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Proceedings Paper

New degradation mechanism of blue-emitting layers in organic electroluminescence devices (Conference Presentation)
Author(s): Youngmin You

Paper Abstract

Despite the advances, the exploitation of the full utility of organic electroluminescence devices (OLEDs) has been retarded by the short lifetime of blue-emitting devices. The poor longevity originates from irreversible, chemical degradation of emitting layers. However, the molecular mechanism by which degradation initiates has yet to be fully elucidated to date. My group proposed that the degradation involves exciton-mediated formation of polaron pairs (radical ion pairs) between wide hosts and dopants. To examine this hypothesis, we performed mechanistic studies with employing chemical techniques. Electrochemical studies predicted a thermodynamic allowance for the occurrence of reductive electron transfer from a dopant to host exciton to form a polaron pair involving positive polaron of a dopant and a negative polaron of host. Photoinduced EPR spectroscopy was employed to monitor the generation of the polaron pair. In particular, nanosecond laser photolysis experiments were successful in monitoring the annihilation of the polaron pair that occurred in the Marcus-inverted region of electron transfer. The annihilation competed with chemical degradation, and our analyses of degradation byproducts indicated an occurrence of CN bond breakage of both host and dopant molecules. Finally, a linear correlation was found between device lifetimes and rate constants for the annihilation of the polaron pair. This result supports our mechanism which involves the exciton-mediated generation of labile radical ion species. Further, our findings demonstrate the importance of controlling exciton-induced electron transfer within an emitting layer, and provide novel molecular strategies to improved device longevity.

Paper Details

Date Published: 10 September 2019
Proc. SPIE 11093, Organic and Hybrid Light Emitting Materials and Devices XXIII, 110930G (10 September 2019); doi: 10.1117/12.2530989
Show Author Affiliations
Youngmin You, Ewha Womans Univ. (Korea, Republic of)

Published in SPIE Proceedings Vol. 11093:
Organic and Hybrid Light Emitting Materials and Devices XXIII
Chihaya Adachi; Jang-Joo Kim; Franky So, Editor(s)

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