Text

theses

The pioneering work by Tang and Van Slyke in 1987 that invented organic light emitting diodes (OLEDs) resulted in considerable attention to these devices in both academic and industrial circles. OLEDs have very unique properties compared to traditional light-emitting devices such as synthetically tunable emission colors and color temperatures. There are two general types of OLED device structures: bottom-emitting OLEDs and top-emitting OLEDs. Electrons and holes are injected into the organic semiconducting emissive layer via electrical contacts (one metallic and one transparent, e.g. indium-tin oxide (ITO)) in combination with an electron injection layer and a hole injection layer, respectively. In the organic semiconducting emissive layer, holes and electrons combine to emit light (photons). However, because of the high refractive indices of ITO and glass used on the transparent side of most bottom-emitting OLED devices, the emitted light tends to get trapped in the ITO or glass substrate due to total internal reflection at the interfaces thus reducing the light extraction efficiency. In contrast, top-emitting OLEDs can have reduced waveguiding losses due to thinner or lower refractive index transparent layers. The hypothesis of this thesis is that the efficiency of organic conjugated polymer–based top-emitting OLEDs is greater than that of bottom-emitting OLEDs because of reduced total internal reflection and waveguiding losses. Organic conjugated polymer semiconductors are of interest in this work as the emissive layer instead of more-common small-molecule organic semiconductors because they offer solution process-ability which can lower the overall cost of the OLEDs. The objectives of this project are: to compare the performance of polymer-based bottom-emitting and top-emitting OLEDs using optoelectronic simulation software, to compare current - voltage, light flux - voltage, light flux - current density, light flux - input power relationships; and to determine the OLED external quantum efficiency. Additionally, fabrication methods for both device types are developed and the optical and electrical properties of both the devices are compared.

ETD_11605

M.S.

Includes bibliographical references

ETD graduate

doi:10.7282/t3-bdp6-bh09