Photovoltaic Effects of Dye-Sensitized Solar Cells Using Double-Layered TiO2 Photoelectrodes and Pyrazine-Based Photosensitizers.

ABSTRACT

In this study, to obtain high performances of the dye-sensitized solar cells using the optimal TiO2 photoelectrode for the synthesized pyrazine-based organic photosensitizers, three types of TiO2 photoelectrodes were fabricated and evaluated for comparison. The double-layered nanoporous TiO2 photoelectrode (SPD type) consisted of a dispersed TiO2 layer and a transparent TiO2 layer. The single-layered nanoporous TiO2 photoelectrodes (D type and SP type) consisted of a dispersed TiO2 layer and a transparent TiO2 layer, respectively. The surface area, pore volume, and crystalline structures of the three types of TiO2 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 TiO2 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 TiO2 photoelectrodes were investigated under a light intensity of 100 mW/cm2 at AM 1.5. The DSSC device using double-layered SPD type TiO2 photoelectrodes displayed 1.31∼2.64% efficiency, compared to single-layered SP type TiO2 photoelectrodes (1.31∼2.50%) and D type TiO2 photoelectrodes (0.90∼1.54%), using organic photosensitizers. The DSSC device using the SPD type TiO2 photoelectrode and trifluoromethylbenzopyrazine (TPPF) as a photosensitizer showed the highest performances J sc of 5.69 mA/cm2, 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 TiO2 photoelectrodes could be interpreted from interfacial resistances according to frequency through impedance analysis.