This book focuses on the essential scientific ideas and breakthroughs in the last three decades for organic solar cells that have realized practical applications. The motivation for publishing this book is to explain how those essential ideas have arisen and to provide a foundation for future progress by target readersstudents, novices in the field, and scientists with expertise. The main topics covered in the book include the fundamental principles and history of organic solar cells, blended junction, nanostructure control, photocurrent generation, photovoltage generation, doping, practical organic solar cells, and possible ideas for the future. The editors enthusiastically anticipate the vigorous development of the field of organic solar cells by young scientists of the next generation.

Masahiro Hiramoto received his Ph.D. in Chemistry from Osaka University in 1986. He started the research on organic semiconductors and organic solar cells in 1988 in Graduate School of Engineering, Osaka University. He joined the Institute for Molecular Science in 2008 as a Professor. He has published over 140 papers. His research interests include the photoelectric properties of organic semiconductors and organic single crystals, especially doping effects and their application to organic solar cells. He is an inventor of the blended junction and tandem junction for organic solar cells. He won the Fellow Award from Japan Society of Applied Physics.
Seiichiro Izawa is an Assistant Professor in the Institute for Molecular Science, Japan, since 2016. He received his Ph.D. from the University of Tokyo in 2015 and worked at RIKEN in Japan and University of California, Santa Barbara, as a Postdoctoral Fellow from Japan Society for the Promotion of Science. His research interests are effects of nanostructure and chemical structure on optoelectronic properties in organic semiconductors, doping mechanism and utilizing doping for organic electronic devices, especially for organic photovoltaics.

1. Principle and History.- 2. Blended Junction.- 3. Nanostructure control.- 4. Realization of 10 m-thick organic solar cells.- 5. Polymer solar cells.- 6. Carrier generation mechanism.- 7. Doping effects.- 8. Open-circuit voltage.- 9.  Practical Application.- 10. Future Perspective.