Jin Ah Seo

Structure control of organized mesoporous TiO2 films templated by graft copolymers for dye-sensitized solar cells

Randomly microphase-separated graft copolymers have been self-reorganized so as to exhibit a micellar structure with excellent connectivity upon tuning the solvent affinity. These copolymers are used as a structure-directing agent for organized mesoporous TiO(2) films with no grain boundaries, leading to enhanced solar conversion efficiency of dye-sensitized solar cells.

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.

Fabrication of 3D interconnected porous TiO2 nanotubes templated by poly(vinyl chloride-g-4-vinyl pyridine) for dye-sensitized solar cells

Porous TiO(2) nanotube arrays with three-dimensional (3D) interconnectivity were prepared using a sol-gel process assisted by poly(vinyl chloride-graft-4-vinyl pyridine), PVC-g-P4VP graft copolymer and a ZnO nanorod template. A 7 µm long ZnO nanorod array was grown from the fluorine-doped tin oxide (FTO) glass via a liquid phase deposition method. The TiO(2) sol-gel solution templated by the PVC-g-P4VP graft copolymer produced a random 3D interconnection between the adjacent ZnO nanorods during spin coating. Upon etching of ZnO, TiO(2) nanotubes consisting of 10-15 nm nanoparticles were generated, as confirmed by wide-angle x-ray scattering (WAXS), energy-filtering transmission electron microscopy (EF-TEM) and field-emission scanning electron microscopy (FE-SEM). The ordered and interconnected nanotube architecture showed an enhanced light scattering effect and increased penetration of polymer electrolytes in dye-sensitized solar cells (DSSC). The energy conversion efficiency reached 1.82% for liquid electrolyte, and 1.46% for low molecular weight (M(w)) and 0.74% for high M(w) polymer electrolytes.

Templated formation of silver nanoparticles using amphiphilic poly(epichlorohydrine-g-styrene) film

This work has demonstrated that a novel amphiphilic poly(epichlorohydrine)-graft-polystyrene (PECH-g-PS) copolymer at 34:66 wt% was synthesized via atom transfer radical polymerization (ATRP) of styrene using PECH as a macroinitiator. The structure of the graft copolymer was characterized by nuclear magnetic resonance (1H NMR) and FTIR spectroscopy, demonstrating that the “grafting from” method using ATRP was successful. The self-assembled graft copolymer was used as a template film for thein-situ growth of silver nanoparticles from AgCF3SO3 precursor under UV irradiation. Thein situ formation of silver nanoparticles with 6-8 nm in average size in thesolid state template film was confirmed by transmission electron microscopy (TEM), UV-visible spectroscopy and wide angle X-ray scattering (WAXS). Differential scanning calorimetry (DSC) also displayed the selective incorporation and thein situ formation of silver nanoparticles within the hydrophilic PECH domains, probably due to stronger interaction of the silvers with the ether oxygens of PECH backbone than that with hydrophobic PS side chains.

Use of graft copolymer for preparation of organized mesoporous TiO 2 films

Randomly microphase-separared graft copolymers have been self-reorganized so as to exhibit a micellar structure with excellent connectivity upon tuning the solvent affinity. These copolymers are used as a structure-directing agent for organized mesoporous TiO2 films with non grain boundaries, leading to enhanced solar conversion efficiency of dye-sensitized solar cells.