Papers by Author: Dong Yoon Lee

Abstract: The effect of molybdenum substitution in electronic structures of manganese dioxide has been calculated by the DV-Xα molecular orbital method. The molybdenum atom substituted for manganese atom located in center-sited of (Mn15O56)-52 cluster model. By the molybdenum substitution the energy band gap between the highest occupied molecular orbital (HOMO) of valence band and the lowest unoccupied molecular orbital (LUMO) was decreased, also the interaction of Mn-3d and O-2p was weakened but that of Mo-4d and O-2p was intensified. Both bonds of (Mn15O56)-52 and (Mn14MoO56)-52 was composed of not only ionic but also partially covalent.

Abstract: Dye sensitized solar cells (DSSC) have great potential alternative to expensive conventional solar cells, since high efficiency and relatively simple fabrication process. However, in large size cell, there is a key factor that delayed the entry of such cells in commercial market. Performance of large size cell is lower than small size cells, since a carrier loss occurs in high resistive TCO glass substrate. Here we demonstrate a simple method to reduce resistive loss and efficient collection of photo generated carriers via strip type cells with metal grids. Using strip type cells, we constitute series and parallel type DSSC panels in order to achieve required voltage and current respectively. Stripe cells were prepared from commercial TiO2 powder by screen printing method. In addition, metal grids were established adjacent to sealant line. Using these as unit cell, portable DSSC panels were assembled and I-V performance was carried out in indoor light condition (fluorescent light, 30mW/cm2) and standard condition (Pin 100 mW/cm2, AM 1.5).

Abstract: Dye-sensitized solar cell (DSSC) is of great interest as one of renewable energy sources. So far, many investigations related to TiO2 electrode, dye, electrolyte, Pt counter electrode, etc. were carried out. Here, we focus on Pt counter electrode for providing an enhanced catalytic property and physical stability. Pt has high-conductivity and superior catalytic properties. However, in case of Pt as counter electrode for DSSC, there exists partial problem due to poor adhesion between Pt and FTO glass. In this work, we tried to enhance the properties of Pt catalyst by two methods; first, the insertion of buffer layer under Pt thin film; second, the heat treatment of Pt films. We report the effect of buffer layer using Cr and Ti and the effect of heat treatment on Pt electrode under 400oC. Electrochemical characteristics of Pt electrodes were measured using electrochemical impedance spectroscopy and cyclic-voltammetry. A degree of electrode reaction, current density, electrode potential and interface resistance, etc were discussed with measured electrochemical data. In comparison with sputtered Pt counter electrode with and without buffer layers, heat-treated Pt counter electrode showed good performance in terms of the current density and interface resistance properties.