Hierarchical Nanoscale Structuring of Solution-Processed 2D van der Waals Networks for Wafer-Scale, Stretchable Electronics.

Two-dimensional (2D) semiconductors are promising for next-generation electronics that are lightweight, flexible, and stretchable. Achieving stretchability with suppressed crack formation, however, is still difficult without introducing lithographically etched micropatterns, which significantly reduces active device areas. Herein, we report a solution-based hierarchical structuring to create stretchable semiconducting films that are continuous over wafer-scale areas via self-assembly of two-dimensional nanosheets. Electrochemically exfoliated MoS 2 nanosheets with large lateral sizes (∼1 μm) are first assembled into a uniform film on a prestrained thermoplastic substrate, followed by strain relief of the substrate to create nanoscale wrinkles. Subsequent strain-relief cycles with the presence of soluble polymer films produce hierarchical wrinkles with multigenerational structures. Stretchable MoS 2 films are then realized by curing an elastomer directly on the wrinkled surface and dissolving the thermoplastic. Three-generation hierarchical MoS 2 wrinkles are resistant to cracking up to nearly 100% substrate stretching and achieve drastically enhanced photoresponsivity compared to the flat counterpart over the visible and NIR regimes, while the flat MoS 2 film is beneficial in creating strain sensors because of its strain-dependent electrical response.