Electronic energy states of certain sensitizers and dielectrics

Abstract— The electron affinities and ionization potentials of amorphous sulfur, vitreous selenium and several phthalocyanines were measured by Nelson's electron beam retardation method and photoelectric emission, respectively. The electron affinities (A_c) measured were: 4.5 eV for sulfur, 3.4eV for selenium, and approximately 4.3 eV for all the phthalocyanines measured. Photoemission thresholds (I_c) were 7.0 eV for sulfur and 6.0 eV for selenium. Two photoionization thresholds (at about 5.2 and 6.1 eV) were found for both α-copper and α-metal-free phthalocyanine; the former is attributed to impurity levels, the latter to bulk states. In each case, the band gap calculated from I_c and A_c was found to be approximately equal to the optical threshold for photoconductivity.