This book explores solar energy harvesting using semiconductor-based photocatalysts. It begins by explaining how photocatalysis works through light-induced electron excitation and its applications in solar power generation, water splitting, and pollutant degradation. The book discusses how traditional photocatalysts mainly absorb UV light and how researchers are working to extend activity into the visible spectrum using techniques like metal doping and dye sensitization. It also examines challenges such as charge carrier recombination and nanoparticle aggregation, and how mesoporous structures and better charge separation can improve efficiency. Overall, this book reviews the science and innovations driving more effective solar energy utilization through photocatalysis.