N. Rajeswari Yogamalar

Quantum confined CdS inclusion in graphene oxide for improved electrical conductivity and facile charge transfer in hetero-junction solar cell

We employed a simple mechanism in tuning the electrical conductivity of graphene oxide (GO) by the inclusion of nano cadmium sulphide (CdS) and thereby, utilized it in a pn hetero-junction based solar cell. Two different kinds of hetero-junction solar cell devices are fabricated; one with CdS acting as a separate buffer layer in GO and in another, the GO was functionalized with quantum confined CdS particles. In both kinds, the n-type junction was interfaced with the p-type semiconductor Rose Bengal (RB). The nano CdS has the ability to harvest a useful spectral range of the solar spectrum and to retard the recombination rate between the junction interfaces and hence, promote the facile charge carrier transport within the device. The CdS functionalized GO exhibited a remarkable short circuit current density (Jsc) of 4 mA cm−2, and an open circuit voltage (Voc) of 685 mV, giving rise to an enhanced power conversion efficiency (η) of 1.97% in comparison to the planar GO hetero-junction. The enhancement in power conversion efficiency and the influence of nano CdS inclusion is analyzed and interpreted on the basis of the electrical studies performed with cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS). From the electrical measurements, the charge storage capacitance of 138 F g−1 and the minimal resistance of 440 Ω are incurred in GO/CdS nanocomposites. The obtained results are further supported by the various physico-chemical characterizations such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), absorption and luminescence emission studies and demonstrate their significance in photovoltaic applications.

BLUE EMISSION AND BANDGAP MODIFICATION IN N:ZnO NANORODS

Nanorods of nitrogen-doped ZnO(N:ZnO) are grown by hydrothermal chemical precipitation method. The average crystallite size, surface morphology, and particle size distribution are estimated and characterized from powder X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The characteristic vibration mode of metal-oxide is confirmed from Fourier transform infrared spectroscopy (FT-IR) study. The absorption spectra of N:ZnO in the ultraviolet visible (UV-vis) region and their variations are recorded as a function of dopant concentration. The Tauc plot elucidates that the bandgap of N:ZnO increases up to 6 atomic percent (at.%) of dopant concentration and then decreases for heavy doping. The widening and narrowing in bandgap is interpreted in terms of impurity induced absorption edge shift due to N doping. Photoluminescence (PL) spectra revealed the existence of visible band, arising from impurity related defects.

ESTIMATION OF LATTICE STRAIN, STRESS, ENERGY DENSITY AND CRYSTALLITE SIZE OF THE SPHERICAL YTTRIUM OXIDE NANOPARTICLES

Yttria nanoparticles are synthesized by co-precipitation method and as-prepared nanoparticles are annealed at various temperatures. The as-prepared and annealed particles are characterized by X-ray diffraction and transmission electron microscope (TEM). Here we estimated the lattice strain, crystallite size, deformation stress, and deformation energy density for annealed (800°C) yttrium oxide nanoparticles by Williamson-Hall-Isotropic Strain Model (W-H-ISM), W-H-Anisotropic Strain Model (W-H-ASM) and W-H-Energy Density Model (W-H-EDM) based on W-H plot from powder X-ray diffraction data. The shape and size of the nanoparticles are determined using TEM. The results of the estimated crystallite size of yttria nanoparticles by various methods agreed with the TEM results.

Rectifying behaviour of spin coated pn hetero-junction

Rectifying pn hetero- junction is fabricated with an acceptor p-type organic semiconductor namely tetra- chloro dihydroxy tetra-iodo fluorescein (Rose Bengal (RB)) followed by an inorganic n-type ZnO semiconductor on indium tin oxide (ITO) substrate. The n-type ZnO films are formed by unintentional doping and doping with aluminium (Al) and yttrium (Y) donors. The surface morphology and the distribution of grains are observed from scanning electron microscopy (SEM) and atomic force microscopy (AFM). The current-voltage (I-V) characteristic of the rectifying diode is measured to characterize the junction properties. The I-V plots obtained from the hetero- junction with electric contact shows a diode characteristic different from that of an ideal behavior. The overall efficiency of the diode exhibits a greater dependency on the film crystallinity, carrier concentration, and reverse saturation current.

Absorption‐Emission study of Zn1−xAlxO nanostructures

One‐dimensional aluminum doped ZnO (ZnO:Al) nanorod is achieved by the controlled addition of metal nitrate as precursors in the presence of long chain poly‐ethylene glycol (PEG) at 160 °C for 20 h through hydrothermal method. The as‐synthesized ZnO nanorods are single crystalline, exhibiting an oriented growth along (0001) direction. Comprehensive structural analyses using X‐ray diffraction (XRD) and energy dispersive X‐ray spectroscopy (EDX) indicate that the dopant Al atom occupies Zn sites in ZnO. XRD pattern of the Zn1−xAlxO sample shows the formation of wurtzite hexagonal phase however, when the dopant concentration exceeds 9 at.% impurity phase corresponding to Al2O3 appears. The dopant effects on lattice vibration and electronic transitions of the ZnO nanocrystals have been investigated by Fourier transform infrared spectroscopy (FT‐IR), Ultraviolet visible spectroscopy (UV‐vis) absorption and photoluminescence (PL) emission recorded at room temperature. The characteristic absorption peak of doped...

Annealed Ce Doped ZnO Coated Fiber Optic Gas Sensor

Fiber optic sensor based on cladding modification method for detecting various gas emissions such as ammonia methanol, and ethanol is proposed. The Ce doped ZnO annealed at 500 and 1200 °C are used as a gas sensing material. The spectral characteristics of the gas sensor are studied for different concentrations (0–500 ppm) of gases. The sensor exhibits a linear variation in the output light intensity with the concentration. The gas sensitivity and selectivity of the sensor is discussed briefly.