Structural, Magnetic Properties and Dye-Sensitized Solar Cells Application of Pure and La Doped BiFeO₃ Powders Prepared by Sol-Gel

Abstract

Multifunctional materials Bi_1-xLa_xFeO₃ (x = 0.05, 0.10, 0.15, 0.20) powders with and without annealing (700°C) were prepared by sol-gel method to improve the magnetic and optical properties. The particle size, chemical structures, and chemical compositions of the powders were investigated by bright-field TEM, XRD, SADP, and XRF. The bright-field TEM results show the particle size of the prepared Bi_1-xLa_xFeO₃ powders without annealing (around 200 nm) is less than that of the annealed Bi_1-xLa_xFeO₃ powders (more than 500 nm). The XRD results of the powders without annealing show the formation of rhombohedral structure of BiFeO₃ with Bi₂₄Fe₂O₃₉ as impurity phase in all samples, whereas the prepared powders annealed at 700°C have a higher phase purity. The M – H hysteresis loop of the powders with annealing and without annealing were measured by vibrating sample magnetometer at room temperature up to the field of 10 kOe. The results demonstrate that the powders with higher purity phase and larger particle size were larger saturation magnetization. The saturation magnetizations were increased by increasing the La doping content. The optical absorption edge result can be considered energy band gap (∼2.0–2.2 eV) of all prepared powders. The prepared powders were used as photoelectrode in dye-sensitized solar cell applications. The current density versus voltage characteristics of solar cell were measured under illumination of simulated sunlight coming from a solar simulator with the radiant power of 100 mW/cm² to obtain photocurrent, photovoltage, and overall photoconversion efficiency of solar cells. The power conversion, photocurrent density and photovoltage depending on purity, particle size with and without annealing powders using as photoelectrode in dye sensitized solar cells are discussed.

Keywords:

• Bismuth ferrite
• magnetic properties
• dye sensitized solar cells
• sol-gel synthesis

Acknowledgments

The authors would like to thank the Department of Physics, Khon Kaen University for providing VSM facilities. This work is supported by Suranaree University of Technology (SUT) and by the Office of the Higher Education Commission under NRU project of Thailand.