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The present paper describes the green synthesis of Zinc oxide nanoparticles (ZnO NPs) from the flowers of L. nepetifolia. The synthesis of ZnO nanoparticles and examined by using Ultraviolet-visible spectroscopy, Fourier Transform-Infrared spectroscopy, X-ray Diffraction analysis, Dynamic Light Scattering analysis, Raman spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-ray spectroscopy, Transmission Electron Microscopy, and Thermogravimetric Analysis. The photocatalytic studies were followed using methylene blue (MB) dye by ZnO nanoparticles by using sunlight as a source. The degradation of MB dye is found to be 90 %. Then the synthesized ZnO nanoparticles help to evaluate the antioxidant activities. The antioxidant activities of ZnO nanoparticles were exhibiting through scavenging of Nitric oxide, Hydrogen peroxide, and DPPH free radicals. Furthermore, the electrochemical analysis of reduced Graphene Oxide-Zinc oxide (rGO-ZnO) nanocomposite shows that the prepared rGO-ZnO nanocomposite has a high specific capacitance of about 667 F g-1 in comparison with the pure Zinc oxide nanoparticles (200 F g-1) and has good cycling stability of around 1000 cycles. The synthesis of multifunctional ZnO nanoparticles by using natural plant products like seeds, leaves, flowers, etc may help to explore as environment-friendly which is opposite to chemical synthesis.

Understanding the carrier transport mechanisms is critical for electronic devices based on 2D semiconductors. Here, using a two-terminal device configuration, we show that the carrier transport behaviours in chemical vapour deposited few-layer MoS2 transition from resonant tunnelling to hopping, and eventually to band transport as the temperature increases from 5 K to 370 K. Specifically, the transport in the channel is dominated by resonant tunnelling when T < 30 K is reflected in the temperature-independent conductance. At 50 K < T < 110 K, the channel conductance exhibits a dependence of exp(T 1/2), a signature of Efros–Shklovskii type variable range hopping (VRH). At 110 K < T < 160 K, carrier transport behaves in a transition region with potential attribution to Mott-type VRH. At 160 K < T < 210 K, the nearest neighbour hopping mechanism is confirmed by the linear dependence from the resistance curve derivative analysis. For VRH, the localization length, hopping distance and energy, Coulomb gap energy and density of states are extracted. At T > 210 K, the carrier transport is dominated by thermally activated band transport based on AC conductance and mobility analysis. These findings are significant for revealing the material properties for future 2D semiconductor device applications.

We report supercapacitors based on thiolated-graphene (T-graphene) with stable charging and discharging performance at high current density. The T-graphene was synthesized using low cost NaSH as a reducing agent to reduce graphene oxide. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) studies reveal that NaSH is an effective reducing agent in removing oxygen containing groups from graphene oxide. The highly reduced T-graphene with a C/O ratio of 28 was used as the supercapacitor electrode material. At a current density of 2.5 Ag-1, the T-graphene supercapacitor exhibited an electrochemical capacitance of 195 Fg-1, a power density of 4.3 kWkg−1and an energy density of 83.4 Whkg−1. The time required to discharge 83.4Whkg−1 at 2.5 Ag-1 is around 69 s. At a current density of 7.5 Ag-1, the cell exhibited a specific capacitance of about 137 Fg-1 and retained 98% of its initial capacitance value after 10,000 cycles. This superior performance of supercapacitor can be ascribed to highly reduced and porous T-graphene with minimum restacking due to its crumpled nature. The resulting supercapacitors having stable performance at high current density are suitable for fast charging-discharging applications.

We explored the photophysics of an all polymeric solar system based on the combination of the wide bandgap polymers poly(3-hexylthiophene) (P3HT) as donor and low bandgap polymer poly{[N,N-9-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)} (P(NDI2OD-T2)) as an acceptor blend active layer in 2-methyl anisole using airbrush spray coating method. Polyethyleneimine ethoxylated (PEIE) is used as the surface modifier and SnO 2 as an anode, to minimize the chemical damage of the transparent conducting electrode. The molecular aggregations were investigated by means of absorbance, photoluminescence measurements and atomic force microscopy. The current density–voltage characteristics were examined using an Oriel 1000W solar simulator under the illumination condition through the simulated solar light with 100 mW cm −2 (AM 1.5G). The power conversion efficiency (PCE) of about 5.6% is been reported for the photovoltaic device and this outcome indicates that these spray coating method can be a feasible technique when compared with other high-cost vacuum deposition techniques for mass production and low-cost roll to roll based fabrication.

