Since Valasek's discovery of the ferroelectric properties of Rochelle salt nearly 60 years ago, ferroelectricity has been regarded as one of the tradi tional branches of dielectric physics. It has had important applications in lattice dynamics, quantum electronics, and nonlinear optics. The study of electron processes in ferroelectrics was begun with VUL's investigations of the ferroelectric properties of barium titanate [1.1]. In trinsic and extrinsic optical absorption, band structure, conductivity and photoconductivity, carrier mobility. and transport mechanisms were examined in this compound, and in other perovskite ferroelectric semiconductors. An important discovery was that of the highly photosensitive photoconducting ferroelectrics of type AVBVICVIII (e.g. SbSI) by MERZ et al. in 1962 [1.2,3]. A large number of ferroelectric semiconductors (some photosensitive, some not) are now known, including broad-band materials (e.g. lithium niobate, lithium tantalate, barium and strontium niobate, and type-A~B~I compounds), BI and narrow-band semiconductors (e.g. type_AIVB compounds). A series of improper ferroelectric semiconductors and photosensitive ferroelastics have been discovered, of which Sb 0 I is an example. s 7 Owing to the uncertainty of their band structure, the difficulty in deter mining the nature of the levels, the complexity of alloying, and their gen erally low mobility values, ferroelectrics are rarely of interest regarded as nonlinear semiconductors. The most fruitful approach has been the study of the influence of electrons (especially nonequilibrium electrons) and electron excitations on phase transitions and ferroelectric properties. A large group of phenomena have recently been discovered and investigated.

This book covers the recent advances in photovoltaics materials and their innovative applications. Many materials science problems are encountered in understanding existing solar cells and the development of more efficient, less costly, and more stable cells. This important and timely book provides a historical overview, but concentrates primarily on the exciting developments in the last decade. It includes organic and perovskite solar cells, photovoltaics in ferroelectric materials, organic-inorganic hybrid perovskite, materials with improved photovoltaic efficiencies as well as the full range of semiconductor materials for solar-to-electricity conversion, from crystalline silicon and amorphous silicon to cadmium telluride, copper indium gallium sulfide selenides, dye sensitized solar cells, organic solar cells, and environmentally-friendly copper zinc tin sulfide selenides.

Ferroelectric materials, in addition to possessing the unique property of a reversible, spontaneous polarization, exhibit a range of other significant and useful properties. These include high values of piezoelectric, pyroelectric, nonlinear optic, electrooptic, photorefractice and dielectric permittivity coefficients. Another fascinating property of ferroelectric materials is their photovoltaic effect. Photovoltaic effects have been extensively studied in the past in symmetric materials such as silicon. This volume is the first concentrated treatment of the characteristics, theory and potential applications of the photovoltaic effect in noncentrosymmetric materials, which include ferroelectrics and piezoelectrics. The book also deals with the relationship between the photovoltaic and the photorefractive effects. The latter has already been well-studied and is finding many applications in optical processing and computing. This volume should prove to be an important text as well as a comprehensive reference source for basic and applied researchers working on photovoltaic, photorefractive and other photoeffects in ferroelectrics and related materials.

This book, intended for students, researchers and engineers, is a collection of classic papers on photorefractive nonlinear optics. Included are landmark papers on fundamental photorefractive phenomena, two-wave mixing, four-wave mixing, phase conjugators and resonators, material growth and physics, and applications in image processing, optical storage and optical computing.