Jungsup Lee

Enhanced Electroresponsive Performance of Double-Shell SiO2/TiO2 Hollow Nanoparticles

The double-shell SiO2/TiO2 hollow nanoparticles (DS HNPs) are successfully fabricated and adopted as dispersing materials for electrorheological (ER) fluids to investigate an influence of shell structure on ER properties. The DS HNPs-based ER fluid exhibits outstanding ER performance which is 4.1-fold higher compared to that of single shell SiO2/TiO2 hollow nanoparticles (SS HNPs)-based ER fluid. The significantly improved ER property of DS HNPs-based ER fluid is ascribed to the enhanced interfacial polarization. In addition, the ER activities of DS HNPs-based ER fluids are examined depending on the particle diameter. The yield stress of DS HNPs-based ER fluids increases up to 302.4 kPa under an electric field of 3 kV mm(-1) by reducing the particle size, which is remarkable performance enough to promise sufficient probability for practical and industrial applications. The enhanced ER performance of the smaller DS HNPs is attributed to the increased surface area of large pores (30-35 nm) within the shells, resulting in a large achievable polarizability determined by dielectric constants. Furthermore, the antisedimentation property is analyzed in order to offer an additional insight into the effect of particle size on the ER fluids.

Size-controlled SiO2 nanoparticles as scaffold layers in thin-film perovskite solar cells

Perovskite-based solar cells have received much recent research attention for renewable-energy applications because of their high efficiency and long-term stability. Here, we report perovskite solar cells formed using a scaffold layer composed of size-controlled SiO2 nanoparticles (NPs). The infiltration of perovskite into the scaffold layer depended strongly on the size of the SiO2 NPs. We investigated the effects of scaffold layers comprised of SiO2 NPs that were 15, 30, 50, 70, and 100 nm in diameter on the properties of perovskite films. The performance of perovskite solar cells based on 50 nm diameter SiO2 NPs exhibited a current density (Jsc) of 16.4 mA cm−2, a open-circuit voltage (Voc) of 1.05 V, and a power-conversion efficiency (PCE) of 11.45%, which represent a significant improvement compared with perovskite solar cells fabricated using a TiO2 scaffold layer, where Jsc = 17.3 mA cm−2, Voc = 0.94 V, and the PCE was 10.29%.

Optical, dielectric and thermal properties of nanoscaled films of polyalkylsilsesquioxane composites with star-shaped poly(ε-caprolactone) and their derived nanoporous analogues

Abstract Nanoscaled films of poly(methylsilsesquioxane-co-ethylenylsilsesquioxane) (PMSSQ–BTMSE) and polymethylsilsesquioxane (PMSSQ) were prepared from the respective soluble prepolymers, and their thermal, optical, and dielectric properties were characterized. The PMSSQ–BTMSE nanofilm containing an ethylenyl bridge comonomer unit BTMSE was found to be thermally more stable than the nanofilm of PMSSQ, a representative polyalkylsilsesquioxane. Further, in comparison to the PMSSQ film the PMSSQ–BTMSE film exhibits a larger refractive index and a larger dielectric constant but a smaller out-of-plane thermal expansion coefficient, when both prepolymers are cured under the same conditions. These characteristics of PMSSQ–BTMSE films are due to the ethylenyl bridge provided by the BTMSE comonomer unit, which promotes the formation of a tighter, more perfect network structure in cured PMSSQ–BTMSE films. Composite films were prepared by solution-blending the pore generator (referred to as the porogen), a star-shaped poly(e-caprolactone), with the soluble prepolymers then drying the resulting solution, and the nature of their curing reactions and extent of porogen calcination were investigated. It was found that the thermal curing and calcination processes of the composite films successfully produce PMSSQ–BTMSE and PMSSQ films containing pores that are about 400 nm in diameter. It was confirmed that the presence of these generated nanopores significantly reduces the refractive indices and the dielectric constants of the dielectric films but increases their out-of-plane thermal expansivity, depending on the initial porogen loading. The porosities of the nanoporous dielectric films were estimated from the measured refractive indices. The surface topographies of these films were also investigated, giving information about the sizes of the pores generated in the films. It was also found that prior to calcination the presence of the porogen increases the refractive index and dielectric constant of the composite dielectric films because of its inherent high polarizability, and also increases the thermal expansivity of MSSQ–BTMSE composite films but very slightly decreases the thermal expansivity of MSSQ composite films. It is demonstrated that PMSSQ–BTMSE films and the related nanometer scale nanoporous films are candidates for use as low and ultra-low dielectric interlayers in the fabrication of advanced microelectronic devices.

