Excited charge-transfer complexes, or exciplexes, have attracted significant attention due to their potential applications to improving the performance of organic light-emitting diodes (OLEDs) and organic photovoltaic cells (OPVs). In solid states, exciplexes exhibit extraordinary characteristics, including broad emission spectra, multiexponential photoluminescence (PL) decay curves, and spectral red shifts as time delays in transient PL. Here, we present experimental and theoretical evidence that all of the emission characteristics of solid-state exciplexes originate from differences in their dimer configurations, which have different charge transfer rates, emission energies, singlet–triplet energy gaps, kinetic rate constants, and emitting dipole orientations. This conclusion is based on experimental observations, quantum chemical calculations, and molecular dynamics simulations. These results enabled us to develop a model of the electronic structure of an exciplex in a solid-state medium. This comprehensive model accommodates all of the characteristics of the exciplex and can be used to further our understanding of OLEDs and OPVs.
The use of exciplex hosts is attractive for high-performance phosphorescent organic light-emitting diodes (PhOLEDs) and thermally activated delayed fluorescence OLEDs, which have high external quantum efficiency, low driving voltage, and low efficiency roll-off. However, exciplex hosts for deep-blue OLEDs have not yet been reported because of the difficulties in identifying suitable molecules. Here, we report a deep-blue-emitting exciplex system with an exciplex energy of 3.0 eV. It is composed of a carbazole-based hole-transporting material (mCP) and a phosphine-oxide-based electron-transporting material (BM-A10). The blue PhOLEDs exhibited maximum external quantum efficiency of 24% with CIE coordinates of (0.15, 0.21) and longer lifetime than the single host devices.
In contrast to the red and green regions, conventional fluorescent emitters continue to serve as blue emitters in commercialized organic light-emitting diodes. Many researchers have studied anthracene moieties as blue emitters, given their appropriate energy levels and good emission properties. We herein report two new deep blue-emitting anthracene derivatives that include p-xylene as moieties connecting the anthracene cores to side groups. We enhanced the efficiency by maximizing triplet–triplet fusion (TTF) without sacrificing emission color. The large steric hindrance imposed by the methyl groups of p-xylene creates a perpendicular geometry between p-xylene and the neighboring aromatic rings. Any extension of π-conjugation is thus disrupted, and the isolated core anthracene moiety emits a deep blue color with a high photoluminescence quantum yield. Moreover, the extensive steric hindrance suppresses vibration and rotation because the molecules are rigid. The high horizontal dipole ratio attributable to the large aspect ratio increases the outcoupling efficiency of the emitted light. Furthermore, the charge mobility and triplet harvesting ability are enhanced by decreasing the bulkiness of the side groups. Molecular dynamics simulation revealed that the bulkiness of the side group significantly impacted molecular density, which in turn affected the charge transport and TTF. We used two molecules, 2PPIAn (containing a phenyl side group) and 4PPIAn (containing a terphenyl side group), to form nondoped emission layers that exhibited maximum external quantum efficiencies of 8.9 and 7.1% with Commission Internationale de L'Eclairage coordinates of (0.150, 0.060) and (0.152, 0.085), respectively.
In this study, we demonstrate a blue OLED with the EQE of 34% and power efficiency of 79.6 lm W-1 using low refractive index electron transporting layer which are the highest efficiencies ever reported in blue OLEDs. In addition, we quantitatively calculated maximum achievable outcoupling efficiencies according to change of refractive indices, which can be used to estimate the achievable outcoupling efficiency of OLEDs without fabrication. The simulation indicates that EQE over 60% can be achievable in PhOLEDs if refractive indices of consisting organic materials' are close to 1.5.
J.-J. Kim and co-workers achieve highly efficient blue organic light-emitting diodes (OLEDs) using a low-refractive-index layer. As described on page 4920, an external quantum efficiency over 34% is achieved, owing to the low refractive index of the materials. A milepost and a shining entrance of the castle are the metaphor indicating the way to highly efficient blue OLEDs. On the way to the castle, the depicted chemical structures serve as the light-emitting layer.
Most virtual reality (VR) experiences are held in limited physical space; therefore, increasing the physical space's spatial efficiency is an essential task for the VR industry. Redirected walking maps a virtual path and a real path with unnoticeable distortion, enabling users to walk through a much bigger virtual space than physical space. To hide the distortion from the user, detection thresholds have been measured, entirely focusing on forward steps. However, it is not uncommon for the user to walk non-forward, that is, sideward and backward in VR. In addition to a forward step, adding options for a non-forward step can expand the VR locomotion in any direction. In this work, we measure the translation and curvature detection thresholds for non-forward steps. The results show similar translation detection thresholds with forward-step and wider detection thresholds for the curvature gain in both backward and sideward step experiments. Having sideward and backward steps in the redirected walking arsenal can add freedom to virtual world design and lead to efficient space usage.
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