Application of photoconductivity effect in BaTiO3 / TiO2 hybrid heterostructure for solar cells

Abstract

TiO 2 is known as material with excellent chemical and photochemical stability. It exists in three different crystalline phases: anatase, rutile and brookite. It was found that anatase is photocatalytically more active than rutile due to its large surface area. This activity depends not only on the phase of TiO 2 but also on the crystallite size and porosity. One of the most applied synthesis is electrochemical eteching of titanium foil to obtained thin TiO 2 nanotubes array. The morphology parameters, e.g., nanotube length, diameter, smoothness, depend on the anodization conditions, such as voltage, electrolyte composition, temperature, and duration. After anodization, the amorphous nanotubes can be annealed to increase the electron mobility, sensitized with dyes or polymers to increase solar photon absorption, and doped or surface‐functionalized to adjust the density of states. Because of these properties the titania nanostructures can be used for photo‐catalysis, in solar cells (DSSC) and sensors. On the other hand BaTiO 3 is a well known and widely investigated dielectric material. Barium titanate is also used for electronic devices in technological ceramic industry because of its ferroelectric, thermoelectric and piezoelectric properties when it assumes the tetragonal structure. As such it have application in production of capacitors, positive temperature coefficient resistors, dynamic random access memories, electro mechanics and nonlinear optics. In this research we will study effect on optical and electrical properties of hydrothermal growth of BaTiO 3 nanoparticles at the surface of TiO 2 nanotubes obtained by electrochemical etching of titanium foil and titanium film deposited on FTO glass. Due to ferroelectric effect of BaTiO 3 we believed the charge separation in this type of heterostructure will be improved compared to pristine TiO 2 nanotubes. The nanotubes will be synthesized by electrochemical oxidation of Ti‐foil. The parameters of the TiO 2 nanotubes will be finely tuned together with the size of BaTiO 3 nanoparticle, with the aim to obtained highest photoconductivity effects and allowing the optimization of device fabrication for different types of solar cells hybrid solar cells. Preliminary results show that TiO 2 nanotubes have diameter around 80 nm and grown BaTiO 3 nanoparticles 30–50 nm (Fig. 1 and 2). AFM measurements confirmed the size of BaTiO 3 nanoparticles and local measurements of piezoelectric effect shown that in ours system exists preferred polarization in the direction of applied external electrical field. This study will be performed with the aim to optimize the dimensions of TiO 2 and BaTiO 3 nanoparticles to increase the efficiency of solar cells. For the structural characterization of all the titanate nanostructures we will used conventional and analytical transmission electron microscopy (TEM) techniques, scanning electron microscopy (SEM), XRD and Raman spectroscopy, Impedance spectroscopy, SPM microscopy and UV‐Vis spectroscopy.