The Microstructure, Electric, Optical and Photovoltaic Properties of BiFeO3 Thin Films Prepared by Low Temperature Sol–Gel Method

Abstract

Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices due to their abnormal photovoltaic effect. However, the current reported efficiency is still low. Hence, it is urgent to develop narrow-band gap ferroelectric materials with strong ferroelectricity by low-temperature synthesis. In this paper, the perovskite bismuth ferrite BiFeO3 (BFO) thin films were fabricated on SnO2: F (FTO) substrates by the sol–gel method and they were rapidly annealed at 450, 500 and 550 °C, respectively. The microstructure and the chemical state’s evolution with annealing temperature were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), and the relationship between the microstructure and electric, optical and photovoltaic properties were studied. The XRD, SEM and Raman results show that a pure phase BFO film with good crystallinity is obtained at a low annealing temperature of 450 °C. As the annealing temperature increases, the film becomes more uniform and has an improved crystallinity. The XPS results show that the Fe3+/Fe2+ ratio increases and the ratio of oxygen vacancies/lattice oxygen decreases with increasing annealing temperature, which results in the leakage current gradually being reduced. The band gap is reduced from 2.68 to 2.51 eV due to better crystallinity. An enhanced photovoltaic effect is observed in a 550 °C annealed BFO film with a short circuit current of 4.58 mA/cm2 and an open circuit voltage of 0.15 V, respectively.

Ferroelectric, quantum efficiency and photovoltaic properties in perovskite BiFeO 3 thin films: First principle calculations and Monte Carlo study

“…As shown in Figure 8, the maximum short circuit current density was 4.72 mA/cm 2 . This result is near to that obtained by experiment results 11,49 . The open circuit voltage is related to the band gap Eg via the following equation 50,51 : …”

“…This band gap value allows the BFO to absorb a relatively wide solar spectrum and to obtain a relatively high photoelectric conversion efficiency. The reinforced photovoltaic effect is observed in a BFO film annealed at 550°C with a short‐circuit current of 4.58 mA.cm −2 , the hysteresis loop is not saturated 11 and external quantum efficiency (EQE) remarkable electron photon of about 9% 12 . The ferromagnetic behavior was associated with the partially filled orbitals d of Fe 3+ by iron‐oxygen‐iron super‐exchange interactions 13 .…”

“…This ferroelectricity is due to the stereochemical hybridization of pair‐isolated Bi (6s 2 ) electrons and O (2p 6 ) states 9 . On the other hand, the BFO presents a relatively small band gap 10,11 . This band gap value allows the BFO to absorb a relatively wide solar spectrum and to obtain a relatively high photoelectric conversion efficiency.…”

Phase Structure and Electrical Properties of Sm-Doped BiFe0.98Mn0.02O3 Thin Films

“…To further study the oxygen vacancy content in the BSFM films, the O1s orbital of the films was fitted, as shown in Figure 6 a–d. In the figure, O1s is fitted into two peaks, which are lattice oxygen with binding energy of 529 eV (from metal) and oxygen vacancy of 531 eV (from defect) [ 41 , 42 ]. To calculate the oxygen vacancy ratio of the thin films, the two peaks were integrated to calculate the area, and the oxygen vacancy ratios of the four groups of samples were 0.24, 0.16, 0.14, and 0.15.…”

Magnetoelectric Coupling in Bismuth Ferrite—Challenges and Perspectives

“…A challenge for many of the applications of BFO is the leakage current. It depends mainly on phase-purity, size of the particles and defects like oxygen vacancies [53].…”