We report on Photocurrent (PC) and optical absorption spectroscopy analyses of the electronic density of states (DOS) distribution around the band-edge of pentacene films of different thickness (from 50 to 300 nm). Both experimental methods allowed us to independently monitor the increase with increasing film thickness of the Davydov splitting of the first absorption band, correlated with modifications in the film molecular structure and packing when passing from a dominant “thin film” to a dominant “bulk” phase. We show how PC spectroscopy has the remarkable ability to detect the modification of the DOS distribution in a noninvasive way, thus allowing the study of fully operational organic thin film transistors.
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