Photocurrent action spectra of organic semiconductors

Abstract

Photocurrents are reported for vacuum-deposited pentacene thin films as a function of incident photon energy, applied bias, photon flux, film thickness, and measurement temperature in order to develop a better understanding of the mechanisms underpinning photoinduced charge carrier generation, injection, and transport in molecular semiconductors. Intrinsic photocurrents caused by dissociation of photogenerated hole–electron geminate pairs in the bulk film are observed in the photocurrent action spectra at photon energies above a threshold value of 2.25 eV corresponding to the transport energy gap of the pentacene film, EG. Aluminum electrodes form blocking contacts which substantially reduced extrinsic photocurrents attributed to exciton-enhanced charge injection and transport, enhancing the visibility of the intrinsic processes.