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Phase-pure alpha-iron-oxide (α-Fe2O3) nano-powders were obtained via Pechini gel-combustion using iron nitrates as an oxidant and different organic compounds (L-alanine, glycine, citric acid, oxalic acid, tartaric acid and urea) as fuels. The complex precursors isolated before the system's combustion were characterized by thermal analysis (TGA). After combustion, the as-synthesized powders were calcined at 600°C to obtain the α-Fe2O3 phase and eliminate the residual carbon. The powders prepared using different fuels were characterized using x-ray diffraction and field emission scanning electron microscopy. n-type gas sensitivity of thick film resistive sensors fabricated by using α-Fe2O3 powders was investigated in detail and it was observed that amongst the different fuels, citric acid-derived α-Fe2O3 is methane selective at 120°C operating temperature, examined in the presence of other similar types of resistive gas analyses of the same concentrations.

A device, supporting negative differential resistance, has been fabricated. Aluminum top contacts have been deposited on electrochemically synthesized porous silicon layer on p-type silicon substrate for this purpose. Top-bottom DC current vs. voltage (I-V) characteristics of the fabricated device have been recorded at room temperature under dark condition and injecting photons. Dark I-V characteristics of this device indicate the presence of negative differential resistance (NDR). Similar kind of I-V characteristics has been observed under illumination. At the same time, fabricated device shows photovoltaic effect after injecting photons. This may be due to some series and parallel combination of multiple junctions with photovoltaic nature.

Large quantities of free standing quasi mono-disperse silicon nanocrystal/silicon oxide core-shell structured particles have been segregated by a cyclic process of sonication and centrifugation of mechanically milled and chemically treated colloidal suspension of silicon powders in ethanol medium. Narrowing of size distribution with the enhancement of centrifugation time has been evidenced from different structural characterisations as well as optical absorption and photoluminescence study. Gradual shifting of photoluminescence peak positions towards higher energy region in samples, prepared through longer centrifugation time, is also detectable with unaided eye when different samples are exposed to laser beam of wavelength ~405 nm. Controlled optoelectronic properties of the final sample achieved after four such cycles indicate a narrow core size distribution centering at 2.15 nm; can also be evidenced from the TEM micrograph.

Here, we have reported the synthesis of three-dimensional, mesoporous, nano-SnO2 cores encapsulated in nonstoichiometric SnO2 shells grown by chemical as well as physical synthesis procedures such ...

Amine-functionalized reduced graphene oxide (af-rGO) has been synthesized wet-chemically by modified Hummer's method. Raman spectroscopy has been carried out to confirm the presence of the amine group in rGO network. Photoluminescence (PL) spectroscopy has been conducted to reveal the PL conversion property of the af-rGO. Af-rGO colloids with different densities have been coated on a baseline amorphous silicon (a-Si:H) solar cell and the respective optical and solar performances have been compared with the baseline solar cell to optimize the suitable density, which is further validated by investigating the respective field emission scanning electron microscope (FESEM) micrograph of the surface area coverage by rGO on the top of the indium tin oxide (ITO) of the a-Si:H solar cell. The application of af-rGO on the baseline solar cell of the area of 1 cm2 demonstrated an enhancement in efficiency and short-circuit current density ( J SC) of ∼1% and ∼2 mA/cm2, respectively. External quantum efficiency (EQE) measurement reveals that the reductions in sheet resistance and PL converted photons have contributed additional current toward enhanced efficiency for the af-rGO-coated a-Si:H solar cell along with reflectance benefits.

Colloidal suspension of nano-dimensional Si–SiOX core–shell has been synthesized by step down mechanical process followed by thermo-chemical treatments. Graphene oxide (GO) has been synthesized by modified hummer's method. A wet chemical in situ co-deposition/reduction technique has been performed in amine rich medium to encapsulate the Si–SiOX core–shell nanostructure by amine functionalized reduced graphene oxide (af-rGO). The presence of silicon nano-crystals and af-rGO in the nanocomposite has been confirmed by Raman, FTIR and XRD studies. Core–shell structure of the nanocomposite has been confirmed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). A simple two terminal device has been fabricated with the synthesized nanocomposite in between two aluminium electrodes on glass substrate. In spite of the symmetric architecture of the device, the current–voltage (I–V) characteristics exhibits an asymmetry in nature, suggesting the formation of rectifying junction at the interfaces. Surface potential mapping has been obtained by Kelvin probe force microscopy (KPFM) to reveal the developed built-in potential at the interfaces. A chemical model has been postulated that assures the formation of dipoles and traps at the respective af-rGO/SiOX and SiOX/Si interfaces. The role of trapped charges has been established by solving Poisson's equation, validated by the trap density estimation from the capacitance–voltage (C–V) curve. This newly developed nano-structure has immense potential in the field of photovoltaics and electronics as a basic building block.

