Device physics of polymer light-emitting diodes

Organic light emitting diodes have the structure metal_A/organic/metal_B. The physical processes which determine the operating characteristics of these devices are carrier injection into the organic material from the metal contacts, carrier transport through the organic, and carrier recombination in the organic layer. The philosophy employed here is to study these processes in simple situations where they can be studied independently to as large a degree as possible, and then to apply the understanding gained from simple systems to successively more complex systems. This is done by using experiments in parallel with a device model to describe the experimental results.; First single carrier single layer devices are considered. Current voltage characteristics are measured for series of electron and hole only devices both as a function of device thickness and of energy barrier to carrier injection. These measurements were described by a device model and carrier mobilities were extracted. The energy barriers to injection were measured independently.; Then the current voltage characteristics were measured for series of bipolar single layer devices both as a function of device thickness and energy barrier to carrier injection. These measurements were described by the carrier mobilities and energy barriers determined from single carrier experiments with no additional fitting parameters. The device model also gave a qualitative description of single layer device luminances. The calculated current voltage characteristics were found to be relatively insensitive to the magnitude of the recombination rate used in the device model.; Organic materials which have desirable electroluminescence properties may not have the necessary physical characteristics to make an efficient single layer LED. Device model results are presented which show that if the injection or transport of one carrier is lacking in a material, an efficient device can be made by introducing a second material which improves the injection or transport of the lacking carrier, and which also blocks transport of the other carrier.; Finally, cost reduction in a-Si:H based photovoltaics is explored by three methods: increased growth rates; reduced materials usage; and reduced processing temperatures.