Exciton diffusion length in titanyl phthalocyanine thin films as determined by the surface photovoltage method
Abstract
Exciton diffusion length was measured by the generalized surface photovoltage (SPV) method. Theoretical calculations of the photocurrents from the SCR and from the bulk of the layers were carried out and illustrated to show how the different parameters influence the form and relative size of the photogenerated signal.
We studied titanyl phthalocyanine (TiOPc) thin films prepared using evaporation and surface polymerization by ion-assisted deposition (SPIAD). Bilayer (TiO2/TiOPc) thin films were also prepared, where the TiO2 layer was sputtered from TiO2 target.
All films were characterized by the surface photovoltage method using absorption coefficients evaluated from measurement of the optical transmission and reflection. We found that the drift lengths of the charge carriers were shorter than the SCR thickness, which means recombination in this depletion region.
Typically, the thickness of the SCR was higher than that of the bulk and the diffusion length of excitons was ~15 nm.