Charge and light in polymers: Steady-state and transient electroluminescence studies in organic light emitting diodes

Since the discovery of electroluminescence in organic materials, increasing interest has been directed to these materials. Easy processing and mechanical flexibility make them promising candidates for cheap technology applications in many fields as biosensors, transistors, displays and more. Polymers are attractive not only for the obvious market-applications but also for their unique characteristics of highly disordered and amorphous systems. In the recent years, remarkable progress has been done in this field. While new polymer-based products are now commercially available, the chemistry is very active in the synthesis of materials tailored for specific applications. The physics mechanisms that regulate their properties have been widely debated and some of them have finally reached a general consensus.; This work describes several examples of how electrical measurements on Organic Light Emitting Diodes (OLEDs) devices can be performed to determine the transport properties of the polymeric materials. Single layer PAni/MEH-PPV/Al and TiN/MEH-PPV/Ca devices have been fabricated and their current-voltage characteristics and temperature-dependence have been considered to derive the electron and hole mobilities in single polarity devices where the current flow is dominated by one charge species only.; The approximated and full expression of Murgatroyd (Murgatroyd 1970) space charge limited formulae have been used to fit the experimental data and to derive the temperature and electric field dependence of the mobility. Transient electroluminescence in single and multilayer polyfluorene diodes has been measured to determine the mobility and the trapping behavior. The results are then compared with those from the steady state behavior. This series of measurements provides insight into the details of operation of OLED devices.