Interaction of semiconductor colloids with J-aggregates of a squaraine dye and its role in sensitizing nanocrystalline semiconductor films

The role of bis(2,4,6-trihydroxyphenyl)squaraine, Sq, in sensitizing large bandgap semiconductors has been investigated in the present study. The dye in its aggregate form readily interacts with the TiO₂ colloids giving rise to a new charge transfer band in the red region. The apparent association constant for the dye aggregate and TiO₂ colloid as determined from a Benesi-Hildebrand plot is 1600 M^-1. Nanocrystalline semiconductor films prepared from TiO₂, ZnO, and SnO₂ colloids have been modified with Sq to probe the photosensitization effects. Both dye monomers and aggregates were found to participate in the charge injection process. An incident photon-to-photocurrent efficiency up to 0.7% has been observed.