DYE CAPPED SEMICONDUCTOR NANOCLUSTERS - ROLE OF BACK ELECTRON-TRANSFER IN THE PHOTOSENSITIZATION OF SNO2 NANOCRYSTALLITES WITH CRESYL VIOLET AGGREGATES

Adsorption of a cationic dye, cresyl violet, on SnO2 and SiO2 nanoclus ters and nanocrystalline thin films results in the formation of H-aggr egates. These dyes are photochemically and electrochemically active an d extend the photoresponse of large bandgap semiconductors such as SnO 2. Photocurrent generation in dye capped nanocrystalline films of SnO2 has been demonstrated with visible light excitation. A photon-to-phot ocurrent generation efficiency around 1% has been observed at 510 nm. Back electron transfer between the photoinjected electron and the oxid ized sensitizer plays an important role in controlling the efficiency of net electron transfer. Transient absorption and microwave absorptio n measurements of the dye aggregate capped SnO2 films suggest that the back electron transfer is multiexponential and most is completed with in a few hundred nanoseconds. The activation energy of the back electr on transfer process is very low (similar to 1.7 kJ/mol).