Jaehyung Hwang

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Considerable research and development means have been focused in the past decade on organic semiconductor thin films and devices with applications to full color displays, flexible electronics and photovoltaics. Critical areas of these thin films are their interfaces with electrodes, with other organic films and with dielectrics, as these interfaces control(More)
The structure of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT Æ PSS) consists of an insulating PSS layer surrounding doped PEDOT grains. In this study, X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) are used to investigate the composition and electronic structure of as-loaded and lightly sputtered PEDOT Æ PSS films. The(More)
The occupied and unoccupied states of poly(9,9′-dioctylfluorene) (F8) and poly(9,9′-dioctylfluorene-co-bisN,N′-(4-butylphenyl)diphenylamine) (TFB) are investigated using ultraviolet photoelectron and inverse photoemission spectroscopies, cyclic voltammetry, and density functional theory calculations. Hole injection barriers are determined for interfaces(More)
Virtual platform (ViP), or ESL (Electronic System Level) simulation model, is one of the most widely renowned system level design techniques. In this paper, we present a case study of creating and applying the ViP in the development of a new hard disk system called Hybrid-HDD that is one of the main features in the Windows VISTA (R). First, we summarize how(More)
Modern electronics is based on the ability to dope semiconductors, that is, to purposely introduce small amounts of impurities to control the electronic properties of the material. A similar approach is used in organic electronics, although impurity concentrations are generally significantly higher than those used for materials such as Si and GaAs. The(More)
Identically configured bulk heterojunction organic solar cells based on merocyanine dye donor and fullerene acceptor compounds (see figure) are manufactured either from solution or by vacuum deposition, to enable a direct comparison. Whereas the former approach is more suitable for screening purposes, the latter approach affords higher short-circuit current(More)
A series of p- and n-GaAs-S-C(n)H(2n+1) || Hg junctions are prepared, and the electronic transport through them is measured. From current-voltage measurements, we find that, for n-GaAs, transport occurs by both thermionic emission and tunneling, with the former dominating at low forward bias and the latter dominating at higher forward bias. For p-GaAs,(More)
The aim of this work is to improve charge injection by interposing an appropriately oriented dipole layer between contact and semiconductor in organic thin-film transistors (OTFTs). OTFTs are fabricated with pentacene semiconductor and gold source and drain contacts. The contacts are modified with self-assembled monolayers (SAMs) made of alkane or(More)
Thermal co-evaporation of C(60) fullerene and two merocyanine dyes affords bulk heterojunction solar cells with improved short-circuit currents and power conversion efficiencies in comparison with the respective single donor cells. These results are rationalized by the formation of three distinct subphases driven by differences in molecular shape and(More)
C60 is used as an electron acceptor in small molecule photovoltaic devices in combination with various electron donors. The transport of excitons, i.e., bound electron/hole pairs, is an important factor determining the efficiency of such devices. Here we investigate the exciton diffusion length in C60 with the electrodeless time-resolved microwave(More)