Excitonic stimulation of current flowing along thin tetracene layer

The photocurrent stimulated by excitons in tetracene layers was investigated. Mechanism of the stimulation follows from triplet exciton—trapped charge carrier interaction. The measurements were made on tetracene films evaporated onto glass substrate in vacuum. The samples were equipped with gold electrodes, deposited in planar configuration, directly on the glass substrate (bottom contacts) or on the top (non-substrate side) of the organic layer (top contact). Both types of samples were illuminated by monochromatic light directed perpendicularly to the surface, either from substrate or non-substrate side of examined layers. It was shown that the current-wavelength characteristics obtained under illumination onto the non-substrate side are reversely proportional to the absorption coefficient, while in case of illumination onto the substrate side of the sample the dependence on the absorption coefficient is proportional. The phenomena follows from different efficiency of charge carrier detrapping by excitons from substrate and non-substrate side.