The authors are actively involved in the development of Elgraphy: a novel image acquiring system that combines electrophotography and liquid crystal technology. The intermediate medium for image storage in Elgraphy (image receptor) consists of an organic photosensor layer (Elgraphic photosensor) and a liquid-crystal layer. The Elgraphic photosensor, through which a dark current of several μA/cm2 flows when a voltage of 10 V/μm is applied at room temperature, exhibits marked photocurrent amplification: exposure to light yields a photocurrent greater than the number of photons absorbed. Upon exposure to light, the quantum yield rises very fast and exceeds unity within about 30 msec. The ionization potential of the charge transfer material (CTM) are shown to be related to photocurrent amplification. The state of space charges trapped in the photoconductive layer is probably affected by the diffusion of the CTM into the charge generation layer (CGL). It has been found that several types of deep traps with a trap depth of more than 1 eV play an important role in this phenomenon. The authors propose that these traps capture electrons generated near the electrode/photoconductive layer interface, thus lowering the barrier to hole injection.
D. Aoki, M. Okabe, S. Hikosaka, E. Inoue, "Organic Photosensor in Elgraphy (I): Amplification of Photocurrent and its Mechanism" in Journal of Imaging Science and Technology, 2000, pp 120 - 128, https://doi.org/10.2352/J.ImagingSci.Technol.2000.44.2.art00004