Photovoltaic Effects of Dye-Sensitized Solar Cells Using Double-Layered TiO 2 Photoelectrodes and Pyrazine-Based Photosensitizers.

In this study, to obtain high performances of the dye-sensitized solar cells using the optimal TiO 2 photoelectrode for the synthesized pyrazine-based organic photosensitizers, three types of TiO 2 photoelectrodes were fabricated and evaluated for comparison. The double-layered nanoporous TiO 2 photoelectrode (SPD type) consisted of a dispersed TiO 2 layer and a transparent TiO 2 layer. The single-layered nanoporous TiO 2 photoelectrodes (D type and SP type) consisted of a dispersed TiO 2 layer and a transparent TiO 2 layer, respectively. The surface area, pore volume, and crystalline structures of the three types of TiO 2 photoelectrodes were analyzed by Brunauer-Emmett-Teller method, field-emission scanning electron microscopy, and X-ray diffractometry to confirm their crystallinity and surface morphology. The structures of the three types of TiO 2 photoelectrode-adsorbed organic sensitizers were investigated using X-ray photoelectron spectroscopy. The photovoltaic performances of DSSC devices using three organic photosensitizers adsorbed onto the three types of TiO 2 photoelectrodes were investigated under a light intensity of 100 mW/cm 2 at AM 1.5. The DSSC device using double-layered SPD type TiO 2 photoelectrodes displayed 1.31∼2.64% efficiency, compared to single-layered SP type TiO 2 photoelectrodes (1.31∼2.50%) and D type TiO 2 photoelectrodes (0.90∼1.54%), using organic photosensitizers. The DSSC device using the SPD type TiO 2 photoelectrode and trifluoromethylbenzopyrazine (TPPF) as a photosensitizer showed the highest performances: J sc of 5.69 mA/cm 2 , V oc of 0.69 V, FF of 0.67, and efficiency of 2.64%. The relationship between photovoltaic effects and interfacial resistance characteristics of DSSCs using the three organic photosensitizers adsorbed onto the three types of TiO 2 photoelectrodes could be interpreted from interfacial resistances according to frequency through impedance analysis.