Surface photocurrents in tetracene layers

Abstract

Abstract The surface current stimulated by light in tetracene layers was investigated. The tetracene sample was prepared by evaporation in vacuum on the glass substrate. The sample was equipped with the gold electrodes deposited on the glass or on the top of the tetracene layer. Illumination of the tetracene layers was perpendicular to the flat area. Two methods of illumination were applied—from glass substrate side (S) or from non-substrate side (NS). Photocurrent characteristics as a function of wavelength ( λ ), light intensity ( I 0 ) and voltage ( U ) were measured. We concluded that mechanism of the photocurrent stimulation results from triplet exciton-trapped charge carrier interaction, which leads to detrapping of charge carriers and enhancement of the current. It was shown that current–wavelength characteristics have antibatic behaviour (reverse proportionally to the absorption coefficient) under illumination of non-substrate side, and symbatic (proportionally to the absorption coefficient) under illumination of substrate side of the sample. Based on the experimental results, it is thought that the phenomenon results from non-uniform distribution of the trapping charge carriers in the tetracene layers in perpendicular direction, which leads to non-uniform detrapping of charge carriers by excitons.