High Speed micro-OLEDs for the Development of Electrically Pumped Organic Laser Diodes

This thesis presents the fabrication, characterisation, and optimisation of high-speed micro-organic light-emitting diodes (µOLEDs) for applications in electrically pumped organic lasers. Organic semiconductors have attracted significant attention in op- toelectronics due to their wavelength tunability through chemical modification, potential for low-cost processing, and monolithic integration into photonic systems. However, achieving electrically pumped lasing in organic materials remains chal- lenging, primarily due to the high current density required for operation and loss mechanisms associated with charge carriers, excitons, and device heating. Suc- cessfully realising such a device would substantially impact diverse fields including healthcare, data transmission, communication, and sensing applications. This research presents high-performance µOLEDs that were designed and charac- terised, with a particular emphasis on investigating charge carrier and exciton dynam- ics near the lasing threshold and assessing device performance under high current- density conditions. Simulation and experimental methodologies were utilised to examine internal interactions between charge carriers and excited states, elucidating mechanisms that may contribute to reducing the lasing threshold. Experimental findings demonstrated successful operation of µOLEDs at current densities exceed- ing 2.5 kA.cm−2 under 100 ns excitation pulses, achieving radiances surpassing 20 kW.m−2.sr−1. By fitting a robust laser model to experimental data, estimates for lasing threshold and lifetime were derived across a variety of material systems, including both fluorescent and thermally activated delayed fluorescence (TADF) emitters.