Photo-Enhanced Electron Emmision from Alkali Metal Contacts into Anthracene

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Abstract
Dark- and photo-current measurements are used to study trap characteristics and optical de-trapping processes in anthracene samples provided with alkali and alkaline-earth metal contacts. The spectral response of the photocurrent yield in the entire photon-energy range studied (0.95–3.4 eV) originates from optical excitation of electrons from a single discrete set of traps which is continuously filled by electron injection from the active metal contact. The traps are 0.95 eV deep and are present with a density of about 1013 cm−3. De-trapping appears to occur by direct photoexcitation into the conduction band at long wavelengths and by interaction of occupied traps with triplet and singlet excitons at shorter wavelengths. The spectral yield curve exhibits considerable structure which can be advantageously used to study the various electronic-vibronic states in anthracene.