We present an ideal host-guest concept for highly efficient phosphorescent OLEDs (PHOLEDs). Highly efficient
PHOLEDs with an extremely low doping concentration of 1% are developed. The origin of such a low doping is
revealed by energy transfer mechanism studies and ideal host-guest concept. Simple architectures for PHOLEDs are
realized based on this ideal host guest concept. Organic bi-layered and triple-layered architectures for PHOLEDs with
high efficiency are reported. Results reveal a practical way to fabricate the highly efficient simple structure devices for
trouble-free manufacturing processes.
We present highly efficient red and green phosphorescent devices comprising only two organic layers. Novel host
materials having good electron transporting and new narrow band-gap fluorescent characteristics lead to the fabrication
of simplified high efficiency devices. The driving voltage value of 3.3 V to reach luminance of 1000 cd/m2 is reported in
simple bi-layer red and green phosphorescent OLEDs, respectively. The maximum current- and power-efficiency values
of 38.30 cd/A and 46.60 lm/W are demonstrated in this green device. The current and power efficiencies of bi-layered
red PHOLED are 9.38 cd/A and 11.72 lm/W. Results reveal a practical way to fabricate highly efficient truly bi-layer
organic devices for trouble-free manufacturing processes.
We report novel bipolar host materials for high efficiency red and green phosphorescent OLEDs (PHOLEDs). Phenyl
moieties were inserted in a 4,4'-N,N'-dicarbazolebipheyl (CBP) compound to provide much easier electron injection and
to increase electron mobility. The efficiency increase and voltage reduction by this modification were observed in red
and green PHOLEDs. At a given constant luminance of 1000 cd/m2, the power efficiency was enhanced at least by
twenty percent in the general red and green PHOLED devices.
As a result of intensive research on polymer light-emitting diodes (PLEDs) for the last several years, the device
performances have been remarkably improved. Recently, several researchers reported on a PLEDs with an interlayer
between poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) and an emissive polymer. It improved
the device efficiency as well as the device lifetime. The role of the interlayer is to block the electron from back diffusion
to PEDOT:PSS and/or to reduce luminescence quenching at the PEDOT:PSS interface.
We studied the improvement of the PLED by inserting an octadecyltrichlorosilane (OTS) as the interlayer between
PEDOT:PSS and the emissive layer. The OTS was treated on PEDOT:PSS through the self-assembled monolayer (SAM)
process. It improved the device efficiency of the PLED from 3.86 to 4.76 cd/A, and increased the operation lifetime from
270 to 340 minute comparing the non-OTS treated PLED with the OTS treated PLED for 10 min. In blue PLED,
inserting the OTS layer between blue polymer and PEDOT:PSS is promoted hole injection from an anode. Therefore, the
device efficiency is improved, which appears to be due to the increase of balanced recombination as a result of the
accumulated electrons near the interface between emissive layer and PEDOT:PSS.
In this work, multi-physics simulation software (CA/MEMS) and design-optimization software (DS/MEMS) tailored for MEMS devices are introduced. The CA/MEMS, which is a simulation engine for DS/MEMS, is a 3-D multi-physics analysis code utilizing various numerical methods such as FEM, BEM and FVM to efficiently model MEMS application problems. The current CA/MEMS includes analysis- modules for structural, thermal, electric, electromagnetic and fluidic fields and is capable of the analyses of various coupled- field problems for MEMS applications. DS/MEMS is design optimization engine for MEMS devices. With integrating CA/MEMS and pre/post processor into CAD environment, DS/MEMS is organized to work in parametric CAD platform. DS/MEMS consists of optimal design module and robust design module. The optimal design module provides users three methods nonlinear programming, Taguchi parameter design and the response surface method. The robust design module, which is specially developed for MEMS application, can be used to minimize the perturbation of performances of MEMS devices under uncertainties of MEMS devices, such as process tolerance and the change of operating environments. To verify the efficiency and accuracy of CA/MEMS and the practical usefulness of DS/MEMS, we have been comparing the simulated results of CA/MEMS with those of other commercial codes and experimental data of manufactured MEMS devices, and investigating the performances of the optimized designs through DS/MEMS.
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