(주)주암

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Bomi Sim, Jong Soo Kim, Hyejin Bae, Sungho Nam, Eunsuk Kwon, Ji Whan, Kim, Hwa-Young Cho, Sunghan Kim*, Jang-Joo Kim*, “Comprehensive Model of the Degradation of Organic Light-Emitting Diodes and Application for Efficient, Stable, Blue Phoshphorescent Devices with Reduced Influence of Polarons”, Physical Review Applied, 14, 024002 (2020)

Min Jung Kim, Soyun Lee, Chang-Ki Moon, Jang-Joo Kim, Jae Ryoun Youn*, Young Seok Song*, ” A broadband Multiplex Living Solar Cell”, Nano Lett. 20, 6, 4286-4291 (2020)
Developing renewable and sustainable energy sources is a compelling goal in materials science and engineering. In particular, natural photosynthesis with its infinite energy reservoir provides profound inspiration for energy conversion and storage systems. Here, we report a multiplex living solar cell that offers a drastic power enhancement by harnessing the broadband spectra of the visible wavelength range for photosynthesis. Cyanobacteria are embedded into a nanostructural complex composed of Au nanoparticles (NPs) and ZnO nanorods (NRs). This nanocomposite system is capable of not only generating excitons but also amplifying the photosynthetic performance of the cell via a far-field scattering effect in the broadband region of the light, resulting in multiplex energy harvesting with a peak power density of 6.15 mW/m2. We envision that this study will provide a strategic way to enhance the performance of biophotovoltaics, enabling efficient and durable energy generation.

Hwang-Beom Kim, Jang-Joo Kim*
“Simple method to extract extinction coefficients of films with the resolution of 10-5 using just transmission data and application to intermolecular charge-transfer absorption in an exciplex-forming organic film”
Opt. Express 28, 8, 11892-11898 (2020)
A simple method is presented to determine the thickness, refractive index and extinction coefficient of a film with the resolutions of ±1 nm, ±2 × 10−3, and 6 × 10−5, respectively. The method requires only ultraviolet-visible-near-infrared spectroscopy measurement of the transmittance of films with thicknesses of a few micrometers. A very small extinction coefficient of intermolecular charge transfer (CT) absorption of an exciplex-forming organic film is measured in the sub-bandgap wavelength region. This is to demonstrate that the CT absorption with extinction coefficient in the range of 10−3 to 10−5 can be measured indeed using the method, which is in the same resolution as photothermal deflection spectroscopy and Fourier transform photocurrent spectroscopy. The simplicity and feasibility of the proposed approach is expected to promote active study of intermolecular CT absorption in exciplex-forming films.

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Jin-Suk Huh(+), Yeon Hee Ha(+), Soon-Ki Kwon, Yun-Hi Kim*, Jang-Joo Kim*
“Design Strategy of Anthracene-Based Fluorophores toward High-Efficiency Deep Blue Organic Light-Emitting Diodes Utilizing Triplet-Triplet Fusion”
ACS Appl. Mater. Interfaces 12, 13,15422-15429 (2020)
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.

Jin-Suk Huh, Kwon-Hyeon Kim, Jang-Joo Kim*“Emitting dipole orientation and molecular orientation of homoleptic Ir(III) complexes”Org. Electron. 82, 105715 (2020)
Origin and significance of emitting dipole orientation (EDO) of emitters in organic light-emitting diodes (OLEDs) have been studied extensively in recent years. However, EDO of homoleptic Ir(III) complexes (Homo-IrCs) have received less attention due to their three-fold molecular symmetry and resulting expectation to have random EDO. Herein, we report the EDOs of Homo-IrCs doped in various host materials. Interestingly the EDO of Homo-IrCs varies from preferred horizontal direction to rather vertical direction depending on dopant and host molecules. The variation of EDO of Homo-IrCs is correlated with the direction of the transition dipole moment (TDM) against the molecular C3 axis and the orientation of C3 axis of the dopants in films. The average orientations of the Homo-IrCs are extracted from measured the horizontal dipole ratios (Θs) and calculated TDM directions. Angle between the TDM direction and C3 axis in the Homo-IrCs under investigation are larger than 54.7° corresponding to the mutually orthogonal axes among the three transition dipole vectors so that the EDO of Homo IrCs can deviate from random orientation depending on the orientation of the C3 axis in films. Average molecular orientation of a HOMO-IrC in films varies by 10°–13° depending on host materials. In contrast, smaller variation (< 5°) is observed among different Homo IrCs in a same host. The results indicate that host material is one of the dominating factors determining orientation of Homo-IrC molecules. Tris[(3,5-difluoro-4-cyanophenyl)-pyridine]iridium(III) (FCNIr) shows exceptionally high horizontal orientation, which likely originates from the dipole-dipole interaction between the dopant and hosts. FCNIr doped in diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide (TSPO1) shows strong preferred horizontal EDO with the Θ of 0.78, demonstrating the possibility of large Θ value of Homo-IrCs.

