• Journal of Adhesion and Interface
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• v.20 no.4
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• pp.162-168
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• 2019

• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.277-279
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• 2014

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.181-181
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• 2013

Recently, nanostructure and the molecular orientation of organic thin films have been largely paid attention due to its importance in organic electronics such as organic thin film transistors (OTFTs), organic light emitting diodes (OLEDs), and organic photovoltaics (OPVs). Among various methods, the diffraction and scattering techniques based on synchrotron x-rays have shown powerful results in organic thin film systems. In this work, we introduce the in-situ annealing system installed at PLS-II (Pohang Light Source II) for organic thin films by simultaneously conducting various x-ray scattering measurements of x-ray reflectivity, conventional x-ray scattering, grazing incidence wide angle x-ray scattering (GI-WAXS) and so on. Using the in-situ measurement, we could obtain real time variation of nanostructure as well as molecular orientation during thermal annealing in metal-phthalocyanine thin films. The variation of surface and interface also could be simultaneously investigated by the x-ray reflectivity measurement.

• Journal of Adhesion and Interface
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• v.25 no.1
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• pp.143-151
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• 2024

Organic photovoltaics (OPVs) have shown great potential as a new generation of energy harvesters because they possess many unique properties, including mechanical flexibility, lightweight, semi-transparency, and low-fabrication costs. Recent advancements in molecular structure and device engineering have led to achieving power conversion efficiency (PCE) exceeding 19%. However, these highly efficient active layer materials have been hampered in their commercialization by complex synthesis steps that result in high manufacturing costs. To address this issue, research is actively underway on low-cost active layer materials with simple structures. This paper introduces such cost-effective active layer materials and strategies for their synthesis.

• Journal of Adhesion and Interface
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• v.3 no.3
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• pp.22-29
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• 2002

UV curable coating system described here consists of double layers, namely under layer and top laser coatings. The former consists of organic-inorganic conductive materials and the latter consists of multifunctional acrylates. Transparent double layer coatings were prepared on the transparent substrates i.e. PMMA, PC, PET etc. by the wet and wet coating procedure. Their surface resistances and film properties were measured as a function of the top layer thickness and relative humidity. As the thickness of the top layer was less than $10{\mu}m$, the surface resistance in the range of $10^8{\sim}10^{10}{\Omega}/cm^2$ was obtained. The surface properties of the two-layer coating were remarkably improved compared with the single layer coating. The effects of migration of conducting materials on the film properties of multilayer coating were investigated by using contact angle and Fourier transform infrared/attenuated total reflection(FT-IR/ATR). It was found that the migration of dopant(dodecyl benzenesulfonic acid, DBSA) molecules were occurred from film-substrate interface to film-air interface in the organic conductive coating system but not in the inorganic one.

• Journal of Adhesion and Interface
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• v.21 no.4
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• pp.129-134
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• 2020

Understanding charge trapping at the interface between conjugated semiconductor and polymer dielectric basically gives insight into the development of long-term stable organic field-effect transistors (OFET). Here, the charge transport properties of OFETs using polymer dielectric with various molecular weights (MWs) have been investigated. The conjugated semiconductor, pentacene exhibited morphology and crystallinity, insensitive to MWs of polymethyl methacrylate (PMMA) dielectric. Consequently, transfer curves and field-effect mobilities of as-prepared devices are independent of MWs. Under bias stress in humid environment, however, the drain current decay as well as transfer curve shift are found to increase as the MW of PMMA decreases (MW effect). The charge trapping induced by MW effect is irreversible, that is, the localized charges are difficult to be delocalized. The MW effect is caused by the variation in the density of polymer chain ends in the PMMA: the free volumes at the PMMA chain ends act as charge trap sites, corresponding to drain current decay depending on MWs of PMMA.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.68-69
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• 2011

The process of charge transfer at the interface between two semiconductors or between a metal and a semiconductor plays an important role in many areas of technology. The optimization of such devices requires a good theoretical description of the interfaces involved. This, in turn, has motivated detailed mechanistic studies of interfacial charge-transfer reactions at metal/organic, organic/organic, and organic/inorganic semiconductor heterojunctions. Charge recombination of photo-induced electron with redox species such as oxidized dyes or triiodide or cationic HTM (hole transporting materials) at the heterogeneous interface of $TiO_2$ is one of main loss factors in liquid junction DSSCs or solid-state DSSCs, respectively. Among the attempts to prevent recombination reactions such as insulating thin layer and lithium ions-doped hole transport materials and introduction of co-adsorbents, although co-adsorbents retard the recombination reactions as hydrophobic energy barriers, little attention has been focused on the anchoring processes. Molecular engineering of heterogeneous interfaces by employing several co-adsorbents with different properties altered the surface properties of $TiO_2$ electrodes, resulting to the improved power conversion efficiency and long-term stability of the DSSCs. In this talk, advantages of the coadsorbent-assisted sensitization of N719 in preparation of DSSCs will be discussed.

• Current Photovoltaic Research
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• v.9 no.4
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• pp.145-159
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• 2021

Light soaking (LS) stability in polymer solar cells (PSCs) has always been a challenge to achieve due to unstable photoactive layer-electrode interface. Especially, the electron transport layer (ETL) and photoactive layer interface limits the LS stability of PSCs. Herein, we have modified the most commonly used and robust zinc oxide (ZnO) ETL-interface using an organic dye molecule and a co-adsorbent. Power conversion efficiencies have been slightly improved but when these PSCs were subjected to long term LS stability chamber, equipped with heat and humidity (45℃ and 85% relative humidity), an outstanding stability in the case of ZnO/dye+co-adsorbent ETL containing devices have been achieved. The enhanced LS stability occurred due to the suppressed interfacial defects and robust contact between the ZnO and photoactive layer. Current density as well as fill factors have been retained after LS with the modified ETL as compared to un-modified ETL, owing to their higher charge collection efficiencies which originated from higher electron mobilities. Moreover, the existence of less traps (as observed from light intensity-open circuit voltage measurements and dark currents at -2V) are also found to be one of the reasons for enhanced LS stability in the current study. We conclude that the mitigation ETL-surface traps using an organic dye with a co-adsorbent is an effective and robust approach to enhance the LS stability in PSCs.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1348-1351
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• 2007

We demonstrated that the threshold voltage shift owing to a gate-bias stress is originated from the trapped charges at the interface between semiconductor layer and dielectric layer, and such drawback can be settled by applying long-term delay time to the gate electrode.

• Macromolecular Research
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• v.10 no.2
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• pp.75-79
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• 2002

Organic materials have considerable attention as active semiconductors for device applications such as thin-film transistors (TFTs) and diodes. Pentacene is a p-type organic semiconducting material investigated for TFTs. In this paper, we reported the morphological and electrical characteristics of pentacene TFT films. The pentacene transistors showed the mobility of 0.8 $\textrm{cm}^2$/Vs and the grains larger than 1 ${\mu}{\textrm}{m}$. Deep-level transient spectroscopy (DLTS) measurements were carried out on metal/insulator/organic semiconductor structure devices that had a depletion region at the insulator/organic-semiconductor interface. The duration of the capacitance transient in DLTS signals was several ten of seconds in the pentacene, which was longer than that of inorganic semiconductors such as Si. Based on the DLTS characteristics, the energy levels of hole and electron traps for the pentacene films were approximately 0.24, 1.08, and 0.31 eV above Ev, and 0.69 eV below Ec.