Strong excitonic effects in the optical properties of graphitic carbon nitride g-C3N4 from first principles

Graphitic carbon nitride (g-C3N4) has recently triggered extensive investigations due to its potential applications, such as in direct photochemical water splitting, CO2 activation, and transition-metal-free spintronics. However, electronic, and particularly the optical properties of g-C3N4 still have not been well established. Based on one of the state-of-the-art approaches-many-body Green's function theory (i.e., GW + BSE)-absorption of ultraviolet light by g-C3N4 is found to be determined by strong excitonic effects with a significantly large binding energy assigned to the bound excitons. Dark states have also been found in g-C3N4, which can affect the photoluminescence yield of g-C3N4. We find that the band gap of g-C3N4 probably can be tuned by adjusting the condensation (dimensionality) to initiate excitonic absorption in the visible light region, which might help improve the solar energy conversion efficiency. DOI: 10.1103/PhysRevB.87.085202