Passivated emitter rear contact (PERC) solar cell involves upgraded adaptation of technology over the existing silicon wafer-based aluminium back surface field (Al-BSF) solar cell. The lower efficiency of Al-BSF is caused by a few drawbacks e.g. higher rear surface recombination and weaker electric field at the rear surface. These technical shortcomings can be mitigated by incorporating field-effect passivation (FEP) layer viz. aluminium oxide (Al2O3) at the rear surface with a capping layer of SiNX on it. Conventionally two new processing steps utilizing two expensive equipments, green laser (532 nm) for laser ablation of the FEP and SiNX capping layer stack at the rear surface and single side etcher for rear side polishing of wafer are used for manufacturing of PERC cells. In this paper, we have shown that instead of these two new expensive processing equipments we can use the IR laser (1024 nm) and RIE etcher, which are commonly available for Al-BSF manufacturing line, for the fabrication of PERC solar cells. Using p-type wafers of rather modest quality (minority carrier lifetime of ≥10 µs) we have demonstrated improvement of the efficiency from 18.71 to 19.62% and enhancements in VOC and JSC from 628 to 646 mV and 38.59 mA/cm2 to 39.82 mA/cm2, respectively. A thorough root-cause analysis has been carried out to optimize the two new approaches within the existing Al-BSF line for the fabrication of PERC solar cell.

Selection of suitable metal-oxide type dielectric passivation layer enhances the open circuit voltage of the Passivated Emitter Rear Contact (PERC) solar cell to a great extent. Incorporation of Aluminium oxide (Al 2 O 3 ) as passivation layer has been a common practice for the fabrication of PERC solar cell both in industry and research laboratory. However, the optically unmatched refractive index of Al2O3 does not redirect the transmitted photons (Wavelength ranging 900nm to 1100nm) through ~180µm thick c-Si p-type substrate to the solar cell. Hafnium oxide (HfO 2 ) with optically matched RI exhibits comparable passivation property. If HfO 2 can be used instead of Al 2 O 3 increase the possibility of redirecting the transmitted photons to the solar cell again without compromising the passivation property, which may increases the solar cell performance. It has been observed that 93% transmitted photons can be reflected back to the solar cell structure for optimized double dielectric stack.

Highly sensitive and selective tin dioxide (SnO2)-based sensor material was wet-chemically synthesized by sonication-assisted simultaneous precipitation method, and their sensing characteristics for various environmentally important combustible and reducing gases were investigated by resistance measurements on an assembled “Taguchi-type” sensor prototype. Characteristics and morphologies of the synthesized powder were examined by thermal, physico-chemical, spectral, and optical studies and their effect(s) on sensing properties were correlated. Small amount of gold addition along with palladium in the metal–oxide–semiconductor, such as SnO2, leads to enhanced sensing properties toward environmentally important and combustible gases such as liquefied petroleum gas (mainly butane), compressed natural gas (mostly methane), carbon monoxide, and hydrogen (H2). A particular composition of SnO2 with bi-metallic catalysts (Pd and Au) exhibits excellent sensitivity and butane selectivity. Use of graphene on the final sensor prototype is improved durability in terms of prolonged shelf life by forming a semi-exchangeable coating.

We report synthesis of colloidal suspension of silicon (Si) nanoparticle (NP) with native silicon dioxide (SiO2) layer by mechanical milling. Different size distribution of Si NPs in the colloid has been obtained by varying the centrifugation time. Width of the particle distribution curve of Si NPs was found to decrease with increasing centrifugation time of the colloidal suspensions, which has been established from the FESEM analysis. The variation of particle size also put its signature in the photoluminescence (PL) properties of the prepared materials.

