Analysis and Optimisation of an Organic Optical Link
Organic light-emitting diodes (OLEDs) have been historically used extensively for displays, and more recently for lighting applications. However, the low-cost of materials and direct-deposition manufacturing processes involved in organic semiconductor fabrication means that OLEDs are uniquely placed for low-cost integrated optical interconnects. This thesis presents novel high-speed analysis and optimisation of OLEDs for communications purposes. DC and small-signal measurement results for small-molecule OLEDs fabricated by Dr. Kou Yoshida at the University of St. Andrews are presented and are used to inform a detailed 5-layer OLED simulation model. Correlation is drawn between the experimental small signal impedance measurements and the experimental luminescent output, from which a novel electrical model is built to predict bandwidth. Extension of the OLED physical simulation shows for the first time that by using a constant fraction of the overall simulated device resistance (a ‘luminescent resistance’), this RC-based model can be used to predict device small signal bandwidths, which suggests validity of both the simulation and the electrical modelling approach, provided that the exciton lifetime is less than the RC time-constant. This simulation is then used to forecast trends in device performance, allowing traditional inorganic semiconductor engineering tools to be brought into the field of organic device optimisation. Finally, these OLEDs are used in an optical link to provide a world-record equalisation-free OLED communications data rate of 130 Mbps.