Flexible optoelectronic devices play a crucial role in the field of wearable electronics. However, their potential and development have been hindered by the lack of high-performance, durable, and flexible transparent electrodes. Here, we developed ultrathin Ag mesh electrodes using a direct writing technique by a Chinese brush. Through precise control over the writing process, the printed Ag mesh with an ultrathin thickness of ~ 100 nm and a high width resolution of ~ 20 μm was achieved. The resulted composite electrodes of Norland Optical Adhesive 63 (NOA63)/Ag mesh/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) possess a low sheet resistance of ~ 12 Ω/sq and a high transmittance of ~ 91%. Benefiting from the ultrathin Ag mesh and embedded structure, the composite electrode shows the quite low surface roughness (~ 0.9 nm), along with exceptional mechanical flexibility with a micrometer-scale bending radius. Furthermore, stretchable organic light-emitting devices (OLEDs) based on this composite electrode present an impressive current efficiency of 88.6 cd/A. Significantly, the OLEDs remain 86% initial current efficiency over 1000 bending cycles and maintain 88% initial luminance at the 50% strain. Interestingly, this direct writing technique possesses the remarkable capability to print transparent electrodes on curved or uneven substrate surfaces, expanding its potential for universal applications. This work presents a straightforward and general printing method for constructing high-performance flexible transparent electrodes for various flexible electronics.

All inorganic metal halide perovskite nanocrystals (NCs) have attracted much attention for their outstanding optoelectronic properties, which can be tuned by the composition, surface, size and morphology in nanoscale. Herein, we report the microfluidic synthesis of hollow CsPbBr₃ perovskite NCs through the nanoscale Kirkendall effect. The formation mechanism of the hollow structure (Kirkendall void) controlled by the temperature, flow rate, ratios of precursors and ligands was investigated. Compared with the solid CsPbBr₃ NCs of the same size, the hollow CsPbBr₃ NCs exhibit blue shifts in ultraviolet−visible (UV−vis) absorption and photoluminescence (PL) spectra, and remarkably longer PL average lifetime (~ 98.2 ns). Quantum confinement effect, inner surface induced additional trap states and lattice strain of the hollow CsPbBr₃ NCs were discussed in understanding their unique optoelectronic properties. The hollow CsPbBr₃ NC based photodetector exhibits an outstanding negative photoconductivity (NPC) detectivity of 8.9 × 10¹² Jones. They also show potentials in perovskite NC based photovoltaic and light emitting diodes (LEDs).

The progress of stretchable organic light-emitting devices (OLEDs) has brought about new possibilities for highly functional wearable electronics. However, the efficiency and durability of stretchable OLEDs have been limited by the performance of stretchable transparent electrodes. Here, we proposed an interface engineering strategy that involves anchoring the growth of silver (Ag) atoms with amine-enriched biomaterials for high-quality stretchable transparent electrodes. The strong interactions between the Ag atom and the amine group enable the uniform Ag electrodes at an ultralow thickness of 7 nm, and provide remarkable mechanical flexibility and strain endurance to the Ag electrodes. The distinct effects of different amino acids were investigated, and a deep understanding of their unique contributions to the film formation process was gained. The resulting ultrathin Ag electrodes exhibit outstanding optoelectrical properties (transmittance of ~ 98% and sheet resistance of ~ 8.7 Ω/sq) and excellent stretchability during 500 stretching cycles at 100% strain. Stretchable green phosphorescent OLEDs based on the Ag electrodes have been demonstrated with a current efficiency of up to ~ 70.4 cd/A. Impressively, the devices show excellent stretching stability, retaining ~ 89% of the original luminance and ~ 78% of the original current efficiency after 200 stretching cycles at 100% strain. This work opens up new possibilities for stretchable transparent electrodes, fostering advancements in wearable displays and other innovative flexible devices.