W 4 PCl 11 monolayer: an unexplored 2D material with moderate direct bandgap and strong visible-light absorption for highly efficient solar cells.

The discovery of novel two-dimensional (2D) materials with excellent electronic and optoelectronic properties have attracted much scientific attention. Based on the first-principles calculations, we predict an unexplored 2D W 4 PCl 11 monolayer, which is potentially strippable from its bulk counterpart with the exfoliation energy of only 0.16 J m -2 . The dynamical, thermal, and mechanical stabilities have also been confirmed. Remarkably, W 4 PCl 11 monolayer is direct semiconductor with a bandgap of 1.25 eV, which endows the monolayer with very strong visible-light absorption in the magnitude of 10 5 cm -1 . Meanwhile, the calculated carrier mobilities of W 4 PCl 11 monolayer can reach to 10 3 cm 2 V -1 s -1 . Considering the moderate direct bandgap and high carrier mobility, W 4 PCl 11 monolayer should be a superior candidate for the donor material of excitonic solar cells. The estimated power conversion efficiency of the fabricated W 4 PCl 11 /Bi 2 WO 6 heterojunction reaches as high as 21.64%, which much superior to those of most recently reported 2D heterojunction. All these outstanding properties accompanied with its experimental feasibility endows W 4 PCl 11 monolayer with promising photovoltaic applications.