S. P. Koiry

Synthesis of vertically aligned polyaniline (PANI) nanofibers, nanotubes on APTMS monolayer and their field emission characteristics

Growth of aligned polyaniline (PANI) nanostructures on silicon modified with amino-silane self-assembled (3-aminopropyl)trimethoxysilane (APTMS) monolayer has been carried out by chemical polymerization in the presence of strong (HCl) and weak (CH3COOH) acids as dopant. Self assembly of aniline monomer leading to formation of aligned nanostructures on the APTMS monolayer is due to the amino (–NH2) moieties acting as growth centers. Interestingly, the nature of dopant acid (strong/weak) is found to determine the resultant form of the PANI nanostructures, either as nanofibers or nanotubes. The formation of PANI nanofibers and nanotubes has been revealed by scanning and transmission electron microscopy, whereas confirmation of the conducting phase of PANI is obtained from UV-visible and FTIR analysis. A plausible explanation illustrating the growth mechanism has been presented. Field emission studies of the PANI films have been carried out in a planar diode configuration at base pressure of ∼1 × 10−8 mbar. The turn-on field required to draw an emission current of 1 nA was found to 1.6 and 2.4 V μm−1 for aligned nanofibers and nanotubes, respectively. Interestingly, both the emitters exhibit good stability of the emission current over a duration of 4 h. The ease of the synthesis route and interesting field emission characteristics indicate the aligned PANI nanofibers and nanotubes as promising materials for field emission based applications.

Electrochemical grafting of octyltrichlorosilane monolayer on Si

The octyltrichlorosilane (OTS) monolayer on hydrated Si (111) surfaces has been grafted by cyclic voltammetry (CV) using tetrabutylammonium perchlorate in dry methanol as supporting electrolyte. The percentage of OTS coverage, calculated from the current value at −1V, after 30 CV scans was found to be >97%, which is independently confirmed by atomic force microscopy. A mechanism of electrochemical grafting of OTS on Si via formation of Si–Si bonds is proposed. Current-voltage characteristics and impedance spectroscopic measurements on Al/OTS/Si structures reveal realization of a true OTS/Si interface.

Promising Field Emission Characteristics of Polyaniline Nanotubes

Polyaniline (PANI) nanotubes have been synthesized employing chemical polymerization with acetic acid as dopant. The synthesized PANI nanotubes were characterized by Scanning electron microscope (SEM), Transmission electron microscope (TEM), Uv-visible spectroscopy and Fourier transform infrared spectroscopy (FTIR). The SEM and TEM analysis clearly reveals the formation of PANI nanotubes, with outer diameter in the range of 50-150 nm and length in several microns. The Uv-visible and FTIR spectra exhibit characteristic features corresponding to electrically conducting phase of doped PANI. Field emission (FE) studies of the PANI nanotubes were performed in planar diode configuration at a base pressure of ∼1 x 10 ―8 Torr. From the FE results, value of the turn on field required to draw an emission current density of 1 μA/cm 2 was found to be 1.55 V/μm and current density of 1 mA/cm 2 has been drawn at an applied field of 3.8 V/μm. The PANI nanotubes emitter exhibited good emission current stability at pre-set value of 1 μA over duration of more than 3 h. The ease of synthesis route and interesting field emission properties recommend the PANI nanotubes as a promising material for field emission based applications in vacuum micro-nanoelectronic devices.

Investigation on the effects of thermal annealing on PCDTBT:PCBM bulk-heterojunction polymer solar cells

Bulk heterojunction solar cells of 3×3 array have been fabricated using a blend of PCDTBT:PCBM as active layer. Among nine devices fabricated, the best device exhibited efficiency 5% with standard deviation ∼ 20% in efficiency. Thermal annealing of the devices resulted in decrease of photovoltaic properties of all devices which was attributable to the change at the active layer/cathode interface of devices as supported by electrical and spectroscopic studies.

Graphene composite for improvement in the conversion efficiency of flexible poly 3-hexyl-thiophene:[6,6]-phenyl C71 butyric acid methyl ester polymer solar cells

The solution of thin graphene-sheets obtained from a simple ultrasonic exfoliation process was found to chemically interact with [6,6]-phenyl C71 butyric acid methyl ester (PCBM) molecules. The thinner graphene-sheets have significantly altered the positions of highest occupied molecular orbital and lowest unoccupied molecular orbital of PCBM, which is beneficial for the enhancement of the open circuit voltage of the solar cells. Flexible bulk heterojunction solar cells fabricated using poly 3-hexylthiophene (P3HT):PCBM-graphene exhibited a power conversion efficiency of 2.51%, which is a ∼2-fold increase as compared to those fabricated using P3HT:PCBM. Inclusion of graphene-sheets not only improved the open-circuit voltage but also enhanced the short-circuit current density owing to an improved electron transport.

