N. Muthukumarasamy

Influence of the Cd/S Molar Ratio on the Optical and Structural Properties of Nanocrystalline CdS Thin Films

Nanocrystalline CdS thin films have been deposited using precursors with different thiourea concentration onto glass substrates by sol-gel spin coating method. The crystalline nature of the films has been observed to be strongly dependent on thiourea concentration and annealing temperature. The CdS films are found to be nanocrystalline in nature with hexagonal structure. The grain size is found to be in the range of 7.6 to 11.5 nm depending on the thiourea concentration and annealing temperature. The high resolution transmission electron microscopy (HRTEM) results of the CdS films prepared using cadmium to thiourea molar ratio of 0.3:0.3 indicate the formation of nanocrystalline CdS with grain size of 5 nm. Fourier transform infrared (FTIR) analysis shows the absorption bands corresponding to Cd and S. The optical study carried out to determine the band gap of the nanostructured CdS thin films shows a strong blue shift. The band gap energy has been observed to lie in the range of 3.97 to 3.62 eV following closely the quantum confinement dependence of energy on crystallite radius. The dependence of band gap of the CdS films on the annealing temperature and thiourea concentration has also been studied. The photoluminescence (PL) spectra display two main emission peaks corresponding to the blue and green emissions of CdS.

High performance inverted organic solar cells with solution processed Ga-doped ZnO as an interfacial electron transport layer

We demonstrate solution-processed Ga-doped ZnO incorporated as an interfacial electron transport layer into inverted organic solar cells with active layers comprising either PCDTBT or PTB7 mixed with PC71BM. The 5.03 at% Ga-doped ZnO showed the best efficiencies of 5.56% and 7.34% for PCDTBT and PTB7 polymers respectively.

Natural dye sensitized TiO2 nanorods assembly of broccoli shape based solar cells

TiO2 nanorods based thin films with rutile phase have been synthesized using template free low temperature hydrothermal method. The scanning electron microscope images showed that the prepared TiO2 samples were made of TiO2 nanorods and the nanorods had arranged by itself to form a broccoli like shape. The X-ray diffraction studies revealed that the prepared TiO2 samples exhibit rutile phase. The grown TiO2 nanorods had been sensitized using the flowers of Sesbania (S) grandiflora, leaves of Camellia (C) sinensis and roots of Rubia (R) tinctorum. Dye sensitized solar cells had been fabricated using the natural dye sensitized TiO2 nanorods based thin film photoelectrode and the open circuit voltage and short circuit current density were found to lie in the range of 0.45-0.6 V and 5.6-6.4 mA/cm(2) respectively. The photovoltaic performance of all the fabricated natural dye sensitized TiO2 solar cells indicate that natural dyes have the potential to be used as effective sensitizer in dye sensitized solar cells.

Synthesis and Characterization of Selenium Nanowires

Selenium nanowires have been grown by chemical method. The effect of annealing on the properties of the prepared selenium nanowires has been studied. The X-ray diffraction studies indicated the formation of selenium with trigonal phase, and no secondary phase was observed. The composition analysis results show that selenium is present in the sample. HRTEM images reveal that selenium nanowires have diameter ranging from 30–50 nm and length of 1-2 𝜇m. The diameter and length of nanowires have been found to increase with increase in annealing temperature.

Annealing Induced Shape Transformation of CZTS Nanorods Based Thin Films

Here we studied the annealing induced shape transformation of 1D Cu2ZnSnS4 (CZTS) nanorods from nanospheres and nanocubes by simple sol-gel method without using any toxic chemicals or complicated vacuum based technology. X-ray diffraction pattern and Raman spectra reveal the formation of kesterite structure CZTS thin films. The energy dispersive X-ray analysis results indicate the presence of Cu, Zn, Sn, and S. The elemental distribution of all the CZTS samples was studied using elemental mapping. The Hall effect studies of the CZTS thin film composed of nanorods exhibits the lowest resistivity values which indicates efficient charge transfer for unidirectional structure. The obtained optical band gap energy of CZTS thin film is in the range of 1.46-1.54 eV, which is quite close to the optimum theoretical value required for solar cell applications.

