Modulating Carrier Density and Transport Properties of MoS₂ by Organic Molecular Doping and Defect Engineering

Using first-principles calculations, we investigate the effect of molecular doping and sulfur vacancy on the electronic properties and charge modulation of monolayer MoS₂. It is found that tetrathiafulvalene and dimethyl-p-phenylenediamine molecules are effective donors, whereas tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) are effective acceptors, and all these molecules are able to shift the work function of MoS₂. For MoS₂ containing sulfur vacancies, these molecules are able to change the position of the defect levels within the band gap and modulate the carrier density around the defect center. Charge transfer analysis shows that TCNE and TCNQ induce a free-carrier depletion of the defect states, which is beneficial for the suppression of the nonradiative trionic decay and a higher excitonic efficiency due to a decrease in the screening of excitons. Furthermore, the effects of molecular adsorption on Seebeck coefficient of MoS₂ are also explored. Our work suggests that an enhanced excitonic efficiency of MoS₂ may be achieved via proper defect engineering and molecular doping arising from the charge density modulation and charge screening.