Thermal treatment effect on structure, electrical conductivity and transient photoconductivity behavior of thiourea modified TiO2 sol–gel thin films

Thiourea modified nanocrystalline titanium dioxide (TiO2) thin films were prepared by sol–gel route and were thermally treated at five different temperatures (400, 500, 600, 800 and 1000 °C). The films were studied using GIXRD, PIGE and UV–vis spectroscopy. It was observed that the anatase to rutile phase transformation of TiO2 was inhibited by the thiourea modification. The transmittance of the modified films appeared reduced which was attributed both to the modification of TiO2 with thiourea and the light scattering in the films. The dark conductivity and the transient photoconductivity of the modified TiO2 sol–gel thin films were studied in vacuum and in air. The environment does not influence significantly the dark conductivity, because of the almost equivalent competition between oxygen and water adsorption. The photoconductivity reaches high values for all samples in both environments, with the sample treated at 500 °C to present the highest value. The larger values in vacuum can be attributed to the reduced amount of adsorbed oxygen at the surface, which acts as electron scavenger.

► Thiourea modified TiO2 sol–gel thin films.
► Structure and UV–vis spectra.
► Heat treatment at several temperatures influences conductivity and photoconductivity.
► Photoconductivity is drastically reduced in air.
► The treatment at 500 °C consists the optimum choice for the higher photoconductivity.