Enhancement of the carrier mobility of conducting polymers by formation of their graphene composites

Conducting polymers (CP) with high charge carrier mobility are crucial for flexible organic electronic devices. However, the inherent carrier mobility of these polymers is very low. Therefore, methodologies need to be explored to improve the carrier transport in these polymers so that they can be efficiently used in organic electronic devices. Graphene, due to its exceptional electrical and mechanical properties, is a promising material to be examined for its possible incorporation in CP matrix to achieve the objective. We have prepared graphene composites of the conducting polymers following an optimized procedure and these were investigated for their charge transport properties. The mobility values were measured using electric field induced second harmonic generation (EFISHG) and field effect transistor (FET) transfer characteristics. Both the transient and average mobilities were found to increase significantly with the inclusion of graphene. This enhancement in mobility has been attributed to an ordered packing of the thinner and smaller graphene sheets with polymer chain and interfacial π–π interaction. To substantiate its usefulness in device applications, the effect of graphene inclusion was also investigated for polymer solar cells and it was observed that despite of reduction in open circuit voltage, device fabricated using graphene composites yielded about 20% higher efficiencies as compared to pristine conducting polymer devices.

One pot, single step, room temperature dielectrophoretic deposition of gold nanoparticles clusters on polyethylene terephthalate substrate.

The major challenge of plastic electronics is the deposition of gold nanoparticles (AuNPs) on flexible substrates at room temperature. Here, we show fast, single step, room temperature deposition of AuNPs on polyethylene terephthalate (PET) and biaxially oriented PET (BoPET) substrate by employing dielectrophoresis. The deposition has been carried out using two‐electrode system, with BoPET (or PET) and metallic (Pt or stain steel) mesh, under an AC signal of 20 kHz and 20 V peak‐to‐peak (Vpp) (signal for PET is 6 Vpp and 6 kHz). In this method, we show how to deposit AuNPs on PET‐like insulator by exploiting its polarization capability under an AC signal. The polarization of PET has been confirmed by change in the Raman spectra of the PET film under in situ AC signals. Furthermore, we show that using this dielectrophoretic deposition method, the PET films can be patterned by AuNPs at room temperature without any pre‐ and posttreatment.

Effect of Co-sensitization and acid treatment on TiO2 photoanodes in dye-sensitized solar cells

The performance of dye-sensitized solar cells is improved by simple formic acid treatment of TiO2 photoanodes. The treatment increases number of hydroxyl groups at TiO2 surface and thereby result in enhanced dye-loading and device efficiency. The best device showed an open circuit voltage of 0.62V, short-circuit current density 6.34mA/cm2, fill factor of 60%, and a power conversion efficiency of ∼12 % under 20mW/cm2 white light illumination.

Poly(2,7-carbazole) derivative based air stable and flexible organic field effect transistor

Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) which is known to be air stable, has been used as active layer to fabricate flexible organic field effect transistor. Poly(methyl methacrylate) has been used as gate dielectric. The mobility and on-off ratio for these devices were found to be 7×10−4cm2V−1s−1 and 1.5×102, respectively.

Enhanced Field Emission From The Gold‐ Polyaniline (Au‐PANI) Nanocomposite

The gold‐polyaniline nanocomposite was synthesized by electrochemical route in two steps. In the first step polyaniline film was deposited by cyclic voltammetry on the ITO coated glass substrate, and then synthesis of gold‐polyaniline nanocomposite via chronoamperometry. The synthesized gold‐polyaniline nanocomposite film was characterized using scanning electron microscope (SEM), X‐ray diffraction (XRD), Ultra‐violet spectroscopy (UV‐vis) and Fourier Transform Infrared Spectrometry (FTIR). The SEM analysis shows well adherent gold nanoparticles on the surface of polyaniline nanofibers. The XRD and UV‐Vis spectra indicate formation of gold nanoparticles. From the field emission studies, the value of the turn on field, corresponding to 1 nA emission current, is found to be 0.65 V/μm and emission current density of 1 μA/cm2 has been drawn at an applied field of 1.1 V/μm. These values are observed to be superior than the reported ones. The field emission current stability investigated at 1 μA over duration o...