In the present work, Zinc Oxide (ZnO) nanostructures have been prepared by microwave assisted synthesis method. ZnO powders from four different precursor solutions were synthesized followed by calcination at 600°C to form polycrystalline ZnO nanostructures. The wurzite crystal structure of ZnO powders were determined by X-ray diffraction (XRD). Surface morphology of the prepared four ZnO powders were studied using Field Emission Scanning Electron Microscopy (FESEM) and showed four different types of surface alignments. Gas sensing characteristics for four Volatile Organic Compounds (VOCs), namely, acetone, formaldehyde, isopropanol and toluene in their vapor forms, were studied to investigate the response behavior of the prepared ZnO powders. ZnO synthesized from the zinc nitrate precursor showed the highest sensitivity compared with the rest three powders synthesized from acetate, chloride and sulphate precursors of zinc. The sensitivity of the ZnO (nitrate) sensor was found to exhibit the highest response [%S = 50.54% & 66.21%] for 10 and 20 ppm formaldehyde, respectively at room temperature, in presence of the other three VOCs and thus, it can be inferred that the synthesized ZnO is selective to formaldehyde. The mechanism of sensing has been explained according to the ionosorption model. The influence of the precursor on the morphology of derived ZnO samples and the effect of the morphologies on the gas sensing activities has been discussed.

In this paper a comprehensive theoretical analysis has been carried out for Passivated Emitter Rear Contact (PERC) solar cells with the help of numerical modeling using Sentaurus TCAD simulation software. For the rear passivation we have explored various dielectric layers, such as, Aluminium Oxide (Al2O3), Silicon Oxide (SiO2), Hafnium Oxide (HfO2) and Aluminium Nitride (AlN) along with the Silicon Nitride (SiNx) capping layer. Optical generation near the rear side the passivating stacks was analyzed. Recombination current densities were also evaluated for assorted defects with various concentration, hole and electron capture cross sections and position of quasi Fermi level for surface passivation. Thicknesses of the passivating and capping layers were optimized with respect to optical and electrical losses. Field effect passivation (FEP) property of the rear passivating stacks was also investigated. For simulated textured Al-BSF solar cell on silicon wafer of bulk lifetime 250µs, an efficiency of 19.5% was obtained. This solar cell has been used here for reference. We have achieved efficiency of 22.6% for PERC solar cells of rear contact area of 8% on similar type of wafer. It was noticed from few articles that industrial PERC solar cells were fabricated using rear metal contact less than 10% which is well validating our study. It was also perceived that employing Passivated Emitter Rear Totally Diffused (PERT) structure with optimized design parameters further improved the efficiency to ∼ 24%.

Crumpled graphene oxide (cGO) was synthesized using a facile liquid phase exfoliation technique mediated by OHˉ cutter; followed by the synthesis of cGO/Co3O4 composite through hydrothermal route involving the as-synthesized cGO and cobalt salt precursors. Co3O4 is a mixed oxide of cobalt that exhibits good redox and charge cycling attributes owing to the presence of Co(II) and Co(III) oxidation states within it. This report includes thorough investigation on the electrochemical and charge storage properties of the fabricated electrodes using cyclic voltammetry, charge – discharge and impedance analyses, and also by endurance test. The report also describes detailed evaluation of the structural properties of the products (cGO and cGO/Co3O4 composites). Two sets of prototype ‘symmetric’ supercapacitors were fabricated using aqueous and gel KOH based electrolytes that successfully lit up LED and run a DC motor. The gel KOH electrolyte based device showed best performance and yielded 44 Wh/Kg specific energy and 1202 W/Kg specific power. The results are quite promising which open up a new avenue for using cGO/Co3O4 composite as a low cost alternative for conventional and costly carbon nanomaterial based supercapacitors.

