Wafer-scale 2D PtTe₂ layers-enabled Kirigami heaters with superior mechanical stretchability and electro-thermal responsiveness

With increasing interests in emergent wearable technologies such as e-skin healthcare devices, it is essential to develop new materials that can satisfy their demanded attributes; e.g., mechanical strain-invariant electrical and thermal properties. In this regard, two-dimensional (2D) transition metal dichalcogenide (TMD) layered materials have received tremendous attention owing to their intrinsic suitability, such as large tolerance limits under mechanical deformation coupled with decent electrical and thermal properties. However, these intrinsic advantages are often compromised upon their large wafer-scale integrations onto deformable substrates, which is commonly observed with conventional liquid-based or mechanical exfoliation approaches. In this paper, we demonstrate high-performance electrically-stretchable heaters by combining 2D platinum ditelluride (PtTe₂) layers – a relatively unexplored class of 2D TMDs – with a strain engineering design scheme. We directly grew wafer-scale 2D PtTe₂ layers on soft polyimide (PI) substrates by taking advantage of their low growth temperature. We verified their intrinsically low sheet resistance as low as 19.4 Ω/□ (thus, high electrical conductivity), which is superior to most other 2D TMDs. We then explored their Joule heating efficiencies and demonstrated they greatly surpass the performances of previously explored flexible heaters employing state-of-the-art nanomaterials including graphene, silver nanowires (Ag NWs), carbon nanotubes (CNTs) and their hybrids. By employing Kirigami patterning approaches for judicious strain engineering, we developed high-efficiency skin attachable 2D PtTe₂ layers-based Kirigami heaters, which exhibited nearly strain-invariant excellent electrical-thermal properties; e.g., voltage-driven reliable heat generation upon a cyclic application/termination of 70% tensile stretch for 1000 times. We believe this study on intrinsically metallic 2D layered material will open up new venues for futuristic high-performance large-scale stretchable electronic applications of wearable thermotherapy, e-textile, and soft actuators.