Degree Type

Thesis

Date of Award

2020

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

Major

Condense d Matter Physics

First Advisor

Joseph Shinar

Abstract

Enhancing light extraction from Organic Light Emitting Diodes (OLEDs) is an ongoing scientific and industrial challenge that is particularly important for lighting applications. Light extraction, or the outcoupling factor out of conventional OLEDs devoid of any extraction means is limited to ~20%. This limit stems mainly from three photon loss processes: (i) so-called "external" waveguiding in the substrate, (ii) internal waveguiding in the high refractive index anode and organic layers, and (iii) excitation of surface plasmon polaritons at the metal cathode/organic interface. The ~30% external waveguided light can be extracted via a microlens array or a hemispherical lens at the air-side of the OLEDs' substrate. However, mitigating the internal waveguided light and surface plasmon excitation losses, which amount to ~50% of the lost photons, in a cost-effective approach remains a challenge. Substrate corrugation is one of the innovative approaches used for addressing this issue. In this work, corrugated plastic substrates of polycarbonate and polyethylene terephthalate/cellulose acetate butyrate of various designs, such as different patterns' height and periodicity, were evaluated. Detailed substrates' design is a crucial metric for device performance; hence it requires in-depth analysis. Tapping mode atomic force microcopy (AFM) was used for probing the geometry, uniformity, and smoothness of the various plastic substrates. The essence of the work performed in this dissertation is combining promising substrate designs with carefully stacked green and white OLEDs that resulted in ~2x enhancements in out due to the patterns only, i.e., without additional means for extracting the externally waveguided light. In addition to broad optoelectronic characterization of the OLEDs, analyses of device stack conformality and top surface structure were performed via focused ion beam, SEM and AFM techniques.

DOI

https://doi.org/10.31274/etd-20200624-84

Copyright Owner

Rajiv Kaudal

Language

en

File Format

application/pdf

File Size

126 pages

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