Sunyoung Sohn

Electronic and Optical Properties of Indium Zinc Oxide Thin Films Prepared by Using Nanopowder Target

Indium zinc oxide (IZO) films were deposited on glass substrates using the rf-magnetron sputtering method and a powder target made up of nanoparticles with a size less than 100 nm. In this study, the optical, structural, and electrical properties of the IZO films deposited using a nanopowder target compared with those of the IZO films deposited using a micropowder target made up of microparticles with a size greater than 30 µm were examined. The IZO films deposited using nanopowder at room temperature were amorphous and showed a low resistivity of 4.5 ×10-4 Ωcm and a high transmittance over an average of 85% in the visible range, indicating that these films showed more enhanced properties than the IZO film deposited using micropowder. The enhanced properties of the IZO film prepared with nanopowder were considered to be caused by the marked improvement in packing density with increases in refractive index and surface roughness from atomic force microscopy (AFM) images due to the powder target consisting of nanoparticles.

Characteristics of Organic Light Emitting Diodes with Tetrakis(Ethylmethylamino) Hafnium Treated Indium Tin Oxide

The surface of indium tin oxide (ITO) in organic light emitting diodes (OLEDs) was treated using an atomic layer deposition with tetrakis(ethylmethylamino) hafnium (TEMAH) and O2 precursors. The treatment for 5 cycles at room temperature resulted in a significant improvement in the electroluminescent characteristics resulting from the increased hole injection. According to the various characterizations, an ultra-thin HfOx layer without any insulating properties was formed, which modified the electronic band structure of the ITO anode. When the number of cycles or temperature was increased, an electrically insulating HfOx was formed, and the resulting OLED properties deteriorated. [DOI: 10.1143/JJAP.46.L461]

Enhanced Permeability Property of Silicon Oxide Thin Films Deposited by Facing Target Sputtering System for OLED Application

ABSTRACT The thin silicon oxide (SiOx) films were deposited by using the facing target sputtering(FTS) apparatus for the thin film passivation application of OLEDs. The deposition system was investigated under various process conditions such as the array of cathode magnets, oxygen concentration[O2/(Ar + O2)] during deposition, distance between two targets, and working pressure. The optimum conditions for FTS apparatus for the deposition of thin silicon oxide films are as follows: distances between target and substrate (T-S) as well as two targets (T-T) are 90 mm and 120 mm, respectively. Dense structured SiOx film with maximum deposition rate is obtained under a gas pressure of 2 mTorr with an oxygen concentration of 3.3%. Under the optimum conditions, SiOx thin films were grown with deposition rate of 25 nm/min by rf-power of 4.5 W/cm2, which was remarkably enhanced as compared with a deposition rate(3–4 nm/min) of conventional sputtering system. The SiOx thin film showed a very low water vapor transmission rate(WVTR) less than 3 × 10−2 g/m2/day compared to the conventional sputtering system.

Low-Temperature Process for Atomic Layer Chemical Vapor Deposition of an Al2O3 Passivation Layer for Organic Photovoltaic Cells.

Flexible organic photovoltaic (OPV) cells have drawn extensive attention due to their light weight, cost efficiency, portability, and so on. However, OPV cells degrade quickly due to organic damage by water vapor or oxygen penetration when the devices are driven in the atmosphere without a passivation layer. In order to prevent damage due to water vapor or oxygen permeation into the devices, passivation layers have been introduced through methods such as sputtering, plasma enhanced chemical vapor deposition, and atomic layer chemical vapor deposition (ALCVD). In this work, the structural and chemical properties of Al2O3 films, deposited via ALCVD at relatively low temperatures of 109 degrees C, 200 degrees C, and 300 degrees C, are analyzed. In our experiment, trimethylaluminum (TMA) and H2O were used as precursors for Al2O3 film deposition via ALCVD. All of the Al2O3 films showed very smooth, featureless surfaces without notable defects. However, we found that the plastic flexible substrate of an OPV device passivated with 300 degrees C deposition temperature was partially bended and melted, indicating that passivation layers for OPV cells on plastic flexible substrates need to be formed at temperatures lower than 300 degrees C. The OPV cells on plastic flexible substrates were passivated by the Al2O3 film deposited at the temperature of 109 degrees C. Thereafter, the photovoltaic properties of passivated OPV cells were investigated as a function of exposure time under the atmosphere.

Post‐annealing Effects of CuInSe2(CIS)Absorber Layer at Thin Film Solar Cells with Compound Semiconductor Prepared by Co‐sputtering Method

In this study, we investigated the electrical and structural properties of CuInSe2(CIS) absorber layer with various post‐annealing temperatures in thin‐film solar cells prepared by co‐sputtering method. The CIS film annealed at 550 °C compared with the films without and with annealing temperatures below 550 °C has the main growth peaks of chalcopyrite‐like structure with CuInSe2 (112), CuInSe2 (220/204), and CuInSe2 (312/116), which resulted in increase of grain sizes and the improvement of crystallinity from the results of full width half maximum (FWHM) values and the intensity of peaks. And also, the carrier concentration and the mobility of the CIS thin film annealed at 550 °C were increased compared with the film without thermal treatment. Particularly, we suggest that the post‐annealing of the CIS absorber layer at an optimized temperature can be applied for improving the device efficiency at the thin‐film solar cells because the resistivity of the film annealed at 550 °C was decreased about 10−2 ord...

Admittance Spectroscopic Analysis of Polymer Light Emitting Diodes with the LiF Cathode Buffer Layer

Admittance Spectroscopic analysis was applied to study the effect of LiF buffer layer and to model the equivalent circuit for poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV)-based polymer light emitting diodes (PLEDs) with the LiF cathode buffer layer. The single layer device with ITO/MEH-PPV/Al structure can be modeled as a simple combination of two resistors and a capacitor. Insertion of a LiF layer at the Al/MEH-PPV interface shifts the lowest unoccupied molecular orbital (LUMO) level and the vacuum level of the MEH-PPV layer as a result of which the barrier height for electron injection at the Al/MEH-PPV interface is reduced. The admittance spectroscopic analysis of the devices with the LiF cathode buffer layer shows reduction in contact resistance (RC), parallel resistance (RP) and increment in parallel capacitance (CP).