The urgent need for efficient energy storage devices greatly stimulates the development of high power, highly efficient, environmentally friendly, and low-cost energy storage devices. Supercapacitors, unlike batteries, store energy by ion adsorptions on high surface area electrodes. The physical ion migration provides a high charging/discharging rate, power density, and reversibility. In this work, we synthesize graphene materials by a rapid thermal annealing process and examine the material properties. With the synthesized graphene as electrodes, the outstanding electrochemical performance of these supercapacitors is demonstrated. This provides a new method for developing supercapacitors with high charge/energy storage capability at low cost.

In recent years dendrimers have fascinated the investigators towards targeted drug delivery because of their versatile framework and exhibit immense potentiality in entrapping drug moieties through host-guest interactions and serve as a promising vector in biological applications. The current investigation is focused on developing pegylated citric acid cefotaxime dendrimers through the divergent method and its characterization through spectroscopic, microscopic, thermal and microscopic techniques. Among the spectroscopic techniques, 1H NMR and 13C NMR elucidated the key functional groups at various chemical shifts while ESI-MS pointed out the molecular weight of cefotaxime sodium in various generations. Similarly, FTIR, DSC, and AFM investigations detailed that the generations are devoid of incompatibilities, structural deformities and can be opted for targeted drug delivery. The drug entrapment studies and in-vitro drug release studies highlight CFTX G5 containing 92.4% entrapment efficacy and 83.8% drug release in 48 h and specifies a sustain release characteristics. In connection to the above, the in-vivo studies reveal a potent antibacterial activity against various gram-positive and gram-negative microorganisms with a decreased hemolysis and cytotoxicity effects and reflect a high margin of safety regarding pegylated CFTX dendrimers. Further, the antibacterial activities are supported through confocal microscopy that clarified the cellular uptake of dendritic molecules and their internalization.

Graphene supercapacitors with a high electrode surface area have great potential in efficient energy storage. For practical applications, it is critical to develop highly-manufacturable methods to synthesize graphene nanosheets with high ion accessibility and uniform pore-sizes. Here we demonstrate a nontoxic approach for graphene synthesis which involves a low vacuum annealing at an easy-to-reach temperature. The supercapacitors based on the low-temperature exfoliated graphene materials show excellent electrochemical performance superior to those synthesized by high-temperature methods. Our investigation presents an efficient, yet industry-compatible and low cost way that can be scaled up for mass production of graphene for electrochemical energy storage application.

In the present work, we have demonstrated high-performance organic solar cells with spray coated active layers. The influence of the nanomorphology on the power conversion efficiency of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-phenyl-C71-butyric acid (PC71BM) methyl ester bulk heterojunction solar cells is presented. Active layers were prepared using a chlorobenzene solvent containing a small volume of 1,8-diiodooctane as an additive by spray coating with conventional handheld airbrushes. The surface morphology of the active layers deposited for various spray-coating times was examined using atomic force microscopy. The resulting devices were measured under AM 1.5G (100 mW/cm2) conditions in an ambient atmosphere. The optimized spray-coated PTB7:PC71BM film showed a high solar cell performance with a short-circuit current density of 14.20 ± 0.41 mA/cm2, a fill factor of 56.00 ± 0.02% and a power conversion efficiency of 5.96 ± 0.15%.

Organic solar cells have been significantly attracted due to the need to develop an inexpensive clean and sustainable renewable energy source. We report on the fabrication of poly [N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]/[6, 6]-phenyl-C71-butyric acid methyl ester blend active layer using airbrush spray-coating method in mixed solvents. Optical absorption of the active layers was analyzed using UV–visible spectral studies in the wavelength range from 300 to 800 nm. The surface morphology of the active layers deposited with different parameters (spraying time and substrate-nozzle distance) was examined using atomic force microscopy. The current density–voltage (J–V) characteristics of photovoltaic cells were measured under the illumination of simulated solar light with 100 mW cm−2 (AM 1.5G) by an Oriel 1000 W solar simulator. The power conversion efficiency of the solar cell is more than 5 %.

