For the ultrathin two-dimensional (2D) materials and lateral heterojunction, the formation of unstable but elastic ripples is commonly observed but is rarely studied, especially their correlations with different material properties. To fill the knowledge gap in this field, this work systematically explores transition metal dichalcogenides (TMDCs) in a single component and lateral heterojunction with a series of ripple structures. The ripple formation energy is quantitatively classified into the initial elastic strain stage and fracture threshold stage based on Fermi-like distribution. Electronic structures reveal that the formation of ripples is accompanied by electron accumulations from flat surfaces to ripples. By comparing the unilateral, decaying, and bilateral ripples in 2D lateral heterojunction, we confirm that Fermi-like distribution is still valid regardless of the shape of the ripples, where the thermodynamic and electronic properties are modulated by ripples-induced uneven strain. The main features of optical properties are not affected while the sensitivity to ripple-induced strains is distinguished. More importantly, the phonon properties further demonstrate the potential of ripples in promoting thermal conductivity, which are strongly correlated with the optical branch of anion vibrations. This work provides important theoretical guidance for the design and optimization of high-performance optoelectronic devices based on TMDC heterojunctions.

During the development of ultrathin two-dimensional (2D) materials, the appearance of ripples has been widely observed. However, the formation mechanisms and their influences are still rarely investigated, especially their contributions to the electronic structures and optical properties. To compensate for the knowledge gap, we have carried out comprehensive theoretical studies on the monolayer WSe₂ with a series of ripple structures from 0 to 12 Å in different lattice sizes. The sensitivity of the formation energy, band structures, electronic structures, and optical properties to the ripple structures have been performed systematically for the first time. The formation of ripples in Armchair and zigzag simultaneously are more energetically favorable, leading to more flexible optimizations of the optoelectronic properties. The improved charge-locking effect and extension of absorption ranges indicate the significant role of ripple structures. The spontaneous formation of ripples is associated with orbital rearrangements and structural distortions. This leads to the unique charge carrier correlate inversion between W-5d and Se-4p orbitals, resulting in the pinning of the Fermi level. This work has supplied significant references to understand ultrathin 2D structures and benefit their future developments and applications in high-performance optoelectronic devices.