• Korean Journal of Materials Research
• /
• v.20 no.11
• /
• pp.606-610
• /
• 2010

Films consisting of a silicon quantum dot superlattice were fabricated by alternating deposition of silicon rich silicon nitride and $Si_3N_4$ layers using an rf magnetron co-sputtering system. In order to use the silicon quantum dot super lattice structure for third generation multi junction solar cell applications, it is important to control the dot size. Moreover, silicon quantum dots have to be in a regularly spaced array in the dielectric matrix material for in order to allow for effective carrier transport. In this study, therefore, we fabricated silicon quantum dot superlattice films under various conditions and investigated crystallization behavior of the silicon quantum dot super lattice structure. Fourier transform infrared spectroscopy (FTIR) spectra showed an increased intensity of the $840\;cm^{-1}$ peak with increasing annealing temperature due to the increase in the number of Si-N bonds. A more conspicuous characteristic of this process is the increased intensity of the $1100\;cm^{-1}$ peak. This peak was attributed to annealing induced reordering in the films that led to increased Si-$N_4$ bonding. X-ray photoelectron spectroscopy (XPS) analysis showed that peak position was shifted to higher bonding energy as silicon 2p bonding energy changed. This transition is related to the formation of silicon quantum dots. Transmission electron microscopy (TEM) and electron spin resonance (ESR) analysis also confirmed the formation of silicon quantum dots. This study revealed that post annealing at $1100^{\circ}C$ for at least one hour is necessary to precipitate the silicon quantum dots in the $SiN_x$ matrix.

• Polymer(Korea)
• /
• v.33 no.5
• /
• pp.407-412
• /
• 2009

Vacuum deposited N,N-di-1-naphthyl-N,N-diphenyl-1,1'-biphenyl-4,4'-diamine (NPD) as a hole transporting (HTL) materials in OLEDs was placed on PEDOT-PSS, a hole injection layer (HIL). PEDOT-PSS was spin-coated on to the ITO glass. $C_{60}$-doped NPD-$C_{60}$(10 wt%) film was formed via co-evaporation process and the morphology of NPD-$C_{60}$ films was investigated using XRD and AFM. The J - V, L - V and current efficiency of multi -layered devices were characterized. According to XRD results, the deposited $C_{60}$ thin film was partially crystalline, but NPD-$C_{60}$ film was observed not to be crystalline, which indicates that $C_{60}$ molecules are uniformly dispersed in the NPD film. By using $C_{60}$-doped NPD-$C_{60}$ film as a HTL, the current density and luminance of multi-layered ITO/PEDOT-PSS/NPD-$C_{60}/Alq_3$/LiF/Al device were significantly increased by about 80% and its efficiency was improved by about 25% in this study.

• Journal of the Microelectronics and Packaging Society
• /
• v.13 no.4
• /
• pp.51-56
• /
• 2006

Polymer light emitting diodes (PLEDs) with ITO/EDOT:PSS/PVK/PFO-poss/LiF/Al structures were prepared by the spin coating method on ITO(indium tin oxide)/glass substrates. PFO-poss[Poly(9,9-dioctylfluorenyl-2,7-diyl) end capped with poss] was used as light emitting polymer. PVK[poly(N-vinyl carbazole)] and PEDOT:PSS [poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)] polymers were used as the hole injection and transport materials. The effect of PFO-poss concentration and the heating temperatures on the electrical and optical properties of the devices were investigated. At the same concentration of PFO-poss solution, the current density and luminance of PLED device tend to increase as the annealing temperature increase from $100^{\circ}C$ to $200^{\circ}C$. The maximum luminance was found to be about 958 cd/m2 at 13V for the PLED device with 1.0 wt% PFO-poss at the annealing temperature of $200^{\circ}C$. In addition, the PLED device showed bluish white emission through the strong greenish peak with 523 nm in wavelength. As the concentration of PFO-poss increase from 0.5 wt% to 1.0 wt% and temperature of PLEDs increase from $100^{\circ}C$ to $200^{\circ}C$, the emission color tend to be shifted from blue with (x, y) = (0.17,0.14) to bluish white with (x, y) : (0.29,0.41) in CIE color coordinate.

