High-Resolution Multicolor Transfer Printing of Perovskite Nanocrystals for Ultrathin Skin-Attachable Displays.

Over the past decade, the development of wearable displays with ultrahigh definition has garnered considerable attention in the information technology. Wearable displays exhibit mechanical deformability, allowing them to conformally attach to various objects with curvilinear surfaces. Technological advances to achieve deformable form factors enable mechanical changes such as bending, rolling, and twisting. In parallel to the advanced at form factors, high-definition red/green/blue (RGB) subpixels are crucial for visualizing diverse information on the compact screens of wearable displays. Despite the recent advancements in display technology, the development of high-definition full-color wearable light-emitting diodes (LEDs) remain an unresolved problem.<br/>Metal halide perovskite have gained attention as promising light-emitting substances due to their narrow full-width half-maximum, high photoluminescence, and color tunability. Furthermore, the extremely thin construction of perovskite light-emitting diode (PeLEDs) (&lt;1 μm, excluding the thickness of the substrate) make them highly promising for candidates for application to ultrathin and deformable displays. With recent advances in synthesis and device engineering, progress in this field has led to impressive external quantum efficiency (EQE) values, with red, green, and blue PeLEDs achieving 25.8%, 28.9%, and 18%, respectively. Most previous studies predominantly centered on optimizing PeLED performance via monochromatic perovskite nanocrystal (PeNC) films produced by spin-coating techniques. However, manufacturing full-color displays on the commercial scale requires the development of patterning methods to ensure the seamless integration of RGB subpixels within electroluminescent (EL) devices.<br/>Conceptually, the RGB patterning of PeNCs have several requirements : 1) Preservation of device layer integrity and no contamination during the patterning process 2) high reproducibility and 3) high-resolution patterning capabilities, particularly at the sub-micrometer scale. Unfortunately, conventional patterning methods (e.g., photolithography and inkjet printing) of perovskite materials are unsuitable for the fabrication of highly efficient PeLEDs. Photolithography suffer from the degradation of perovskite materials by ultraviolet(UV) light , moisture and polar solvents, owing to their ionic bonding nature. Ink jet printing is applicable to multicolor pixelation of PeNCs through additive patterning. However, the additives (i.e., polymer matrix, surfactant, and viscosity modifier) suppress the EL device performance. Dry transfer printing employing a viscoelastic stamp represents a strategic choice for producing high-definition PeNC pixels for EL devices. This method circumvents the use of wet chemicals, mitigating concerns about solvent compatibility and cross-contamination between different colored pixels. Nonetheless, this approach has seen limited application in the case of PeNCs. The low interaction energy among PeNCs can lead to internal film cracking during the transfer process<br/>Here, we demonstrate high-resolution dry transfer printing for ultrathin wearable displays. Specifically, we employ a simple and effective double-layer transfer printing method with an additional organic layer between PeNCs and a poly(dimethylsiloxane) (PDMS) stamp. The organic layer serves to prevent internal cracks in the transferred PeNCs layer. Furthermore, the pressure applied during the transfer printing process reduces the interparticle distance in the transfer-printed PeNCs layer, enabling the highly efficient PeLEDs, which exhibit peak EQE of 15.3%, 14.8%, and 2.5% for red, green, and blue PeLEDs, respectively. Finally, we demonstrate ultrathin, skin-attachable PeLEDs based on this patterning method. The realization of high-resolution RGB patterns using double-layer transfer printing may open up unique opportunities for wearable displays with various form factors.