Photovoltaic (PV) technology, which enables the direct conversion of sunlight into electricity using semiconductors, has evolved from a scientific discovery in the 19th century into a cornerstone of modern clean energy systems. This chapter provides a comprehensive overview of PV technology, beginning with its historical origins and progressing through its basic working principles, technological classifications, applications, advantages, challenges, and recent developments. First-generation crystalline-silicon solar cells continue to dominate the market due to their efficiency and reliability, while second- and third-generation technologies, including thin-film and perovskite solar cells, promise improved flexibility, cost reduction, and integration possibilities. The chapter explores the broad and growing applications of PV systems across residential, commercial, industrial, and space-based sectors. It also critically examines the economic, technical, and environmental challenges that must be addressed for large-scale adoption. Finally, it highlights recent advancements in efficiency, storage integration, and policy support, and looks ahead to future innovations such as building-integrated PVs and artificial intelligence-driven energy systems. Through continuous innovation and global collaboration, PV technology is poised to play a pivotal role in the transition to a sustainable, low-carbon energy future.

This chapter explores the evolution and technological enhancements of bulk heterojunction (BHJ) organic photovoltaic (OPV) devices, highlighting their potential in sustainable energy solutions amid growing global energy demands. BHJ OPV devices, characterized by their blend of donor and acceptor materials, offer a promising approach to enhancing the efficiency of solar energy conversion. We detail the operational mechanisms underlying BHJ OPV devices, including light absorption, exciton diffusion and dissociation, and charge collection, which collectively contribute to their efficiency. The architecture of BHJ OPV devices incorporates various layers, such as the electron transport layer and the hole transport layer (HTL), optimizing the photoactive layer for improved power conversion. By examining recent advancements and the impact of nanostructured morphologies on performance, this study underscores the critical role of materials science in advancing the efficiency and applicability of OPV technologies. The potential of BHJ OPVs to meet future energy requirements is discussed, with a focus on the continuous improvement in device architecture and material properties.