Effects of Porphyrin Substituents and Adsorption Conditions on Photovoltaic Properties of Porphyrin-Sensitized TiO₂ Cells

A series of meso -tetraphenylzincporphyrins have been prepared to examine the effects of the porphyrin substituents and adsorption conditions on photovoltaic properties of the porphyrin-sensitized TiO 2 cells. The cell performance strongly depended on the linking bridge between the porphyrin core and the TiO 2 surface, the bulkiness around the porphyrin core, and the immersing solvents and times for the porphyrin adsorption. In particular, the high cell performance of the porphyrin-sensitized TiO 2 cells was achieved when protic solvent (i.e., methanol) and short immersing time (0.5−1 h) were used for the conditions of the dye adsorption on TiO 2, which is in sharp contrast with Ru dye-sensitized TiO 2 cells. The highest cell performance was obtained with 5-(4-carboxyphenyl)-10,15,20-tris(2,4,6-trimethylphenyl)porphyrinatozinc(II) as a sensitizer and methanol as an immersing solvent with an immersing time of 1 h: a maximal incident photon-to-current efficiency of 76%, a short circuit photocurrent density of 9.4 mA cm −2, an open-circuit voltage of 0.76 V, a fill factor of 0.64, and a power conversion efficiency of 4.6% under standard AM 1.5 sunlight. These results will provide basic and valuable information on the development of dye-sensitized solar cells exhibiting a high performance.