Intense deep blue exciplex electroluminescence from NPB/TPBi:PPh3O-based OLEDs and their intrinsic degradation mechanisms (Conference Presentation)

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CONFERENCE: Proceedings of SPIE

Proceedings of SPIE, Vol: 9941, Page: 994106

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10.1117/12.2238816; 10.1117/12.2238816.5167077771001
Franky So; Chihaya Adachi; Jang-Joo Kim; Joseph Shinar; Chamika Hippola; Dusan Danilovic; Ujjal Bhattacharjee; Jacob W. Petrich; Ruth Shinar
SPIE-Intl Soc Optical Eng
Organic light emitting diodes; Electroluminescence; Bipolarons; Magnetism; Magnetic sensors; Luminous efficiency; Nitrogen; Polarons; Resonance enhancement; Time metrology
conference paper description
We describe intense and efficient deep blue (430 – 440 nm) exciplex emission from NPB/TPBi:PPh3O OLEDs where the luminous efficiency approaches 4 Cd/A and the maximal brightness exceeds 22,000 Cd/m2. Time resolved PL measurements confirm the exciplex emission from NPB:TPBi, as studied earlier by Monkman and coworkers [Adv. Mater. 25, 1455 (2013)]. However, the inclusion of PPh3O improves the OLED performance significantly. The effect of PPh3O on the EL and PL will be discussed. The NPB/TPBi:PPh3O-based OLEDs were also studied by optically and electrically detected magnetic resonance (ODMR and EDMR, respectively). In particular, the amplitude of the negative (EL- and current-quenching) spin 1/2 resonance, previously attributed to enhanced formation of strongly EL-quenching positive bipolarons, increases as the OLEDs degrade in a dry nitrogen atmosphere. This degradation mechanism is discussed in relation to degradation induced by hot polarons that are energized by exciton annihilation.