We investigated the effect of additives on the morphology of a poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT):(6,6)-phenyl C71-butyric acid methyl ester (PC71BM) blended onto a surface of poly (3, 4-ethylendioxythiophene): poly(styrensulfonate)(PEDOT:PSS) to form photoactive films. Films of PCPDTBT: PC71-BM bulk heterojunctions were prepared by spin-coating from a solution in chlorobenzene (CB) and were processed with and without the addition of 2%, 4%, and 6 vol% 1-chloro naphthalene (CN) or 1, 8-octanedithiol (ODT) as additives. For all samples, the PCPDTBT:PC71BM molar ratio was 1:2 (wt%), and the additives in 1 ml were prepared with a concentration of 30 mg of PCPDTBT:PC71BM. Optical absorption spectroscopy measurements of the films indicated shifts in the absorption peaks in the range from 500–800 nm which was attributed to PCPDTBT. XRay diffraction (XRD) was used to investigate the nature of the molecular stacking in the polymer thin films. Topographic images which were obtained by using an atomic force microscope, of the PCPDTBT:PC71BM layers with 2 vol% ODT additive, were found to have the highest surface roughness. The best performing device shows a power conversion efficiency of 2.15% for a 2-vol% ODT additive.

Organic solar cell devices were fabricated using poly[9-(1-octylnonyl)-9H-carbazole-2.7-diyl]-2.5-thiophenediyl-2.1.3-benzothiadiazole-4.7-diyl-2.5-thiophenediyl] PCDTBT/ [6,6]-phenyl butyric acid methyl ester (PC71BM) active layer deposited by spin coating. Moreover, the relationship between solar cell performance and buffer layer thickness was investigated by spin coating speed and AFM imaging of the buffer layer surface. The performance of the organic solar cell with spin-coated active layer was then evaluated, and the power conversion efficiency of the solar cell was determined to be > 5%.

Bulk heterojunction organic solar cell devices were fabricated using the spray deposited poly [N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]/[6,6]-phenyl-C61-butyric acid methyl ester blend active layer. The spray coating parameters such as spraying time, substrate-nozzle distance for the deposition of active layers were analyzed. Optical absorption of the active layers was analyzed using UV–visible spectral studies in the wavelength range from 300 to 800 nm. The surface morphology of the active layers deposited with different parameters was examined using atomic force microscopy. Surface morphology of the active layers deposited with the substrate-nozzle distance of 20 cm and for 20 s shows smooth morphology with peak-valley value of 4 nm. The devices fabricated using the selected active layer show overall power conversion efficiency of 1.08%.

Supercapacitors, based on fast ion transportation, are specialized to provide high power, long stability, and efficient energy storage using highly porous electrode materials. However, their low energy density excludes them from many potential applications that require both high energy density and high power density performances. Using a scalable nanoporous graphene synthesis method involving an annealing process in hydrogen, here we show supercapacitors with highly porous graphene electrodes capable of achieving not only a high power density of 41 kW kg-1 and a Coulombic efficiency of 97.5%, but also a high energy density of 148.75 Wh kg-1. A high specific gravimetric and volumetric capacitance (306.03 F g-1 and 64.27 F cm-3) are demonstrated. The devices can retain almost 100% capacitance after 7000 charging/discharging cycles at a current density of 8 A g-1. The superior performance of supercapacitors is attributed to their ideal pore size, pore uniformity, and good ion accessibility of the synthesized graphene.

