Won Seok Chi

Direct Assembly of Preformed Nanoparticles and Graft Copolymer for the Fabrication of Micrometer‐thick, Organized TiO2 Films: High Efficiency Solid‐state Dye‐sensitized Solar Cells

Solid-state dye-sensitized solar cell with 7.1% efficiency at 100 mW/cm(2) is reported, one of the highest observed for N719 dye. Excellent performance was achieved via a graft copolymer-templated, organized mesoporous TiO(2) film with a large surface area using spindle-shaped, preformed TiO(2) nanoparticles and solid polymer electrolyte.

Employing electrostatic self-assembly of tailored nickel sulfide nanoparticles for quasi-solid-state dye-sensitized solar cells with Pt-free counter electrodes

A low cost, low-temperature processable, highly efficient nickel sulfide counter electrode is demonstrated. Using the tailored, preformed nickel sulfide nanoparticles and electrostatic self-assembly, a novel counter electrode was fabricated that exceeded the efficiency of a conventional Pt-based cell.

One‐Dimensional Hierarchical Nanostructures of TiO2 Nanosheets on SnO2 Nanotubes for High Efficiency Solid‐State Dye‐Sensitized Solar Cells

Hierarchical nanostructures of TiO2 nanosheets on SnO2 nanotubes (SNT@TNS) are uniformly dispersed in an organized mesoporous (OM) TiO2 film with large pores, high porosity, and good interconnectivity. The solid-state dye sensitized solar cells (ssDSSCs) fabricated with 10 wt% SNT@TNS dispersed in a OM-TiO2 film show an energy conversion efficiency of 7.7% at 100 mW cm(-2) , which is one of the highest values for N719-based ssDSSCs and much larger than that of a randomly oriented TiO2 nanoparticles-based cell (4.0%).

Facile synthesis of size-tunable mesoporous anatase TiO2 beads using a graft copolymer for quasi-solid and all-solid dye-sensitized solar cells

Multi-functional mesoporous TiO2 (M-TiO2) beads with high porosity and good interconnectivity in the anatase phase were synthesized via a solvothermal reaction at low temperature (100 °C) using a graft copolymer, i.e., poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM), as a structure-directing agent. Field-emission scanning electron microscopy (FE-SEM), energy-filtering transmission electron microscopy (EF-TEM) and X-ray diffraction (XRD) revealed that the TiO2 beads consisted of 13 nm interconnected nanocrystallites and were monodisperse with tunable sizes of approximately 120, 250, 500 and 750 nm. The photoelectrodes fabricated with M-TiO2 beads showed a high surface area (86.5 m2 g−1) and a stronger light scattering effect, as confirmed by Brunauer–Emmett–Teller (BET) and incident photon-to-electron conversion efficiency (IPCE) measurements. The structures of M-TiO2 beads effectively offered better pore infiltration of the polymer electrolyte. Furthermore, the improved interconnectivity of M-TiO2 beads improved the electron diffusion coefficient and electron lifetime, resulting in an improvement in the light harvesting efficiency. Thus, quasi-solid-state polymer electrolyte dye-sensitized solar cells (DSSCs) with M-TiO2 beads showed a higher efficiency (4.8% at 100 mW cm−2) than those with conventional P25 (3.8%). A structure–property relation among M-TiO2 beads was investigated in terms of surface area and light scattering. Upon utilizing double layer structures and a solid polymerized ionic liquid (PIL), the efficiency was increased up to 6.7% at 100 mW cm−2, one of the highest values for all-solid-state DSSCs.

