Inyoung Jeong

Enhancing Stability of Perovskite Solar Cells to Moisture by the Facile Hydrophobic Passivation

In this study, a novel and facile passivation process for a perovskite solar cell is reported. Poor stability in ambient atmosphere, which is the most critical demerit of a perovskite solar cell, is overcome by a simple passivation process using a hydrophobic polymer layer. Teflon, the hydrophobic polymer, is deposited on the top of a perovskite solar cell by a spin-coating method. With the hydrophobic passivation, the perovskite solar cell shows negligible degradation after a 30 day storage in ambient atmosphere. Suppressed degradation of the perovskite film is proved in various ways: X-ray diffraction, light absorption spectrum, and quartz crystal microbalance. This simple but effective passivation process suggests new kind of approach to enhance stability of perovskite solar cells to moisture.

Unbiased Sunlight-Driven Artificial Photosynthesis of Carbon Monoxide from CO2 Using a ZnTe-Based Photocathode and a Perovskite Solar Cell in Tandem

Solar fuel production, mimicking natural photosynthesis of converting CO2 into useful fuels and storing solar energy as chemical energy, has received great attention in recent years. Practical large-scale fuel production needs a unique device capable of CO2 reduction using only solar energy and water as an electron source. Here we report such a system composed of a gold-decorated triple-layered ZnO@ZnTe@CdTe core-shell nanorod array photocathode and a CH3NH3PbI3 perovskite solar cell in tandem. The assembly allows effective light harvesting of higher energy photons (>2.14 eV) from the front-side photocathode and lower energy photons (>1.5 eV) from the back-side-positioned perovskite solar cell in a single-photon excitation. This system represents an example of a photocathode-photovoltaic tandem device operating under sunlight without external bias for selective CO2 conversion. It exhibited a steady solar-to-CO conversion efficiency over 0.35% and a solar-to-fuel conversion efficiency exceeding 0.43% including H2 as a minor product.

Ordered mesoporous tungsten suboxide counter electrode for highly efficient iodine-free electrolyte-based dye-sensitized solar cells.

A disulfide/thiolate (T(2)/T(-)) redox-couple electrolyte, which is a promising iodine-free electrolyte owing to its transparent and noncorrosive properties, requires alternative counter-electrode materials because conventional Pt shows poor catalytic activity in such an electrolyte. Herein, ordered mesoporous tungsten suboxide (m-WO(3-x)), synthesized by using KIT-6 silica as a hard template followed by a partial reduction, is used as a catalyst for a counter electrode in T(2)/T(-)-electrolyte-based dye-sensitized solar cells (DSCs). The mesoporous tungsten suboxide, which possesses interconnected pores of 4 and 20 nm, provides a large surface area and efficient electrolyte penetration into the m-WO(3-x) pores. In addition to the advantages conferred by the mesoporous structure, partial reduction of tungsten oxide creates oxygen vacancies that can function as active catalytic sites, which causes a high electrical conductivity because of intervalence charge transfer between the W(5+) and W(6+) ions. m-WO(3-x) shows a superior photovoltaic performance (79 % improvement in the power conversion efficiency) over Pt in the T(2)/T(-) electrolyte. The superior catalytic activity of m-WO(3-x) is investigated by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization curve analysis.

Solution-Processed Ultrathin TiO2 Compact Layer Hybridized with Mesoporous TiO2 for High-Performance Perovskite Solar Cells

The electron transport layer (ETL) is a key component of perovskite solar cells (PSCs) and must provide efficient electron extraction and collection while minimizing the charge recombination at interfaces in order to ensure high performance. Conventional bilayered TiO2 ETLs fabricated by depositing compact TiO2 (c-TiO2) and mesoporous TiO2 (mp-TiO2) in sequence exhibit resistive losses due to the contact resistance at the c-TiO2/mp-TiO2 interface and the series resistance arising from the intrinsically low conductivity of TiO2. Herein, to minimize such resistive losses, we developed a novel ETL consisting of an ultrathin c-TiO2 layer hybridized with mp-TiO2, which is fabricated by performing one-step spin-coating of a mp-TiO2 solution containing a small amount of titanium diisopropoxide bis(acetylacetonate) (TAA). By using electron microscopies and elemental mapping analysis, we establish that the optimal concentration of TAA produces an ultrathin blocking layer with a thickness of ∼3 nm and ensures that the mp-TiO2 layer has a suitable porosity for efficient perovskite infiltration. We compare PSCs based on mesoscopic ETLs with and without compact layers to determine the role of the hole-blocking layer in their performances. The hybrid ETLs exhibit enhanced electron extraction and reduced charge recombination, resulting in better photovoltaic performances and reduced hysteresis of PSCs compared to those with conventional bilayered ETLs.

Direct confinement of Ru nanoparticles inside nanochannels of large pore mesoporous aluminosilicate for Fischer–Tropsch synthesis

Metal/ordered mesoporous aluminosilicates (OMAS) have received great attention as bifunctional Fischer–Tropsch (FT) catalysts that directly convert syngas into liquid fuels. However, both synthesis of OMAS with large pores and efficient pore confinement of metal nanoparticles still remain challenging. Here, we report a simple method to synthesize Ru nanoparticles confined in the nanochannels of OMAS (Ru@OMAS). This method eliminates laborious multi-processes that are typically required for pore confinement of metal nanoparticles. We prepare three types of Ru@OMAS with different Si/Al molar ratios (denoted as Si/Al-x, x = 10, 30, and 50) having the same large pore size (∼30 nm) and Ru NP loading (3 wt%). Changing the Si/Al ratio strongly affects the number/strength of acid sites and the metal–support interaction, thereby mediating the catalytic activity and product selectivity. With increasing Al content (decreasing Si/Al ratio), supports acidity and metal–support interactions increase, whereas the reducibility of Ru decreases significantly. As a consequence, among the Si/Al-x catalysts, the Si/Al-50 shows the highest selectivity (63.6%) for liquid fuels (C5–C20) and excellent FT activity (CO conversion of 47.8%) due to its mild acidity and relatively good reducibility.