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 W₄PCl₁₁ 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, W₄PCl₁₁ 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 10⁵ cm^-1. Meanwhile, the calculated carrier mobilities of W₄PCl₁₁ monolayer can reach to 10³ cm² V^-1 s^-1. Considering the moderate direct bandgap and high carrier mobility, W₄PCl₁₁ monolayer should be a superior candidate for the donor material of excitonic solar cells. The estimated power conversion efficiency of the fabricated W₄PCl₁₁/Bi₂WO₆ 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 W₄PCl₁₁ monolayer with promising photovoltaic applications.