Kwang-Dae Kim

Metal−Organic Framework@Microporous Organic Network: Hydrophobic Adsorbents with a Crystalline Inner Porosity

This work reports the synthesis and application of metal-organic framework (MOF)@microporous organic network (MON) hybrid materials. Coating a MOF, UiO-66-NH2, with MONs forms hybrid microporous materials with hydrophobic surfaces. The original UiO-66-NH2 shows good wettability in water. In comparison, the MOF@MON hybrid materials float on water and show excellent performance for adsorption of a model organic compound, toluene, in water. Chemical etching of the MOF results in the formation of hollow MON materials.

Towards fabrication of high-performing organic photovoltaics: new donor-polymer, atomic layer deposited thin buffer layer and plasmonic effects

Using a novel polymer (polythienothiophene-co-benzodithiophenes 7 F-20) as a donor and phenyl-C71-butyric acid methyl ester as an acceptor of bulk heterojunction, inverted organic photovoltaics (OPVs) were fabricated. Wet-chemically prepared ZnO and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were used as buffer layers. Particularly, for PEDOT:PSS deposition, no annealing step was employed. This inverted OPV showed a power conversion efficiency (PCE) of ∼7.0%, which is comparable to the hitherto reported highest efficiency of the inverted OPV with vacuum-deposited MoO3 as hole-collecting buffer layers without plasmonic enhancements. Incorporation of Au nanoparticles into PEDOT:PSS was performed for plasmonic enhancement of the electromagnetic field, whereas ZnO thin layers were deposited on ZnO using atomic layer deposition for quenching electron–hole recombination at surface defects of ZnO ripples. These additional treatments could be used for improving the performance of OPV, which ultimately resulted in a PCE of 7.9%.

Role of additional PCBM layer between ZnO and photoactive layers in inverted bulk-heterojunction solar cells

In order to induce greater light absorption, nano-patterning is often applied to the metal-oxide buffer layer in inverted bulk-heterojunction(BHJ) solar cells. However, current homogeneity was significantly disturbed at the interface, leading to an efficiency that was not fully optimized. In this work, an additional PC61BM layer was inserted between the ZnO ripple and the photoactive layer to enhance the electron extraction. The insertion of additional PC61BM layer provided substantial advantages in the operation of inverted BHJ solar cells; specifically, it enhanced current homogeneity and lowered accumulation and trapping of photogenerated charges at the ZnO interface. Inclusion of the additional PC61BM layer led to effective quenching of electron–hole recombination by a reduction in the number of accumulated charges at the surface of ZnO ripples. This resulted in a 16% increase in the efficiency of inverted BHJ solar cells to 7.7%, compared to solar cells without the additional PC61BM layer.

Influence of surface roughness of aluminum-doped zinc oxide buffer layers on the performance of inverted organic solar cells

Aluminum-doped zinc oxide (AZO) films (70 nm thick) with dissimilar surface roughness were created on indium tin oxide coated glass and were used as electrodes for inverted organic solar cells. The photovoltaic performance of the devices depended strongly on the surface roughness of the AZO films. Increases in the surface root-mean-square roughness of AZO films from 2.5 to 10.9 nm enhanced power conversion efficiency from 0.5% to 1.4% due to increased contact area between electrode and active layer.

Surface Modification of a ZnO Electron-Collecting Layer Using Atomic Layer Deposition to Fabricate High-Performing Inverted Organic Photovoltaics

A ripple-structured ZnO film as the electron-collecting layer (ECL) of an inverted organic photovoltaic (OPV) was modified by atomic layer deposition (ALD) to add a ZnO thin layer. Depositing a thin ZnO layer by ALD on wet-chemically prepared ZnO significantly increased the short-circuit current (Jsc) of the OPV. The highest power conversion efficiency (PCE) of 7.96% with Jsc of 17.9 mA/cm2 was observed in the inverted OPV with a 2-nm-thick ALD-ZnO layer, which quenched electron-hole recombination at surface defects of ZnO ripples. Moreover, an ALD-ZnO layer thinner than 2 nm made the distribution of electrical conductivity on the ZnO surface more uniform, enhancing OPV performance. In contrast, a thicker ALD-ZnO layer (5 nm) made the two-dimensional distribution of electrical conductivity on the ZnO surface more heterogeneous, reducing the PCE. In addition, depositing an ALD-ZnO thin layer enhanced OPV stability and initial performance. We suggest that the ALD-ZnO layer thickness should be precisely controlled to fabricate high-performing OPVs.

