In situTEM imaging reveals the dynamics of micelle formation and nanoparticle encapsulation.

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 MoSi2N4 and WSi2N4 monolayers provides a compelling material platform for developing high‐performance ultrathin excitonic solar cells and photonics devices. Using first‐principle calculations, 51 types of MoSi2N4 and WSi2N4‐based [(Mo,W)Si2N4] vdWHs composed of various metallic, semimetallic, semiconducting, insulating, and topological 2D materials are constructed and classified. Intriguingly, MoSi2N4/(InSe, WSe2) 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)Si2N4 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)Si2N4/α2‐(Mo,W)Ge2P4 vdWHs. The findings unravel the enormous potential of (Mo,W)Si2N4 vdWHs in designing ultimately compact excitonic solar cell device technology.

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van der Waals Heterostructures MoSi2N4 and WSi2N4 monolayers have recently emerged as promising 2D semiconductors for solid‐state device applications. In article number 2201856 by Guangzhao Wang, Yee Sin Ang, and colleagues, 51 species of MoSi2N4‐and WSi2N4‐based van der Waals heterostructures are comprehensively catalogued using first‐principle simulations. These heterostructures are found to exhibit exceptional electronic and optical properties, thus unravelling their enormous potential as building blocks of high‐performance solar cell and UV optoelectronic device technology.