Sung-Hae Park

A novel quasi-solid state dye-sensitized solar cell fabricated using a multifunctional network polymer membrane electrolyte

A series of liquid junction dye-sensitized solar cells (DSCs) was fabricated based on polymer membrane-encapsulated dye-sensitized TiO2 nanoparticles, prepared using a surface-induced cross-linking polymerization reaction, to investigate the dependence of the solar cell performance on the encapsulating membrane layer thickness. The ion conductivity decreased as the membrane thickness increased; however, the long term-stability of the devices improved with increasing membrane thickness. Nanoparticles encapsulated in a thick membrane (ca. 37 nm), obtained using a 90 min polymerization time, exhibited excellent pore filling among TiO2 particles. This nanoparticle layer was used to fabricate a thin-layered, quasi-solid state DSC. The thick membrane prevented short-circuit paths from forming between the counter and the TiO2 electrode, thereby reducing the minimum necessary electrode separation distance. The quasi-solid state DSC yielded a high power conversion efficiency (7.6 → 8.1%) and excellent stability during heating at 65 °C over 30 days. These performance characteristics were superior to those obtained from a conventional DSC (7.5 → 3.5%) prepared using a TiO2 active layer with the same thickness. The reduced electrode separation distance shortened the charge transport pathways, which compensated for the reduced ion conductivity in the polymer gel electrolyte. Excellent pore filling on the TiO2 particles minimized the exposure of the dye to the liquid and reduced dye detachment.

Thermodynamic Control over the Competitive Anchoring of N719 Dye on Nanocrystalline TiO2 for Improving Photoinduced Electron Generation

TiO(2) electrodes, sensitized with the N719 dye at high immersion temperatures during the sensitization process, were found to have large fractions of weakly bound N719 on the electrode surface, which resulted in dye aggregation and decreased device longevity. These disadvantages were ameliorated using a low-temperature stearic acid (SA)-assisted anchoring method described here. The activation energy (ΔE(NS)(++)) and relative fraction of strongly bound N719 were twice as large as the respective values obtained without the use of SA. Slowing of adsorption, both by thermal means and through SA-mediated processes, effectively controlled the binding mode of N719 on the surface of TiO(2). The resulting sensitized electrodes displayed enhanced device longevity and improved generation of photoinduced electrons.

Reduced charge recombination by the formation of an interlayer using a novel dendron coadsorbent in solid-state dye-sensitized solar cells

3,4,5-Tris(dodecyloxy)benzoic acid (DOBA) and the Z907 dye were coadsorbed to form a light-sensitizing monolayer in a solid-state dye-sensitized solar cell (sDSC). Coadsorption of DOBA which has three hydrocarbon chains permitted preparation of a denser monolayer of dyes and DOBA. This dense monolayer formed interlayer between TiO2 and Spiro-OMeTAD (hole conductor), effectively preventing charge recombination, while half of the photocurrent was dissipated via recombination reaction when Z907 solely anchored on the surface of TiO2. Moreover, the DOBA induced a lower population of density-of-state (DOS) in the surface of TiO2, shifting the position of the conduction band (CB) toward negative values. This resulted in higher open-circuit voltage (VOC) for the device made with Z907 and DOBA than that of the Z907-sensitized device. These surface properties were investigated using electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent/photovoltage spectroscopy (IMPS and IMVS).