Host-Guest P₂C₉: A Wide-Band-Gap Two-Dimensional Semiconductor with Appreciable Electron Mobility

Two-dimensional wide-band-gap (2D WBG) semiconductors have attracted considerable interest due to their unique physical properties and potential applications. However, most existing 2D WBG semiconductors suffer from low carrier mobilities, which severely constrain their utility in electronic and optoelectronic devices. Inspired by the ultrahigh mobility arising from the delocalized π-electron network in graphene, we propose a design strategy that reconciles wide band gaps with efficient charge transport by confining π electrons into discrete C₆rings embedded within a fullysp³-hybridized host framework. Following this concept, we successfully predict a P₂C₉monolayer featuring a direct band gap of 2.9 eV. Advanced carrier transport calculations, explicitly incorporating acoustic deformation potential, polar optical phonon, and ionized impurity scattering, yield an electron mobility of ~153 cm²V^-1s^-1at an impurity concentration of 10¹⁰cm^-2. Furthermore, while excitonic calculations reveal a strongly bound exciton with a binding energy of 1.31 eV. These results demonstrate that the P₂C₉monolayer simultaneously achieves a WBG, appreciable mobility and robust excitonic effects, thereby establishing π-bond isolation as the promising strategy for designing 2D WBG semiconductors.