Ball/dumbbell-like structured micrometer-sized Sb 2 S 3 particles as a scattering layer in dye-sensitized solar cells

To improve the light harvesting efficiency in dye-sensitized solar cells (DSSC) the light scattering layer is important. In this Letter, we present ball/dumbbell-like structured micrometer-sized Sb2S3 particles for photon propagation in DSSCs and demonstrate their effective usage in photoelectrodes. The analysis of the photoelectrode by a UV-vis spectrophotometer indicates that the absorption wavelength of an electrode with scattering layer can be obviously promoted from ultraviolet to visible light. The synthesized Sb2S3 particle structures were also characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The photovoltaic performance of the ball/dumbbell-like structured Sb2S3 based cell exhibits excellent power conversion efficiency.

Improved performance of dye sensitized ZnO nanorod solar cells prepared using TiO 2 seed layer

Zinc oxide (ZnO) nanorods of different structures have been grown on indium-doped tin oxide substrates by using TiO2 as seed layer. The ZnO nanorods have been prepared using TiO2 seed layers annealed at different temperatures via a simple sol–gel method. The X-ray diffraction result indicates that the prepared samples are of wurtzite structure. Dye sensitized solar cells have been fabricated using the prepared ZnO nanorods. The open circuit voltage, short circuit current density, fill factor, and power conversion efficiency of the ZnO nanorod based dye sensitized solar cells prepared using TiO2 seed layers annealed at different temperatures have been determined. The improvement in power conversion efficiency may be due to the flower like structured ZnO nanorods with smaller diameter and large specific surface area which paves way for the efficient electron transfer in hybrid solar cells.

Effect of solvents in the extraction and stability of anthocyanin from the petals of Caesalpinia pulcherrima for natural dye sensitized solar cell applications

Anthocyanin, a flavonoid pigment is responsible for wide range of coloration in petals of flowers and fruits, absorbs broad range of visible light. This makes them suitable to be used as dyes for DSSC. But, the efficiency of natural dyes is not up to the mark mainly due to anthocyanin instability. The stability issues in vitro are mainly due to the effect of solvents on extraction of anthocyanins and their respective pH. Taking this factor into consideration, in the present work, the anthocyanins were extracted from the flower Caesalpinia pulcherrima (C. pulcherrima) with various solvents and their respective stability and pH values are discussed. The usage of citric acid as solvent to extract anthocyanin has shown good stability than other solvents. It also helps in enhancing the sensitization properties of anthocyanins with titanium dioxide (TiO2) nanorods. The IPCE spectra show higher photovoltaic performance for dye sensitized TiO2 nanorods using citric acid as solvent. The natural DSSC using citric acid as solvent shows a higher efficiency of 0.83% compared to other solvents. Hence citric acid performs to be a safe solvent for natural DSSC in boosting the photovoltaic performance and maintaining the stability of anthocyanins.

Effect of Chromium and Cobalt Addition on Structural, Optical and Magnetic Properties of NiO Nanoparticles

Abstract Nanocrystalline nickel oxide (NiO), chromium and cobalt doped NiO nanoparticles have been prepared successfully by chemical precipitation method. NiO, Cr and Co-doped NiO nanoparticles have been characterised using various analytical techniques such as X-ray diffraction, FESEM, HRTEM, UV absorption and M-H curves. The average grain size of NiO, Cr and Co-doped NiO nanoparticles are 10.33 nm, 9.54 nm and 8.70 nm respectively. The UV absorbance study shows a strong absorption edge at 314.96 nm, 308.64 nm and 305.37 nm respectively. The band gap values of NiO, Cr and Co-doped NiO nanoparticles are 3.936 eV, 4.017 eV and 4.060 eV. The incorporation of chromium and cobalt into NiO nanoparticles have strongly influenced the magnetic behaviour and the material got converted from super paramagnetic to ferromagnetic material.

Preparation and Characterization of Al2O3 Doped TiO2 Nanocomposites Prepared from Simple Sol-Gel Method

Abstract Al2O3 doped TiO2 samples were prepared by the simple sol-gel method. The prepared samples were annealed at 400°C for 1 h in an open air atmosphere. The dielectric properties, AC electrical conductivity (σac), dielectric constant (ε′), dielectric loss (ε″) and the loss tangent (tan δ) of the prepared Al2O3 doped TiO2 nanocomposites were studied under a wide frequency and temperature range. The dielectric loss values of the prepared samples were measured at 50 Hz and 5 MHz and the values were found to be in the range of 0.11–1.73 at 40°C and 0.13–4.39 at 100°C. The microstructures of the prepared samples were also studied using high-resolution transmission electron microscopy (HRTEM) analysis.