Enhanced Performance of Mixed-Matrix Membranes through a Graft Copolymer-Directed Interface and Interaction Tuning Approach

Herein, a high performance mixed-matrix membrane (MMM) is reported with simultaneously large improvements in the CO2 permeability by 880 % from 70.2 to 687.7 Barrer (1 Barrer=1×10(-10)  cm(3)  cm cm(-2)  s(-1)  cmHg(-1) ) and CO2 /N2 selectivity by 14.4 % from 30.5 to 34.9. These findings represent one of the most dramatic improvements ever reported for MMMs. These improvements are obtained through an interface and interaction tuning approach based on an amphiphilic grafted copolymer. Poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer plays a key role as a soft organic matrix to provide good permeation properties, uniform distribution of zeolite imidazole frameworks-8 (ZIF-8), and better interfacial contact with inorganic compounds. In particular, the CO2 /C3 H8 and CO2 /C3 H6 selectivities reached 10.5 and 42.7, respectively, for PVC-g-POEM/ZIF (40 %) MMMs; this indicates that it could be a promising membrane material for the purification of C3 hydrocarbons.

Mesoporous TiO 2 Bragg Stack Templated by Graft Copolymer for Dye-sensitized Solar Cells

Organized mesoporous TiO2 Bragg stacks (om-TiO2 BS) consisting of alternating high and low refractive index organized mesoporous TiO2 (om-TiO2) films were prepared to enhance dye loading, light harvesting, electron transport, and electrolyte pore-infiltration in dye-sensitized solar cells (DSSCs). The om-TiO2 films were synthesized via a sol-gel reaction using amphiphilic graft copolymers consisting of poly(vinyl chloride) backbones and poly(oxyethylene methacrylate) side chains, i.e., PVC-g-POEM as templates. To generate high and low index films, the refractive index of om-TiO2 film was tuned by controlling the grafting ratio of PVC-g-POEM via atomic transfer radical polymerization (ATRP). A polymerized ionic liquid (PIL)-based DSSC fabricated with a 1.2-μm-thick om-TiO2 BS-based photoanode exhibited an efficiency of 4.3%, which is much higher than that of conventional DSSCs with a nanocrystalline TiO2 layer (nc-TiO2 layer) (1.7%). A PIL-based DSSC with a heterostructured photoanode consisting of 400-nm-thick organized mesoporous TiO2 interfacial (om-TiO2 IF) layer, 7-μm-thick nc-TiO2, and 1.2-μm-thick om-TiO2 BS as the bottom, middle and top layers, respectively, exhibited an excellent efficiency of 7.5%, which is much higher than that of nanocrystaline TiO2 photoanode (3.5%).

Ionic liquid crystals: Synthesis, structure and applications to I2-free solid-state dye-sensitized solar cells

AbstractA novel type of ionic liquid crystal (ILC) was synthesized and used as a solid electrolyte in I2-free solidstate dye-sensitized solar cells (ssDSSCs). In particular, the properties of two ILCs, 1-[(4-ethenylphenyl)methyl]-3-butyl-imidazolium iodide (EBII) with a single aliphatic C=C bond and 1-[(4-ethenylphenyl)methyl]-3-vinyl-imidazolium iodide (EVII) with two aliphatic C=C bonds, were evaluated. The structures and morphologies of the ILCs were characterized using Fourier transform infrared spectroscopy (FTIR) and polarized optical microscopy (POM). Ultraviolet (UV)-visible spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analyses revealed that EBII exhibited weaker π-π stacking interactions, longer d-spacing, and a lower melting temperature. The energy conversion efficiency of I2-free ssDSSC with EBII (4.7% at 100 mW/cm2) was higher than with EVII (3.8%) due to facile charge transport and lower electron recombination in the former, as supported by electrochemical impedance spectroscopy (EIS).

One-step Synthesis of Vertically Aligned Anatase Thornbush-like TiO2 Nanowire Arrays on Transparent Conducting Oxides for Solid-State Dye-Sensitized Solar Cells

