Comparison of the effect of C doping on the photovoltaic properties of the defect state transition metal sulfur compounds MX2 (M=Mo, W; X=S, Te): a first-principles study

Two-dimensional layered materials are widely used due to their favorable electrical and optical properties. In this paper, the electronic structure, DOS, charge transfer, and optical properties of the defect state C-MX 2 system of transition state metal-sulfur compounds are investigated using first-principle calculations. The electronic structure, DOS, charge transfer and optical properties of three systems, MoS 2 , MoTe 2 and WS 2 , are systematically compared and analyzed. The results show that MoS 2 , MoTe 2 , and WS 2 are all direct band-gap semiconductors. After the occurrence of vacancy defects, MoTe 2 and WS 2 are transformed from direct band-gap to indirect band-gap, while MoS 2 still maintains the direct band-gap. We chose C atoms to dope the defective state MX 2 system. After doping with a low concentration of C atoms, the Fermi energy level decreases, the valence band shifts upward, and the system undergoes a semiconductor-to-metal transition. In terms of density of states, the Mo-d and W-d orbitals as well as the S-p and Te-p orbitals are gradually enhanced under the effect of defect states and C doping, with the contribution of MoTe 2 > MoS 2 > WS 2 . In terms of optical properties, the absorption and reflection peaks of all three systems are blue-shifted after the change of defect states and C doping.