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Dissertation/Thesis Abstract

Light Extraction and Degradation Mechanism Study of Organic Light Emitting Diodes
by Peng, Cheng, Ph.D., University of Florida, 2017, 123; 13847495
Abstract (Summary)

The light extraction efficiency of common bottom emission OLEDs is limited to 25-30%. One of the commonly used approaches to exceed this limitation is to corrugate the interfaces. Herein, a simple process will be introduced to fabricate a corrugated OLED containing a corrugated bilayer ETL by thermal annealing due to the big difference between the glass transition temperatures between the two materials. We show that the morphology of the corrugated structure can be tuned by the annealing temperature and the layer thicknesses. The corrugated OLED with the corrugated bilayer ETL shows better efficiency and stability than the control planar OLED.

The scattering efficiency of waveguide and SPP mode by the corrugation remains challenging to quantify. Herein, we demonstrate a quantitative analysis on the scattering efficiency of the corrugation of waveguide mode and SPP mode. The calculation is based on optical simulation using Bragg diffraction equation and fitting with the measured data of corrugated OLEDs. We successfully quantified the extraction efficiency of waveguide mode and SPP mode using a hexagonal close-packed corrugation and a random corrugation.

The scattering strength of waveguide mode by corrugation remains an open topic. Herein, we applied the reciprocity theorem in finite difference time domain simulation and compared the scattering strength of TMWG from different corrugations. We studied the combined effect of optical diffraction and non-uniform electric field.

The control of emission zone is crucial to OLED stability. It is challenging to probe the emission zone. A new and simple methodology will be introduced to quantitatively probe the emission zone of OLEDs by comparing the PL degradation of OLEDs with the EL degradation during continuous electrical operation. This approach is first validated by investigating OLEDs using the well-known 4CzIPN. We then applied this approach to investigate the emitter concentration effect on the stability of OLEDs using Dopant 1. Based on our results, the Dopant 1 OLEDs show much less pronounced emitter concentration effect due to the relatively worse electron transport in the EML, compared with 4CzIPN OLEDs. We were able to widen the emission zone by the use of a mixed host.

Indexing (document details)
Advisor: So, Franky
Commitee: Gila, Brent, Pearton, Stephen, Rinzler, Andrew, Singh, Rajiv, So, Franky
School: University of Florida
Department: Materials Science and Engineering
School Location: United States -- Florida
Source: DAI-B 80/07(E), Dissertation Abstracts International
Subjects: Nanotechnology, Optics, Materials science
Keywords: Light extraction, OLED, Organic electronics
Publication Number: 13847495
ISBN: 978-0-438-94750-4
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