Herein, we report a facile synthesis of high-density anatase-phase vertically aligned thornbush-like TiO2 nanowires (TBWs) on transparent conducting oxide glasses. Morphologically controllable TBW arrays of 9 μm in length are generated through a one-step hydrothermal reaction at 200 °C over 11 h using potassium titanium oxide oxalate dehydrate, diethylene glycol (DEG), and water. The TBWs consist of a large number of nanoplates or nanorods, as confirmed by SEM and TEM imaging. The morphologies of TBWs are controllable by adjusting DEG/water ratios. TBW diameters gradually decrease from 600 (TBW600) to 400 (TBW400) to 200 nm (TBW200) and morphologies change from nanoplates to nanorods with an increase in DEG content. TBWs are utilized as photoanodes for quasi-solid-state dye-sensitized solar cells (qssDSSCs) and solid-state DSSCs (ssDSSCs). The energy-conversion efficiency of qssDSSCs is in the order: TBW200 (5.2%)>TBW400 (4.5%)>TBW600 (3.4%). These results can be attributed to the different surface areas, light-scattering effects, and charge transport rates, as confirmed by dye-loading measurements, reflectance spectroscopy, and incident photon-to-electron conversion efficiency and intensity-modulated photovoltage spectroscopy/intensity-modulated photocurrent spectroscopy analyses. TBW200 is further treated with a graft-copolymer-directed organized mesoporous TiO2 to increase the surface area and interconnectivity of TBWs. As a result, the energy-conversion efficiency of the ssDSSC increases to 6.7% at 100 mW cm(-2) , which is among the highest values for N719-dye-based ssDSSCs.

A shape- and morphology-controlled metal organic framework template for high-efficiency solid-state dye-sensitized solar cells

This report provides a facile process to produce shape- and morphology-controlled MIL-125(Ti), a subclass of metal organic frameworks (MOFs) using poly(ethylene glycol) diglycidyl ether (PEGDGE) as a structure directing agent. Upon deliberate calcination, MIL-125(Ti) is converted to mesoporous hierarchical TiO2 (hier-TiO2) with an anatase phase, a large surface area and a variety of nanostructures. The morphology changes from 200 nm circular plates to 1 μm bipyramids with increasing PEGDGE amount, indicating the pivotal role of PEGDGE as a shape controller. When the hier-TiO2 is deposited onto a nanocrystalline TiO2 (nc-TiO2) layer as the scattering layer, the dye-sensitized solar cell (DSSC) with a quasi-solid-state polymer electrolyte records a high conversion efficiency (7.1% at 100 mW cm−2), which is much higher than that of DSSCs with a nc-TiO2 layer only (4.6%) or with commercial scattering TiO2 (cs-TiO2) on a nc-TiO2 layer (5.0%). A solid-state DSSC using a single component solid polymer, i.e., poly((1-(4-ethenylphenyl)methyl)-3-butyl-imidazolium iodide) (PEBII), also exhibits an excellent efficiency of up to 8.0%. The improved efficiency results from the pivotal role of the hier-TiO2 in improving the surface area and light harvesting properties, as demonstrated by N2 adsorption/desorption isotherm, reflectance spectroscopy, incident photon-to-current efficiency (IPCE), and electrochemical impedance spectroscopy (EIS) analyses.

Plasmonic, interior-decorated, one-dimensional hierarchical nanotubes for high-efficiency, solid-state, dye-sensitized solar cells

We report a high energy conversion efficiency of 8.4% at 100 mW cm−2, which is one of the highest values for N719-based, solid-state, dye-sensitized solar cells (ssDSSCs). Our solar cells are based on one-dimensional (1D) hierarchical hetero-nanotubes consisting of Au cores and SnO2/TiO2 nanosheet double shells (referred to as Au@SnO2@TNSs). Carbonaceous nanofibers (CNFs) with tellurium (Te) cores are used as dual templates for the inner-deposition of gold and the outer-deposition of the metal oxide layers. An organized mesoporous TiO2 (OM-T) film, with high porosity, large pores, and good interconnectivity, is also prepared via a graft copolymer template approach and utilized as a matrix to disperse the 1D hierarchical nanostructures. Such nanostructures provide good pore-filling for solid electrolytes, faster electron transfer, and enhanced light scattering, as confirmed by reflectance spectroscopy, incident photon-to-electron conversion efficiency (IPCE) spectroscopy, and intensity-modulated photocurrent spectroscopy (IMPS)/intensity-modulated photovoltage spectroscopy (IMVS).