Showing papers by "Seunghyup Yoo published in 2023"
TL;DR: In this paper , phenylpyridazine-based bidentate ligands are synthesized and subsequently utilized for the preparation of dinuclear Pt(II) complexes (1−6).
Abstract: Deep‐red (DR)‐to‐near‐infrared (NIR) phosphorescent organic light‐emitting diodes (OLEDs) have potentials for application in various fields ranging from phototherapy to sensing. Accordingly, herein, phenylpyridazine‐based bidentate ligands are synthesized and subsequently utilized for the preparation of dinuclear Pt(II) complexes (1–6). The molecular structures of 1–3 is investigated by single‐crystal X‐ray diffraction, and the results suggest that these complexes have substantially shortened Pt···Pt distances (2.906–2.911 Å). Complexes 1–6 exhibit intense emissions in the NIR region (700–726 nm), high photoluminescence quantum yield (PLQY) (0.11–0.18), and short phosphorescence decay lifetimes (τ = 0.64–0.95 µs) in a CH2Cl2 solution. To examine the effect of N‐substitution on the dinuclear Pt complexes, the phenylpyrimidine‐based Pt(II) emitters 7 and 8 are prepared and discovered to have Pt···Pt distances of 2.933 Å. 7 and 8 demonstrate strong emissions in the 628–650 nm range with high PLQY of 0.52–0.65. Theoretical studies indicate that the functional groups or atoms in the ligands play crucial roles in the formation of emitters with significantly shortened Pt···Pt distances. 3 and 7 are employed as non‐doped emitters to fabricate NIR OLEDs, and the resulting OLEDs exhibit electroluminescence peaks at 754 and 692 nm with maximum external quantum efficiencies of 3.0 and 4.4%, respectively.
2 citations
TL;DR: In this article , an inverted microlens array (IMLA) was used to realize foldable organic light-emitting diodes (OLEDs) that can be bent at sub-100 μm bending radius while exhibiting very high light outcoupling efficiency.
Abstract: Foldable organic light-emitting diodes (OLEDs) are essential building blocks for portable devices with expandable screens as well as more futuristic systems such as wearable or body-attachable electronic devices. Although various approaches have been proposed to realize foldable OLEDs, the efficiency enhancement techniques developed for their rigid counterparts are not always applicable due to the strict thickness limitations, making it challenging to achieve very high efficiency in a foldable OLED. Here, we propose ultrathin substrates embedded with an inverted microlens array (IMLA) as a platform on which to design and realize OLEDs that can be bent at sub-100 μm bending radius while also exhibiting very high light outcoupling efficiency. By noting the periodic arrangement of the patterns in the IMLA, the potential effects of optical diffraction on the overall emission pattern and efficiency enhancement are carefully analyzed by incorporating a bidirectional scattering distribution function via a trans-scale approach. Neutral-plane engineering is also done with finite element method simulations that examine the effect of the IMLA structures on the local modulation of the strain and stress in ultrathin devices, where the feature size of the IMLA is comparable to the overall thickness of the whole device. With the proposed method, highly efficient foldable OLEDs are demonstrated that show the maximum external quantum efficiency to be as high as 58% without optical side effects and that can withstand 10,000 trials of repeated folding cyclic tests at a bending radius of 50 μm.
TL;DR: In this article , the authors designed Ir(III)-based heteroleptic NIR materials with two types of auxiliary ligand and achieved a highly oriented horizontal dipole ratio (Ir(mCPDTiq)2tmd, complex 1: 80% with a short radiative lifetime (1: 386 ns, 2: 323 ns).
Abstract: Near-infrared organic light-emitting diodes (NIR OLEDs) with heavy metals are regularly reported due to the advantages of their various applications in healthcare services, veil authentication, and night vision displays. For commercial applications, it is necessary to look at radiance capacity (RC) instead of radiance because of power consumption. However, recent papers still reported only simple high radiance performance and do not look at device from the point of view of RC. To overcome this hurdle, we designed Ir(III)-based heteroleptic NIR materials with two types of auxiliary ligand. The proposed emitters achieve a highly oriented horizontal dipole ratio (Ir(mCPDTiq)2tmd, complex 1: 80%, Ir(mCPDTiq)2acac, complex 2: 81%) with a short radiative lifetime (1: 386 ns, 2: 323 ns). The device also shows an extremely low turn-on voltage (Von) of 2.2 V and a high RC of 720 mW/sr/m2/V. The results on the Von and RC of the device is demonstrated an outstanding performance among the Ir(III)-based NIR OLEDs with a similar emission peak.
