Dielectric and optical properties of BiFeO3–(Na0.5Bi0.5)TiO3 thin films deposited on Si substrate using LaNiO3 as buffer layer for photovoltaic devices

Highly (100)-oriented BiFeO3–(Na0.5Bi0.5)TiO3 thin films without undesirable phases were synthesized by chemical solution deposition. The preparation of BiFeO3–(Na0.5Bi0.5)TiO3 sol and deposition procedure were studied. BiFeO3–(Na0.5Bi0.5)TiO3 thin films were deposited onto SiO2/Si substrates via a sol–gel method, with LaNiO3 as buffer layer. X-ray diffraction analyses show that the BiFeO3–(Na0.5Bi0.5)TiO3 films are highly (1 0 0)-oriented due to lattice match growth. Smooth surface with evenly distributed grains as small as about 50 nm were observed by scanning electron microscope. The dielectric and insulating characteristics against applied field, and optical properties were studied. It is found that the introduction of Ti4+ reduces the number of oxygen vacancy greatly and thus can suppress the leaking current. The film has a conspicuous absorption in the blue and green light region, and band gap of about 2.74 eV.

► BiFeO3–(Na0.5Bi0.5)TiO3 photovoltaic thin films with pure perovskite structure were synthesized for the first time.
► Highly (1 0 0)-oriented thin films were obtained using LaNiO3 films as the buffer layers.
► Leakage current decreased significantly as increasing the ratio of (Na0.5Bi0.5)TiO3.
► Such thin films had a direct band gap within visible wavelength of about 2.74 eV using ellipsometrical measurement.