Suk Jun Kim

Highly conductive polymer-decorated Cu electrode films printed on glass substrates with novel precursor-based inks and pastes

Novel inks and pastes based on a copper(II) formate tetrahydrate precursor were formulated with controllable viscosities in the range 5000–10u2006000 cP for use in printed electrodes. In particular, the addition of ethyl cellulose increased the adhesion of the printed paste films to the glass substrates. For the facile fabrication of electrodes with improved performance, the formulated pastes were printed on glass substrates under ambient conditions by a doctor-blade method. The printed films were thermally sintered at 170–250 °C in air and subsequently reduced under a formic acid atmosphere. The phase and microstructural evolution of the electrode films were systematically investigated by X-ray diffraction (XRD) and cross-sectional, focused ion beam scanning electron microscopy (FIB-SEM) in each processing step. Highly adhesive, polycrystalline Cu electrode films decorated by ethyl cellulose with a vermicular microstructure and large interconnected pore channels were well formed on the glass substrates. The electrode films sintered for 1 min in air and then reduced for 5 min under formic acid atmosphere at 250 °C showed the lowest electrical resistivity of ∼8 μΩ cm (electrical conductivity of ∼125u2006000 Ω cm−1, equivalent to ∼22% of bulk Cu), despite their maximum porosity of 27.31%.

Exploiting metallic glasses for 19.6% efficient back contact solar cell

An interdigitated back contact silicon solar cell with conversion efficiency of 19.6% was fabricated by screen-printing the Ag paste. In the Ag paste, oxide glass frits were totally replaced by Al85Ni5Y8Co2, Al-based metallic glass (MG) ones. The thermoplastic forming of the MG in the super cooled liquid region led to large contact area at the interface between Ag electrodes and Si layers and thus to specific contact resistance (ρc) as low as 0.86u2009mΩu2009cm2. The specific contact resistance was a function of both contact area and thickness of the interlayer formed at the interface working as a tunneling barrier.

Formation of Ag nanostrings induced by lyotropic liquid-crystalline phospholipid multilayer.

Morphological variation of the Ag nanoparticles embedded in a lyotropic phospholipid (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine, DOPE) membrane during hydration was investigated. Hydration at 5 °C resulted in transformation of the Ag nanoparticles into a bundle of Ag nanostrings as the Ag nanoparticles conformed to the H(II) phase of the DOPE molecules. Above 30 °C, the nanoparticles quickly coarsened into large polygonal-shaped particles since high mobility of the lipid molecules overwhelmed the tendency for the Ag nanoparticles to order. The result provided an insight into the long-term stability of nanoparticles trapped in different lipid membranes depending on the structural ordering of the molecules.

Molecular dynamics simulation of interlayer water embedded in phospholipid bilayer.

1,2-dioleoyl-sn-glycero-3-phosphocholine lipid bilayer with a thin layer of water molecules inserted in the hydrophobic region was simulated at 300K to observe the pore structure formation during escape of the water molecules from the hydrophobic region. The transformation of the water slab into a cylindrical droplet in the hydrophobic region, which locally deformed the lipid monolayer, was prerequisite to the pore formation. If the thickness of the interlayer water was increased beyond a critical value, the local deformation was suppressed as such deformation would rupture the lipid bilayer. Hence, it was demonstrated that the pore structure formation or local permeability of the lipid membrane is closely related to the rigidity of the lipid membrane.

Effect of in-situ application of ultrasonic waves during formation of silver nanoparticles embedded in phospholipid membrane

Effect of in-situ application of ultrasonic waves (up to 1u2009MHz) on the Ag nanoparticles spontaneously produced inside the 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) membrane by thermal evaporation of Ag was studied by placing the membrane on a ultrasonic transducer during the metal deposition. Application of the ultrasonic vibration promoted spatial ordering of the deposited nanoparticles due to the induced phase transition from Lα to HII for DOPE. Arising from the agitation effect, particle size refinement, which depended on the amplitude of the ultrasonic vibration, was observed. It was also shown that a stiff gel state 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane can be made locally permeable to incident Ag atoms by introducing DOPE molecules into the DPPC membrane as the Ag nanoparticles preferentially nucleated in the DOPE-rich region. Application of ultrasonic vibration with increasingly higher amplitude or frequency made the Ag nanoparticles uniformly distributed in the DPP...