Effects of precursor concentration on the microstructural, optical and photoelectrochemical properties of Bi2O3 films synthesized by sol-gel method

beta-Bi2O3 films were prepared by sol-gel method process from solutions with different precursor concentration (M = 0.05-0.20). The films were characterized by X-rays diffractions (XRD), field emission electron microscopy (FESEM), atomic force microscopy (AFM), UV-vis spectroscopy, photoluminescence spectroscopy (PL), photoelectrochemical (PEC) and electrochemical impedance measurements. The Bi2O3 deposited film had single phase beta-Bi2O3 on ITO substrate while it exhibited mixed phases of epsilon-, delta- and beta-Bi2O3 on glass substrate. By increasing M above 0.05, more XRD patterns were observed and lattice parameter c increased. Besides, crystallite size of films increased first from 19.2 to 26.4 nm at M = 0.05 - 0.15 and then decreased to 19.4 nm at M = 0.20. From AFM, the films consisted of polyhedron-like shape islands with height and distribution increased with increment of M. The surface roughness increased from 10.3 to 18.5 nm for film with M = 0.05 and 0.15, respectively, and then decreased to 14.8 nm for film M = 0.20. Optical band gap decreased from 3.24 eV for film M = 0.05 to 2.89 eV for film M = 0.20. From PEC, photocurrent of films increased with increment of M and had maximum value 3.8 x 10(-4) A/cm(2) for film M = 0.20 at 0 V versus Ag/AgCl. Electrochemical impedance analysis showed a gradual reduction of charge transfer resistance with increasing M. Finally, beta-Bi2O3 films with tailored microstructure were prepared which make it attractive for many applications.