Hyunkook Kim

Graphene counter electrodes for dye-sensitized solar cells prepared by electrophoretic deposition

The graphene counter electrodes (GCEs) for dye-sensitized solar cells (DSSCs) prepared by electrophoretic deposition (EPD) are reported. Thermogravimetric analysis (TGA) was carried out to find the optimum annealing temperatures. It was found that charge transfer resistance (Rct1) related to the interface between electrolyte and counter electrode was significantly reduced by proper annealing. DSSC with GCE annealed at 600 °C demonstrated by the best conversion efficiency of 5.69% under AM 1.5 and 1 sun condition. Once GCE prepared by EPD is fully developed, it could be utilized for a low-cost, high throughput process for DSSCs.

Fabrication and characterization of carbon-based counter electrodes prepared by electrophoretic deposition for dye-sensitized solar cells

Three different carbon-based counter electrodes are investigated in light of catalytic activities such as electrochemical frequencies and interface impedances. We fabricated carbon-based counter electrodes of dye-sensitized solar cells [DSSCs] using graphene, single-walled carbon nanotubes [SWNTs], and graphene-SWNT composites by electrophoretic deposition method. We observed the optical and electrochemical properties of the carbon-based counter electrodes. The DSSC with the graphene-deposited counter electrode demonstrated the best conversion efficiency of 5.87% under AM 1.5 and 1 sun condition. It could be utilized for a low-cost and high-throughput process for DSSCs.

Effect of Electrochemical Properties and Optical Transmittance of Carbon Nanotubes Counter Electrodes on the Energy Conversion Efficiency of Dye-sensitized Solar Cells

In this work, electrochemical characteristics and optical transmittance of carbon nanotubes (CNTs) counter electrodes which had different amount of CNTs in CNTs slurries were analyzed. Two-step heat treatment processes were applied to achieve well-fabricated CNTs electrode. Three sets of CNTs electrodes and dye-sensitized solar cells (DSSCs) with CNTs counter electrodes were prepared. As the amount of CNTs increased, sheet resistance of CNTs electrode decreased. CNTs electrode with low sheet resistance had low electrochemical impedance and fast redox reaction. On the other hand, in case of CNTs counter electrode with low density of CNTs, performance of the dye-sensitized solar cell was improved due to its high optical transmittance. We found that the transmittance of CNTs counter electrode influence the performance of dye-sensitized solar cells.

Study on Electro-optic Characteristics and Dynamic Stability Depending on the Pretilt Angle for the Twisted Nematic(TN) and Fringe-field Switching(FFS) Mode

We studied on the electro-optic characteristics and dynamic stability according to an undesirably defined pretilt angle induced in high step coverage of pixel area for the Twisted Nematic (TN) / Fringe-Field Switching (FFS) mode. In case of the TN mode, LC directors twist reversely near the edges of thin-film-transistor and black matrix where the pretilt angle of the LC is not well defined. Therefore, the voltage-dependent dynamics of the LC in TN mode is unstable and shows the bad electro-optic characteristics. On the other hand, in case of the FFS mode, the LCs are twisted parallel to the bottom substrate by fringe electric field and the electro-optic characteristic is not influenced by the pretilt angle of the LC which is not well defined.