TL;DR: In this paper , the authors demonstrate a new simulation method, named the diffraction matrix method (DMM), that can accurately predict the optical characteristics of periodically corrugated OLEDs while achieving calculation speed that is a few orders of magnitude faster.
Abstract: Increasing the light extraction efficiency has been widely studied for highly efficient organic light-emitting diodes (OLEDs). Among many light-extraction approaches proposed so far, adding a corrugation layer has been considered a promising solution for its simplicity and high effectiveness. While the working principle of periodically corrugated OLEDs can be qualitatively explained by the diffraction theory, dipolar emission inside the OLED structure makes its quantitative analysis challenging, making one rely on finite-element electromagnetic simulations that could require huge computing resources. Here, we demonstrate a new simulation method, named the diffraction matrix method (DMM), that can accurately predict the optical characteristics of periodically corrugated OLEDs while achieving calculation speed that is a few orders of magnitude faster. Our method decomposes the light emitted by a dipolar emitter into plane waves with different wavevectors and tracks the diffraction behavior of waves using diffraction matrices. Calculated optical parameters show a quantitative agreement with those predicted by finite-difference time-domain (FDTD) method. Furthermore, the developed method possesses a unique advantage over the conventional approaches that it naturally evaluates the wavevector-dependent power dissipation of a dipole and is thus capable of identifying the loss channels inside OLEDs in a quantitative manner.
TL;DR: In this article , sterically hindered peripheral phenyl groups are introduced to reduce intermolecular interactions, leading to excimer formation and thus making the pure narrowband emission character far less sensitive to concentration.
Abstract: Boron-based compounds exhibiting a multiresonance thermally activated delayed fluorescence are regarded promising as a narrowband blue emitter desired for efficient displays with wide color gamut. However, their planar nature makes them prone to concentration-induced excimer formation that broadens the emission spectrum, making it hard to increase the emitter concentration without raising CIE y coordinate. To overcome this bottleneck, we here propose o-Tol-ν-DABNA-Me, wherein sterically hindered peripheral phenyl groups are introduced to reduce intermolecular interactions, leading to excimer formation and thus making the pure narrowband emission character far less sensitive to concentration. With this approach, we demonstrate deep-blue OLEDs with y of 0.12 and full width at half maximum of 18 nm, with maximum external quantum efficiency (EQE) of ca. 33%. Adopting a hyperfluorescent architecture, the OLED performance is further enhanced to EQE of 35.4%, with mitigated efficiency roll-off, illustrating the immense potential of the proposed method for energy-efficient deep-blue OLEDs.
TL;DR: In this paper , two improvements are proposed for transparent OLEDs (TrOLEDs) that will be critical for visual applications: zinc sulfide with high surface energy and a high refractive index is explored as a seed and capping layer.
Abstract: Optoelectronics devices utilizing organic light‐emitting diodes (OLEDs) are emerging as new platforms for healthcare applications. In particular, wearable optoelectronics such as visual stimulus systems offer a distinctive advantage to intervene in and improve sleep disorders. In this study, two improvements are proposed for transparent OLEDs (TrOLEDs) that will be critical for visual applications. First, zinc sulfide with high surface energy and a high refractive index is explored as a seed and capping layer. An ultra‐thin silver cathode of 8 nm is demonstrated to be feasible in TrOLEDs, and luminous transmittance of 91% is achieved. Second, in general, achieving the operational stability of TrOLEDs with high transmittance is challenging due to the vulnerability of thin electrodes. By introducing a doping process to the electron transport layer, a lifetime comparable to that of control OLEDs with thick cathodes (>90%) is secured. Last, a preclinical model using blue light is proposed to modulate sleep patterns. Melanopsin is stimulated at the highest level of sleep desire, reducing non‐rapid eye movement sleep duration in mice by up to 14%. Based on these results, the proposed TrOLEDs are promising candidates for modulating sleep disorders such as insomnia and narcolepsy–cataplexy with the convenience of wearable form factors.