Colloidal suspension of free standing silicon/silicon oxide core/shell nanoparticles has been synthesized using a mechanochemical top-down approach. Quasi-mono-dispersed core size distribution of synthesized nanoparticles has been confirmed using different structural, morphological, and optoelectronic characterizations. Raman, continuous wave photoluminescence and time-resolved photoluminescence studies have been performed on synthesized colloidal nanoparticles in ethanol medium. Asymmetric broadening of the Raman peak (red shifted with respect to that of bulk silicon) has been observed. Intensities and positions of photoluminescence emission peaks are prominently dependent on excitation photon energy. Moreover, the photoluminescence decay time varies from sub-nanoseconds to tens of nanoseconds. The decay time also exhibits a strong dependence on the excitation wavelength, while the emission wavelength is kept unaltered. The abovementioned observations indicate the slow relaxation of photo-excited carriers in silicon quantum dots. This particular phenomenon takes place due to phonon mode discretization, which is further responsible for the radiative recombination of hot-carriers and consequent strong visible emission. The enhancement of hot-carrier lifetime in colloidal silicon quantum dots is the key requirement for the active material of the hot-carrier solar cell. Runny texture of the synthesized material inhibits practical device implementation; therefore, the synthesized nanoparticles have been embedded in the silica xerogel matrix. The impression of phonon mode confinement, in silicon quantum dots embedded in a hard matrix, has been observed, resulting in increased hot-carrier lifetime. The enhanced hot-carrier lifetime can lead to the realization of a silicon-based active material for the hot-carrier solar cell.

Zinc oxide (ZnO) nanoparticles have been synthesized by wet chemical processing from four different zinc precursor materials at room temperature. Synthesis of phase pure material with four different morphologies and orientations have been confirmed through different characterization techniques like, X-ray diffraction, field emission SEM, fourier transformed IR etc. The band gap energies of the synthesized materials were within specific semiconductor limits and the same have been determined from UV–Visible and photoluminescence spectra of the synthesized nanostructured ZnO materials. Thus it is possible to control ZnO nanostructures and morphologies through facile room temperature synthesis and tailor their band gaps for different application purposes.

Photoluminescence active amine-functionalized reduced graphene oxide (af-RGO) has been synthesized at room temperature with prolonged sonication to obtain a free floating, hexagonally arranged carbon network having larger dimensions ∼(20 μm × 15 μm) in aqueous medium. The presence of amine in an RGO network has been confirmed by Raman, FTIR and photoluminescence (PL) studies. It has been used as the top layer on c-Si solar cells. Its effect on solar cell parameters was investigated. The effect of dilution (10% to 90%) of aqueous af-RGO and its coverage on c-Si solar cells leading to optimum cell parameters has been studied. The respective reflected and transmitted photon fraction through the af-RGO thin film obtained from a spectral response graph was estimated. The suitability of the synthesized material for c-Si cells has been established through different characterization supports, like height profile and the surface coverage on a polished silicon surface, analysed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). It was observed that the 50% diluted sample shows the best performance with respect to the baseline parameters of solar cells. An enhancement of 4.6% in short-circuit current density (JSC) and 4.8% in fill factor (FF) was achieved over the baseline parameters of the cell, while dip coating the baseline cell in the optimized dilution of af-RGO.

Multilayered graphene deposited on a flat resistive surface has twofold benefits. Less electronic scattering reduces the sheet resistance of the combined bilayer and high photon scattering through the unavoidable wrinkles on the chemically synthesized graphene layer leads to decreased effective reflection. In this paper, wet‐chemically‐synthesized reduced graphene oxide (RGO) has been employed on the top of the indium‐doped tin‐oxide (ITO) layer. The ITO layer of optimized thickness has been deposited as an alternative antireflection coating (ARC) on a p/n junction based crystalline silicon solar cell with standard textured surface. Variation in spectral response has been studied experimentally for different thickness and surface coverage of RGO on ITO. The combined effect of reduced sheet resistance due to high surface conductivity and increased photon injection efficiency due to scattering from the wrinkles of RGO results in significant improvement in the performance of the solar cell. By employing optimum thickness of RGO, percentage enhancements of about 18% and 10%, respectively, in efficiency and short‐circuit current density have been achieved over the baseline cell structure. RGO also exhibits an additional benefit as a moisture repelling layer.

