Hyun-Jun Jo

Contactless Electroreflectance Spectroscopy of In 0.5 (Ga 1-x Al x ) 0.5 P/GaAs Double Heterostructures

We have investigated the contactless electroreflectance (CER) properties of /GaAs double heterostructures grown by metal-organic chemical vapour deposition (MOCVD). The CER measurements on the sample were studied as a function of temperature, modulation voltage (), and dc bias voltage (). Five signals observed at room temperature are related to the GaAs, , , , and transitions, respectively. From the temperature dependence of CER spectrum, the Varshni coefficients and broadening parameters were determined and discussed. In addition, we found that the behavior of the CER amplitude for the reverse bias is larger than that of the forward.

Effect of electrolyte redox potentials on the photovoltaic performance in dye-sensitized solar cells based on porphyrin dye

ABSTRACT We have investigated the effect of two different kinds of cobalt electrolytes on the photovoltaic performance in dye-sensitized solar cells (DSSCs) using the established porphyrin dye (YD-2). We have characterized the photovoltaic performance of DSSCs containing iodide/triiodide and two different Co3+/2+ electrolytes to confirm the relationship between redox potential of cobalt(III/II) tris(2,2′-bipridine), [Co(bpy)3]3+/2+, cobalt(III/II) tris(1,10-phenanthroline), [Co(phen)3]3+/2+ and the photovoltaic characteristics in DSSCs. Compared to the iodine-based electrolyte, the photovoltage of the DSSCs based on [Co(phen)3]3+/2+ was increased by 15%. The current densities in [Co(bpy)3]3+/2+ and [Co(phen)3]3+/2+-based devices decrease due to their larger size and decrease in difference bewteen HOMO level of dye and redox potential of electrolytes.

Improved performance of dye-sensitized solar cells based on solution treated PEDOT as efficient counter electrode

ABSTRACT The dye-sensitized solar cell (DSSC) is a promising alternative to the Si solar cell because of its low-cost and easy fabrication. The conductive polymer counter electrode, PEDOT has attracted much attention on DSSCs. To enhance efficiency, the electrochemical deposition of PEDOT onto FTO glass was carried out in 4 solution deposition ratios 4:6, 6:4, 8:2 and 9:1 of distilled water and acetonitrile. The best efficiency of the resulting DSSCs with 9:1/ PEDOT as compared to the reference cell. The excellent photoelectric properties, and low cost allow the PEDOT electrode to be a credible alternative electrode for use in DSSCs.

Fluorescent material concentration dependency: Förster resonance energy transfer in quasi-solid state DSSCs

Förster resonance energy transfer (FRET) is critical for wide spectral absorption, an increased dye loading, and photocurrent generation of dye-sensitized solar cells (DSSCs). This process consists of organic fluorescent materials (as an energy donor), and an organic dye (as an energy acceptor on TiO2 surfaces) with quasi-solid electrolyte. The judicious choice of the energy donor and acceptor facilitates a strong spectral overlap between the emission and absorption regions of the fluorescent materials and dye. This FRET process enhances the light-harvesting characteristics of quasi-solid state DSSCs. In this study, DSSCs containing different concentrations (0, 1, and 1.5 wt%) of a fluorescent material (FM) as the energy donor are investigated using FRET. The power conversion efficiency of DSSCs containing FMs in a quasi-solid electrolyte increased by 33% over a pristine cell. The optimized cell fabricated with the quasi-solid state DSSC containing 1.0 wt% FM shows a maximum efficiency of 3.38%, with a short-circuit current density (JSC) of 4.32 mA/cm−2, and an open-circuit voltage (VOC) of 0.68 V under illumination of simulated solar light (AM 1.5G, 100 mW/cm−2).