Cataloguing MoSi₂N₄ and WSi₂N₄ van der Waals Heterostructures: An Exceptional Material Platform for Excitonic Solar Cell Applications

Abstract

Abstract 2D materials van der Waals heterostructures (vdWHs) provide a revolutionary route toward high‐performance solar energy conversion devices beyond the conventional silicon‐based pn junction solar cells. Despite tremendous research progress accomplished in recent years, the searches of vdWHs with exceptional excitonic solar cell conversion efficiency and optical properties remain an open theoretical and experimental quest. Here, this study shows that the vdWH family composed of MoSi 2 N 4 and WSi 2 N 4 monolayers provides a compelling material platform for developing high‐performance ultrathin excitonic solar cells and photonics devices. Using first‐principle calculations, 51 types of MoSi 2 N 4 and WSi 2 N 4 ‐based [(Mo,W)Si 2 N 4 ] vdWHs composed of various metallic, semimetallic, semiconducting, insulating, and topological 2D materials are constructed and classified. Intriguingly, MoSi 2 N 4 /(InSe, WSe 2 ) are identified as Type II vdWHs with exceptional excitonic solar cell power conversion efficiency reaching well over 20%, which are competitive to state‐of‐the‐art silicon solar cells. The (Mo,W)Si 2 N 4 vdWH family exhibits strong optical absorption in both the visible and UV regimes. Exceedingly large peak UV absorptions over 40%, approaching the maximum absorption limit of a freestanding 2D material, can be achieved in (Mo,W)Si 2 N 4 /α 2 ‐(Mo,W)Ge 2 P 4 vdWHs. The findings unravel the enormous potential of (Mo,W)Si 2 N 4 vdWHs in designing ultimately compact excitonic solar cell device technology.