The subject of the proposed publication is to study electronic processes in a nonideal heterojunction in order to use this material in a high-quality optical fashion and for X-ray image sensor development. The effects of accumulation and erasure of recorded optical information, as well as a satisfactory consistent theory of phenomena and effects are fully described and discussed in this book. The academic level of this book is advanced: It is for specialists studying photoelectronics, the physics of surfaces and sensorics as well as university professors, lecturers and higher school teachers. It could be used also as a textbook for post-graduate students, Masters of Sciences and undergraduates. This contribution describes properties, characteristics and formation processes for nonideal heterojunction structures based on micro- and nano-crystalline thin-film semiconductors applied for optical sensors. The experimental studies concerning the nature of the conductivity features of the nonideal heterojunctions are described in detail. A new model of tunnel-hopping transport over local centers in the space-charge region of heterojunctions with a continuously changing barrier potential is developed and experimentally tested. The characteristic density and morphology of defects at the boundary and in the space charge region of a nonideal heterojunction are calculated. A comprehensive model for the recombination of carriers moving along localized states at the recombination centers of the heteroborder is created. For the first time, the nature of the photosensitivity features of the nonideal heterojunction, associated with the presence of deep centers in the space charge region and their charge exchange under conditions of photoexcitation is described. A prototype of an optical and X-ray image sensor, the equipment and software for reading and visualizing recorded information are analyzed.