InN nano-columns were grown on Au-coated silicon (111) substrates by using metal organic chemical vapor deposition. Here, the indium pre-deposition was performed before InN nano-column growth. The formation of InN nano-columns was conducted by forming Au + In solid solution droplets on the Au-coated substrate and subsequently nitriding those Au + In droplets. This study investigated the morphological changes in the InN nano-columns due to changes in the growth conditions such as the growth temperature, the trimethylindium (TMI) flow rate and the growth pressure. The scanning electron microscopy (SEM) investigation showed that the InN nano-columns were single crystals with diameters ranging from 90 to 180 nm and lengths of about 2.5 µm. The Raman microscopy spectrum of the nano-columns showed peaks at 495 cm 1 and 594 cm 1 , which were assigned to degree what are E2 (high) at 492 cm 1 and A1 (LO) at 596 cm 1 of InN, respectively. In the high-resolution X-ray diraction

GaN epilayers were grown on lens-shaped-pattern sapphire substrate (PSS) (0 0 0 1) and unpatterned sapphire substrate (UPSS) (0 0 0 1) by metal-organic chemical vapor deposition (MOCVD). The quality of the grown GaN epilayers on the PSS and UPSS were compared. Structural characteristics, surface morphology and optical properties of the GaN epilayers were investigated using double crystal X-ray diffraction (DCXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and photoluminescence (PL). A lens-shaped pattern was formed on the sapphire substrate to reduce threading dislocation (TD) density and also to improve the optical emission efficiency by internal reflection on the lens. SEM images show the growth of GaN epilayers at various times. Full coalescence is observed at a growth time of 80 min. It is seen from the DCXRD rocking spectrum that full width at half maximum (FWHM) of the GaN grown on PSS was 438.7 arcsec which is less than UPSS value. The lower value of FWHM indicates that the crystalline quality of the GaN epilayers grown on PSS is improved compared to GaN grown on UPSS. It is clearly seen from the AFM images that the dislocation density is less for the GaN grown on PSS. A strong and sharp PL band edge emission was observed for the GaN grown on PSS compared to UPSS. Defect related yellow luminescence was observed for GaN grown on UPSS which did not appear for PSS. The FWHM at the 364.3 nm peak position was evaluated to be 50.7 meV from the PL spectra for GaN grown on PSS. The above result indicates GaN epilayers can be grown on PSS with low TD density and will be useful for optical emission.

Gallium nitride (GaN) epilayers were grown on a patterned sapphire substrate (0001) (PSS) using metalorganic chemical vapor deposition (MOCVD) for various growth time from 10 to 80 min. Structural characteristics, surface morphology and optical properties of the GaN epilayer were investigated using double crystal X-ray diffraction (DCXRD), scanning electron microscopy (SEM) and photoluminescence (PL). A lens shaped pattern was formed on the sapphire substrate to reduce threading dislocation density and also to improve the optical emission efficiency by internal reflection on the lens. From the DCXRD rocking spectrum, full width at half maximum (FWHM) was decreased with increasing growth time. The FWHM of the sample grown at 80 min was 473.48 arcsec which indicates good crystalline quality. From the SEM images, full coalescence takes place at 80 min growth time. It was observed that the threading dislocation densities were reduced as the growth time increased thereby obtaining a smooth and defect free GaN epilayer at high growth time. From the PL spectra, a decrease in the FWHM and an increase in the peak position were observed as the growth time was increased. Similarly, the yellow luminescence was decreased as the growth time increased and disappeared at growth time 80 min. From the band edge emission spectra, FWHM was 82.2 meV at peak position 363.9 nm for the sample grown at 80 min which indicates a low threading dislocation density. Our results show that by using PSS for growing GaN epilayer with high growth time, threading dislocation density could be reduced thereby improving the crystalline and optical quality of the GaN layers.