SiO2/TiO2 based hollow nanostructures as scaffold layers and Al-doping in the electron transfer layer for efficient perovskite solar cells

Perovskite solar cells (PSCs) have been developed intensively recently due to their excellent efficiency. In this study, PSCs were fabricated using a hollow structure as a scaffold layer and Al doped TiO2 (Al-TiO2) as a compact layer. The hollow structure showed effective loading of perovskite (CH3NH3PbI3Cl3−x) on the working electrode of the PSCs. In particular, using SiO2/TiO2 hollow nanoparticles (STHNPs) instead of TiO2 hollow nanoparticles (THNPs) as insulators improved the open circuit voltage, because STHNPs did not allow photogenerated electrons to transfer easily from the perovskite. Al-TiO2 compact layers synthesized using a low temperature procedure (≤150 °C) promoted electron extraction and reduced the recombination, leading to enhanced power conversion efficiency (PCE). An optimum PCE of 14.7% was achieved for PSCs based on STHNP scaffold layers with Al doping in the electron transfer layer.

Fabrication of SiO2/TiO2 double-shelled hollow nanospheres with controllable size via sol-gel reaction and sonication-mediated etching.

Size-controllable double-shell SiO2/TiO2 hollow nanoparticles (DS HNPs) were fabricated using a simple sol-gel reaction and sonication-mediated etching. The size of the DS HNPs was controlled using SiO2 core templates of various sizes. Moreover, monodisperse DS HNPs were produced on a large scale (10 g per 1 batch) using the sol-gel method. The surface area and porosity of intrashell and inner-cavity pores were measured by Brunauer-Emmett-Teller analysis. As a result, 240 nm DS HNPs (240 DS HNPs) exhibited the highest surface area of 497 m(2) g(-1) and a high porosity. Additionally, DS HNPs showed excellent light-scattering ability as a scattering layer in dye-sensitized solar cells due to their structural properties, such as a composite, double-shell, hollow structure, as well as intrashell and inner cavity pores. The DSSCs incorporating 240 DS HNPs demonstrated an 18.3% enhanced power conversion efficiency (PCE) compared to TiO2 nanoparticles.

Multifunctional Ag‐Decorated Porous TiO2 Nanofibers in Dye‐Sensitized Solar Cells: Efficient Light Harvesting, Light Scattering, and Electrolyte Contact

Designing the photoanode structure in dye-sensitized solar cells (DSSCs) is vital to realizing enhanced power conversion efficiency (PCE). Herein, novel multifunctional silver-decorated porous titanium dioxide nanofibers (Ag/pTiO2 NFs) made by simple electrospinning, etching, and chemical reduction processes are introduced. The Ag/pTiO2 NFs with a high surface area of 163 m(2)  g(-1) provided sufficient dye adsorption for light harvesting. Moreover, the approximately 200 nm diameter and rough surface of the Ag/pTiO2 NFs offered enough light scattering, and the enlarged interpores among the NFs in the photoanode also permitted electrolyte circulation. Ag nanoparticles (NPs) were well dispersed on the surface of the TiO2 NFs, which prevented aggregation of the Ag NPs after calcination. Furthermore, a localized surface plasmon resonance effect by the Ag NPs served to increase the light absorption at visible wavelengths. The surface area and amount of Ag NPs was optimized. The PCE of pTiO2 NF-based DSSCs was 27 % higher (from 6.2 to 7.9 %) than for pure TiO2 NFs, whereas the PCE of Ag/pTiO2 NF-based DSSCs increased by about 12 % (from 7.9 to 8.8 %). Thus, the PCE of the multifunctional pTiO2 NFs was improved by 42 %, that is, from 6.2 to 8.8 %.

