Glenn Bryant

Novel low voltage and solution processable organic thin film transistors based on water dispersed polymer semiconductor nanoparticulates

Two novel organic thin film transistor structures that combine a hygroscopic insulator with the use of water-dispersed polymer nanoparticles as the active layer are presented. In the first device structure, the semiconducting layer was fabricated from a nanoparticulate suspension of poly-(3-hexylthiophene) prepared through a mini-emulsion process using sodium dodecyl sulfate as the surfactant whereas a surfactant-free precipitation method has been used for the second device structure. In both cases, fully solution processable transistors have been fabricated in a top gate configuration with hygroscopic poly(4-vinylphenol) as the dielectric layer. Both device structures operate at low voltages (0 to -4V) but exhibit contrasting output characteristics. A systematic study is presented on the effect of surfactant on the synthesis of semiconducting nanoparticles, the formation of thin nanoparticulate films and, consequently, on device performance.

Effect of a calcium cathode on water-based nanoparticulate solar cells

Water-based nanoparticulate (NP) and bulk heterojunction (BHJ) organic photovoltaic (OPV) devices based on blends of poly(9,9-dioctylfluorene-co-N,N-bis(4-butylphenyl)-N,Ndiphenyl-1,4-phenylenediamine) (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole (F8BT) have been fabricated with aluminium and calcium/aluminium cathodes. The NP devices exhibit power conversion efficiencies (PCEs) that are double that of the corresponding BHJ device. Moreover, the addition of calcium into the cathode structure results in a dramatic increase in open circuit voltage and PCEs approaching 1% for water-based polyfluorene OPV devices.

Solution processable interface materials for nanoparticulate organic photovoltaic devices

Nanoparticulate zinc oxide can be prepared at low temperatures from solution processable zinc acetylacetonate. The use of this material as a cathode interfacial layer in nanoparticulate organic photovoltaic devices results in comparable performances to those based on reactive calcium layers. Importantly, the enhanced degradation stability and full solution processability make zinc oxide a more desirable material for the fabrication of large area printed devices.

Synthesis of indium oxide nanowires encapsulated in amorphous carbon nanostructures on indium tin oxide substrate

Abstract Indium oxide nanowires encapsulated in amorphous carbon nanostructures have been synthesised on iron coated indium tin oxide substrate via the chemical vapour deposition of acetylene (C2H2). The growth of indium oxide nanowires encapsulated in amorphous carbon nanostructures via solid–liquid–solid mechanism was suggested. The morphology, composition and structure of indium oxide nanowires encapsulated in amorphous carbon nanostructures were characterised by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy.

Accelerated hydrothermal ageing of Pd/Al2O3 for catalytic combustion of ventilation air methane

In this report, the characteristics of Pd/Al2O3 catalyst after long-term stability tests in catalytic combustion of simulated ventilation air methane gas were investigated with the objective of understanding catalyst deactivation phenomena. It was found that the deactivation is primarily due to palladium migration and particle growth and is the most prominent in the presence of water vapour. The formation of α-Al2O3 during long-term stability tests explains the changes in pore structures which is responsible for re-dispersion of palladium particles. Four accelerated ageing procedures were performed with an aim of mimicking the properties of used catalysts which have been operating continuously for extended time periods (over 1100 h). XRD patterns of aged catalysts disclose the absence of an alpha-alumina phase, suggesting that the transformation of alumina phase occurred at a very slow rate. Among the four procedures, ageing under wet-oxidizing atmosphere provides the catalyst bed that is the best match to the properties of long-term used catalysts in terms of performance and the characterization employed. Increasing the aging temperature up to 830 °C leads to depletion of surface palladium, which permanently reduces the performance of the catalyst.

High‐Performance Thin Film Transistor from Solution‐Processed P3HT Polymer Semiconductor Nanoparticles

Nanoparticulate suspensions of semiconducting polymer poly‐3‐hexylthiophene (P3HT) have been prepared in water through a mini‐emulsion process using sodium dodecyl sulphate (SDS) as the surfactant. Using these suspensions, we have fabricated organic thin film transistors (OTFTs) in a top gate configuration. These devices operate at a low voltage and show output characteristics similar to those achieved when the P3HT film is spun from chloroform. To characterize the properties of the film made from the nanoparticle suspension, differential thermal analysis (TGA), differential scanning calorimetry (DSC), atomic force microscopy (AFM), fluorescence spectra analysis, ultraviolet/visible (UV/VIS) spectrophotometry and X‐ray photoelectron spectroscopy (XPS) have been used.

Surfactant Free P3HT / PCBM Nanoparticles for Organic Photovoltaics (OPV)

Initial attempts to prepare conducting polymer nanoparticles with ethanol as a solvent are described. Using poly (3‐hexylthiophene) (P3HT)/1‐(methoxycarbonylpropyl)‐1‐phenyl‐[6,6]C61 (PCBM) blends we demonstrate surfactant‐free synthesis and characterization of polymer nanoparticles in ethanol dispersion. The spectral features of the nanoparticles were investigated by UV‐vis spectrophotometry show that P3HT has an absorption maximum at ∼520 nm, while the absorption peak of PCBM lies at ∼330 nm. Corresponding fluorescence spectra of the nanoparticles show an emission peak at 630 nm with a shoulder visible at 720 nm. TEM spectra show that the particle size is in the range 35 to 100 nm. Using the ethanol suspension of these particles, we have fabricated and characterized working OPV (organic photovoltaic) devices. This approach is shown to be an effective way to control active layer morphology in OPV devices.

Organic solar cells: evaluation of the stability of P3HT using time- delayed degradation

Despite the fact that the performance of organic solar cells is generally susceptible to degradation by moisture exposure, there has been suggestion that the photoactive layer (P3HT) is surprisingly resilient. This work attempts to confirm the stability of P3HT as an organic solar cell material by deliberately introducing water into the photoactive layer. A dramatic step drop in device performance during cell characterization is observed approximately one day after the device has been fabricated. The time-delayed step drop in output efficiency strongly suggests that moisture has little effect on the P3HT conducting polymer.

Templated growth of poly(p-phenylenevinylene) nanostructures by chemical vapour deposition

Abstract Poly(p-phenylenevinylene) nanostructures have been successfully synthesised via chemical vapour deposition into a porous alumina template. Poly(p-phenylenevinylene) layers with different textures were created by varying the angle between the template and the precursor gas flow. These different morphologies are characterised by differences in their optical emission spectra, in which the synthesis of these nanostructures opens up perspectives for nanoelectronic devices and sensors application.

Plasmonic nanostructure embedded within photoactive layer for enhanced power conversion efficiency of organic solar cells

Gold quantum dots have been successfully embedded into the photoactive layer of a P3HT:C60 bilayer solar cell. I–V and EQE measurements confirm that the demonstrated bilayer device shows a 67% increase in conversion efficiency.