• Journal of the Korean institute of surface engineering
• /
• v.39 no.3
• /
• pp.93-97
• /
• 2006

Polymer light emitting diodes (PLEDs) are expected to be commercialized as next generation displays by advantages of the fast response time, low driving voltage and easy manufacturing process for large sized flexible display. Generally, the electrical and optical properties of PLEDs are affected by the surface conditions of transparent electrode. The PLED devices with ITO/PEDOT:PSS/PVK/PFO-poss/LiF/Al structures were prepared by using the spin coating method. For this, PEDOT:PSS(poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)) Al 4083 and PVK(N-vinylcabozole) were used as hole injection and transport layers. The PFO-poss(poly(9,9-dioctylfluorene)) was used as the emitting layer. The dependence of $O_2$ plasma treatment of ITO electrode on the electrical and optical properties of PLEDs were investigated. The sheet resistances increased slightly with an improved surface roughness of ITO electrode as the RF power increased during $O_2$ plasma treatment. The PLED devices prepared on the ITO/Glass substrates, which were plasma-treated at 40 watt in RF power for 30 seconds under 40 mtorr $O_2$ pressure, showed the maximum external emission efficiency of 0.86 lm/W and the maximum luminance of $250\;cd/m^2$, respectively. The CIE color coordinates are ranged $X\;=\;0.13{\sim}0.18$ and $Y\;=\;0.10{\sim}0.16$, showing blue color. emission.

• Journal of the Korean Vacuum Society
• /
• v.10 no.1
• /
• pp.16-21
• /
• 2001

Optical properties of $Ag_2CdSnSe_4$ and $Ag_2CdSnSe_4:Co^{+2}$ quaternary semiconductor single crystals grown by the chemical transport reaction method were investigated. The analysis of the X - ray powder diffraction measurements showed that these crystals have a wurtzite structure with lattice constants a = 4.357 $\AA$, c = 7.380 $\AA$, for $Ag_2CdSnSe_4$ and a = 4.885 $\AA$, c = 7.374 $\AA$, for $Ag_2CdSnSe_4:CO^{2+}$. The direct band gap at 298K, obtained from the optical absorption measurement, is found to be 1.21 eV for $Ag_2CdSnSe_4$ and 1.02 eV for $Ag_2CdSnSe_4:CO^{2+}$. The shrinkage of the band gap due to Co-doping is observed and is about 190 meV, We observed four absorption bands of $Co^{2+}$ ions in two near infrared regions of optical absorption spectra of $Ag_2CdSnSe_4$:$Co^{+2}$. These absorption bands were assigned as due to electronic transitions between the split energy levels of $Co^{2+}$ ions in $T_d$ crystal field under spin-orbit interactions.

• Clean Technology
• /
• v.18 no.4
• /
• pp.366-372
• /
• 2012

Three acrylic copolymers containing tris(8-hydroxyquinoline) aluminum (AlQ3) pendant group (25 wt%), acrylateco-HEMA-$AlQ_3$ (25 wt%), were successfully synthesized by free radical polymerization from acrylates [methyl methacrylate (MMA), acrylonitrile (AN) or 2-hydroxyethyl methacrylate (HEMA)] with HEMA functionalized with AlQ3 pendant groups (HEMA-p-$AlQ_3$). The glass transition temperatures ($T_g$) of MMA-co-HEMA-p-$AlQ_3$ (copolymer 1), AN-co-HEMA-p-$AlQ_3$ (copolymer 2) and HEMA-co-HEMA-p-$AlQ_3$ (copolymer 3) were found to be 158, 150 and $126^{\circ}C$, respectively. They have good thermal stability: a very desirable feature for the stability of OLEDs. Their solubility, thermal properties, UV-visible absorption and photoluminescence behaviors were investigated. They were found to be soluble in various organic solvents such as tetrahydrofuran (THF), dimethylformamide (DMF), toluene and chloroform. It was also found that the UV-visible absorption and photoluminescence behaviors of these copolymers were similar to those of pristine $AlQ_3$. Green organic light-emitting diodes (OLEDs) have also been fabricated using these copolymers as light emission/electron transport components obtained easily by spin coating, and their current density voltage (J-V) curves were compared. The OLED device of the copolymer 3 had the lowest turn-on voltage of about 2 V compared to other copolymer types devices.