Dae Hun Kim

Efficiency enhancement of organic light-emitting devices due to the localized surface plasmonic resonant effect of Au nanoparticles embedded in ZnO nanoparticles

Organic light-emitting devices (OLEDs) were fabricated utilizing Au-ZnO nanocomposites (NCs) with various Au nanoparticles (NPs) concentrations synthesized by using a sol-gel process to enhance their current efficiency, and these devices were compared with OLEDs fabricated utilizing ZnO NPs only. The electroluminescence intensity of the OLEDs with Au-ZnO NCs at a wavelength of 535 nm was significantly larger than that of the OLEDs with ZnO NPs by a factor of 1.89. The current efficiency of the OLEDs with 10 wt. % Au-ZnO NCs at 1000 cd/m2 was higher by 16.7 cd/A than that of the OLEDs with ZnO NPs. This increase in the current efficiency of the OLEDs with Au-ZnO NCs was attributed to an enhancement of the out-coupling efficiency due to the existence of the localized surface plasmonic resonance effect induced by the Au NPs that were embedded in the Au-ZnO NCs.

Significant enhancement of the power conversion efficiency for organic photovoltaic cells due to a P3HT pillar layer containing ZnSe quantum dots

High-efficiency organic photovoltaic (OPV) cells utilizing a poly(3-hexylthiophene) (P3HT) pillar layer containing ZnSe quantum dots (QDs) were fabricated by using a mixed solution method. Scanning electron microscopy and high-resolution transmission electron microscopy images showed that the ZnSe QDs were dispersed in the P3HT layer. The power conversion efficiency of the OPV cells with a P3HT pillar layer containing ZnSe QDs was as much as 100% higher than that of the OPV cells with a planar layer due to an enhancement of the photon-harvesting ability of the congregated P3HT particles containing ZnSe QDs and to an increase of the interfacial region for efficient charge transport.

Microstructural and optical properties of CdSe/CdS/ZnS core-shell-shell quantum dots.

CdSe/CdS/ZnS core-shell-shell quantum dots (QDs) were synthesized by using a solution process. High-resolution transmission electron microscopy images and energy dispersive spectroscopy profiles confirmed that stoichiometric CdSe/CdS/ZnS core-shell-shell QDs were formed. Ultraviolet-visible absorption and photoluminescence (PL) spectra of CdSe/CdS/ZnS core-shell-shell QDs showed the dominant excitonic transitions from the ground electronic subband to the ground hole subband (1S(e)-1S(3/2)(h)). The PL mechanism is suggested; the carriers generated by the exciting high-energy photons in the shell region are relaxed to the band-edge states of the core region and recombined to emit lower-energy photons. The activation energy of the carriers confined in the CdSe/CdS/ZnS core-shell-shell QDs, as obtained from temperature-dependent PL spectra, was 200 meV. The quantum efficiency of the CdSe/CdS/ZnS core-shell-shell QDs at 300 K was estimated to be approximately 57%.

Efficiency enhancement of organic light-emitting devices due to a localized surface plasmonic resonance effect of poly(4-butylphenyl-diphenyl-amine):dodecanethiol functionalized Au nanocomposites

Organic light-emitting devices (OLEDs) were fabricated utilizing a poly(4-butylphenyl-diphenyl-amine) (poly-TPD):dodecanethiol functionalized Au (DDT-Au) nanocomposite (NC) layer to enhance their current efficiency. The photoluminescence intensity of the poly-TPD:DDT-Au NC film at 514 nm was significantly increased, being about 1.3 times that of the poly-TPD film due to the coupling between the excitons in the emitting layer and the localized surface plasmonic resonance of the DDT-Au nanoparticles. The current efficiency of the green OLEDs with a poly-TPD:DDT-Au NC layer at 1000 cd/m2 was 3.1 cd/A larger than that with a poly-TPD layer, resulting in an enhanced out-coupling efficiency due to the coupling effect.

Enhancement of the power conversion efficiency for inverted organic photovoltaic devices due to the localized surface plasmonic resonant effect of Au nanoparticles embedded in ZnO nanoparticles

The absorption spectra and input photon-to-converted current efficiency curves showed that Au nanoparticles increased the plasmonic broadband light absorption, thereby enhancing the short-circuit current density of the inverted organic photovoltaic (OPV) cells with a Au–ZnO nanocomposite electron transport layer (ETL). The power conversion efficiency of the inverted OPV cell fabricated with a Au–ZnO nanocomposite ETL was higher by 40% than that of the inverted OPV cell fabricated with a ZnO nanoparticle ETL, which could be attributed to the enhanced photon absorption in the active layer due to the localized surface plasmonic resonance of the Au nanoparticles.

Enhancement of the power conversion efficiency for inverted polymer solar cells due to an embedded CuxO interlayer formed by using Cu(I) acetate and Cu(II) acetate

Structural, optical, and photovoltaic properties of copper-oxide (CuxO) thin films formed by using a sol–gel method were investigated. X-ray diffraction patterns showed that the CuxO films prepared utilizing Cu(I) acetate or Cu(II) acetate and annealed under ambient atmosphere at various temperatures were polycrystalline with two phases, Cu2O and Cu64O. Transmittance spectra showed that the energy band gaps of the CuxO thin films formed by using Cu(II) acetate were smaller than those formed by using Cu(I) acetate. Current–voltage results showed that the power conversion efficiencies of the inverted polymer solar cells utilizing the CuxO interlayer formed by using Cu(II) acetate were better than those utilizing the CuxO interlayer formed by using Cu(I) acetate due to the multiple band gaps of the Cu(II) acetate.

Charge transfer mechanisms of P3HT: PCBM photovoltaic cells containing a tungsten oxide hole transport layer

Organic photovoltaic (OPV) cells containing a tungsten oxide (WO3) layer inserted between the indium-tin-oxide and the poly(3-hexylthiophene) and the derivative [6,6]-phenyl-C61-butyric acid methyl ester active layer were fabricated. The short circuit current density, the open circuit voltage, the fill factor, and power conversion efficiency of the OPV cells under an AM 1.5G were 7.45 mA/cm2, 0.63 V, 0.59, and 2.8%, respectively. The charge transfer mechanisms of the OPV cells containing a WO3 layer are described on the basis of the experimental results and energy band diagrams.