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Chung, Il Jun,Kim, Wook,Jang, Wonjun,Park, Hyun-Woo,Sohn, Ahrum,Chung, Kwun-Bum,Kim, Dong-Wook,Choi, Dukhyun,Park, Yong Tae The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.7
<P>Triboelectric nanogenerators (TENGs) are considered promising next-generation mechanical energy harvesters owing to their desirable attributes such as light weight, portability, eco-friendliness, and low cost. However, cost-effective, scalable, and facile manufacturing methods are still required for the commercialization of TENGs, especially for textile-type TENGs compatible with a variety of textile products. In this work, we report for the first time the layer-by-layer (LbL) assembly of graphene multilayers for low-cost, durable, scalable, and wearable TENGs. The LbL-based graphene multilayers are fabricated on polymer substrates with flat, undulated, and textile surfaces, where graphene multilayers play dual roles as a positive tribo-material and as an electrode. The polymer substrate here is utilized as a negative tribo-material. We identify the optimal number of layers for graphene composites and analyze this outcome using their morphological and electrical properties. Due to the hydrogen bonding-based LbL wet processes, graphene composite multilayers could be well deposited on undulated surfaces as well as on large-scale fabric textiles. These LbL-deposited graphene multilayers yield graphene based-TENGs (G-TENGs) with high durability and high performance. Finally, a graphene multilayer on a textile sample is demonstrated as a scalable and wearable textile-based G-TENG (TG-TENG) operated in a single electrode mode, thereby enabling low-cost manufacturing and high compatibility with textile products such as cloths, curtains, bags and so on. The simple, cost-effective, scalable, and versatile LbL assembly can therefore enable the fabrication of wearable energy harvesting sources for many portable personal microelectronic devices (<I>e.g.</I>, self-powered wireless sensors).</P>
Park, Hyun-Woo,Chung, Kwun-Bum The Korean Vacuum Society 2017 Applied Science and Convergence Technology Vol.26 No.3
Aluminum-doped ZnO (AZO) thin films were deposited by atomic layer deposition (ALD) with respect to the Al doping concentrations. In order to explain the chemical stability and electrical properties of the AZO thin films after hydrogen peroxide ($H_2O_2$) solution immersion treatment at room temperature, we investigated correlations between the electrical resistivity and the electronic structure, such as chemical bonding state, conduction band, band edge state below conduction band, and band alignment. Al-doped at ~ 10 at % showed not only a dramatic improvement of the electrical resistivity but also excellent chemical stability, both of which are strongly associated with changes of chemical bonding states and band edge states below the conduction band.
Kim, Han-Ki,Chung, Kwun-Bum,Kal, Jinha Elsevier 2019 Journal of Alloys and Compounds Vol.778 No.-
<P><B>Abstract</B></P> <P>We compared the electrical, optical, structural, and morphological properties of radio-frequency (RF) magnetron-sputtered ZnO and solution-processed ZnO nanoparticle (NP) buffer layers on ITO cathodes for use in inverted polymer solar cells (IPSCs). Continuous sputtering resulted in integration of the ZnO buffer layer in the ITO cathodes, which were then used as transparent cathodes for IPSCs. Although the electrical, optical, and morphological properties as well as work function of RF-sputtered ZnO film were similar to those of solution-processed ZnO NP film, the power conversion efficiency (PCE) of IPSCs with an RF-sputtered ZnO buffer layer was much lower than that of IPSCs with a solution-processed ZnO NP buffer layer due to vertical phase segregation of the organic active layer. However, intentional bias sweeping of IPSCs with an RF-sputtered ZnO buffer layer improved performance due to diffusion of PC<SUB>70</SUB>BM through the PV-D4610 donor layer and formation of a suitable heterojunction structure. Based on transmission electron microscope examination and dark current-voltage curves, we suggest a possible mechanism to explain the difference in behavior of RF-sputtered ZnO and solution-processed ZnO NP buffer layers in IPSCs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Comparison of spin-coated ZnO nanoparticle film and RF-sputtered ZnO film. </LI> <LI> Sputtered ZnO integrated ITO cathodes for inverted polymer solar cells. </LI> <LI> Bias-sweeping of inverted polymer solar cells to remove vertical phase segregation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Cho, Young Joon,Chung, Kwun-Bum,Chang, Hyo Sik Elsevier 2018 THIN SOLID FILMS - Vol.649 No.-
