AVS 49th International Symposium
    Photonic Materials Topical Conference Thursday Sessions
       Session PH-ThM

Paper PH-ThM8
Macroscopic and Microscopic Investigations of Dye Sensitization

Thursday, November 7, 2002, 10:40 am, Room C-111B

Session: Photonic Nanostructures
Presenter: B.A. Parkinson, Colorado State University
Authors: B.A. Parkinson, Colorado State University
N. Takeda, Brookhaven National Laboratory
C.B. France, Colorado State University
Correspondent: Click to Email
Dye sensitization of large band gap semiconductors has been extensively studied both from a fundamental perspective and due to its practical importance. Electron injection from excited states of dyes into the conduction band of semiconductors is the principal processes of silver halide based photography and is also a key element of possible solar-to-electrical energy conversion devices. Photoelectrochemical methods have been used for many years to study the dye sensitization process but despite this a complete picture of the interfacial structure of the dye on the semiconductor surface is still lacking. We use a combination of scanning probe microscopies (AFM and STM), photocurrent spectroscopy and absorbance spectroscopy to obtain a more complete picture of the dye absorbance, sensitization efficiency and dye morphology on the semiconductor surface. Two semiconductors will be discussed, SnS@sub 2@ and TiO@sub 2@. SnS@sub 2@ has a bandgap of 2.2 eV is a useful model system for studying sensitization since atomically flat, reproducible surfaces can prepared. We have studied the morphology of several squaraine dyes on this material and were able to correlate it with the spectral response and the quantum yield for photocurrent generation. Quantum yield for electron collection per absorbed photon of 100% were observed with monolayer coverage of some dyes. The sensitization of titanium dioxide electrodes was also studied using both a ruthenium based sensitizer and a series of carbocyanine dyes with two pendant carboxylate groups to bind to the oxide surface. Rutile, anatase and brookite crystals were all investigated and the face dependence of the sensitized photocurrents was measured. The face dependence of photocurrent yield and the adsorption and desorption kinetics for a particular dye were explained by the ability of the carboxylate groups to both attach to binding sites on a given TiO@sub 2@ face.