In recent years there has been an increasing interest in syscems which enable the conversion of solar energy into electri calor chemical energy. Many types of systems have been proposed and studied experimenta11y, the fundamentals of which extend from solid state physics to photo- and electrochemistry. For most of the systems considered excitation of an electron by absorption of a photon is fo1lowed by charge separation at an interface. It follows that the different fields involved (photovo1taics, photo electrochemistry, photogalvanics, etc.) have several essential aspects in common. It was the main purpose with the NATO Advanced Study Insti tute held at Gent, Belgium, from August 25 to September 5, 1980, to bring together research workers specializing in one of these fields in order to enab1e them not only to extend their knowledge into their own field but also to promote the interdisciplinary exchange of ideas. The scope of the A.S.I. has been 1imited to systems which have not or have hardly reached the stage of prac tica1 development. As a consequence, no lectures on economica1 aspects of solar energy conversion have been included. The topics covered in this volume are the fundamentals of recombination in solar ce1ls (P. Landsberg), theoretical and experimental aspects of heterojunctions and semiconductor/metal Schottky barriers (J.J. Loferski, W.H. Bloss and W.G. Townsend), photoelectrochemica1 ce11s (H. Gerischer and A.J. Nozik), pho- v PREFACE vi ga1vanic ce11s (W.J. Albery) and fina11y, surfactant assemb1ies (M. Grätzel).

This volume aims at bringing together the results of extensive research done during the last fifteen years on the interfacial photoelectronic properties of the inorganic layered semiconducting materials, mainly in relation to solar energy conversion. Significant contributions have been made both on the fundamental aspects of interface characteristics and on the suitability of the layered materials in photoelectrochemical (semiconductor/electrolyte junctions) and in solid state photovoltaic(Schottky and p-n junctions) cells. New insights into the physical and chemical characteristics of the contact surfaces have been gained and many new applications of these materials have been revealed. In particular, the basal plane surface of the layered materials shows low chemical reactivity and specific electronic behaviour with respect to isotropic solids. In electrochemical systems, the inert nature of these surfaces characterized by saturated chemical bonds has been recognized from studies on charge transfer reactions and catalysis. In addition, studies on the role of the d-band electronic transitions and the dynamics of the photogene rated charge carriers in the relative stability of the photoelectrodes of the transition metal dichalcogenides have deepened the understanding of the interfacial photoreactions. Transition metal layered compounds are also recognized as ideal model compounds for the studies Involving surfaces: photoreactions, adsorption phenomena and catalysis, scanning tunneling microscopy and spectroscopy and epitaxial growth of thin films. Recently, quantum size effects have been investigated in layered semiconductor colloids.

There has been a resurgence of interest in light-induced water splitting as the search for storable carbon neutral energy becomes more urgent. Although the history of the basic idea dates back more than four decades, efficient, economical and stable integrated devices have yet to be realized. In the continuing quest for such devices, the field of photoelectrochemistry is entering a new phase where the extraordinary interdisciplinary of the research and development efforts are opening new avenues. This aspect of current research effort is reflected in the chapters of this book, which encompass present thinking in the various disciplines such as materials science, photo-electrochemistry and interfaces that can contribute to realization of viable solar fuel generators. This book presents a blend of the background science and recent advances in the field of photoelectrochemical water splitting, and includes aspects that point towards medium to long term future realization. The content of the book goes beyond the more traditional approaches to the subject by including topics such as novel excitation energy processes that have only been realized so far in advanced photonics. The comprehensive overview of current activities and development horizons provided by the impressive collection of internationally renowned authors therefore represents a unique reflection of current thinking regarding water splitting by light.

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