{"626109":{"#nid":"626109","#data":{"type":"event","title":"Ph.D. Dissertation Defense - Xiaoqing Zhang","body":[{"value":"\u003Cp\u003E\u003Cstrong\u003ETitle\u003C\/strong\u003E\u003Cem\u003E:\u0026nbsp; \u003C\/em\u003E\u003Cem\u003EHighly Efficient Organic Light-Emitting Diodes from Thermally Activated Delayed Fluorescence\u003C\/em\u003E\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Cstrong\u003ECommittee:\u003C\/strong\u003E\u003C\/p\u003E\r\n\r\n\u003Cp\u003EDr. Bernard Kippelen, ECE, Chair , Advisor\u003C\/p\u003E\r\n\r\n\u003Cp\u003EDr. Wenshan Cai, ECE\u003C\/p\u003E\r\n\r\n\u003Cp\u003EDr. Oliver Brand, ECE\u003C\/p\u003E\r\n\r\n\u003Cp\u003EDr. Benjamin Klein, ECE\u003C\/p\u003E\r\n\r\n\u003Cp\u003EDr. Elsa Reichmanis, ChBE\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Cstrong\u003EAbstract: \u003C\/strong\u003E\u003C\/p\u003E\r\n\r\n\u003Cp\u003EOrganic light-emitting diodes (OLEDs) are emerging as a technology that advances the performance of display and lighting applications. This thesis presents recent progress made in the design, fabrication, modeling, testing, and application of state-of-the-art highly efficient OLEDs employing emitters exhibiting thermally activated delayed fluorescence (TADF), and focuses on a reevaluation of the design of emissive layers (EMLs) with a goal to increase device efficiency and reduce efficiency roll-offs. Challenging the conventional EML design strategy, our work shows that high efficiency performance can be achieved in devices employing heavily doped or host-free EMLs. To understand the influence of host\/guest ratio in the EML on the external quantum efficiency (EQE) performance, a series of OLEDs doped with oBFCzTrz, a blue-emitting TADF emitter, at various concentrations were fabricated and their electrical and optical properties were systematically studied. Results showed that aggregation-induced fluorescence quenching in heavily doped EMLs is small. A time-resolved electroluminescent decay experiment was conducted, and an analysis based on a Correlated-Charge-Pair model reveals significant differences in charge trapping and recombination in devices as a function of emitter concentration. After optimizing the concentration of oBFCzTrz at 50 wt.% in the EML, devices yielded a maximum EQE of 25.5% at 10 cd\/m2; host-free devices achieved a high EQE of 14.0% with zero efficiency roll-off at luminance value of 1,000 cd\/m2. Employing the same strategy, a newly-developed yellow-green-emitting TADF emitter, TCZPBOX, was used as a host-free EML in devices and achieved a state-of-the-art maximum EQE of 21.2% at 10 cd\/m2, and retains a value of 13% at 10,000 cd \/m2.\u003C\/p\u003E\r\n","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":"","field_summary_sentence":[{"value":"Highly Efficient Organic Light-Emitting Diodes from Thermally Activated Delayed Fluorescence "}],"uid":"28475","created_gmt":"2019-09-12 21:24:40","changed_gmt":"2019-09-25 16:19:36","author":"Daniela Staiculescu","boilerplate_text":"","field_publication":"","field_article_url":"","field_event_time":{"event_time_start":"2019-09-25T10:00:00-04:00","event_time_end":"2019-09-25T12:00:00-04:00","event_time_end_last":"2019-09-25T12:00:00-04:00","gmt_time_start":"2019-09-25 14:00:00","gmt_time_end":"2019-09-25 16:00:00","gmt_time_end_last":"2019-09-25 16:00:00","rrule":null,"timezone":"America\/New_York"},"extras":[],"groups":[{"id":"434381","name":"ECE Ph.D. Dissertation Defenses"}],"categories":[],"keywords":[{"id":"100811","name":"Phd Defense"},{"id":"1808","name":"graduate students"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[{"id":"1788","name":"Other\/Miscellaneous"}],"invited_audience":[{"id":"78771","name":"Public"}],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[],"email":[],"slides":[],"orientation":[],"userdata":""}}}