Study Regarding Photoelectric Performance And Controlled Deposition Of CdS And CdSe On The Surfaces Of TiO₂ Films

The semiconductor TiO₂ was restricted in the application as solar cell materials because of its wide band gap and low quantum efficiency. In present study, porous ITO/TiO₂ nanostructural thin films were prepared, which were further used as substrates for the deposition of narrow band gap semiconductors CdS and CdSe by means of cathode potentiostatic electrodeposition technique for obtaining ITO/TiO₂/CdS and ITO/TiO₂/CdSe nanostructural composite thin film. Furthermore, the effect of different experimental conditions on the composition and surface appearances were investigated. Also, the photoelectric performance of the prepared ITO/TiO₂/CdS and ITO/TiO₂/CdSe thin films was studied as photoanodes of solar cells.Anatase TiO₂ nanoparticles were prepared by hydrothermal method, in which Ti(OBu)4 was used as precursor, while TiO₂ colloids were obtained by Sol-Gel technique. And finally, using obtained nanoparticles and colloids, TiO₂ colloid thin film, TiO₂ particle thin film, and TiO₂ colloid-particle thin film were prepared by as-dipped and coating methods. Subsequently, the crystal structures of the prepared films were characterized by XRD and Raman spectra, and the surface morphologies of thin films were further observed by SEM and AFM techniques. Also, the particle size of TiO₂ was determined based on the XRD and SEM results. Porous structure and specific surface area of the prepared thin films were characterized by means of N2 adsorptiondesorption analysis, while photoelectric performances of different TiO₂ films were investigated by UV absorption spectrum and other photoelectrochemistry measure techniques. The experimental results indicate that the prepared TiO₂ colloid-particle thin films with homogeneous distribution of particles and rough surface as well as large specific surface area possess uniform porous structure, leading to strong absorption for UV radiation. Furthermore, we believe that the better photoelectric performance of the colloid-particle thin films results from the large specific surface area which can effectively decrease the grain boundary resistance and increase the contract district.By means of cathode electrodeposition technique, the ITO/TiO₂/CdS composite films were prepared using the ITO/TiO₂ colloid-particle films as substrate in acid water solution including CdCl2 and Na2S3O2 followed by the characterization for the crystal structures and compositions by XRD and XPS methods and for the surface morphologies, particles sizes, and film thickness by SEM technique. In our experiments, the effects of different experimental conditions, such as deposition potentials and times, electrolyte composition including electrolyte concentrations and addition of EDTA, experimental temperatures, etc., on the sizes of CdS particles and surface morphologies of ITO/TiO₂/CdS films were also evaluated. The results demonstrate that the spherical CdS particles with mixed crystal phase but hexagonal structure as the primary phase were uniformly deposited not only on the ITO/TiO₂/CdS film surface but also inside the ITO/TiO₂ substrate. At the conditions of deposition potential of -1.00 V and deposition time of 20 min, the prepared ITO/TiO₂/CdS thin films possess cauliflower-like morphology and Cd/S atom ratio of near 1:1. By controlling deposition potential and time, the deposition rate can be adjusted, results in high controllabilities for particle size and film thickness.In experiments, the photoelectric performance of the ITO/TiO₂/CdS composite semiconductor thin films and the effect of experimental condition on the photoelectric performance were also discussed photocurrent-potential curve and photocurrent action spectrum techniques, while SPS spectrum was used to estimate charge transfer mechanism of semiconductor film electrodes. The experimental results show that the sensitization of CdS for TiO₂ effectively improves the separation of photogenerated electrons and holes, increases photocurrent, and ameliorates initial photocurrent response, which will result in a high photoelectric transition efficiency within the absorption range of 400 500 nm.Furthermore, we also deposited narrow band gap semiconductor CdSe on the porous ITO/TiO₂ substrate by cathode potentiostatic deposition technique. Whereafter, the crystal structures and particle sizes as well as the film compositions and surface morphologies were analyzed by XRD and SEM techniques. The photoelectric performance of ITO/TiO₂/CdSe films was investigated in detail by UV-Vis, SPS, current-potential, and transient state photocurrent spectra. The results indicate that the sensitization of CdSe for TiO₂ effectively improves the photoabsorption and expand the photoelectric response to the range from 400 nm to 700 nm.