James R. Sandifer

Nonradiative recombination centers and electrical aging of organic light-emitting diodes: Direct connection between accumulation of trapped charge and luminance loss

Organic light-emitting diodes (OLEDs) are attractive for display applications because of their high brightness, low driving voltage, and tunable color. Their operating lifetimes, hundreds or thousands of hours, are sufficient for only a limited range of applications. The luminance efficiency decreases gradually as the device is operated (electrically aged), for reasons that are poorly understood. A prototypical OLED has the structure anode|HTL|ETL|cathode, where the HTL and ETL are hole- and electron-transporting layers, and the recombination and emission occur at or near the HTL|ETL interface. We find that the decreasing luminance efficiency is linearly correlated with an accumulation of immobile positive charge at the HTL|ETL interface, and the magnitude of the charge is comparable to the total charge at that interface when an unaged device is operated. A natural explanation of the connection between the two phenomena is that electrical aging either generates hole traps (and trapped holes) or drives met...

A review of biosensor and industrial applications of pH-ISFETs and an evaluation of Honeywell's DuraFET

Abstract Biosensors were viewed by earlier workers as possibly lucrative applications for ion selective field effect transistor (ISFET) technology. Such products have yet to find widespread use, however, for a number of reasons that will be reviewed in this article. Some have to do with the inherent nature of biosensor applications per se. For example, biocompatibility is an issue that must be faced regardless of the mechanism of transduction. Others have to do with the inherent nature of the sensor itself. Encapsulation of electronically sensitive parts can prove to be so problematical that lengthy timelines and costly overruns compromisecommercial promise. Intermediate applications, which will be referred to here as “industrial” appear to be commercially viable, however, and can be used to provide profits that will drive further development in the biosensor area. Such applications will also be reviewed. Finally, a specific application will be described in detail (exclusive of proprietary concerns), to illustrate the remarkable ruggedness, stability, and accuracy of a particular commercially available pH-ISFET – Honeywell’s “DuraFET”– a truly useful ion selective field effect transistor.

Electrochemical characteristics of the lithium/carbon monofluoride battery and its component half-cells

The impedance spectrum of the Matsushita lithium/carbon monofluoride battery was studied extensively as a function of load, temperature, state of charge, and time after discharge. Resolution of the battery impedance spectrum into frequency domains characteristic of the electrolyte, the anode, and the cathode permitted the polarization and kinetic parameters of the individual battery electrodes to be measured. Most of the battery voltage loss is attributed to the carbon monofluoride cathode. Comparisons of the interfacial electrochemical properties of lithium half-cells in the battery electrolyte (1.0 mol dm−3 LiBF4/γ-butyrolactone) with those of thein situ battery anode show that the battery anode is coated with a film. Attempts to correlate the high-frequency (> 1 Hz) parameters of the battery impedance with state of charge proved unsuccessful.

33.1: Invited Paper: OLED Aging Mechanisms: from Fluorescence Quenchers to Nonradiative Recombination Centers

A recently introduced technique to measure fixed charge densities inside OLEDs was applied to study the electrical aging phenomenon. Strong linear correlations between luminance efficiency and deeply trapped positive charge were observed. Correlations between these non-trivially evolving quantities in OLEDs of various chemical composition were interpreted in terms of a common degradation mechanism— generation of nonradiative recombination centers.

Bipolar pulse conductivity measurements applied to ion-selective electrodes

Abstract Bipolar pulse conductivity (BICON) measurements were evaluated as a means of using calciumion-selective electrodes with an upoised reference electrode. The study shows a change in total cell conductivity with Ca 2+ concentration at low concentrations in the absence of other electrolytes but no change in conductivity with Ca 2+ concentration in the presence of 0.1 M KCl. The computed voltage at zero current varied with Ca 2+ concentration but electroactive species interfered with the measurements. For the conditions used, it is concluded that there is no change in conductivity of the ion-selective membrane with Ca 2+ concentration and that reliable quantitation of Ca 2+ is not feasible.