Ganesh R. Bhand

Effect of deposition time on the properties of Al doped ZnO films prepared by DC magnetron sputtering

Aluminum-doped zinc oxide (AZO) thin films were successfully prepared on glass substrates at room temperature by DC magnetron sputtering. The sputtering time varied from 5 minute to 30 minute, while the power was kept at 230W for all depositions. The structural and optical properties of AZO films were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Raman Spectroscopy, Photoluminescence, and UV–visible spectrophotometer. Polycrystalline AZO thin films with hexagonal wurtzite structure were recorded by XRD analysis. The crystallinity and surface morphologies of the films are strongly dependent on the growth time, which in turn exerts a great effect on structural and optical properties of the AZO films. The transmittance for all the AZO films was above 92% in the visible region, and the largest band gap achieved as compare to intrinsic ZnO (3.3 eV). The defect distribution was analyzed by PL analysis.

Electrochemically synthesized CuInSe2 thin films from non-aqueous electrolyte for solar cell applications

Highly polycrystalline CuInSe2 (CIS) thin films have been electrodeposited from non-aqueous ethylene glycol (EG) solvent on fluorine-doped tin-oxide-coated glass substrates at 130 °C. The co-deposition potential for Cu, In and Se was optimized by using cyclic voltammetry. CIS layers have been electrodeposited from −1.1 V to −1.5 V versus the Ag/AgCl reference electrode. The effect of selenization on structural, morphological, optical and compositional properties has been studied extensively. Highly crystalline CIS thin films are electrodeposited for all reported growth potentials without post-annealing treatment. The Raman spectra of stoichiometric CIS thin films showed a dominant A1 mode with features receptive to the crystalline quality of the layers. Noticeable changes in the surface morphology and composition of films deposited at different deposition potential were observed. All CIS layers were void free, compact, uniform, and well adherent to the substrates with particle size ~1–3 μm. Both as-deposited and selenized samples were Cu-rich, however, the composition of selenium remained closer to the ideal value, 50%. A typical solar cell prepared at −1.3 V measured V OC = 0.316 V, J SC = 26 mA, FF = 49, and η = 4.2, under illuminated conditions at 100 mW cm−2.

Synthesis and Characterization of Controlled Size CdSe Quantum Dots by Colloidal Method

Monodispersed and highly luminescence cadmium selenide (CdSe) quantum dots (QDs) have been prepared in a single pot by colloidal reaction method. The QDs were characterized using X-ray diffraction (XRD), Raman Spectroscopy, transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), UV-visible absorption spectroscopy and photoluminescence (PL) spectroscopy to study the structural, morphological, compositional and optical properties. The growth temperature played an important role to control the particle size. The optical wavelength was found to be shifted systematically from 460 nm to 575 nm upon increasing the reaction temperature from 110 °C to 260 °C. The size of CdSe QDs, ~2-4 nm was estimated from absorption data. The emission tail exhibited at higher wavelength in PL measurement for the QDs synthesized for lower reaction temperature revealed the presence of surface trap-states. A cubic crystal structure of CdSe QDs was revealed by XRD analysis. The spherical QDs of size 2 to 4.5 nm were observed from TEM analysis for the samples prepared at 140 °C, 200 °C and 260 °C. The sizes of QDs obtained by TEM are in good agreement with the results obtained from optical and XRD data. High resolution transmission electron microscopy (HRTEM) confirmed the cubic crystal structure of CdSe QDs. The Selected area diffraction (SAD) pattern exhibited diffused ring corresponds to (111), (220) and (311) reflections of cubic structure of CdSe. The compositional analysis studied by EDS revealed the growth of nearly stoichiometric CdSe QDs. The LO1 vibrational mode observed about 202-205 cm-1 decreases the broadening systematically upon increasing the reaction temperature.

CdS quantum dots synthesized by low-cost wet chemical technique

Cadmium sulphide (CdS) quantum dots (QDs) have been prepared by low-cost solution processable colloidal technique. Cadmium (Cd) and Sulphur (S) precursor solutions were prepared separately. The concentration of Cd and S source along with surfactant and the reaction temperature were optimized for synthesis of the CdS QD’s. UV-Vis shows the absorption peak at 437 nm which corresponds to bandgap of 2.8 eV. The photoluminescence (PL) results are in good agreement with absorption data.Cadmium sulphide (CdS) quantum dots (QDs) have been prepared by low-cost solution processable colloidal technique. Cadmium (Cd) and Sulphur (S) precursor solutions were prepared separately. The concentration of Cd and S source along with surfactant and the reaction temperature were optimized for synthesis of the CdS QD’s. UV-Vis shows the absorption peak at 437 nm which corresponds to bandgap of 2.8 eV. The photoluminescence (PL) results are in good agreement with absorption data.