Ultrasound-assisted fabrication of nanoporous CdS films

A new method for fabricating nanoporous CdS films is reported. It involves exposing the CdS solution with ultrasound waves during the process of dip coating. Indium tin oxide (ITO)-coated glass and plastic (commercial transparency) were used as substrates. In each case three different precursors were used for dip coating. The precursors used were CdCl2 and thiourea in one case and CdS nanoparticles prepared by sonochemical and microwave-assisted methods in the other two cases. X-ray diffraction studies performed on these powders show a phase corresponding to cubic CdS. The Field Emission Scanning Electron Microscopy (FE-SEM) images of the films on plastic showed uniform pores with a diameter of 80 nm for all three methods. Optical absorption measurements indicated a blue shift and multiple peaks in the absorption curve. The FE-SEM observations of the films on an ITO/glass substrate indicated a crystalline film with voids. The UV-vis absorption results indicated a blue shift in the absorption with an absorption edge at 435, 380, and 365 nm for CdS films made by solution growth, sonochemical, and microwave routes, respectively. The magnitude of the absorption is dependent on film thickness, and the observed blue shift in the absorption can be explained on the basis of quantum confinement effects.     

Porous alumina templates and nanostructured CdS for thin film solar cell applications

Nanostructured CdS was grown by electrodeposition of cadmium sulfide inside a porous alumina template. Uniform pore size and spacing in the template was achieved when the starting material for the template was aluminum foil. Typical pore size was 45 nm. Nanostructured CdS was also deposited by electrodeposition on indium tin oxide (ITO)-coated glass and by solution growth on ITO-coated glass. Schottky diodes were formed on nanocrystalline CdS and the analysis of their current–voltage characteristics yielded a diode ideality factor (n) of 2.6 and a reverse saturation current density (J_S) of 1.00×10⁻⁵ A/cm². Corresponding values for the Schottky diode on polycrystalline CdS were 3.4 and 1.93×10⁻⁶ A/cm².     

Characteristics of nanocrystalline CdS films fabricated by sonochemical, microwave and solution growth methods for solar cell applications

Nanocrystalline CdS was synthesized by sonochemical and microwave methods. Characterization of nano-CdS was carried out by optical absorption, X-ray diffraction, TEM, SEM and EDX. A hyperbolic band model was used to calculate a shift in energy over that of the band gap of bulk CdS. Colloidal films comprising of nanocrystalline CdS were fabricated by the dip coating method. A comparison of optical absorption of CdS films on indium tin oxide (ITO)/glass by sonochemical and microwave methods was made with solution grown CdS films on ITO/glass. A blue shift in energy level at the nanoscale is demonstrated by optical absorption, and X-ray diffraction of nano-CdS shows a cubic structure. Electron microscopy studies with an FE-SEM and TEM show a particle size of 15 nm and diffraction patterns show a crystalline nature. Overall reduction in optical absorption due to blue shift is expected to result in higher performance, especially in short-circuit currents in CdS/CdTe solar cells.