On Microcavity and Triplet Exciton Behaviour in Organic and Hybrid Light Emitting Diodes

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Material Information

Title:
On Microcavity and Triplet Exciton Behaviour in Organic and Hybrid Light Emitting Diodes
Physical Description:
1 online resource (136 p.)
Language:
english
Creator:
Xiang, Chaoyu
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.
Publication Date:

Thesis/Dissertation Information

Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Materials Science and Engineering
Committee Chair:
SO,FRANKY FAT KEI
Committee Co-Chair:
XUE,JIANGENG
Committee Members:
SINGH,RAJIV K
MYERS,MICHELE V
GUO,JING

Subjects

Subjects / Keywords:
efficiency -- microcavity -- oleds -- qdleds -- rolloff -- triplet -- upconversion
Materials Science and Engineering -- Dissertations, Academic -- UF
Genre:
Materials Science and Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
Instead of describing the behaviors of free carriers in energy diagram formed from periodic lattice structures as in inorganic semiconductors, a strong bonded hole and electron, named exciton, is used as the basic quasiparticle to characterize the properties of organic semiconductors. With the presence of excitons, more interactions occur such as exciton confinement, exciton exciton annihilation, and exciton polaron annihilation, which will be discussed in this thesis.First, microcavity was used to confine the excitons and modify the electroluminescence characteristics of phosphorescent OLEDs. A systematic study has been conducted on microcavity OLEDs using on green, red and blue phosphorescent emitters to elucidate the microcavity effects for different color emitters. While the luminance enhancements of blue and red phosphorescent microcavity devices are small, the current efficiency as high as 224 cd/A is obtained in green phosphorescent microcavity OLEDs.Quantum dots are other excitonic materials with strong confinement of electrons and holes. We demonstrated blue/violet emitting hybrid LEDs based on cadmium free zinc selenide/zinc sulfide core/shell quantum dots. Using poly N vinylcarbazole with a low lying highest occupied molecular orbital energy for the hole transporting layer, enhanced hole injection and better exciton confinement were observed, resulting in efficient blue/violet emitting devices. Due to the long lifetime and high density of triplet excitons, exciton exciton annihilation and exciton polaron quenching become the dominating loss mechanisms which contribute to the phosphorescent OLED efficiency roll off. We characterized the interactions of triplet excitons and polarons in blue phosphorescent OLEDs with tercarbazole host materials and found that these interactions could be modified and the efficiency roll off is suppressed by changing the host system. Highly efficient blue phosphorescent OLEDs with reduced roll off at high luminance were demonstrated.We also show that exciton interaction can further reduce the operating voltage of fluorescent OLEDs with a luminance turn on below the corresponding bandgap voltage of the emitter. With experiment results from electroabsorption, transient Electronluminescence and Photoluminescence measurements, we verified the energy from the charge transfer state of the donor and acceptor can be acquired by the triplet state, which undergoes an up-conversion path and transfers its energy to higher singlet state.
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Chaoyu Xiang.
Thesis:
Thesis (Ph.D.)--University of Florida, 2014.
Local:
Adviser: SO,FRANKY FAT KEI.
Local:
Co-adviser: XUE,JIANGENG.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-11-30

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Classification:
lcc - LD1780 2014
System ID:
UFE0046466:00001