Fully Printable and Reconfigurable Hufu‐type Electroluminescent Devices for Visualized Encryption

Abstract Hufu , serving as evidence of imperial authorization in ancient China, comprises two parts in the form of tiger‐shaped tallies that only become effective when matched. Drawing inspiration from the concept of Hufu , a reconfigurable electroluminescent (EL) device is designed by separating conventional integral devices into two parts that contain the EL layer (part A) and the transparent electrode (part B), respectively. The key to realizing such strategy is employing an adhesive and stretchable polymer gel composite as the transparent electrodes for the EL devices. The polymer gel composite facilitates robust yet reversible contact between the EL layer and transparent electrode, enabling high‐performance and stretchable EL devices that can be readily disassembled and reassembled: the EL devices can maintain ≈81% of their initial luminance after 1000 times of repeated disassembly and reassembly. Moreover, the precursor ink of the polymer gel composite is compatible with a wide variety of coating and printing technologies, such as spin‐coating, inkjet printing, dispensing, and brush painting. Importantly, the reconfigurable feature of the devices opens up a new path to encryption display systems, and as a proof‐of‐concept, EL encrypted password, and content‐changeable digital clock are demonstrated.