Tunable optoelectronic properties of C3N monolayers via correlation, strain, and doping

• A combined tight-binding, Hubbard model, and Green’s function approach is applied to study the C 3 N monolayer. • The influence of on-site Coulomb repulsion, strain, and electron doping on the electronic and optical properties is analyzed. • Results reveal that the C 3 N monolayer exhibits semi-metallic and nearly opaque optical behavior with minimal transmittance. • Electron doping shifts the main optical conductivity peak to higher photon energies and reduces its intensity. • Findings suggest potential applications of C 3 N in reflective coatings and tunable optoelectronic devices. Two-dimensional (2D) materials with engineered electronic correlations are emerging as versatile platforms for next-generation optoelectronics. Here we present a comprehensive theoretical investigation of the electronic and optical properties of a C 3 N monolayer using a tight-binding framework combined with the Hubbard Hamiltonian and Green’s function formalism. We show that electron–electron interactions, mechanical strain, and carrier doping act as powerful tuning parameters that reshape the optical response. Coulomb correlations drive notable modifications in the density of states (DOS), giving rise to semi-metallic behavior under specific regimes. Optical conductivity calculations reveal a prominent absorption feature near 4 eV, which undergoes systematic blue shifts and intensity modulation upon electron doping, reflecting Fermi-level–controlled interband transitions. External strain further tailors both the spectral position and strength of optical excitations, establishing strain engineering as an effective control knob. Transmission and reflectivity spectra indicate broadband opacity of C 3 N, underscoring its potential for reflective coatings and nanoscale energy-control applications. Our results provide fundamental insights into the interplay of correlations, strain, and doping in 2D C 3 N, and establish design principles for tailoring its optoelectronic functionality in advanced device technologies.