Floating Epitaxy and Stitching Growth of Bilayer Organic Semiconductor Single Crystals on Polymer Dielectric Toward High‐Performance and Ultra‐Flexible Transistors

Bilayer organic semiconductor single crystals (OSSCs) have emerged as a highly promising material platform for the development of flexible organic electronic devices, owing to their exceptional mechanical flexibility and superior charge transport properties. However, in situ growth of bilayer OSSCs on polymer dielectric is greatly hindered by dielectric surface defects and strong molecular interaction between dielectric and organic semiconductor. Here, a floating epitaxy and stitching growth strategy is developed for large-area growth of bilayer OSSCs on polymer dielectric. By exploiting surface-tension-controlled nucleation behaviors of organic molecules, the preferential formation of organic seed crystals is achieved at saturated solution-air interface, thereby eliminating the adverse effects of polymer dielectric on nucleation and growth of OSSCs. Furthermore, the unique stitching growth mode of the crystals during epitaxial process ensures large-area bilayer OSSCs formation. Using this approach, we successfully fabricate sub-centimeter-sized bilayer 2,9-didecyldinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene crystals on polymer dielectric. Notably, organic field-effect transistors (OFETs) based on the crystals retain a high carrier mobility up to 15.1 cm²/Vs even after undergoing 3000 bending cycles at an ultra-small bending radius of 40 µm, outperforming most existing flexible OFETs. This work opens a new avenue for large-area growth of bilayer OSSCs on polymer dielectrics toward high-performance, ultra-flexible transistors.