Photovoltaics (PV) is a promising green and sustainable energy source. Nitride-based materials offer distinct optoelectronic properties with potential to replace conventional materials in next-generation PV devices. Their properties enhance efficiency in III-nitride semiconductors, including InN, GaN, AlN, and their alloys. This chapter provides an overview of research on III-nitride and g-C3N4-based solar cells, covering cell structures, findings, and performance in different environments. © 2024 Elsevier B.V., All rights reserved.