N.L. Tarwal

Synthesis of electrochromic vanadium oxide by pulsed spray pyrolysis technique and its properties

A new improved pulsed spray pyrolysis technique (PSPT) was employed to deposit a vanadium oxide (V2O5) thin film from a methanolic vanadium chloride precursor onto glass and conducting F : SnO2 coated glass substrates. The structural, morphological, electrical, optical and spectroscopic properties of the film deposited at 573 K were studied. Infrared spectroscopy and x-ray diffraction confirmed the presence of the V2O5 phase. The V2O5 film (thickness ~118 nm) is polycrystalline with a tetragonal crystal structure. Scanning electron microscopy reveals compact granular morphology consisting of ~80–100 nm size grains. The film is transparent in the visible region (average %T ~70%) with an optical band gap energy of 2.47 eV involving both direct and indirect optical transitions. The room temperature electrical resistivity (conductivity) of the film is 1.6 × 108 Ω cm (6.25 × 10−9 S cm−1) with an activation energy of 0.67 eV in the temperature range 300–550 K. It exhibited cathodic electrochromism in the lithium containing electrolyte (0.5 M LiClO4 + propylene carbonate).

Single-step synthesis of 3D nanostructured TiO2 as a scattering layer for vertically aligned 1D nanorod photoanodes and their dye-sensitized solar cell properties

In the present investigation we have successfully synthesized 1D vertically aligned rutile TiO2 nanorods (TNR) and 3D TiO2 nanostars (TNS) as a scattering layer by a single step hydrothermal route. The synthesized nanostructures were characterized by X-ray diffraction, scanning-and transmission electron microscopy and X-ray photoelectron spectroscopy. The 1D TiO2 nanorod and 3D TiO2 nanostar samples were further used for N-719 dye sensitized solar cells (DSSC) application. Compared to a nanorod based cell, the photovoltaic performance of the nanostars/nanorods TiO2 cell exhibits excellent DSSC performance, including superior light scattering, rapid electron transport and lower electron recombination rate. The 3D/1D TNS/TNR based DSSC cell exhibits 5.39% power conversion efficiency, which is remarkably higher than that of the bare 1D nanorod based (3.74%) photoelectrode. The detailed interface and transient properties of these nanorod and nanostar based photoanodes in DSSCs were analyzed by electrochemical impedance spectroscopy measurements and open circuit voltage decay measurements in order to understand the critical factors contributing to such high power conversion efficiency. The enhancement of the efficiency for the 3D/1D TNS/TNR photoanode based cell compared to the 1D TNR is mainly attributed to better light scattering capability, faster electron transport and lower electron recombination.

Surfactant mediated growth of ZnO nanostructures and their dye sensitized solar cell properties

Single crystalline and highly aligned ZnO nanorods, faceted microrods, nanoneedles and nanotowers were grown onto glass substrates by a facile aqueous chemical method at relatively low temperature (90xa0°C). Various structure directing agents or organic surfactants such as diaminopropane (DAP), polyacrylic acid (PAA) and polyethylenimine (PEI) were used to modify the surface morphology. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption. It was found that, vertically aligned ZnO nanorods formation takes place with preferential orientation along (002) plane. The organic surfactants play an important role in modifying the morphology. The samples were further used to fabricate dye sensitized solar cells. The highest photocurrent (670 μA) and efficiency were observed for the ZnO:PEI sample.

Thickness dependent photoelectrochemical performance of chemo-synthesized nanostructured CdS thin films

Abstract Thin films of cadmium sulfide (CdS) with different film thicknesses were chemo-synthesized onto soda lime glass and fluorine doped tin oxide (FTO) coated glass substrates. The synthesized CdS films were characterized by using UV-vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD patterns revealed the formation of CdS with a cubic crystal structure. The variation in band gap energies was found to be in the range of 2.42–2.85u202feV. An increase of 0.43u2009eV over the bulk band gap energy of CdS was found due to the quantum size effect in CdS thin films. The atomic force microscopy study depicted a novel egg-like morphology of CdS nanoparticles. Further, photoelectrochemical (PEC) performance of as grown CdS thin films was investigated using two electrode configurations in polysulfide electrolyte. The sample with film thickness 1389u2009Å showed the best PEC performance compared to other samples.

