Photoconductivity in Thin Organic Films

Abstract

Organic films of approximately 1µ thickness were prepared by glow‐discharge polymerization of monomers containing nitrogen, sulfur, selenium, and certain metals and tested for photosensitivity. Conductivities (in the dark ranging from 10−17 to 10−13 mho/cm at room temperature) were enhanced by as much as three orders of magnitude by 10 w/in.2 of white light excitation. Nitrile groups and sulfur appeared most promising as chemical substituents in the polymer films for promoting conductivity to useful levels. Addition of traces of iodine to the discharge during the deposition of a polynaphthalene film increased its dark and photoconductivity over a thousandfold. Activation energies of photoconduction of the order of 0.25 ev were found (25°–175°C). Short‐circuit photocurrents of consistent polarity in all films were observed and attributed to a photovoltaic effect at the interface between the film and the transparent electrode.