Large Grain-Based Hole-Blocking Layer-Free Planar-Type Perovskite Solar Cell with Best Efficiency of 18.20%

There remains tremendous interest in perovskite solar cells (PSCs) in the solar energy field; the certified power conversion efficiency (PCE) now exceeds 20%. Along with research focused on enhancing PCE, studies are also underway concerning PSC commercialization. It is crucial to simplify the fabrication process and reduce the production cost to facilitate commercialization. Herein, we successfully fabricated highly efficient hole-blocking layer (HBL)-free PSCs through vigorously interrupting penetration of hole-transport material (HTM) into fluorine-doped tin oxide by a large grain based-CH3NH3PbI3 (MAPbI3) film, thereby obtaining a PCE of 18.20%. Our results advance the commercialization of PSCs via a simple fabrication system and a low-cost approach in respect of mass production and recyclability.

Paintable Carbon-Based Perovskite Solar Cells with Engineered Perovskite/Carbon Interface Using Carbon Nanotubes Dripping Method

Paintable carbon electrode-based perovskite solar cells (PSCs) are of particular interest due to their material and fabrication process costs, as well as their moisture stability. However, printing the carbon paste on the perovskite layer limits the quality of the interface between the perovskite layer and carbon electrode. Herein, an attempt to enhance the performance of the paintable carbon-based PSCs is made using a modified solvent dripping method that involves dripping of the carbon nanotubes (CNTs), which is dispersed in chlorobenzene solution. This method allows CNTs to penetrate into both the perovskite film and carbon electrode, facilitating fast hole transport between the two layers. Furthermore, this method is results in increased open circuit voltage (Voc ) and fill factor (FF), providing better contact at the perovskite/carbon interfaces. The best devices made with CNT dripping show 13.57% power conversion efficiency and hysteresis-free performance.

Highly efficient perovskite solar cells incorporating NiO nanotubes: increased grain size and enhanced charge extraction

Perovskite solar cells (PSCs) have greatly improved through optimizing the morphology and charge extraction of the perovskite film. To increase the efficiency, we have developed a new method of adding NiO nanotubes (NTs) to the perovskite precursor solution. The NiO NTs promoted the growth of perovskite grains during annealing and facilitated charge extraction. The increase in the grain size improved the crystallinity of the perovskite film and reduced the grain boundaries that could trap charge. Additionally, the NiO NTs located between the grain boundaries transferred holes, which prevented charge recombination. The efficiency of the PSCs increased due to the improved crystallinity and charge extraction of the perovskite film. Devices incorporating the NiO NTs exhibited power conversion efficiencies of 19.3 and 12.82% for planar-type and carbon-based PSCs, respectively.

Fabrication of sinter-free conductive Cu paste using sub-10 nm copper nanoparticles

We herein describe the fabrication of sinter-free copper nanoparticle-based conductive paste (Cu NP paste). The copper nanoparticles with a size below 10 nm enable the formation of integrated structures even without heat treatment. Poly(vinylimidazole-co-vinyltrimethoxysilane) used in the synthesis grants the copper surface a high anti-oxidant ability over a temperature range of up to 300 °C under ambient conditions. Furthermore, the viscosity of the conductive paste could be arbitrarily adjusted while minimizing the change of resistivity. The pattern printed using Cu NP paste demonstrated an electrical resistivity of 1.2 × 10−2 Ω cm for un-sintered conductive paste. We confirmed the potential of the Cu NP paste through dipole tag antenna application.