The world of today must face up to two contradictory energy problems: on the one hand, there is the sharply growing consumer demand in countries such as China and India. On the other hand, natural resources are dwindling. Moreover, many of those countries which still possess substantial gas and oil supplies are politically unstable. As a result, renewable natural energy sources have received great attention. Among these, solar-cell technology is one of the most promising candidates. However, there still remains the problem of the manufacturing costs of such cells. Many attempts have been made to reduce the production costs of "conventional" solar cells (manufactured from monocrystalline silicon using diffusion methods) by instead using cheaper grades of silicon, and simpler pn-junction fabrication. That is the 'hero' of this book; the heterojunction solar cell.The book is aimed at two disparate groups of readers. Firstly, it is aimed at researchers and developers in communication and power electronics who already have a good working knowledge of the field of semiconductors. This concise account has been devised precisely to meet the demands of fast-paced technologies such as these. Secondly, it also satisfies the requirements of students and any other beginners in photovoltaics in that it provides an overview of the current state-of-the art.