Jongmin Roh

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%.

Dual-functional CeO2:Eu3+ nanocrystals for performance-enhanced dye-sensitized solar cells.

Single-crystalline, octahedral CeO2:Eu3+ nanocrystals, successfully prepared using a simple hydrothermal method, were investigated to determine their photovoltaic properties in an effort to enhance the light-harvesting efficiency of dye-sensitized solar cells (DSSCs). The size of the CeO2:Eu3+ nanocrystals (300-400 nm), as well as their mirrorlike facets, significantly improved the diffuse reflectance of visible light. Excitation of the CeO2:Eu3+ nanocrystal with 330 nm ultraviolet light was re-emitted via downconversion photoluminescence (PL) from 570 to 672 nm, corresponding to the 5D0→7FJ transition in the Eu3+ ions. Downconversion PL was dominant at 590 nm and had a maximum intensity for 1 mol % Eu3+. The CeO2:Eu3+ nanocrystal-based DSSCs exhibited a power conversion efficiency of 8.36%, an increase of 14%, compared with conventional TiO2 nanoparticle-based DSSCs, because of the strong light-scattering and downconversion PL of the CeO2:Eu3+ nanocrystals.

Hexagonal β-NaYF4:Yb3+, Er3+ Nanoprism-Incorporated Upconverting Layer in Perovskite Solar Cells for Near-Infrared Sunlight Harvesting

Hexagonal β-NaYF4:Yb(3+), Er(3+) nanoprisms, successfully prepared using a hydrothermal method, were incorporated into CH3NH3PbI3 perovskite solar cells (PSCs) as an upconverting mesoporous layer. Due to their near-infrared (NIR) sunlight harvesting, the PSCs based on the upconverting mesoporous layer exhibited a power conversion efficiency of 16.0%, an increase of 13.7% compared with conventional TiO2 nanoparticle-based PSCs (14.1%). This result suggests that the hexagonal β-NaYF4:Yb(3+), Er(3+) nanoprisms expand the absorption range of the PSC via upconversion photoluminescence, leading to an enhancement of the photocurrent.

Nanosilver-decorated TiO2 nanofibers coated with a SiO2 layer for enhanced light scattering and localized surface plasmons in dye-sensitized solar cells.

Enhanced harvesting of visible light is vital to the development of highly efficient dye-sensitized solar cells (DSSCs). Nanosilver-decorated TiO2 nanofibers (Ag@TiO2 NFs) were synthesized by depositing chemically reduced Ag ions onto the surface of electrospun TiO2 nanofibers (TiO2 NFs). The prepared Ag@TiO2 NFs were coated with SiO2 (SiO2@Ag@TiO2 NFs) by using PVP as coupling agent for protecting corrosion of Ag nanoparticle by I(-)/I3(-) solution. The fabricated SiO2@Ag@TiO2 NFs demonstrated a synergistic effect of light scattering and surface plasmons, leading to an enhanced light absorption. Moreover, an anode consisting of SiO2@Ag@TiO2 NFs incorporating TiO2 nanoparticles (NPs) increased light harvesting without substantially sacrificing dye attachment. The power conversion efficiency increased from 6.8 to 8.7 % for a thick film (10 μm), that is, 28 %. These results suggest that SiO2@Ag@TiO2 NFs are promising materials for enhanced light absorption in dye-sensitized solar cells.

Fabrication of Ag-coated AgBr nanoparticles and their plasmonic photocatalytic applications

Ag-coated AgBr nanoparticles (Ag@AgBr) were fabricated via an aqueous, one-pot route. In this system, poly(vinyl alcohol) (PVA) acted as a stabilizer for the formation of nanoscale AgBr composites through interaction with Ag ions and their hydroxyl (–OH) groups. The mild reducing agent L-arginine was used for partial reduction of AgBr to form metallic Ag nanoparticles on the AgBr surface. The metallic Ag nanoparticles enhanced light absorption in the visible region due to surface plasmon resonance (SPR). The size of the synthesized nanoparticles was controlled by varying the reaction temperature, and was found to influence the light absorption of Ag@AgBr nanocomposites. The prepared nano-photocatalysts exhibited excellent photocatalytic activities under both visible light and direct sunlight.

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%.

SAXS characterization of polymer-embedded hollow nanoparticles and of their shell porosity

Size parameters of SiO2/TiO2 hollow nanoparticles (HNPs) of 25–100 nm in diameter were characterized by small-angle X-ray scattering (SAXS). On the basis of the decoupling and the Percus–Yevick approximations, and using a hollow sphere model, size information on HNPs was extracted, including average outer diameter, average inner diameter and polydispersity. Application of an alternative form factor based on hollow ellipsoids, and of a sticky hard sphere structure factor, did not improve the fit significantly. The shell porosity of the HNPs and the size of the pores in the HNP shell were further characterized by combining SAXS with gas adsorption methods. The above HNPs were then supported on a porous poly(ethylene oxide) scaffold by freeze drying from aqueous solution. To characterize the product, a multishell model was applied to fit the experimental SAXS curves and extract the following morphological information: distribution of HNPs between the surface and interior of the polymer, thickness of the polymer layers lining the outer and inner surfaces of HNPs, and densities of the outer and inner polymer layers. The work demonstrates the versatility of SAXS in obtaining key information on dissolved and polymer-supported HNPs in applications such as drug delivery and catalysis.