<P><B>Abstract</B></P> <P>We investigated the effects of the thermal stability of atomic layer deposition (ALD) oxidants on the surface passivation of ALD-Al<SUB>2</SUB>O<SUB>3</SUB> film. The results showed good passivation at temperatures not greater than 780 °C. However, we found that Al<SUB>2</SUB>O<SUB>3</SUB> films with an ozone oxidant showed better surface passivation at high temperatures than the water-based samples. The Al<SUB>2</SUB>O<SUB>3</SUB> films with a water oxidant yielded an additional interfacial oxide upon high-temperature annealing. In the case of the ozone-based samples, the interfacial SiO bonds that formed during deposition were more stable. This structural change degraded chemical passivation, which increased the interface-trap density to ~10<SUP>12</SUP> eV<SUP>−1</SUP> cm<SUP>−2</SUP>. The passivation performance of ALD-Al<SUB>2</SUB>O<SUB>3</SUB> films showed that at temperatures over 780 °C the passivation quality was affected more by defective passivation at the Si/SiOx interface than by a negative-fixed charge.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We compared surface passivation of ozone- and water-based ALD-Al<SUB>2</SUB>O<SUB>3</SUB> film. </LI> <LI> Ozone-based ALD-Al<SUB>2</SUB>O<SUB>3</SUB> film shows excellent thermal stability for passivation. </LI> <LI> The passivation quality of O<SUB>3</SUB>-based Al<SUB>2</SUB>O<SUB>3</SUB> is affected by interface defect over 780 °C. </LI> <LI> Degradation of passivation performance was different according to ALD oxidants. </LI> </UL> </P>
Maeng, Wan Joo,Choi, Dong-won,Chung, Kwun-Bum,Koh, Wonyong,Kim, Gi-Yeop,Choi, Si-Young,Park, Jin-Seong American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.20
<P>Highly conductive indium oxide films, electrically more conductive than commercial sputtered indium tin oxide films films, were deposited using a new liquid precursor Et<SUB>2</SUB>InN(SiMe<SUB>3</SUB>)<SUB>2</SUB> and H<SUB>2</SUB>O by atomic layer deposition (ALD) at 225–250 °C. Film resistivity can be as low as 2.3 × 10<SUP>–4</SUP>–5.16 × 10<SUP>–5</SUP> Ω·cm (when deposited at 225–250 °C). Optical transparency of >80% at wavelengths of 400–700 nm was obtained for all the deposited films. A self-limiting ALD growth mode was found 0.7 Å/cycle at 175–250 °C. X-ray photoelectron spectroscopy depth profile analysis showed pure indium oxide thin film without carbon or any other impurity. The physical and chemical properties were systematically analyzed by transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, optical spectrometer, and hall measurement; it was found that the enhanced electrical conductivity is attributed to the oxygen deficient InO<SUB><I>x</I></SUB> phases.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-20/am502085c/production/images/medium/am-2014-02085c_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am502085c'>ACS Electronic Supporting Info</A></P>
Low-temperature photoluminescence of WO<sub>3</sub> nanoparticles
Cho, Hak Dong,Yoon, Im Taek,Chung, Kwun Bum,Kim, Deuk Young,Kang, Tae Won,Yuldashev, Sh.U. Elsevier 2018 Journal of luminescence Vol.195 No.-
<P><B>Abstract</B></P> <P>In this paper we report the results on the study of the low-temperature photoluminescence of WO<SUB>3</SUB> nanoparticles uncoated and coated by carbon. The photoluminescence spectra of WO<SUB>3</SUB> nanoparticles at T = 15K demonstrate the two sharp emission bands at 369nm and 374nm, respectively. The energy position, the small full width at half maximum (FWHM) of these bands and the strong quenching of the intensity with increasing temperature allowed us to attribute these emission bands to the radiative recombination of bound excitons. These excitons are localized on the donor states in the conduction band of WO<SUB>3</SUB>. The difference in the relative intensities of the bound exciton emission bands in the uncoated and the carbon coated WO<SUB>3</SUB> nanoparticles is explained by the charge (electrons) transfer from the WO<SUB>3</SUB> nanoparticles to the carbon coating layer.</P>
Cho, In-Hwan,Park, Hai-Woong,Chung, Kwun-Bum,Kim, Chan-Joong,Jun, Byung-Hyuk Institute of Physics 2018 Semiconductor science and technology Vol.33 No.8
<P>The effects of lithium doping on the electrical properties and ageing effect of ZnSnO (ZTO) thin films fabricated using a sol–gel process were investigated. As the Li content increased from 0 to 15 at%, the saturation mobility increased until 3 at% of Li and then decreased. The sub-threshold swing and on/off ratio were improved with the increase in Li content. In addition, Li (3 at%)–ZTO showed the smallest <I>V</I> <SUB>TH</SUB> change of 2.52 V among the thin film transistors (TFTs) in a positive bias stress (PBS) test. To observe the influence of Li on the ageing effect of TFTs, un-passivated Li–ZTO TFTs were stored under ambient conditions for 120 days. As a result of comparing the electrical characteristics of Li–ZTO TFTs after different durations of air exposure, the on/off ratio and sub-threshold swing of the Li (7 at%)–ZTO sample were almost unchanged when compared to those of ZTO. An x-ray photoelectron spectroscopy analysis of the O 1s core level showed that the relative area of oxygen vacancies (<I>V</I> <SUB>O</SUB>) decreased from 27.2 to 19.6% as the Li content increased from 0 to 15 at%. A spectroscopic ellipsometer analysis showed that Li (3 at%)–ZTO had the smallest optical band gap of 3.68 eV. From the result of the band alignment, it was confirmed that the Fermi level (<I>E</I> <SUB>F</SUB>) of Li (3 at%)–ZTO was located at the closest position to the conduction band minimum. Despite the reduction of the oxygen vacancy, the reason for the increasing electron concentration was due to the Li atom being preferentially located in the interstitial site, which released the free electron in the ZnO matrix. As a result, Li (3 at%)–ZTO showed improved electrical properties in the saturation mobility and PBS with stability under an ambient environment.</P>