Browsing by Author "Liao, HH"

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General method to solution-process multilayer polymer light-emitting diodes
(2006-04-17)
Tseng, SR
;
Lin, SC
;
Meng, HF
;
Liao, HH
;
Yeh, CH
An intermediate liquid buffer layer is introduced to overcome the dissolution problem of solution-processed multilayer conjugated polymer light-emitting diodes. This method can be applied to arbitrary combinations of polymers with no restriction on solvents. As an example, a hole-blocking layer is successfully spin coated on the common p-type emissive polymer layers. One green- and two blue-emitting polymers are chosen as the emissive layers. The electron-hole balance and efficiency are significantly improved by the addition of hole-blocking layer. The electroluminescence efficiency can be increased up to nine times, while the luminance up to seven times. In particular, 1.5 cd/A is obtained for deep blue emission from poly(9,9-dioctyl-fluorene) with 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene spin coated as the hole-blocking material. (c) 2006 American Institute of Physics.
Triplet exciton formation and decay in polyfluorene light-emitting diodes
(2005-09-01)
Liao, HH
;
Meng, HF
;
Horng, SF
;
Shy, JT
;
Chen, K
We study the triplet excitons in poly (9,9-dioctylfluorene-2,7-diyl) light-emitting diode using infrared induced absorption. The infrared absorption is exclusively due to the triplet excitons and there is no spectral overlap with any other species. A strong suppression of the triplet exciton density relative to the singlet by voltage is observed. Through an unique independent measurement on the triplet exciton lifetime it is shown that the suppression solely comes from triplet exciton quenching by current injection. The triplet-to-singlet exciton formation ratio is independent of voltage as well as temperature, implying a spin-independent exciton formation.