Nanostructured organic light-emitting diodes with electronic doping, transparent carbon nanotube charge injectors, and quantum dots

Organic light-emitting diodes (OLEDs) and polymeric light-emitting diodes (PLEDs) are rapidly-emerging technologies which are being studied extensively in industrial, academic, and government laboratories for applications in displays and solid-state lighting. Their thin film structure (with total thickness of active layers less than a micron) and the inherent flexibility of the constituent materials give them promise in the flat panel display industry as well as open new areas of possible applications for flexible transparent displays and even textile displays. The materials also show high electroluminescence efficiency, and with proper device engineering these devices demonstrate efficiencies and lifetimes which surpass current methods of lighting such at incandescent bulbs, which average approximately 1% efficiency. Lastly, the materials offer easy processing through well studied and developed methods such as thermal evaporation, solution spin-casting and ink jet printing. Ink jet printing of polymeric layers in PLEDs offers many advantages when considering mass production of display and lighting panels, as it allows uniform films to be produced on large area substrates using a simple roll-to-roll method.; In this dissertation, we discuss several new methods and procedures which we have developed and used to produce OLEDs and PLEDs. More specifically these are electronic doping of transport layers, fluorescent doping of emissive layers by semiconductor nanocrystals (NC) (also known as quantum dots (QD)), and electrode engineering, namely by the use of transparent carbon nanotube sheets as charge injectors. We expand on the existing field of molecular doping and introduce a doped device with a very thick hole transport layer. Such a device is more resistant to failure due to excessive current density. We also investigate the effects of the presence of dopant molecules in the emissive layer of a multilayer OLED. This portion of the work introduces the negative effects of electronic doping at high concentrations, when the dopant molecules are able to diffuse into the emissive layer and quench luminescence by various processes.; In Chapter 5, we discuss novel OLED and PLED structures which are based on a novel carbon nanotube sheet which was developed recently at the Nanotech Institute at the University of Texas at Dallas. We introduce new possibilities for structures which are not possible with the standard anode and cathode materials, including inverted structures for active matrix displays, and transparent PLEDs.; In Chapter 6, we investigate another nanomaterial, quantum dots, and its application in OLEDs and PLEDs. We discuss briefly the importance of white OLEDs for solid-state lighting and demonstrate our ability to produce white-emitting OLEDs using several simple structures. We also conduct a study on the mechanisms of exciton transfer to the quantum dot emitters.