Prediction of 2D XC2N4 (X= Ti, Mo, and W) monolayers with high mobility as an encouraging candidate for photovoltaic devices

Abstract

In this study, the impacts of strain and an electric field on the electronic and optical characteristics of monolayer XC2N4 (X=Ti, Mo, and W) were systematically examined using the density functional theory. The results corroborated that the dynamically, mechanically, and thermodynamically stable XC2N4 monolayers displayed semiconductor properties when the Heyd-Scuseria-Ernzerhof (HSE06) method was used. The TiC2N4 monolayer is shown to be a direct-gap semiconductor of 1.179 eV whereas the MoC2N4 and WC2N4 monolayers are indicated to have indirect bandgaps of 2.819 eV and 2.661 eV, respectively. Notably, the TiC2N4, WC2N4, and MoC2N4 monolayers possess comparatively high electron mobilities of 2776.85 cm2/V s, 1576.79 cm2/V s, and 1316.41 cm2/V s, respectively. The influence of strain on the bandgap of the MoC2N4 and WC2N4 monolayers led to a decrease in their gap, whereas in the TiC2N4 monolayer, the applied tensile strain caused an increase in the bandgap. Moreover, the compressive strain significantly caused a transition from semiconducting to metallic characteristics (zero band gap). The optical absorption spectra indicated the existence of three separate maxima for the XC2N4 (X=Ti, Mo, and W) monolayers with an extreme intensity of up to 2.0 × 105 cm−1. Interestingly, compared with pure monolayers, strained monolayers enhance the beginning of coefficient absorption in the visible range, with widespread range absorption in the ultraviolet and visible regions. Our results suggest that these monolayers can be promising options for nanoelectronic, optical and photovoltaic applications.