Akshay Kokil

Enhancing sensing of nitroaromatic vapours by thiophene-based polymer films

Optical sensing, via fluorescence quenching, of nitroaromatic vapours using polythiophenes has received limited attention due to their rather low sensory response. We hypothesized that a dipolar 1,2,3-triazole moiety can enhance the interaction of DNT and TNT with the polymer in thin films and bulky side chains can decrease the chain packing in thin films resulting in enhanced analyte diffusion. Herein we show that thin films of thiophene-based polymers containing 1,2,3-triazole with appropriate alkyl side chains show enhanced fluorescence quenching in the presence of nitroaromatic vapours.

Improved Performances in Polymer BHJ Solar Cells Through Frontier Orbital Tuning of Small Molecule Additives in Ternary Blends

Polymer solar cells fabricated in air under ambient conditions are of significant current interest, because of the implications in practicality of such devices. However, only moderate performance has been obtained for the air-processed devices. Here, we report that enhanced short circuit current density (JSC) and open circuit voltage (VOC) in air-processed poly(3-hexylthiophene) (P3HT)-based solar cells can be obtained by using a series of donor-acceptor dyes as the third component in the device. Power conversion efficiencies up to 4.6% were obtained upon addition of the dyes which are comparable to high-performance P3HT solar cells fabricated in controlled environments. Multilayer planar solar cells containing interlayers of the donor-acceptor dyes, revealed that along with infrared sensitization, an energy level cascade architecture and Förster resonance energy transfer could contribute to the enhanced performance.

A straightforward route to electron transporting conjugated polymers

We report a straightforward synthetic method to generate solution processable electron transporting polymers with low band gap and wide absorption range from readily available acceptor monomers. We show the efficacy of this approach using widely used electron acceptor 2,1,3-benzothiadiazole. The polymers have absorption up to 750 nm with electron mobility comparable to PCBM.

Environmentally benign synthesis of vinyl ester resin from biowaste glycerin

We present here for the first time a novel environmentally benign protocol for the synthesis of vinyl ester resin (VER). Our synthetic strategy utilizes a commercial waste material, glycerin, from biodiesel manufacturing and converts it into a widely utilized resin. The VER was synthesized using bisphenol A (BPA) and glycidyl methacrylate (GMA) as precursors. GMA was synthesized via a multistep synthetic protocol using glycerin obtained from a biodiesel manufacturing waste stream. The structure of the intermediates was confirmed by 1H NMR, HPLC and FT-IR spectroscopy.

Sensitive Detection of Nitroaromatics With Colloidal Conjugated Polymer Nanoparticles

We observe more than two orders of magnitude enhancement of fluorescence quenching in colloidal conjugated polymer nanoparticles by nitroaromatic analytes compared to solution of the same polymer in organic solvents. This observation is surprising as the quantum efficiency of fluorescence of the polymer solution is significantly higher. The colloidal nanoparticle dispersions of substituted polythiophene derivative are fabricated by the surfactant-assisted mini-emulsion technique. Stern–Volmer constants are determined using both one-photon and two-photon excitation methods. We believe strong analyte–nanoparticle interaction results in the large value of the Stern–Volmer constants measured. The nanoparticle-based sensor described here is suitable for developing a field-based sensory device for detecting a broad class of nitroaromatics in solution.

Synthesis and Characterization of Triazolium Iodide Ionic Liquid Electrolyte for Dye Sensitized Solar Cells

Imidazolium iodide compounds have been utilized in the electrolytes for dye sensitized solar cells (DSSC). Most of the investigations with these compounds focus on the formulation of eutectic mixtures that promote efficient dissociation and diffusion of the iodide and triiodide species. Facile alternative synthetic approaches such as click chemistry (Huisgen 3+2 dipolar cycloaddition reaction) can be utilized to broaden the scope of electrochemically stable promising materials for novel electrolyte systems. Here, we report the first example of a triazolium functionalized cyclic siloxane that can be used as an electrolyte component in solvent-based DSSCs. The devices fabricated with this new triazolium salt in the electrolyte yielded short circuit current densities (26 mA/cm2), as well as power conversion efficiencies of 8%, these values are comparable to those obtained for imidazolium salt analogues.

Push–pull triarylamine additives that enhance dye sensitized solar cell performance

A new strategy was developed for improving basic dye sensitized solar cell (DSSC) performance, using push–pull organic triarylamines with tunable frontier energy levels as additives in the DSSC electron shuttling electrolyte solution. A significant improvement in the device performance was observed and attributed to improved dye regeneration and hole transport.

Solution processed flexible planar hybrid perovskite solar cells

Organolead halide perovskites are attracting considerable attention for applications in high performance and flexible hybrid photovoltaic devices. Low temperature solution-processed flexible hybrid solar cells with CH3NH3PbI2Cl, using [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) and Poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt- (benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) as electron transport materials were fabricated on ITO coated plastic substrates in planar configuration. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate was employed as the electron blocking layer. Under standard AM 1.5G solar irradiation, these flexible solar cells yielded power conversion efficiencies of 5.14% and 7.05% with the electron transporting materials PCBM and F8BT, respectively.

Performance enhancement of fullerene based solar cells upon NIR laser irradiation

Photovoltaic performance enhancement of fullerene based solar cells was achieved upon exposure to near-infrared (NIR) laser pulses. The solar cells were fabricated with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) under ambient conditions. The cells were then post-treated with NIR femto-second laser pulses at 800 nm for different intervals of time. An enhancement of 50% in the power conversion efficiency was achieved for the devices with 15 minutes of NIR laser irradiation compared to that of the control device. The enhancement in the power conversion efficiency is attributed to the formation of a covalent linkage between P3HT and PCBM as suggested by Matrix-assisted laser desorption/ionization time of flight mass spectroscopic analysis on a blend of a thiophene oligomer and PCBM before and after NIR laser exposure.

Large-area nanoscale patterning using optical interference

The continuous miniaturization of electronic and photonic devices over the past few decades has demanded the development of adaptable, high-throughput, nanoscale fabrication techniques. Consequently, fabricating well-defined nanostructures is at the forefront of nanomanufacturing challenges. The ability to control the growth of metal and metal-oxide structures at the nanoscale has enabled many interesting observations and applications in the areas of photonics, sensors, photovoltaics, plasmonics, and spectroscopy. Numerous techniques are available for constructing nanoscale patterns, each with its own advantages and limitations. Most fabrication methods, however, involve multiple steps or sophisticated instrumentation. Therefore, the development of simple, cost-effective nanopatterning techniques that are adaptable to a variety of materials (including polymers, metals, and nonmetals) is of paramount importance for sustained innovation and growth. A simple approach to create large-area (a few square centimeters) nanopatterns is by irradiating optical interference patterns on photosensitive polymers and organometallic compounds. We and other groups have shown that with this technique oneand two-dimensional submicron structures can be readily fabricated and the structures’ periodicity can be easily tuned. Additionally, a polymer structure made this way can be used as a template to fabricate an ordered array of metals or inorganic oxides and also as a master or mold for soft lithography. Figure 1 shows the schematic of a typical experimental setup used for photofabricating metallic structures or polymer surface relief gratings (SRGs), in which the surface becomes corrugated. An argon ion laser beam with appropriate polarization is spatially filtered and collimated. A mirror reflects half of the beam, recombining it with the other half to form an interference pattern at the sample plane (orthogonal to the mirror). Exposing the thin film of metal precursor or photoresist to the interference pattern Figure 1. Schematic of a simple laser interference setup. A mirror perpendicular to the sample reflects half of the laser beam so that it interferes with the other half at the sample surface.