Advances in large‐area and high‐quality 2D transition metal dichalcogenides (TMDCs) growth are essential for semiconductor applications. Here, the gas‐phase alkali metal‐assisted metal‐organic chemical vapor deposition (GAA‐MOCVD) of 2D TMDCs is reported. It is determined that sodium propionate (SP) is an ideal gas‐phase alkali‐metal additive for nucleation control in the MOCVD of 2D TMDCs. The grain size of MoS2 in the GAA‐MOCVD process is larger than that in the conventional MOCVD process. This method can be applied to the growth of various TMDCs (MoS2, MoSe2, WSe2, and WSe2) and the generation of large‐scale continuous films. Furthermore, the growth behaviors of MoS2 under different SP and oxygen injection time conditions are systematically investigated to determine the effects of SP and oxygen on nucleation control in the GAA‐MOCVD process. It is found that the combination of SP and oxygen increases the grain size and nucleation suppression of MoS2. Thus, the GAA‐MOCVD with a precise and controllable supply of a gas‐phase alkali metal and oxygen allows achievement of optimum growth conditions that maximizes the grain size of MoS2. It is expected that GAA‐MOCVD can provide a way for batch fabrication of large‐scale atomically thin electronic devices based on 2D semiconductors.

Summary Two-dimensional (2D) organic-inorganic halide perovskites (OIHPs) with an alternating stacked structure of an organic layer and an inorganic layer draw significant attention for photovoltaics, multiple quantum-well, and passivation of three-dimensional perovskites. Although the low-cost and simple spin-coating process of these materials offers a vast platform to study fundamental properties and help them achieve rapid progress in electronics and optoelectronics, chemical vapor deposition (CVD) growth is also necessary for large-area, epitaxial, selective, and conformal growth. Here, one-step CVD strategies for 2D OIHP growth are proposed, and the growth trends depending on the precursor and substrate conditions are discussed. We report a CVD-grown nontoxic, lead-free 2D tin-OIHP flake to show the system offering a universal route to synthesize perovskite crystals based on arbitrary organic and inorganic components.