National Synchrotron Radiation Laboratory

Cadmium sulfide (CdS) and zinc oxide (ZnO) are used in thin film solar cells as buffer layer and transparent conducting oxide, respectively. The effect of annealing conditions on the morphology and physical properties of CdS and ZnO films prepared using chemical bath deposition and sol-gel synthesis techniques, respectively, was investigated. CdS films obtained from the chemical bath deposition (CBD) process were found to be polycrystalline with dense granular morphology. Electrical characterization of the films annealed at 400 • C for 10 min yielded values of 2.2 × 10 −3 cm and 8.3 × 10 12 cm −3 for resistivity and carrier concentration, respectively. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) studies of intrinsic zinc oxide (i-ZnO) films revealed flake-like morphology and transformation of the as-deposited amorphous structure into a hexagonal wurtzite crystal structure upon annealing at 500 • C for 2 h. Optical and electrical characterization results showed that such films had ∼80% transmittance and resistivity values as low as 6.4 × 10 2 cm. These films are being explored for fabrication and testing of copper-indium-gallium-(di)selenide (CIGS) thin film solar cells obtained from simple, cost-effective, solution-based synthesis routes.

Molebdenum (Mo) thin films were deposited on well-cleaned soda-lime glass substrates using DC-plasma magnetron sputtering. In the design of experiment deposition was optimized for maximum beneficial characteristics by monitoring effect of process variables such as deposition power (100–200 W). Their electrical, structural and morphological properties were analyzed to study the effect of these variables. The electrical resistivity of Mo thin films could be reduced by increasing deposition power. Within the range of analyzed deposition power, Mo thin films showed a mono crystalline nature and the crystallites were found to have an orientation along [110] direction. The surface morphology of thin films showed that a highly dense micro structure has been obtained. The surface roughness of films increased with deposition power. The adhesion of Mo thin films could be improved by increasing the deposition power. Atomic force microscopy was used for the topographical study of the films and to determine the roughness of the films. X-ray diffractrometer and scanning electron microscopy analysis were used to investigate the crystallinity and surface morphology of the films. Hall effect measurement system was used to find resistivity, carrier mobility and carrier density of deposited films. The adhesion test was performed using scotch hatch tape adhesion test. Mo thin films prepared at deposition power of 200 W, substrate temperature of 23°C and Ar pressure of 0.0123 mbar exhibited a mono crystalline structure with an orientation along (110) direction, thickness of ∼550 nm and electrical resistivity value of 0.57 × 10−4 Ω cm.

Molybdenum thin¯lms were sputter deposited under di®erent conditions of DC power and chamber pressure. The structure and topography of the¯lms were investigated using AFM, SEM and XRD techniques. Van der Pauw method and tape test were employed to determine electrical resistivity and interfacial strength to the substrate, respectively. All the¯lms are of sub-micron thickness with maximum growth rate of 78 nm/min and crystallite size in the range of 4 to 21 nm. The¯lms produced at high power and low pressure exhibit compressive residual strains, low electrical resistivity and poor adhesion to the glass substrate, whereas the converse is true for¯lms produced at high pressure.

ZnTe thin films were deposited onto soda lime glass substrates by the close space sublimation (CSS) and electron beam evaporation (EBE) techniques under vacuum (as deposited, annealed at 300 uC and Ag doped for 10 min). Structural, morphological, optical and electrical properties of ZnTe films were studied before and after doping. The ZnTe thin films fabricated by EBE technique showed improvement in microstructure, morphology, crystalline orientation and physical parameters such as porosity and density as compared to CSS fabricated thin films. The highest density with very small porosity is observed in EBE fabricated films. The improvement in electrical parameters such as resistivity, mobility, sheet concentration, type of semiconductor (p or n type), bulk concentration and magnetoresistance were observed in EBE fabricated thin films. The highest decrease in electrical resistivity (8?34610 2 V cm) was observed by incorporating Ag dopant via EBE technique. The main purpose of this was a comparative study between EBE and CSS techniques and an improvement in the electrical and optical properties such as electrical conductivity, mobility, sheet resistance/concentration and the band gap of the fabricated thin films. The doping of Ag was performed to observe their effects on morphology, structure, electrical and photovoltaic properties of the as deposited thin films. It was observed that electrical and optical properties of the fabricated films enhanced with dopant and annealing temperature.

