Characterization of TiO2 Photoelectrodes Fabricated via a Low Temperature Sintering Process

Abstract

TiO₂ photoanodes used for water-splitting solar cells or dye-sensitized solar cells (DSSC) have to meet the following properties to assure high efficiency: good connection between TiO₂ grains and a large inner surface area, TiO₂ grain shape and film conductivity. Nanocrystalline TiO₂ films are usually prepared by adding an organic binder to TiO₂ paste on glass substrates, and followed by heating at temperatures ranging from 450 to 500 °C. The organic binder is used to increase viscosity, enabling the formation of uniform TiO₂ films. Heat treatment is used to sinter the nanoparticles, as well as burn out the organic binder. In the case of composite formulations involving organic polymer electrolyte membranes, the conventional preparation technology is not suitable, because of the low temperature resistance of the polymer, on order of 150 °C. Therefore, to make thick TiO₂ films with good interconnection between the nanoparticles at low temperature, it is essential to enhance the viscosity of TiO₂ colloidal solution without using an organic binder. Possible approaches are developed by using acid-base chemistry, where the viscosity of acidic TiO₂ colloidal solution is monitored while adding ammonia solution which acts as a base. Thus the processed TiO₂ photoanode was assembled into a photoelectrochemical cell and tested by measuring I-V characteristics under illumination by white light from a solar simulator. TGA, DSC, IR, XRF, XRD and SEM analyses were performed to characterize the films. The low temperature process yielded titania films that were comparable to the conventional high temperature method.