Polymer solar cells (PSC’s) have received much attention as a promising clean and green energy technology and the power conversion efficiency have steadily increased. There are several ways to improve the device efficiency of PSC, such as changing the active layer, insertion of the electron transport layer and the anode buffer layer. Among the several anode buffer layer materials, Poly(3,4-Ethylenedioxythiophene):Poly(styrene sulfonate) (PEDOT:PSS) is widely used as anode buffer layer due to its high transparency in the visible region, high thermal stability and mechanical flexibility. However, PEDOT:PSS suffers a problem of low conductivity and limits the device application. In this report, we present the preparation of PEDOT:PSS hole transport layer through a secondary doping with flouro compounds such as hexafluoroacetone (HFA) and hexafluoroisoproponal (HIPA) with various concentrations by spin coating technique. High performance of the hole transport layer is attributed to preferential phase segregation of PEDOT:PSS with HFA and HIPA solvent mixture treatment method. The improved performance of PSC was dependent on the structure of organic solvents and the concentration of flouro compounds in PEDOT:PSS solution. Using these optimized buffer layer, conjugated polymer solar cells with a Poly9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3- benzothiadiazole-4,7-diyl-2,5 thiophenediyl] polymer:[6,6]-phenyl-C71-butyric acid methyl esters (PCDTBT:PC71BM) bulk heterojunction have been produced. A detailed analysis of the surface morphology and optical studies are presented. The obtained results show that PEDOT:PSS optimized with HFA and HIPA organic solvents can be a very promising candidate for transparent anode buffer layer in the low cost organic solar cell devices.

Bulk heterojunction (BHJ) solar cells have made great progress during the past decade and consequently are now attracting extensive academic and commercial interest because of their potential advantages: lightweight, flexible, low cost, and high-throughput production. We report on the fabrication of poly((4,8-diethylhexyloxyl) benzo([1,2-b:4,5- b′]dithiophene)-2,6-diyl)-alt-((5-octylthieno[3,4-c]pyrrole-4,6-dione)-1,3-diyl) /[6,6]-phenyl-C71-butyric acid methyl ester blend active layer using airbrush spray coating method in different solvents. The parameters such as spraying time, substrate-nozzle distance for the deposition of active layers were analysed. Optical absorption of the active layers was analyzed using UV-visible spectral studies in the wavelength range from 300 to 800 nm. The surface morphology of the active layers deposited with different parameters was examined using Atomic Force Microscopy. The current densityvoltage (J-V) characteristics of photovoltaic cells were measured under the illumination of simulated solar light with 100 mW/cm2 (AM 1.5G) by an Oriel 1000 W solar simulator. We also notice that both the bottom-up and top-down approaches have played important roles in advancing our fundamental understanding of this new class of nanostructures. Finally we attempt to look into the future and offer our personal opinions on what the future trends will be in organic solar cell research. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

We have studied the InGaN quantum dots (QDs) grown on a GaN pseudo template on a sapphire substrate (0001) using metal organic chemical vapor deposition (MOCVD). Self assembled InGaN QDs was successfully fabricated using nitridation of nano alloyed droplet (NNAD) method. The density, average diameter, and height of the InGaN QDs were estimated to be 1.0×108 cm-2, 50 nm, and 13 nm, respectively. The structural and optical properties of InGaN QDs were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and photoluminescence (PL). From the SEM image, it is clearly seen that In+Ga alloy droplets are uniformly distributed on GaN template. Further, InGaN QDs uniform distribution on the GaN/sapphire surface was observed by AFM. Broad emission from the QDs was observed around 580 nm which indicate the grown QDs have relatively high In composition due to low growth temperature. The broad and separated PL peak of QDs induced by the fluctuation in size and composition. Our result suggests that self-assembled InGaN QDs are fabricated well by using NNAD technique.

Single-crystal GaN nano-column arrays were grown on Au-coated silicon (111) substrate by Au-Ga alloy seeding method using metalorganic chemical vapor deposition (MOCVD). The nano-column arrays were studied as a function of growth parameters and Au thin film thickness. The diameter and length of the as-grown nano-column vary from 100 to 500 nm and 4 to 6 µm, respectively. The surface morphology and optical properties of the nano-columns were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cathodoluminescence (CL) and photoluminescence (PL). The Au+Ga alloy droplets were found to be uniformly distributed on silicon surface. Further, SEM image reveals a vertical growth and cylindrical in shape GaN nano-column. The chemical composition of the nano-column, which composed of gallium and nitrogen ions, was estimated by EDX. CL reveals a strong band edge emission from the GaN nano-column. PL spectra show a peak at 365.7 nm with a full-width half maximum (FWHM) of 65 meV which indicates good optical quality GaN nano-column with low dislocation density. Our results suggest that single crystal GaN nano-column can be grown on Au+Ga alloy on silicon substrate with a low dislocation density for better device performances.