Hae-Seong Lee

Employment of gold-coated silver nanowires as transparent conductive electrode for organic light emitting diodes

This study proposes a simple method of Au coating on silver nanowires (Ag NWs) transparent conductive films as the anode of organic light emitting diodes (OLED) to increase the work function of the film and thus enhance hole transport. We carefully engineer the process conditions (pretreatment, solution concentrations, and coating number) of the coating using a diluted HAuCl4 solution on the Ag NWs film to minimize etching damage on Ag NWs accompanying the galvanic replacement reaction. Ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy show work function increase of Ag NWs upon Au coating. OLED devices based on Au-coated Ag NWs show a lower turn-on voltage and higher luminance, compared with pristine Ag NWs device. Although the Ag NWs device displays poor efficiencies in the low luminance range due to a high leakage, some of the Au-coated Ag NWs devices showed efficiencies higher than those of the ITO device in a high luminance.

Effect of chemically converted graphene as an electrode interfacial modifier on device-performances of inverted organic photovoltaic cells

This study examined the effects of chemically converted graphene (CCG) materials as a metal electrode interfacial modifier on device-performances of inverted organic photovoltaic cells (OPVs). As CCG materials for interfacial layers, a conventional graphene oxide (GO) and reduced graphene oxide (rGO) were prepared, and their functions on OPV-performances were compared. The inverted OPVs with CCG materials showed all improved cell-efficiencies compared with the OPVs with no metal/bulk-heterojunction (BHJ) interlayers. In particular, the inverted OPVs with reduction form of GO showed better device-performances than those with GO and better device-stability than poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)-based inverted solar cells, showing that the rGO can be more desirable as a metal/BHJ interfacial material for fabricating inverted-configuration OPVs.

Selective landing of semiconducting single-wall carbon nanotubes onto tetrathiafulvalene moiety self-assembled on ITO substrate

Semiconducting single-wall carbon nanotubes (SWCNTs) were selectively interacted with tetrathiafulvalene (TTF) moiety self-assembled on indium tin oxide (ITO) substrate by charge-transfer interaction. The charge-transfer phenomena between two molecules were elucidated by cyclic voltammetry (CV) and Raman spectroscopy. CV measurement of TTF-modified ITO substrate as a working electrode presented the difference between heat-treated system and untreated one. The two redox potentials, which are typically related to redox behavior of TTF, were shown in the unheated system during both oxidation and reduction cycles, while the two oxidation peaks were disappeared in the heated system. Raman spectra indicated that the intensities of RBM originated from metallic SWCNTs were much reduced in the heat-treated system, while there were little change in the unheated one. These results revealed that only semiconducting SWNTs were selectively adsorbed on the TTF moiety self-assembled on ITO when the system with heat treatment.