High-efficiency conjugated-polymer-hosted blue phosphorescent light-emitting diodes

Abstract

Highly-efficient blue phosphorescent light-emitting diodes were fabricated based on a conjugated-polymer host by doping bis(2-(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) into poly(9,9-dioctylfluorene) (PFO). Previously, conjugated polymers were not considered as potential hosts for blue phosphorescent dyes because of their low-lying triplet energy levels. Energy back transfer would occur and lead to poor luminescent efficiency in both photoluminescence (PL) and electroluminescence (EL) processes. However, by inserting a hole-transporting layer of poly(N-vinylcarbazole) (PVK), the energy back transfer was suppressed. At low FIrpic-doping concentrations, PFO emissions were completely quenched; with 8 wt% FIrpic, a maximum luminous efficiency of 11.5 cd/A was achieved.

Light-Induced Structural Change in Iridium Complexes Studied by Electron Spin Resonance

“…As a matter of fact, given the alignment of Ircompounds and PFO triplet states (see Figure 5), guest-to-host energy transfer processes are expected to occur in PFO-based systems. 35,45 Such excited state diffusions have already been observed in transient photoluminescence experiments of Ir complexes in different hosts and are also expected to occur in our experiment. 45 Following this mechanism the photogenerated 3 MLCT states (coming from 1 MLCT to 3 MLCT transitions) would diffuse from the complex to the host, hindering the formation of TBP-like structures and thus the observation of a LESR signal.…”

Phosphorescent Molecularly Doped Light‐Emitting Diodes with Blended Polymer Host and Wide Emission Spectra

“…Nonconjugated polymer poly( N -vinylcarbazole) (PVK) has been a commonly used polymer host for phosphorescent dyes [ 13 – 15 ]. But PVK has, however, an inherent defect in that its electron and hole mobility difference are too large [ 16 ]. In contrast to PVK-hosted PLEDs, the performances of PFO-hosted PLEDs could be enhanced from the selective removal of the electron-transporting material during fabrication of the functional layer [ 17 ], so that using PVK as hole transporting layer and PFO blended host layer is more suitable for high efficiency polymer device.…”

Enhancement of Poly(9,9'-di-n-octylfluorenyl-2.7-diyl) Optoelectronic Properties in Novel Conjugated Polymer/Laser Dye Hybrid OLEDs

“…Several studies on the effect of dyes content on the optoelectronic properties of PFO have been reported, such as PFO/PtOEP [9], PFO/FIrpic [10,11] and PFO/TPP [12]. All of these studies claimed the occurrence of energy transfer, which is crucial for excellent the optoelectronic properties of the devices.…”