Yu Kyung Moon(+), Jin-Suk Huh(+), Sonam Kim, Sinheui Kim, Seung Yeon Yi, Jang-Joo Kim*, Youngmin You*
“Synthetic Strategy for Preserving Sky-Blue Electrophosphorescence in Square-Planar Pt(II) Complexes”
ACS Electron. Mater. 2, 2, 604-617 (2020)
Phosphorescent Pt(II) complexes having tetradentate ligands have emerged as promising materials for use in organic light emitting devices (OLEDs). One drawback that retards the full exploitation of their electroluminescence is a strong propensity for bathochromically shifted emissions. The chromic shift results from intermolecular association. Molecular strategies that avoid the intermolecular interactions are needed, particularly for producing blue electrophosphorescence. We have designed and synthesized a series of phosphorescent cycloplatinate complexes having bis(1-pyrazolylphenyl)methane tetradentate ligands (PtSN1–3). The ligands have been systematically modified to incorporate methyl substituents at different positions of the pyrazole moieties (PtSN1, no methyl substituent; PtSN2, 4-methyl substituents; PtSN3, 3-methyl substituents) with the aim of preserving intrinsic sky-blue phosphorescence while suppressing intermolecular interactions. The synthetic modifications control the extent of out-of-plane distortions in the cycloplatinate scaffold. Excimer emission is obtained from PtSN1–2 of planar platinacycles in diluted solutions (10 μM) or in thin mCBP:TSPO1 (8 wt %) films (1:1, wt/wt; mCBP = 3,3-di(9H-carbazol-9-yl)biphenyl; TSPO1 = diphenyl(4-(triphenylsilyl)phenyl)phosphine oxide) due to strong spontaneous excimer formation with free energy changes of −4.4 to −3.1 kJ mol–1. By contrast, helically distorted PtSN3 is capable of preserving its inherent sky-blue phosphorescence in concentrated states as it effectively suppresses excimer formation. An additional benefit of our synthetic control is improved stability against degradation for PtSN3. Finally, electroluminescence performances were evaluated by constructing and analyzing multilayer OLEDs employing the PtSN complexes as dopants. As expected, the PtSN3 devices produced sky-blue electrophosphorescence with a Commission Internationale de l’Éclairage coordinate of (0.16, 0.24) and a peak external quantum efficiency of 8.5%. The electrophosphorescence spectra of the PtSN1–2 devices were contaminated with excimer luminescence. These results collectively demonstrated the effectiveness of the helical distortion approach for obtaining blue electrophosphorescence.

Hwang-Beom Kim, Jang-Joo Kim*
“Diffusion Mechanism of Exciplexes in Organic Optoelectronics”
Phys. Rev. Appl. 13, 024006 (2020)
Excited-state charge-transfer complexes (exciplexes) are actively exploited in organic optoelectronics to understand their nature in the solid state and improve device performance. However, the diffusion of exciplexes is not actively studied, despite its ever-growing importance in such devices due to the lack of apparent charge-transfer (CT) absorption. Here, we report, based on time-resolved photoluminescence spectroscopy, that energy transfer (ET) takes place directly from exciplexes to exciplexes; this is called exciplex-exciplex ET. Recent reports and our own observation of the subband-gap CT absorption in exciplex-forming systems support the direct exciplex-exciplex ET. The ET takes place dominantly via the Dexter-type exchange mechanism, as revealed by the exponential decrease of the ET rate constant with separation between the energy-donating exciplex and the energy-accepting exciplex.

Youngnam Lee, Seung-Je Woo, Jang-Joo Kim*, Jong-In Hong*
“Blue thermally activated delayed fluorescence emitter using modulated triazines as electron acceptors”
Dyes and Pigments 172, 107864 (2020)
Three types of thermally activated delayed fluorescence (TADF) emitters, namely, moTrSAc, tmTrSAc, and motmTrSAc, are reported that emit blue-shifted emission with high external quantum efficiencies (EQEs). These emitters have electron donating spiroacridine in common and various triazine-based electron acceptors. The electronic and structural control on the electron acceptor moiety adjusts the reduction potential of the molecule to shift the emission wavelength to the blue region. Moreover, as these emitters become widened, the light out-coupling efficiency increases due to the enhanced horizontal emitting dipole orientation. As a result, OLEDs based on moTrSAc, tmTrSAc, and motmTrSAc emit blue light in a range of 460–480 nm with high EQEs of 21.3, 15.5, and 19.5%, respectively.

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