Rajesh A. Joshi

Annealing-Induced Modifications in Physicochemical and Optoelectronic Properties of Ag-Doped Nanostructured CdS Thin Films

The Ag-doped nanostructured CdS thin films are grown by simple, cost effective chemical ion exchange technique at room temperature on ITO-coated glass substrate. These as grown thin films are annealed at 100, 200, 300, and 400°C in air atmosphere for 1 hour. To study the effect of annealing on physicochemical and optoelectronic properties, these as grown and annealed thin films are characterized for structural, compositional, morphological, optical, and electrical properties. X-ray diffraction (XRD) pattern reveals polycrystalline nature of these thin films with increase in crystallite size from 6.4 to 11.2 nm, from XRD the direct identification of Ag doping in CdS thin films cannot be judged, while shift in characteristics peak position of CdS is observed. The Raman spectrum represents increase in full width at half maxima and intensity of characteristic peak, confirming the material modification upon annealing treatment. Presence of Cd, Ag, and S in energy dispersive X-ray analysis spectra (EDAX) confirms expected elemental composition in thin films. Scanning electron microscopy (SEM) images represent grain growth and agglomeration upon annealing. Red shift in optical absorbance strength and energy band gap values from 2.28 to 2.14 eV is obtained. I-V response obtained from as grown and annealed thin films shows an enhancement in photosensitivity from 72% to 96% upon illumination to 100 mW/cm2 light source.

Effect of post-deposition treatment on energy conversion efficiency of nanostructured CdS/Cu{sub 2}S thin films

In the present manuscript we report about synthesis of nanostructured CdS/Cu2S thin films by economically viable soft chemical route and effect of post deposition treatments such as annealing in air and swift heavy ion irradiation on solar energy conversion efficiency of the heterojunction device. These as grown, annealed and irradiated thin films are characterized for structural, morphological, optical and I-V properties. X-ray diffraction pattern (XRD) represents structural as well as crystallite modifications, atomic force microscopy (AFM) shows improvement in surface appearance of the materials. The solar energy conversion efficiency calculated from I-V exhibited increase in conversion efficiency i. e. 0.09, 0.24 and 0.48 % for as grown, annealed and SHI irradiated thin films.

Ag induced photo-generated charge trapping in nanostructured CdS/Cu2S thin film for photovoltaic applications

Here we report about Ag induced photo-generated charge-trapping centers in nanostructured CdS/Cu2S thin film. The nanostructured CdS/Cu2S thin films prepared by chemical route while Ag incorporation achieved by cost effective chemical ion exchange route at room temperature. The obtained thin films were annealed at 250°C in air and later characterized for structural, optical and I-V characteristics. X-ray diffraction pattern confirms Ag incorporation in CdS/Cu2S heterojunction with increase in crystallite size from 32 to 50 nm. Scanning electron microscopy shows closed mouth structure of the CdS: Ag/Cu2S than CdS/Cu2S thin films. Blue shift in optical absorbance strength and energy band gap value from Eg = 2.27 to 2.10 eV is observed. Improvement in solar energy conversions efficiency from η = 0.24 % to 0.92 % is obtained upon doping.

Engineering of Wet Chemically Grown Nanostructured Zinc Oxide Thin Film by High Electronic Excitation

Thin films of ZnO are synthesized on ITO substrate using successive ionic layer adsorption and reaction (SILAR) technique. The as‐grown thin films were annealed at 250 °C (pristine) in vacuum atmosphere (10−2 Torr) for 1 h and further irradiated using 120 MeV Au9+ ions with different fluence 3×1012 and 5×1012 ions/cm2. These pristine and irradiated samples were studied for structural and optoelectronic properties. XRD study reveals better crystalline quality of film at 3×1012 ions/cm2 fluence. On the other hand, electrical resistivity of the films decreases from 13.44 Ω‐cm to 3.74 Ω‐cm with increase in irradiation fluence. Also it appears that irradiation does not affect absorption edge.

SHI Induced Modifications in CdS/CuInSe{sub 2} Thin Film: XRD Analysis

CuInSe2 (CIS nanostructured) thin films were prepared by ion exchange method at room temperature on ITO coated glass substrates in an alkaline medium. The as prepared thin films were irradiated by 120 MeV Au9+ swift heavy ion (SHI) at 5×1011 and 5×1012 ions/cm2 fluence respectively. To study the effect of irradiation, the pristine and irradiated nanostructured thin films were characterized by X ray Diffraction (XRD) and analyzed the improvement in crystalline quality and crystallite size. The observed structural modifications discussed considering the high electronic energy deposition by 120 MeV gold heavy (Au9+) ions in CuInSe2 thin films.

Zinc Oxide Nano Particle Grown By Soft Solution Route at Room Temperature

Zinc oxide thin films were deposited by simple soft solution route at room temperature. The as grown thin films of ZnO were characterized for the structural, morphological and optical properties. X‐ray diffraction (XRD) analysis reveals the polycrystalline nature of ZnO thin films with hexagonal structure. The films were highly oriented along (100) and (101) planes. The broad and low intense peaks in XRD pattern indicate the presence of coarsely fine, nano crystalline grains. Transmission Electron Microscopy (TEM) micrographs shows the formation of ZnO nanocrystallites. Atomic Force Microscopy (AFM) image shows uniform deposition of ZnO thin film on the substrate. The optical band gap was found to be 3.37 eV for as grown films.

Evidence of Phonon Condensers at Nanoscale

The values of thermovoltage are observed to enhance in metal chalcogenide materials after heavy ion irradiation. The physical basis behind this process is unclear. Here we treated thermal and electrical currents equally and replaced two dimensional thermal system by electrical network incorporating resistors, connected in series and capacitors, connected in parallel. The physical essence, however, and units of the terms of the equations are different. This scheme is called as ‘electro‐thermal’ analogy and it explains qualitatively the hampered motion of phonons from hot end to cold end. Restricting phonons in thermoelectric materials paves the way to enhancement of Seebeck coefficient.