Journal of Physical Chemistry B, Vol.101, No.14, 2583-2590, 1997
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 nanoclusters and nanocrystalline thin films results in the formation of H-aggregates. These dyes are photochemically and electrochemically active and extend the photoresponse of large bandgap semiconductors such as SnO2. Photocurrent generation in dye capped nanocrystalline films of SnO2 has been demonstrated with visible light excitation. A photon-to-photocurrent generation efficiency around 1% has been observed at 510 nm. Back electron transfer between the photoinjected electron and the oxidized sensitizer plays an important role in controlling the efficiency of net electron transfer. Transient absorption and microwave absorption measurements of the dye aggregate capped SnO2 films suggest that the back electron transfer is multiexponential and most is completed within a few hundred nanoseconds. The activation energy of the back electron transfer process is very low (similar to 1.7 kJ/mol).
Keywords:DIFFUSION-CONTROLLED REACTIONS;CYANINE DYES;COLLOIDAL SILICA;FLUORESCENCE LIFETIMES;PICOSECOND KINETICS;AGBR MICROCRYSTALS;CHARGE INJECTION;RATE CONSTANTS;TIO2;PHOTOCHEMISTRY