Multifunctional SWCNT‐ZnO Nanocomposites for Enhancing Performance and Stability of Organic Solar Cells

Photovoltaic systems have been extensively studied and, among them, organic solar cells (OSCs) have attracted particular attention due to their low price and the possibility of using them in fl exible devices. [ 1–4 ] One of the disadvantages of OSCs is their low chemical stability, which is due to the oxidation of their interfaces by oxygen and water and the photodegradation of the active layers. [ 5–9 ] In order to increase their stability, various methods have been employed. Oxygen and water diffusion barriers were employed to protect the interfaces of OSCs from degradation. [ 10 , 11 ] Recently, an OSC with an inverted structure was developed, which was shown to be more stable than conventional solar cells. [ 12 , 13 ] In conventional structures, holes are injected into the transparent conducting electrode (TCE) and, in many cases, materials such as PEDOT: PSS with a high capability of hole injection are deposited on the TCE. In the inverted structure, in contrast, electrons are injected into the TCE. In the past, the improved stability of the inverted structure based on n-type ZnO layers on a TCE with respect to that of conventional OSCs was reported. [ 12 , 13 ] Carbon nanotubes (CNTs) have been widely used in photovoltaic systems. In many cases, bare CNTs and CNTs combined with C 60 , semiconductive and metallic nanoparticles were incorporated in the active layers, and the high capability of CNTs for electron transport has been exploited. [ 14–20 ] On the other hand,

Fabrication of conductive, transparent and superhydrophobic thin films consisting of multi-walled carbon nanotubes

Polydimethylsiloxane (PDMS) was coated on multi-walled carbon nanotubes (MWCNTs) using a chemical vapour deposition method, and the PDMS-coated MWCNTs were well dispersed in various solvents without additional dispersants. Spin casting of the MWCNT-containing solution on a substrate pre-treated with PDMS-SiO2 nanoparticles resulted in the formation of a uniform thin film. The resulting thin film containing MWCNTs showed high optical transparency, conductivity and superhydrophobicity. We demonstrated that such multifunctional thin films can also be prepared on flexible substrates.

Superhydrophobic carbon fiber surfaces prepared by growth of carbon nanostructures and polydimethylsiloxane coating

AbstractWe prepared nanostructured carbon fiber surfaces using chemical vapor deposition in which Ni nanoparticles were used as carbon nanostructure growth catalysts. The surface of the nanostructured carbon fiber was covered by a thin polydimethylsiloxane film. This surface showed superhydrophobic behavior with a water contact angle close to 170 °C, and its superhydrophobicity was sustained in a wide pH range (1–13).

X-Ray Photoelectron Spectroscopy Studies of Pd Supported MgO/Mg

본 연구에서는 고진공 조건에서 열기화 증착 방법으로 산화막으로 덮인 Mg 리본(MgO/Mg) 위에 Pd을 증착하였다. 고진공 속에서 만든 시료의 전자구조를 in-situ X-선 광전자 분광법 (XPS)을 통하여 분석하였고, 분석 후, FE-SEM을 통해 증착량의 증가에 따른 표면구조의 변화를 확인하였다. Pd 증착량이 1 나노미터 (㎚) 이하인 경우에는 증착량 증가에 따른 Pd 나노입자 크기의 증가를 확인하였으며, Pd을 1 ㎚ 이상의 두께로 증착시킨 경우에는 Pd 입자들의 뭉침에 의해 얇은 필름이 형성됨을 관찰하였다. Pd과 기판사이의 전하이동에 의하여 산화물/금속 계면의 Pd 원자들은 부분적으로 양전하를 띔을 확인하였다.Pd was deposited on magnesium-oxide-covered magnesium ribon substrate by metal thermal evaporation method in high vacuum. The electronic and chemical properties of Pd samples with different coverages were studied using in-situ X-ray Photoelctron Spectroscopy (XPS) and Field Emission Scanning Electron Microscopy (SEM). For relatively lower amounts of Pd deposited(