectively studied the effects of the following process parameters: substrate temperature, working pressure, sputtering time, dysprosium doping amount, and the annealing temperature on the crystalline state of BFO thin films. And we have observed the surface structure of BFO thin films by using scanning electron microscopy. The optimized process parameters of dysprosium doped BFO films preparation is: working pressure=1Pa, substrate temperature=300 ℃, O2:Ar=5:30, sputtering power=80W, sputtering time=2h, annealing temperature=550℃, annealing time=5min. The results show that the crystallization behavior of BFO thin films can be improved by Dy doping, which is also beneficial to decrease the leakage current.（2） We have analyzed the principle of BFO thin film’s photovoltaic effect, prepared a sandwich structure device based on BFO films, and studied the effect of annealing temperature and film thickness of BFO thin film on its photovoltaic effect. We have selectively analyzed the influence of the different dysprosium doping amount, different sputtering time, different pin distance on the prototype device on the open circuit voltage. Researches shows that the BFO films has a larger open circuit voltage with a 2h sputtering time, and the value increases with the increase of the distance between the test electrode, while the Dy doping can improve the open circuit voltage in a certain extent.