The Photovoltaic Behavior in Organic Compounds

When a contact between a semiconductive material and a metal is made, it is expected that a potential barrier occurs at the boundary layer and the photovoltaic effect which is observed with illumination on this barrier. It has been found that this is the case for organic semiconductors. The photovoltaic cell was made with aromatic compounds sandwiched between two metal layers or metal and stannic oxide. One of them was a terminal electrode and the other, the junction electrode, was made with evaporated film of platinum, gold, silver, tin, lead or alkali metal. All observations of photovoltage were carried out in vacuo or in an atmosphere of insert gas. With the illumination of white light from a tungsten lamp, the induced photovoltage varied from several millivolts to one volt, depending on the sorts of metals applied to the junctions. In most of these junctions, the organic solids acted as positive eletrodes with respected to the junction metal. In the alkali metal-aromatics system, a fluctuation was frequently observed concerning the direction of electromotive force, but the value of photovoltage was generally much higher than in the case of the other metals; thus the spectral response of the voltage was measurable. This response was less dependent on the sorts of organic solids but dependent on the sorts of metals. On the other hand, the spectral response in the junction between organic solid and stannic oxide, was a curve which is in good coincidence with the optical absorption curve for solid organics.