Min-Fei Wu

High-efficiency blue organic light-emitting diodes using a 3,5-di(9H-carbazol-9-yl)tetraphenylsilane host via a solution-process

We present a solution-processed blue organic light-emitting diode (OLED) with markedly high current efficiency of 41.2 cd A−1 at 100 cd m−2 and 31.1 cd A−1 at 1000 cd m−2. The high efficiency was partly attributed to the use of a molecular host, 3,5-di(9H-carbazol-9-yl)tetraphenylsilane, which possesses a wide triplet band gap, high carrier mobility, ambipolar transport property and high glass transition temperature. Besides the intrinsically good physical properties, the solution-process also played an important role in fabricating the high-efficiency device, since it could make the molecular distribution of host and guest homogeneous in the emissive layer. Moreover, the device efficiency at higher brightness could be markedly enhanced by using an electron-blocking layer. As the microlens was introduced on the glass substrate to enhance the light outcoupling, the resultant device efficiency of the blue OLED further increased to 50.1 cd A−1 at 100 cd m−2 and 37.3 cd A−1 at 1000 cd m−2.

A New Door for Molecular-Based Organic Light-Emitting Diodes

Long life-time molecular-based organic electronics, such as organic light-emitting diodes (OLEDs), organic solar cells, or organic transistors etc, inevitably demand their constituent molecules to be highly thermal-stable. Coupling with special needs in molecular design, the resultant increasing molecular weight (MW) will eventually make the molecules difficult to deposit if via dry-process, while using wet-process would frequently result in undesired relatively poorer efficiency. Surprisingly, two high-molecule composing OLEDs with relatively high-efficiency were obtained by using solution-process. A blue OLED with a blue dye doped in a novel high-MW, wide band-gap host, 3,5-di(9H-carbazol-9-yl) tetraphenylsilane (SimCP2), yielded 24 lm/W (38 cd/A) at 100 nits, and a green OLED using a novel high-MW green dye, bis[5-methyl-7-trifluoromethyl-5H-benzo (c)(1,5) naphthyridin-6-one] iridium (picolinate) (CF3BNO), yielded 70 lm/W (89 cd/A), while their dry-processed blue and green counterparts yield 1.7 and 21 lm/W, respectively. Importantly, although the comparatively high MW has made the resulting molecules extremely difficult to vacuum-evaporate and has resulted in poor device performance, the wet-process has been proven effective in fabricating two high molecule-containing OLEDs with relatively high efficiency. The successful demonstration suggests that the same approach may as well be extended to other organic devices that compose or should compose high molecules.

Comparison of light out-coupling enhancements in single-layer blue-phosphorescent organic light emitting diodes using small-molecule or polymer hosts

Single-layer blue phosphorescence organic light emitting diodes (OLEDs) with either small-molecule or polymer hosts are fabricated using solution process and the performances of devices with different hosts are investigated. The small-molecule device exhibits luminous efficiency of 14.7 cd/A and maximum power efficiency of 8.39 lm/W, which is the highest among blue phosphorescence OLEDs with single-layer solution process and small molecular hosts. Using the same solution process for all devices, comparison of light out-coupling enhancement, with brightness enhancement film (BEF), between small-molecule and polymer based OLEDs is realized. Due to different dipole orientation and anisotropic refractive index, polymer-based OLEDs would trap less light than small molecule-based OLEDs internally, about 37% better based simulation results. In spite of better electrical and spectroscopic characteristics, including ambipolar characteristics, higher carrier mobility, higher photoluminescence quantum yield, and lar...

39.1: Solution Processed Molecular Materials in the Fabrication of Flexible Phosphorescence-based OLEDs

OLEDs were fabricated by solution process, particularly, having amorphous small molecule SimCP2 as the host material for blue phosphorescence dopant FIrpic. Having SimCP2 as a whole or part of host materials, solution processed flexible OLEDs (2 × 2 cm on ITO-coated PET) exhibit blue electrophosphorescence with CIEx,y coordinates of (0.22, 0.29) and current efficiency as high as 23 and 19 cd/A at 100 and 1000 cd/m2, respectively, has been achieved.

High Performance Host Materials of Electrophosphorescence Blue Dopants

SimCP is a superior host material to mCP for phosphorescent blue dopant of OLEDs. Triphenylsilyl substituent plays a critical role in preventing molecules from aggregation and hence maintaining high triplet-state energy in condense phase. Article not available.

61.3: Blue Dopants and New Host Materials for Phosphorescent Organic Light‐Emitting Diodes

In this paper, we describe two new blue phosphorescent dopant materials FIrtaz and FIrN4. Efficient organic light-emitting diodes(OLEDs) incorporating demonstrate higher-purity blue-lightemission than the long-known FIrpic phosphorophore. New host material SimCP with higher glass-transition temperatures were also found to enhance the blue phosphorescence OLED performance.

Red fluorenes as the efficient host emitter for nondoped red organic light-emitting diodes

Crystallinic red fluorophores based on donor-acceptor substituted spirofluorene, i.e., PhSPDCV show strong fluorescence in solution (Φf ~ 70 %) as well as in solid state (Φf > 30 %). Non-doped red OLEDs fabricated with PhSPDCV exhibit authentic red (CIE, x = 0.65, y = 0.35) electroluminescence with brightness over 12,000 cd m-2 (or > 600 cd m-2 at 20 mA cm-2) and remarkable external quantum efficiency as high as 3.6%. On the other hand, the bis-substituted derivatives of spirofluorene BisPhSPDCV show relatively weak fluorescence both in solution (&PHgr;f < 20 %) and in solid state (Φf < 10%). Although saturated red electroluminescence (CIE, x = 0.65, y = 0.34) is also observed, non-doped red OLED containing BisPhSPDCV performs much worse than PhSPDCV OLEDs. Both PhSPDCV and BisPhSPDCV are not amorphous forming loosely packed crystallinic materials in solid state with no intimate π-π interaction.