This book presents the state-of-the-art in the field of organic semiconductors for sustainable energy conversion into electricity, including optoelectronics and thermoelectrics. It firstly discusses important classes of solution-processable organic semiconductors, followed by the fundamental background of photophysics and phononics in these materials. Then the book introduces the device applications of organic semiconductors in optoelectronics and thermoelectrics, and the integration of these two types of devices. This book is the first to connect the research areas of optoelectronics and thermoelectrics.