Two-Dimensional Direct Semiconductor Boron Monochalcogenide γ-BTe: Room-Temperature Single-Bound Exciton and Novel...

Recently, excitonic solar cells (XSCs) with high photovoltaic performance have raised research interests because of their high power conversion efficiencies (PCEs). Herein, by using first-principles calculations, we predict that γ-BX (X = S, Se, Te) monolayers are direct semiconductors with the band gaps of 2.94, 2.71, and 1.32 eV, respectively, and maintain semiconduction in the broad strain range of 0% ≤ δ ≤ 5%. The moderate direct band gap, high transport property, dramatically high absorption from visible to the ultraviolet region, and extraordinary excitonic behavior of monolayer γ-BTe, render it promising for next-generation optoelectronic and photovoltaic devices. By choosing monolayer GeP₂ as a proper acceptor material, the practical upper limit of PCE for the heterobilayers of γ-BTe/GeP₂ reaches up to 21.76% (22.95% under strain), comparable to typical heterobilayer solar cells, making it a competitive donor material for photovoltaic device applications.