Organic Photosensor in Elgraphy (II): Photoinduced Current Amplifying Layer

摘要

The authors are actively involved in the development of Elgraphy: a novel image acquiring system that combines electrophotography and liquid crystal technology The organic photosensor used in Elgraphy (Elgraphic photosensor) exhibits enhanced hole injection induced by a negative space charge trapped at the electrode/photoconductive layer interface, thus giving rise to photo- current amplification. A new type of photosensor that contains a PICAL (Photoinduced Current Amplifying Layer) between the transparent electrode and the CGL was fabricated. This three layer sensor was found to exhibit significantly larger photocurrent amplification than two layer sensors, that is, the dark current was smaller and the photocurrent was larger in the steady state when the proper voltage was applied. An investigation into how the resistivity of the PICAL and CGL affect the dark current and photocurrent of the three layer photosensor revealed the mechanism involved. The transient variation in the electric field across the PICAL promotes the injection of holes from the electrode, thus enhancing photocurrent amplification. In areas of the sensor that are not exposed to light, the larger resistance of the CGL reduces the voltage across the PICAL, suppressing hole injection from the electrode. In contrast, in areas that are exposed to light, the resistance of the CGL is smaller and the voltage across the PICAL is larger, thus enhancing hole injection.