Some experiments have been made on the formation of images by a photo-charge process using ZnO and resin mixture as its photosensitive layer. In this development process, the toner particles in the developer liquid are attached to the photosensitive layer by an electric field given by the contact potential difference between the photosensitive layer and counter electrode. Though the magnitude of photovoltage is about 1/1,000 of electrostatic voltage in the conventional electrophotographic process, the optical density of developed images of the former is about 1/2-1/3 of the latter. Such a great difference in voltage development efficiency was found to be due to the difference in the mechanisms of development, which can be attributed to the difference in voltage and charge developments.
Further experiments were made for the improvement of developed image density. It was found that the density of developed images can be increased to that of conventional electrophotographic process by the repetition of development and fixing processes, because the photo-voltage is maintained for the repetition of the processes.

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A double-layered electrophotographic receptor with an extended sensitivity towards near infra-red light is reported. This receptor is consisted of an amorphous chalcogenide layer for carrier generation, which is sand-wiched by two Se layers, and a poly-N-vinylcarbazole layer for carrier transport. The wavelength and electric field dependences of the injection efficiency have been measured using the photoinduced discharge technique. It is found that the excitation energy and the applied electric field as well as the energy level matching play an important role for the photoinjection. The injection efficiency at 800nm was determined to be 4.6× 10^-2 at the field of 5× 10⁵ V/cm.

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