This book covers recent technologies developed for energy harvesting as well as energy storage applications. The book includes the fabrication of optoelectronic devices such as high-efficiency c-Si solar cells, carrier selective c-Si solar cells, quantum dot, and dye-sensitized solar cells, perovskite solar cells, Li-ion batteries, and supercapacitors. Aiming at beginners in the respective areas, the basic principles and mechanism of the optoelectronic phenomena behind every application are detailed in the book. The book offers schematics, tables, graphical representations, and illustrations to enable better understanding. Among the nine chapters, the first four chapters are dedicated to various types of high-efficiency solar cells and the remaining chapters discuss the methods for energy storage such as the fabrication of batteries and supercapacitors. The book is a useful reference for active researchers and academicians working in energy harvesting and energy storage areas.