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INVESTIGATION OF THE USE OF RARE-EARTH SULFIDE THIN FILMS AS EFFICIENT CATHODES IN ORGANIC LIGHT EMITTING DIODES

by GARRE, KALYAN

Abstract (Summary)
During the past decade there has been lot of interest in the development of organic light emitting diodes (OLEDs) for display and backlighting purposes. OLEDs are self-emitting, have a very wide viewing angle, operate at lower voltages, and have bright emission. Due to these advantages they have the potential to replace the current display technologies like the CRT (Cathode Ray Tube) and LCDs (Liquid Crystal Displays). Low power bright colorful cell phones, television sets, laptop screens, automotive displays, and wearable electronic displays are some of the areas identified for the potential applications of these devices. However some issues like lifetime and uniform degradation of the basic colors for full color version of displays still need to be resolved before OLEDs reach their full potential market. In this thesis, we have investigated the use of rare-earth sulfide thin films mainly LaS (Lanthanum sulfide) as efficient cathodes for organic light emitting dodes as a result of their low work function at room temperature (around 1 eV) and high chemical and thermal stability. As a result, OLEDs would operate reliably at a lower bias which would reduce the heating effects thereby increasing the lifetime of the devices. In the first part of this thesis, we have developed all the fabrication processes necessary for the demonstration of working ITO/TPD/Alq3/Al OLED prototypes. The best surface emitting devices fabricated in our lab had a lifetime of about 80 minutes without using any encapsulation of the structures. Next, a 2” LaS target was fabricated by a carbon reduction technique and used by collaborators at Wright-Patterson Air Force Base to succesffuly deposit for the first time LaS thin films on various substrates using pulsed laser deposition. A excimer laser beam with an energy of 800mJ/pulse at a repitition rate of 40Hz was used to grow 0.5-1 micron thick LaS films on both Si and InP substrates. The same pulsed laser deposition parameters were used to deposit LaS cathodes a few 100 angstroms thick on top of the organic layers in an attempt to farbicate ITO/TPD/Alq3/LaS OLED prototypes. Even though we were unsuccessful in obtaining working ITO/TPD/Alq3/LaS OLEDs, we have identified alternative approaches to form LaS cathodes based on a combination of a cluster deposition technique to deposit smoother organic layers and the use of a thin buffer Al layer (a few tens of angstroms thick) betweent the top organic layer and the LaS cathode to avoid the damage to the organic material during the pulsed laser deposition of the rare-earth cathode.
Bibliographical Information:

Advisor:

School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:oleds las organic light emitting diodes rare earth sulfides

ISBN:

Date of Publication:01/01/2004

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