In this paper, ZnO/Ag core-shell hybrid nanocomposites have been prepared by a very simple chemical methodology. ZnO nanorods were employed as core material for Ag seeds, and subsequent nucleation and growth of Ag nanoparticle by a cationic surfactant cetyltrimethylammonium bromide (CTAB) formed the ZnO NRs/Ag core-shell nanocomposites. In addition, their morphology, microstructure and optical properties have been characterized by X-ray diffraction, Raman Spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV-Vis absorption and photoluminescence spectroscopy. It was found that face-center-cubic Ag nanoparticles with an average diameter of 20 nm were coated onto the surface of hexagonal phase ZnO nanorods with a minimum of 0.09 mmol concentration of CTAB. The excitonic absorption band and surface plasmon absorption band of the ZnO NRs/Ag nanocomposites revealed red-shifts relative to pure ZnO nanorods and metallic Ag nanoparticles. The coating of Ag nanoparticles onto the ZnO nanorods show red-shift in the near band edge (NBE) luminescence spectra and a reasonable detraction in the deep level emission (DLE) spectra compared with the pure ZnO nanorods. These interpretations demonstrated the strong interfacial interaction between Ag nanoparticles and ZnO nanorods. Furthermore, the annealing of ZnO NRs/Ag nanocomposite at 200°C was done and improvement occurs in the crystallinity and binding strength of Ag nanoparticles.

In this paper, PMMA/ZnO nanocomposites have been prepared by a very simple, facile and versatile chemical approach. The prepared PMMA/ZnO nanocomposites possess no color, high transparency, good thermal stability, UV-shielding capability, luminescence and homogeneity. The chemical process involved solution mixing of ZnO nanoparticles dispersed in DMAc with the Polymethylmethacrylate (PMMA) matrix dissolved in the same solvent. The effect of ZnO content on the physical properties of the PMMA matrix is investigated by X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, UV–Vis absorption and photoluminescence spectroscopy. It was found that pure hexagonal ZnO nanoparticles with an average particle size of 4–8 nm were homogeneously dispersed in the PMMA matrix. A significant improvement in thermal properties was observed with the incorporation of 1.0 wt% ZnO nanoparticles. The prepared nanocomposite films are highly transparent and a clear excitonic peak is observed in their absorption spectra. Measurement of room temperature photoluminescence spectra shows intensive near-band edge emission peak at 3.28 eV without any structural defects for a nanocomposite film with a filler content of 1.0 wt%.

Sputter deposited molybdenum (Mo) thin films are used as back contact layer for Cu (In 1 À x Ga x )(Se 1 À y S y ) 2 based thin film solar cells. Desirable properties of Mo films include chemical and mechanical inertness during the deposition process, high conductivity, appropriate thermal expansion coefficient with contact layers and a low contact resistance with the absorber layer. Mo films were deposited over soda-lime glass substrates using DC-plasma magnetron sputtering technique. A 2 3 full factorial design was made to investigate the effect of applied power, chamber pressure, and substrate temperature on structural, morphological, and electrical properties of the films. All the films were of submicron thickness with growth rates in the range of 34-82 nm/min and either voided columnar or dense growth morphology. Atomic force microscope studies revealed very smooth surface topography with average surface roughness values of upto 17 nm. X-ray diffraction studies indicated, all the films to be monocrystalline with (001) orientation and crystallite size in the range of 4.6-21 nm. The films exhibited varying degrees of compressive or tensile residual stresses when produced at low or high chamber pressure. Low pressure synthesis resulted in film buckling and cracking due to poor interfacial strength as characterized by failure during the tape test. Measurement of electrical resistivity for all the films yielded a minimum v alue of 42 μΩ cm for Mo films deposited at 200 W DC power.