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The quest for electrically pumped organic laser is now conducted in several places around the globe. In this paper we outline our approach to this long-term project and aim to describe both encouraging and challenging (discouraging?) results. We describe experimental results using polymers, polymer blends and triplet emitters in an LED configuration using either CW or pulsed mode of operation. We also describe results of modeling such structures with the aim of being able to design electrical and optical characteristics of future laser structures. Finally we describe an approach to modify material parameters so as to provide a range of building blocks for optoelectronic devices.

We present a range of measurement techniques (time-resolved and CW) of various polymers in a variety of LED configurations. Using time-resolved pulsed electrical excitation, we are able to provide direct evidence for the motion of both types of carriers. We use pulses to probe the decay of carriers on time scales from nanosecond to millisecond. We address the issue of pulsed vs. CW properties and find that the functional form (power law) of the current–voltage curves is affected by the measurement technique; we also discuss a method to produce “intrinsic” curves. We introduce the method of using double electrical pulses to probe the dynamics of the stored charges after the application of a pulse.

We present a numerical model which is capable of time-resolving the electron, hole, and exciton density distribution. To simulate a close to real device, we include effects due to the metal electrode as quenching, modified radiation rate, and enhanced output coupling. Using this model, we provide a framework for the experimental extraction of mobility values from transient light response that accounts for the diffusion-induced broadening of the carrier front.

Emission patterns from the films of polyfluorene derivative on silica substrates are found to show light emission at grazing angles to the substrate. This light is found to be polarised and to have a narrowed emission, as well as enhanced intensity with respect to the light collected in the forward direction. Both the wavelengths of the peaks and their polarisation (s or p) are thickness-dependent. The peak's wavelength positions are used to characterise the spectrum of the refractive indices of the film both in and out of plane. The relative intensity of s- to p-polarised peaks serves as an independent indication of the dipole orientation. The deduced dipole in-plane alignment ratio (88%) and the magnitude of the birefringence (Δ n =0.2 at λ =600 nm) suggest that the main chains of this polymer lie preferentially in plane of the film. These findings seem to be consistent with the rod structure of the polymer studied.

We present theoretical and experimental analysis of conjugated polymer-based devices. We show that by combining a detailed optical and electrical theoretical model with a variety of experimental techniques it becomes possible to access many of the internal processes.

We have studied various two layer polymer light emitting diodes (LEDs) by applying a wide range of voltage pulses (100ns - 1 micosecond, 10–100V). We find that it is possible to move the recombination zone about the polymer/polymer heterojunction as a function of the applied voltage, and that the colour change depends on the charge injection, relative carrier mobilities and their field dependence. Preliminary simulation runs for these devices are also presented. Two current decay components (fast 100ns and slow 1ms) have been observed in the current response of a device after the application of microsecond pulses, which we attribute to the presence of mobile and immobile carriers. IVL and efficiency data presented show that LEDs perform better in pulsed than in d.c. operation. We also report peak brightnesses in LEDs in excess of 10 million Cd/m 2 at current densities of 500A/cm 2 under the application of 1MV/cm electric field.