Electroluminescence in ruthenium(II) complexes

We have investigated the electrochemical, spectroscopic, and electroluminescent properties of a family of diimine complexes of Ru featuring various aliphatic side chains as well as a more extended pi-conjugated system. The performance of solid-state electroluminescent devices fabricated from these complexes using indium tin oxide (ITO) and gold contacts appears to be dominated by ionic space charge effects. Their electroluminescence efficiency was limited by the photoluminescence efficiency of the Ru films and not by charge injection from the contacts. The incorporation of di-tert-butyl side chains on the dipyridyl ligand was found to be the most beneficial substitution in terms of reducing self-quenching of luminescence.     

Chemical and biological sensors based on organic thin-film transistors

The application of organic thin-film transistors (OTFTs) to chemical and biological sensing is reviewed. This review covers transistors that are based on the modulation of current through thin organic semiconducting films, and includes both field-effect and electrochemical transistors. The advantages of using OTFTs as sensors (including high sensitivity and selectivity) are described, and results are presented for sensing analytes in both gaseous and aqueous environments. The primary emphasis is on the major developments in the field of OTFT sensing over the last 5–10 years, but some earlier work is discussed briefly to provide a foundation.     

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

Solid-state electroluminescent devices based on transition metal complexes

Transition metal complexes have emerged as promising candidates for applications in solid-state electroluminescent devices. These materials serve as multifunctional chromophores, into which electrons and holes can be injected, migrate and recombine to produce light emission. Their device characteristics are dominated by the presence of mobile ions that redistribute under an applied field and assist charge injection. As a result, an efficiency of 10 lm/W--among the highest efficiencies reported in a single layer electroluminescent device--was recently demonstrated. In this article we review the history of electroluminescence in transition metal complexes and discuss the issues that need to be addressed for these materials to succeed in display and lighting applications.     

Identification of a quenching species in ruthenium tris-bipyridine electroluminescent devices

We have used matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and micro-Raman spectroscopy to identify a quenching species that is formed during operation of [Ru(bpy)3]2+ electroluminescent devices. We identify this performance-degrading product to be the oxo-bridged dimer [(bpy)2(H2O)RuORu(OH2)(bpy)2]4+ and show this dimer to be an effective quencher of device luminescence. This work is the first to detect a specific chemical degradation product formed during iTMC OLED operation.     

Understanding volumetric capacitance in conducting polymers

Recent measurements in poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films show that capacitance scales with film volume. We discuss the ramifications of this finding and propose a simple model that describes capacitance in terms of sites in which ions injected from the electrolyte replace holes that are extracted from the film by a metal contact. We propose that volumetric capacitance is inversely proportional to the average distance between these sites. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1433–1436     

Tetrathienoacene copolymers as high mobility, soluble organic semiconductors

Increasing the rigidity of the thiophene monomer through the use of an alkyl-substituted core that consists of four fused thiophene rings is shown to be a promising route toward high-performance organic semiconductors. We report on a dialkylated tetrathienoacene copolymer that can be deposited from solution to yield ordered films with a short pi-pi distance of 3.76 A and with a field-effect hole mobility that exceeds 0.3 cm2/V.s. This polymer enables simple transistor fabrication at relatively low temperatures, which is particularly important for the realization of large-area, mechanically flexible electronics.     

Optimization of organic electrochemical transistors for sensor applications

Despite the recent interest in organic electrochemical transistors (OECTs) as chemical and biological sensors, little is known about the role that device architecture and materials parameters play in determining sensor performance. We use numerical modeling to establish design rules in two regimes of operation: We find that for operation as an ion‐to‐electron converter, the response of OECTs is maximized through the use of a gate electrode that is much larger than the channel or through the use of a nonpolarizable gate electrode. Improving the conductivity of the polymer and using a channel geometry that maximizes channel width and thickness, and minimizes channel length helps increase the response. For operation as an electrochemical sensor, the sensitivity is maximized in OECTs with gate electrodes that are smaller than their channels. The sensitivity can be improved by increasing the charge carrier mobility and the capacitance per unit area of the conducting polymer, and also its ability to be penetrated by ions from the electrolyte. A channel geometry that maximizes channel width and minimizes channel length also improves sensitivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

A glucose sensor via stable immobilization of the GOx enzyme on an organic transistor using a polymer brush

Recently, there has been significant research in the area of organic electrochemical transistors (OECTs) because of their superior aptitude of chemical and biological sensing. Here it is shown for the first time the incorporation of polymer brushes to a transistor. Polymer brushes were chosen for their biocompatible properties and their ability to covalently tether enzymes and other biomolecules to different surfaces. OECTs were fabricated from the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate), PEDOT:PSS, and polymerized from the surface a mixed polymer brush of poly(glycidyl methacrylate) and poly(2-hydroxyethyl methacrylate). The brushes were functionalized with glucose oxidase and measured in terms of electrical performance and long-term stability. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 372–377     

Photonic polymers for the devices of the 21st century

This paper describes research activities towards the development of polymer materials and devices for optoelectronics. Electroluminescent devices, lasers and photovoltaic devices from polymers or oligomers are discussed.