Improved photovoltaic effects in Mn-doped BiFeO3 ferroelectric thin films through band gap engineering**Project supported by the National Natural Science Foundation of China (Grant Nos. 11274322, 51402318, 61404080, and 61675066), the National Key Technology Research and Development Program of China (Grant No. 2016YFA0201102), and the China Postdoctoral Science Foundation (Grant No. 2016LH0050).

Abstract

As a low-bandgap ferroelectric material, BiFeO3 has gained wide attention for the potential photovoltaic applications, since its photovoltaic effect in visible light range was reported in 2009. In the present work, Bi(Fe, Mn)O3 thin films are fabricated by pulsed laser deposition method, and the effects of Mn doping on the microstructure, optical, leakage, ferroelectric and photovoltaic characteristics of Bi(Fe, Mn)O3 thin films are systematically investigated. The x-ray diffraction data indicate that Bi(Fe, Mn)O3 thin films each have a rhombohedrally distorted perovskite structure. From the light absorption results, it follows that the band gap of Bi(Fe, Mn)O3 thin films can be tuned by doping different amounts of Mn content. More importantly, photovoltaic measurement demonstrates that the short-circuit photocurrent density and the open-circuit voltage can both be remarkably improved through doping an appropriate amount of Mn content, leading to the fascinating fact that the maximum power output of ITO/BiFe0.7Mn0.3O3/Nb-STO capacitor is about 175 times higher than that of ITO/BiFeO3/Nb-STO capacitor. The improvement of photovoltaic response in Bi(Fe, Mn)O3 thin film can be reasonably explained as being due to absorbing more visible light through bandgap engineering and maintaining the ferroelectric property at the same time.