Highly Stretchable and Self‐Deformable Alternating Current Electroluminescent Devices

DOI: 10.1002/adma.201405486 The development of mechanically “robust” EL devices that can confront different demanding mechanical deformations, such as fl exing, folding, twisting, and stretching without incurring damage, is the primary requirement for fabricating selfdeformable EL devices. Reported attempts have demonstrated polymer light-emitting materials for intrinsically stretchable EL devices. [ 3–7,12 ] Different strategies have also been employed by engineering stretchable structures with assembled rigid inorganic light-emitting elements. [ 1,2,13,14 ] The substrates and electrodes of devices can be stretched while the light-emitting elements are kept intact during stretching. Here, a different method has been developed to fabricate an intrinsically stretchable inorganic EL device with both stretchable conductors and light-emitting layers. The elastic EL device could sustain its performance at stretching strains as large as 100% (close to the mechanical failure of the host elastomer). The simplicity of the device fabrication together with its excellent stretchability enabled the integration with actuators, which could drive the elastic EL devices into dynamic shapes. Dielectric elastomer actuators (DEAs) are emerging “smart materials” that can generate mechanical motions with applied electrical fi elds. DEAs have demonstrated extraordinary mechanical actuation performance with area strain reaching beyond 200% on prestrained elastomers; [ 15–17 ] this exceeds most actuators based on other working mechanisms, such as piezoelectric actuators (≈5%), [ 18 ] ionic gel actuators (≈40%), [ 19 ] and natural muscle (≈100%). [ 20 ] With their intrinsic stretchability, ease of minimization, high power density, and low-cost fabrication, DEAs have been applied in many applications such as wearable tactile display devices, [ 21,22 ] highspeed electromechanical transducers, [ 23,24 ] and smart artifi cial muscles [ 20,25 ] etc. In this report, DEAs are demonstrated to be ideal shape display components to integrate with stretchable EL devices. An unprecedented self-deformable EL device is fabricated by the innovative method in this work. A schematic drawing of the stretchable EL device is represented in Figure 1 a. The stretchable EL device was fabricated with a simple all-solution processable method. In brief, AgNW networks were fi rstly spray-coated onto the polydimethylsiloxane (PDMS) substrate, forming the bottom electrode. ZnS:Cu microparticles mixed with liquid PDMS were then spun onto the bottom electrode. ACEL devices have been developed for display or lighting applications for a few decades and have attracted persistent interest for their simple device architecture and low production cost. [ 26–28 ] ZnS:Cu is a widely available ACEL material with well-studied and understood emission behavior. [ 29,30 ] Its emission colors can be easily tuned by using different active dopants or adjusting the dopant concentrations. After crosslinking, the ZnS:Cu/PDMS composite layer harvests the excellent stretchability from the PDMS matrix with sustained functionality of the emissive material. PDMS is quite Emerging soft electronics that are mechanically deformable and malleable are pushing the boundaries of rigid devices. Electroluminescent (EL) devices with good mechanical compliance can benefi t and inspire a plethora of new applications such as deformable and stretchable displays, conformable visual readout on arbitrary shapes, biomedical imaging, and monitoring devices etc. Previous stretchable EL devices have been mainly demonstrated by the research groups of Rogers and co-workers, [ 1,2 ] Pei and co-workers, [ 3–5 ] and Someya and co-workers, [ 6,7 ] either employing intrinsically stretchable materials or stretchable device structures. Challenges in intrinsically stretchable luminescent devices persist in that their emission intensity is signifi cantly reduced under large strains and the device cannot survive large strain cycles, while devices employing stretchable structures meet diffi culties in their complicated fabrication procedures and non-stretchable lightemitting elements. Moreover, all these pioneering works were geared toward developing EL devices with maintained device functionality while being passively deformed by an external force. We hereby report the fabrication of intrinsically stretchable EL devices with alternating current electroluminescent (ACEL) materials via an all-solution processable method. The stretchable EL device showed excellent stability under large strains and could maintain its good performance under large strain cycles. Furthermore, we demonstrate that the stretchable EL devices can be driven to dynamic shapes upon integration with electrical actuators. The novel functionality offers new opportunities and dimensions in soft electronics, which are unreachable with conventional technologies. For example, volumetric displays that render 3D content physically and are capable of providing users with tactile interaction besides presentation of digital information will offer an immersive display experience. [ 8–11 ] In retrospect, impressive applications have been demonstrated by MIT’s Tangible Media Group with the use of 2D linear actuator arrays. [ 8–11 ] However, their large and heavy mechanical actuation systems impede light-weight and high-resolution realization.