Single-step hydrothermally grown nanosheet-assembled tungsten oxide thin films for sensitive and selective NO2 gas detection

A well-organized tungsten oxide (WO3) nanosheet-assembled microbricks have been synthesized by the hydrothermal route at 180xa0°C with the help of peroxy-tungstic acid sol. The as-synthesized thin films have been characterized for structural, morphological and compositional studies by using X-ray diffraction, scanning electron microscopy and FT-Raman spectroscopy. The deposited WO3 thin films have been found to be polycrystalline in nature with the monoclinic crystal structure. The SEM micrographs revealed the formation of microbrick-like structure which was made up of two-dimensional (2D) nanosheets. The 2D nanosheets act as a nanobuilding blocks for the formation of microbricks. The gas-sensing performance of WO3 thin films was carried out for different gases, and it is observed that sensor exhibited maximum gas response towards Nitrogen dioxide (NO2) gas which is seven times higher than that of other gases at an operating temperature of 300xa0°C over the concentration range of 5–100xa0ppm. WO3 microbricks sensor showed higher response about 11.5 and fast response–recovery characteristics towards NO2 gas, especially a much quicker gas response time of 16xa0s and recovery time of 260xa0s at 100xa0ppm.

Gas sensing properties of 3D mesoporous nanostructured ZnO thin films

Advancing the properties of selective and sensitive metal oxide based gas sensors is a challenging research topic for the detection of toxic, and pollutant gases. In the present research, we successfully deposited a three dimensional (3D) mesoporous ZnO nanostructure on a glass substrate by using a hydrothermal method, and tested the material for its gas sensing performance. These 3D mesoporous ZnO nanostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence techniques. Gas sensing performance analysis was carried out for nitrogen dioxide (NO2) gas at different temperatures and concentrations. The 3D mesoporous ZnO nanostructure revealed excellent gas sensing performance for NO2 gas because of its large surface area. The larger surface area led to an increase in the gas sensitivity. In addition, the sensor based on the 3D mesoporous ZnO nanostructure could be used at a low operating temperature of 150 °C. This work suggests that the 3D mesoporous ZnO nanostructure is a versatile material for NO2 gas sensing applications.

Facile green synthesis of In2O3 bricks and its NO2 gas sensing properties

Recently, metal oxide semiconductor based gas sensors have been used to monitor and maintain amount of toxic gases in environment. Use of In2O3 nano/microstructures have been increased as a heterogeneous catalyst for gas sensing due to its high response, good selectivity, short response and recovery time. In the present work, synthesis of In2O3 bricks was carried by a hydrothermal method using biomolecule as green product. The effect of precursor concentrations of In2O3 thin film was studied in this particular work. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Photoluminescence (PL), scanning electron microscope (SEM), Field emission scanning electron microscope (FE-SEM) and Brunauer–Emmett–Teller (BET) analyses were used for structural, optical, morphological and surface analysis characterizations. The In2O3 thin film displays high sensitivity and selectivity due to its active sites present on sensing layer. The results assures that optimized In2O3 thin films exhibit a high response with very low response and recovery time about 600 for NO2 gas.

Enhanced NO2 response of hydrothermally grown Ti doped WO3 nanostructures

Titanium doped WO3 (Ti doped WO3) nanostructures were synthesized by hydrothermal synthesis by the controlled hydrolysis of Na2WO4 using oxalic acid and Titanium tetrachloride. Prepared samples were characterized by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), and transmission electron microscopy (TEM). As-synthesized pristine WO3 showed nanorods with diameters of about 10–15xa0nm and length about 1.2xa0µm and Ti doped WO3 composed of numerous small nanocrystals. Introduction of Ti doping by chemical synthesis process suppressed the growth of one-dimensional nanorods along their axis direction and shows agglomeration of particulate like morphology and no elongated structures. Ti doping not only lowered the optimal operating temperature of WO3 nanostructures sensors from 250 to 200xa0°C but also increased the maximum value of sensor response. Also the Ti-doped WO3 nanostructures exhibited rapid response characteristic to NO2 gas compared to pristine WO3.