Morphology, Structure and Photophysics of Thin Films of Perylene-3,4,9,10-Tetracarboxylic Dianhydride

The influence of the growth conditions on the properties of PTCDA thin films deposited by organic molecular beam deposition on glass substrates is presented. Powder X-ray diffraction studies show that only the α polymorph is formed, regardless of the growth conditions. By contrast, the film morphology depends specifically upon the deposition parameters, the observed crystal size increasing with growth temperature or after post-growth annealing. The spectroscopic properties (electronic absorption, fluorescence excitation and emission) are also found to be influenced by heat treatment and these are correlated with the changing crystal size in the PTCDA films. A qualitative model is presented in order to account for the photophysical properties of the films.