Semiconductor heterostructures composed of 2D transition metal dichalcogenides (TMDCs) are of considerable interest for fundamental studies and potential applications in atomically thin electronic and optoelectronic devices. [1][2][3][4][5][6][7][8][9] The studies to date have been largely limited to mechanical exfoliation and restacking approach, [10][11][12][13][14][15] with limited yield and scalability for practical device development. To move the field to the next level and enable scalable device integration, much effort has been devoted to developing robust synthetic strategies for scalable synthesis of 2D heterostructures with tailored configuration. In particular, considerable success has been achieved in the synthesis of complex 2D lateral heterostructures and superlattices. [16][17][18][19][20] On the other hand, although a number of TMDCs vertical heterostructures have been reported, [21][22][23][24][25][26][27][28][29][30] the general synthesis of high-quality vertical heterostructures remains a significant challenge due to the difficulties in initiating and controlling nucleation of a new atomic layer on the dangling bond free basal plane of 2D TMDCs. The current synthetic approach generally relies on incidental nucleation or the high-temperature-induced defects in the basal plane, which is difficult to control, only applicable to specific material combinations, and usually produces heterostructures with rich defects, interlayer diffusion/alloying, and a poor control of layer thickness and heterostructure interface, due to the unavoidable atomic substitution [30][31][32][33] and thermal decomposition of the existing TMDCs templates. [10] To our knowledge, the rational growth mechanism and universal growth strategy have never been proposed to be widely applied in the family of 2D TMDCs heterostructures.With density functional theory (DFT) calculations, we provide an in-depth understanding toward the growth mechanism of TMDCs vertical heterostructures in the aspect of nucleation and kinetics. It reveals that active clusters with high diffusion barrier will induce the nucleation on top of TMDC templates to realize vertical heterostructure. In our experiment, through rational control of the metal/chalcogenide ratio in vapor precursors, we realize the effective manipulation of the diffusion The rational control of the nucleation and growth kinetics to enable the growth of 2D vertical heterostructure remains a great challenge. Here, an in-depth study is provided toward understanding the growth mechanism of transition metal dichalcogenides (TMDCs) vertical heterostructures in terms of the nucleation and kinetics, where active clusters with a high diffusion barrier will induce the nucleation on top of the TMDC templates to realize vertical heterostructures. Based on this mechanism, in the experiment, through rational control of the metal/chalcogenide ratio in the vapor precursors, effective manipulation of the diffusion barrier of the active clusters and precise control of the heteroepitaxy direction are rea...

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The stability of hybrid lead iodine perovskite in a humid environment has been a major obstacle to developing long-term photovoltaic devices. However, understanding the detailed degradation mechanism of lead iodine perovskite in moisture is still challenging. Herein, using first-principles calculations, we show that embedded water molecules will facilitate the decomposition of lead iodine perovskite. Alloying FAPbI and CsPbI to form mixed-cation lead iodine perovskites not only can optimize the tolerance factor to obtain better phase stability, but also can improve the moisture stability of them. With the accumulation of water molecules in the perovskite lattice, the optical absorption spectra show a blue-shift and decreased intensity, and the moisture stabilities of lead iodine perovskites are further lowered. The iodine vacancy in lead iodine perovskites can facilitate the water molecule migration and thus is a disadvantage in improving the moisture stability of them, which should be minimized during perovskite growth. These findings provide new insight in understanding the poor moisture stability of lead iodine perovskites, which should be helpful for the future design and optimization of stable perovskite solar cells.

All-inorganic perovskites have gained considerable significance. Despite their superior thermal robustness, poor phase stability has rendered inorganic perovskites adverse. Herein, on the basis of first-principles calculations, we find that the incorporation of rubidium (Rb) and potassium (K) in an appropriate ratio will stabilize CsPbI2Br perovskites considerably, in which the cooperative interactions between Rb/K, I and Br play an important role. Besides, it is verified that 2D orthorhombic CsPbI3 with a thickness of ∼1 nm exhibits outstanding stability, even exceeding the non-perovskite, yellow structure and has a suitable band gap for solar cell applications.