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The origin of low efficiency roll-off in OLEDs based on exciplex forming co-host system
DC Field | Value | Language |
---|---|---|
dc.contributor.advisor | 김장주 | - |
dc.contributor.author | 심봄이 | - |
dc.date.accessioned | 2017-07-14T03:11:49Z | - |
dc.date.available | 2017-07-14T03:11:49Z | - |
dc.date.issued | 2015-08 | - |
dc.identifier.other | 000000066696 | - |
dc.identifier.uri | https://hdl.handle.net/10371/123354 | - |
dc.description | 학위논문 (석사)-- 서울대학교 대학원 : 재료공학부 하이브리드재료전공, 2015. 8. 김장주. | - |
dc.description.abstract | Phosphorescent organic light-emitting diodes (PhOLEDs) have great potentials for applications in displays and lightings. The use of phosphorescent emitter molecules in OLEDs is essential to realize internal electron-photon conversion efficiencies of 100%. However, the efficiencies of phosphorescent OLEDs decline at high current densities ? an effect known as efficiency roll-off that has been known to be mainly dominated by bimolecular interactions and charge carrier imbalance.
In this thesis, the origin of efficiency roll-off is analyzed through quantitative measuring the contribution of monomolecular and bimolecular quenching processes and charge carrier imbalance with newly modified modeling of EQE including microcavity effects and excitons profiles. By combining electrical and optical excitation in time-resolved spectroscopic experiments, the contributions of quenching and charge carrier imbalance to efficiency roll-off are analyzed. To analyze precisely, the exciton profiles and the width of recombination zone in EML are identified by the sensing layer method based on energy transfer from the emitter to the sensitizer. In this work, two different PhOLEDs, one with a single host, 4,4-Bis(carbazol-9-yl)biphenyl(CBP), and the other with an exciplex-forming co-host(TCTA:B3PYMPM), are studied. Both CBP single host system and the exciplex forming co-host system have low efficiency roll-off, however the tendency of efficiency roll-off is significantly different. In exciplex forming co-host system, the high charge carrier balance and less quenching rate with wide recombination zone is the origin of low efficiency roll-off. In CBP single host system, the reduced charge balance and increased quenching rate in narrow recombination zone is mainly contribute to efficiency roll-off. | - |
dc.description.tableofcontents | Abstract i
Contents ii List of Tables vi List of Figures vii Chapter 1. Introduction 1 1.1 Motivation and outline of thesis 1 1.1.1 Motivation 1 1.1.2 Outline of thesis 6 1.2 Organic light emitting diodes at high brightness 7 1.2.1 Organic light emitting diodes in brief 7 1.2.2 Operating principles of OLEDs 9 1.2.3 Exciplex-forming co-hosts for OLEDs 10 1.2.4 Issues in PhOLEDs 13 1.2.5 Processes liading to EQE roll-off in OLEDs 14 Chapter 2. Investigating the role of exciton profiles in OLEDs 17 2.1 Introduction 17 2.2 Sensing layer methodology 19 2.3 Exciton profile in a microcavity structure 28 2.4 Result and Discussion 31 2.5 Conclusion 39 Chapter 3. Combined electrical and optical analysis of the efficiency roll-off in OLEDs 40 3.1 Introduction 40 3.2 Theory 41 3.3 Experimental 47 3.4 Result and Discussion 52 3.5 Conclusion 62 Chapter 4. Summary and out look 64 Bibliography 67 초록 70 List of Publications 72 | - |
dc.format | application/pdf | - |
dc.format.extent | 829087 bytes | - |
dc.format.medium | application/pdf | - |
dc.language.iso | en | - |
dc.publisher | 서울대학교 대학원 | - |
dc.subject | Organic light emitting diodes | - |
dc.subject | efficiency roll-off | - |
dc.subject | exciplex forming co-host | - |
dc.subject | exciton profile | - |
dc.subject | combined electrical and optical analysis | - |
dc.subject | quenching factor | - |
dc.subject | charge balance factor | - |
dc.subject.ddc | 620 | - |
dc.title | The origin of low efficiency roll-off in OLEDs based on exciplex forming co-host system | - |
dc.type | Thesis | - |
dc.description.degree | Master | - |
dc.citation.pages | 71 | - |
dc.contributor.affiliation | 공과대학 재료공학부 | - |
dc.date.awarded | 2015-08 | - |
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