Investigation of Dyes for Dye-Sensitized Solar Cells: Ruthenium-Complex Dyes, Metal-Free Dyes, Metal-Complex Porphyrin Dyes and Natural Dyes

Following the first report on dye-sensitized solar cells (DSCs) by Prof. Grätzel in 1991, thousands of papers have been published with the aim of making DSCs commercially viable (Fig. 1). They are attractive because of their low-cost materials and convenient fabrication by a non-vacuum, high-speed printing process. One of the key materials in DSCs is the sensitizer dye. Ruthenium-complex dyes are used to make DSCs with conversion efficiencies of over 10%; recently, the Grätzel group reported a DSC using ruthenium dye (Z991) which achieved a conversion efficiency of 12.3%. Research into synthetic rutheniumfree dyes, including metal-free organic dyes and metal-complex porphyrin dyes, has intensified because of the high cost of ruthenium. Indoline dyes and oligothiophene dyes are used to make DSCs with conversion efficiencies greater than 9% and 10%, respectively. A zinc-porphyrin dye produced a conversion efficiency of 11.4%.