Absorption spectra of organic semiconductors in IR-range measured by constant photocurrent method

Abstract

Constant photocurrent method has been used to study spectral dependence of the absorption coefficient in copper phthalocyanine thin films formed by the molecules with different peripheral groups. Spectral dependence of the absorption coefficient reveals exponential growth in the energy range 1.4–1.6eV and a series of three bands in the energy below 1.4eV. The maximum observed at 1.12eV is attributed to optical transition from ground state S0 to excited triplet state T1 of a molecule. This transition results in creation of triplet excitons. The correspondence between photoluminescence and absorption spectra measured by constant photocurrent method both with respect to peak positions and relative intensities has been found.