2D polymeric semiconductors particularly graphitic carbon nitride (g-C3N4) is potential material for optoelectronics and solar cells owing to their adjustable characteristics and benefits such as low cost, excellent stability, and absence of metals. 2D g-C3N4 demonstrates exceptional chemical and physical stability, a suitable electronic energy band structure, and commendable semiconductor properties. It is extensively exploited in the domains of interactive innovative research, including photon conversion to electricity. This chapter provides a detailed analysis on g-C3N4 and its modification relevant to certain important applications of photovoltaic technologies, including perovskite solar cells (PSCs), organic photovoltaic cells (OPVs), dye-sensitized solar cells (DSSCs) and a white light-emitting diode (WLED). In addition to this, we have also summarized the mechanisms occurring behind these applications using g-C3N4.