Graphene materials have been widely explored for fabrication of gas sensors because of their atom-thick two-dimensional conjugated structures, high conductivity and large specific surface area. Thin graphene layers with attached functional groups desirable for gas sensing applications were synthesized by a wet chemical route (modified Hummers' method). Sensing performances of reduced graphene oxide (rGO) against carbon monoxide (CO) were studied in terms of percent sensitivity (sensor response), response and recovery times and I/V characteristics at room temperature as well as at elevated temperatures. Sensitivity data indicate the highest activity (∼71% sensitivity against 30 ppm CO) occurs at room temperature (RT), indicating that the sensor is best operated at RT. Sensor response is quick (within 30 s) even to a trace amount (0.001% or, 10 ppm) of CO gas. Selectivity of the sensor was demonstrated by using different n-type reducing gases (like carbon monoxide, ammonia, methane and hydrogen), at different concentrations, showing negligible sensitivity towards gases other than CO. The synthesized material proves to be good as a selective room temperature sensor for harmful and poisonous carbon-monoxide gas.

Passivation of n-type and p-type monocrystalline CZ Si wafers (both polished and textured) with silicon oxide layers prepared by thermal (TO), chemical (CO) and plasma (PO) techniques have been extensively investigated from the measurement of minority carrier lifetime (τ) by transient electrical photoresponse method, density of interface states (NSS) measurement by capacitance – voltage study and silicon oxidation states by X-ray photoelectron spectroscopy (XPS) study of the SiO2/Si interface. It has been observed that NSS and τ have an inverse relation but the dependence is not linear. The method (TO, CO or PO) of oxide layer development has been found to play a crucial role to control the passivation of the c-Si wafer surface. It has been observed that the thermally grown oxide layer (TO) is superior among three oxide layers for all the different c-Si surfaces. Very low density of interface states (

A facile non-equilibrium mechanochemical technique has been adopted for the synthesis of silicon based bulk heterojunctions viz. ZnO/Si and CuO/Si, by discretely combining ZnO and CuO with Si through the process of microstructural refinement. Structural, morphological, thermal and optical properties of the prepared materials have been investigated in detail. Photogenerated charge carriers are the key to the efficient photocatalysis and proper cultivation of such charge carriers can take place by restricting their recombination. This can be achieved through suitable band alignment between the constituting semiconductors; in this case, ZnO/Si and CuO/Si. Such bulk heterojunction results from the mechanochemical process provide a significantly higher exposed surface area than the thin film like 2D heterojunctions. The photocatalytic activity of ZnO/Si and CuO/Si binary systems were evaluated by observing the changes in absorption peak intensity at specific wavelength of the dyes in aqueous medium when irradiated with artificial light source. Such systems were found to be proficient towards the photodegradation of four major hazardous industrial effluents viz. Alizarin Red S, Methylene Blue, Rose Bengal and Indigo Carmine owing to its higher specific surface area and minimized carrier recombination due to synergistic interaction between Si and the metal oxide semiconductor.

Vanadia (V2O5) doped tin dioxide (SnO2) nanocrystallites were synthesized by sonication assisted simultaneous precipitation method, keeping in view their application for LPG (n-butane) gas sensor. The best sensing conditions were determined by studying the sensors under different operating temperatures with different vanadium loading (in the form of V2O5), in presence of 60–65% ambient humidity. 0.50 wt% V2O5 loaded SnO2 exhibits the best sensitivity against butane at 4500C operating temperature, without using any expensive nobel metal catalyst. The same material exhibited a switching in selective sensing of SO2 at a different V2O5 concentration (0.15 wt%), operated at lower temperature (3500C). The nanocrystalline powders were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and current-voltage (I/V) measurement studies. The morphology of V2O5-doped SnO2 nanocrystalline powder is elongated spherical in shape and the distribution of particle size is uniform, having the range of 70–90 nm, as confirmed by SEM and Brunauer-Emmett-Teller (BET) observations.

The fossilized larva of an aquatic beetle, Protodytiscus johillaensis gen. et sp. nov., is described from a ferruginous micaceous siltstone bed of the Permo-Triassic Parsora Formation of the South Rewa Gondwana Basin, Madhya Pradesh, India, and its systematic position and ordinal relationships within the coleopterous suborder Adephaga are discussed. Hitherto, the oldest known fossils of the hydradephagan superfamily Dytiscoidea have been Jurassic. The discovery of P. johillaensis extends the range of the Dytiscoidea back to the Permo-Triassic period.