Juyoung Yun

Fabrication of Au@Ag Core/Shell Nanoparticles Decorated TiO2 Hollow Structure for Efficient Light-Harvesting in Dye-Sensitized Solar Cells

Improving the light-harvesting properties of photoanodes is promising way to enhance the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). We synthesized Au@Ag core/shell nanoparticles decorated TiO2 hollow nanoparticles (Au@Ag/TiO2 HNPs) via sol-gel reaction and chemical deposition. The Au@Ag/TiO2 HNPs exhibited multifunctions from Au@Ag core/shell NPs (Au@Ag CSNPs) and TiO2 hollow nanoparticles (TiO2 HNPs). These Au@Ag CSNPs exhibited strong and broadened localized surface plasmon resonance (LSPR), together with a large specific surface area of 129 m(2) g(-1), light scattering effect, and facile oxidation-reduction reaction of electrolyte from TiO2 HNPs, which resulted in enhancement of the light harvesting. The optimum PCE of η = 9.7% was achieved for the DSSCs using photoanode materials based on TiO2 HNPs containing Au@Ag/TiO2 HNPs (0.2 wt % Au@Ag CSNPs with respect to TiO2 HNPs), which outperformed by 24% enhancement that of conventional photoanodes formed using P25 (η = 7.8%).

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%.

SiO2/TiO2 Hollow Nanoparticles Decorated with Ag Nanoparticles: Enhanced Visible Light Absorption and Improved Light Scattering in Dye‐Sensitized Solar Cells

Hollow SiO2 /TiO2 nanoparticles decorated with Ag nanoparticles (NPs) of controlled size (Ag@HNPs) were fabricated in order to enhance visible-light absorption and improve light scattering in dye-sensitized solar cells (DSSCs). They exhibited localized surface plasmon resonance (LSPR) and the LSPR effects were significantly influenced by the size of the Ag NPs. The absorption peak of the LSPR band dramatically increased with increasing Ag NP size. The LSPR of the large Ag NPs mainly increased the light absorption at short wavelengths, whereas the scattering from the SiO2 /TiO2 HNPs improved the light absorption at long wavelengths. This enabled the working electrode to use the full solar spectrum. Furthermore, the SiO2 layer thickness was adjusted to maximize the LSPR from the Ag NPs and avoid corrosion of the Ag NPs by the electrolyte. Importantly, the power conversion efficiency (PCE) increased from 7.1 % with purely TiO2 -based DSSCs to 8.1 % with HNP-based DSSCs, which is an approximately 12 % enhancement and can be attributed to greater light scattering. Furthermore, the PCEs of Ag@HNP-based DSSCs were 11 % higher (8.1 vs. 9.0 %) than the bare-HNP-based DSSCs, which can be attributed to LSPR. Together, the PCE of Ag@HNP-based DSSCs improved by a total of 27 %, from 7.1 to 9.0 %, due to these two effects. This comparative research will offer guidance in the design of multifunctional nanomaterials and the optimization of solar-cell performance.

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.

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.

Synergistic effects of three-dimensional orchid-like TiO2 nanowire networks and plasmonic nanoparticles for highly efficient mesoscopic perovskite solar cells

TiO2 nanoparticle (TiO2 NP)-based mesoscopic electron transport structures have been frequently used in organic–inorganic hybrid perovskite solar cells (PSCs) for rapid electron transport. However, TiO2 NPs that are densely agglomerated in the scaffold layer may inhibit the penetration of a perovskite solution thereby deteriorating the device performance. Here, we use three-dimensional orchid-like TiO2 nanowires (OC-TiO2 NWs) as scaffold materials to overcome the deficiencies of TiO2 NP-based structures. The perovskite precursor deeply infiltrated into the spacious pores within the OC-TiO2 NW network and crystallized in the scaffold layer, which increased the recombination resistance and charge extraction efficiency. Additionally, Ag NPs were introduced in the form of a silica-coated Ag@OC-TiO2 NW (SiO2@Ag@OC-TiO2 NW) composite to achieve still better performance through localized surface plasmon resonance (LSPR) and exciton dissociation inducement of the Ag NPs. Consequently, a PSC based on this collaborative scaffold consisting of Ag NPs and OC-TiO2 NWs exhibited a high power conversion efficiency (PCE) of 15.09%, which is an improvement of 24% over a PSC based on a TiO2 NP scaffold layer, where the average PCE was 12.17%.

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.