Energy transfer and triplet exciton confinement in polymeric electrophosphorescent devices

Fang-Chung Chen, Shun Chi Chang, Gufeng He, Seungmoon Pyo, Yang Yang*, Masayuki Kurotaki, Junji Kido

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

144 Scopus citations

Abstract

Energy transfer and triplet exciton confinement in polymer/phosphorescent dopant systems have been investigated. Various combinations of host-guest systems have been studied, consisting of two host polymers, poly(vinylcarbazole) (PVK) and poly[9,9-bis(octyl)-fluorene-2,7-diyl] (PF), blended with five different phosphorescent iridium complexes with different triplet energy levels. These combinations of hosts and dopants provide an ideal situation for studying the movement of triplet excitons between the host polymers and dopants. The excitons either can be confined at the dopant sites or can flow to the host polymers, subject to the relative position of the triplet energy levels of the material. For PF, because of its low triplet energy level, the exciton can flow back from the dopants to PF when the dopant has a higher triplet energy and subsequently quench the device efficiency. In contrast, efficient electrophosphorescence has been observed in doped PVK films because of the high triplet energy level of PVK. Better energy transfer from PVK to the dopants, as well as triplet exciton confinement on the dopants, leads to higher device performance than found in PF devices. Efficiencies as high as 16, 8.0, and 2.6 cd/A for green, yellow, and red emissions, respectively, can be achieved when PVK is selected as the host polymer. The results in this study show that the energy transfer and triplet exciton confinement have a pronounced influence on the device performance. In addition, this study also provides material design and selection rules for the efficient phosphorescent polymer light-emitting diodes.

Original languageEnglish
Pages (from-to)2681-2690
Number of pages10
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume41
Issue number21
DOIs
StatePublished - 1 Nov 2003

Keywords

  • Light-emitting
  • Phosphorescence
  • Triplet

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