Bipolar copolymers as host for electroluminescent devices: Effects of molecular structure on film morphology and device performance

Biwu Ma, Bumjoon J. Kim, Lan Deng, Daniel A. Poulsen, Mark E. Thompson, Jean M J Fréchet*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

64 Scopus citations

Abstract

Bipolar transport polymers have been developed as host materials for electroluminescent devices by incorporating both electron-transporting and hole-transporting functionalities into copolymers. Two different copolymers having the same molecular weight (M n ∼ 30 kg/mol) and the same fraction of electron-transporting monomers (f OXA = 0.50) have been synthesized in the form of random and diblock copolymers, respectively. The effect of molecular structure and film morphology of these bipolar polymers on device performance has been studied. For the diblock copolymers, pronounced phase segregation forming different nanomorphologies has been observed by modern microscopic techniques, which is not observed for the random counterparts under the same thin film preparation conditions. The results of single-layer polymer light emitting diodes (PLEDs) show that the nanophase separation morphology of diblock copolymers has a significant effect on device performance: lowering charge transport and facilitating the hole-electron recombination leads to a much higher quantum efficiency. Applying this high triplet block copolymer as host, a high external quantum efficiency of 5.4% at the brightness of 900 cd/m 2 was achieved for single-layer PLEDs with a green-emitting complex dopant.

Original languageEnglish (US)
Pages (from-to)8156-8161
Number of pages6
JournalMacromolecules
Volume40
Issue number23
DOIs
StatePublished - Nov 13 2007
Externally publishedYes

ASJC Scopus subject areas

  • Materials Chemistry

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