Excitation Transport and Trapping in a Two-Dimensional Disordered System: Cresyl Violet on Quartz

Abstract

Excitation transport and trapping processes involving dye molecules on surfaces are relevant to the efficiency of dye sensitizers on semiconductors in liquid-junction solar cells. Such processes have been treated theoretically for two-dimensional disordered systems [1,2], but have not yet been widely investigated experimentally [2,3]. We report here a picosecond photon counting study of cresyl violet (CV) submonolayers adsorbed onto fused quartz. The questions we address are: (i) What are the fluorescing CV species (CV monomers with varied adsorption geometries, CV dimers, etc.)? (ii) To what extent can a data analysis differentiate among different model functions for the time-dependent fluorescing state population? and (iii) How uniquely can the final decay parameters be determined from such an analysis alone? The last question is pertinent, because surface number densities of dyes in submonolayers, which can be difficult to ascertain directly, are important dynamical parameters in excitation transport.