Dong In Kim

Improved Electrochromic Characteristics of a Honeycomb-Structured Film Composed of NiO

Color changes controlled by electronic energies have been studied for many years in order to fabricate energy-efficient smart windows. Reduction and oxidization of nickel oxide under the appropriate voltage can change the color of a window. For a superior nickel oxide (NiO) electrochromic device (ECD), it is important to control the chemical and physical characteristics of the surface. In this study, we applied polystyrene bead templates to nickel oxide films to fabricate a honeycomb-structured electrochromic (EC) layer. We synthesized uniform polystyrene beads using the chemical wet method and placed them on substrates to create honeycomb-structured NiO films. Then, the EC characteristics of the nickel oxide films with a honeycomb structure were evaluated with UV-Visible and cyclic voltammetry. FE-SEM and AFM were used to measure the morphologies of the nanostructures and the efficiencies of the redox reactions related to the specific surface area.

Synthesis and characterization of vanadium doped TiO 2 for the visible light-driven photocatalytic activity

V-doped TiO 2 nanoparticles (NPs) was synthesized by a sol-gel hydrolysis method using titanium butoxide (Ti(OBu) 4 ) and vanadyl acetylacetonate (VO(acac) 2 ) as a precursor and dopant, respectively. The effects of different V : Ti ratios on the crystal structure, band gap energy and photocatalytic activity have been investigated. The photocatalytic activity of V-doped TiO 2 NPs was evaluated using UV-vis absorption spectroscopy through degradation of a methyleneblue (MB) solution under visible light irradiation. Characterization by Raman and X-ray diffraction pattern shows that V was doped effectively and oxygen vacancies and various defects or Ti3+ centers were formed. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) results indicated the presence of V in the TiO 2 . The band gap energy of V-doped TiO 2 NPs was determined to be 2.3 eV, with a distinct red-shift confirmed by diffuse reflectance spectroscopy (DRS). The photocatalytic activity of V-doped TiO 2 NPs exhibited highly enhanced visible-light-induced photocatalytic performance compared with pure TiO 2 NPs.

Fast dipping treatment for dense perovskite thin films

Many groups have tried to make a dense organi-inorganic hybrid perovskite layer with one-step process. And perovskite synthesis method with the diethyl ether has been attempted in their own ways, such as dropping, long time dipping and so on. However, the reports for the solar cell having inverted form, photo-voltaic devices using PEDOT:PSS as hole transport layer, are not enough. In this work, we made the dense perovskite layer through fast-dipping method that casted films was soaked into diethyl ether. We study on the morphology and electrical properties of Methyl ammonium lead iodide (MAPbI3) thin films. The solar cells were consisted with ITO/PEDOT:PSS/MAPbI3/PCBM/Ag. The device performance were investigated with solar-simulator. At the same time, morphology, optical properties and crystalline variations were investigated by field emission scanning electron microscopy (FE-SEM), UV-Vis spectroscopy and X-ray diffraction (XRD) analysis, respectively.

Design of outstanding random-patterns surface for enhancement of light scattering in Perovskite solar cell

Glass texturing is an efficient method for changing the surface morphology to enhance the solar cell spectral response. In this study, we present a method for optimizing the light scattering (LS) properties of uneven surface with random-patterns for perovskite solar cell (PSC) applications. Glass substrates were textured with a random structure assisted wet etching process using diluted hydrofluoric acid solution at a constant concentration of etchants. Then, the light trapping (LT) properties of suitable films were controlled over a wide range by varying the etching time (1–5min.). The optical properties of the surface and the reflection efficiency of the rugged surface should be maximized in the visible region at 5min. As a result in terms of short-circuit current density (Jsc), a gain of 23.0mA/cm2 (more than 29.9%) and power conversion efficiency (PCE) of 12.3% (more than 31.7%) are achieved with the introduction of textured interface.

Enhanced power conversion efficiency of dye-sensitized solar cells assisted with phosphor materials

Theoretically dye-sensitized solar cells (DSSCs) are high efficiency solar cells. However, DSSCs have lower power conversion efficiency (PCE) than silicon based solar cells. In this study, we use scattering layer and phosphor materials, such as ZrO2 and Zn2SiO4:Mn (Green), to enhance the PCE of DSSCs. The scattering layer and phosphor materials were prepared and used as an effective scattering layer on the transparent TiO2 photoelectrode through the doctor blade method. We confirmed that the scattering layer improves the PCE and Jsc due to the enhancement of light harvesting by increasing the scattering and absorbance in the visible range. Under sun illumination AM 1.5 conditions, the PCE of the mesoporous TiO2 based DSSCs was 5.18%. The PCE of the DSSCs with ZrO2 scattering layer was 5.61% and Zn2SiO4:Mn as the scattering layer was enhanced to 5.72%. In order to compare the change in optical properties, DSSCs were measured by EQE, reflectance and PCE. At the same time, FE-SEM and XRD were used to confirm the structural changes in each layer.