Highly Efficient Blue-Light-Emitting Diodes from Polyfluorene Containing Bipolar Pendant Groups

Abstract

A highly efficient blue-light-emitting copolymer with bulky hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) pendant groups at the C-9 position of fluorene was synthesized. The results from photoluminescence and electrochemical measurements reveal that both the side chains and the polyfluorene main chain retain their own electronic characteristics in the copolymer. It shows a pure blue emission with no aggregates or excimers formed even after being annealed at 150 °C under nitrogen for 20 h. In addition, it also demonstrates improved charge injection and balanced charge transport in electroluminescence. The maximum external quantum efficiency of a single-layer device using this copolymer as the emitting layer is 1.21% (at a brightness of 354 cd/m 2 with driving voltage of 7.6 V). The maximum luminance of the device reaches 4080 cd/m 2 at a bias of 12.0 V and a current density of 640 mA/cm 2 .

Time resolved photoluminescence spectroscopy of surface-plasmon-enhanced light emission from conjugate polymers

“…A high efficiency due to better charge injection and more efficient charge recombination was reported by Shu et al for PF-TPA-Q. 13 Liu et al extensively studied such properties of the PF-CNP ͑3:1͒ and PF-CNP ͑1:1͒, where the solid state PL efficiencies were reported as 66% and 48%, respectively. 12 They also attributed the slow electron motion to the higher content of cyano constituents that stabilize the radical anion and the less planar structure of PF-CNP ͑1:1͒.…”

“…1. 12,13 The corresponding conjugated polymers PF-CNP ͑1:1͒, PF-CNP ͑3:1͒, and PF-TPA-Q will be referred to as pf1cnp1, pf3cnp1, and pftpaq, respectively. The conjugated polymers were dissolved in chlorobenzene to form a 2% ͑by volume͒ solution.…”

Liquid crystalline conjugated polymers and their applications in organic electronics

“…Charts 15-17 show some co-PF derivatives with 1,3,4-oxadiazole groups attached on C-9 position of fluorene moiety or 1,3,4-oxadiazole dendritic pendants on the phenylene ring. [49][50][51][52] These polymers were mainly developed for the improvement in EL and/or thermal stabilities; no obvious LC properties were mentioned in those previous literatures. Nevertheless, they should be classified as side-chain conjugated polymers as well.…”

Synthesis and memory performance of a conjugated polymer with an integrated fluorene, carbazole and oxadiazole backbone

“…20 Usually, the OXD units are covalently bonded to emissive polymers or small molecules to enhance the electron injection and transport in the emission layer. [21][22][23][24][25][26][27] For example, Jen et al 26 designed a fluorene-based alternating copolymer, PF-OXD, which contained OXD moieties with their phenyl-end group directly attached to the C-9 carbon in every other fluorene unit. The improved device performance over poly(9,9-dioctylfluorene) is due to the better electron injection and transport in PF-OXD, and the efficient energy transfer from the OXD side chain to the PF main chains.…”