Photochemical Solar Cells Based on Dye-Sensitization of Nanocrystalline TiO2

A photoelectrochemical solar cell that is based on the dye-sensitization of thin nanocrystalline films of TiO2 (anatase) nanoparticles in contact with a non-aqueous liquid electrolyte is described. The cell, fabricated at NREL, shows a conversion efficiency of -9.2% at AM1.5, which approaches the best reported value of 10%-11% by Grätzel at EPFL in Lausanne, Switzerland. The femtosecond (fs) pump-probe spectroscopy has been used to time resolve the injection of electrons into the conduction band of nanocrystalline TiO2 films under ambient conditions following photoexcitation of the adsorbed Ru(11)-complex dye. The measurement indicates an instrument-limited -50 fs upper limit on the electron injection time. We also report the sensitization of nanocrystalline TiO2 by a novel iron-based dye, CIS-[Fe(2,2'-bipyridine-4,4'-dicarboxylic acid)2(CN)2], a chromophore with an extremely short-lived, nonemissive excited state. The dye also exhibits a unique "band selective" sensitization through one of its two absorption bands. The operational principle of the device has been studied through the measurement of electric field distribution within the device structure and studies on the pH dependence of dye-redox potential. The incorporation of WO3-based electrochromic layer into this device has led to a novel photoelectrochromic device structure for "smart window" application.