Progress and Prospects in Stretchable Electroluminescent Devices

Abstract

Stretchable electroluminescent (EL) devices are a new form of mechanically deformable electronics that are gaining increasing interests and believed to be one of the essential technologies for next generation lighting and display applications. Apart from the simple bending capability in flexible EL devices, the stretchable EL devices are required to withstand larger mechanical deformations and accommodate stretching strain beyond 10%. The excellent mechanical conformability in these devices enables their applications in rigorous mechanical conditions such as flexing, twisting, stretching, and folding.The stretchable EL devices can be conformably wrapped onto arbitrary curvilinear surface and respond seamlessly to the external or internal forces, leading to unprecedented applications that cannot be addressed with conventional technologies. For example, they are in demand for wide applications in biomedical-related devices or sensors and soft interactive display systems, including activating devices for photosensitive drug, imaging apparatus for internal tissues, electronic skins, interactive input and output devices, robotics, and volumetric displays. With increasingly stringent demand on the mechanical requirements, the fabrication of stretchable EL device is encountering many challenges that are difficult to resolve. In this review, recent progresses in the stretchable EL devices are covered with a focus on the approaches that are adopted to tackle materials and process challenges in stretchable EL devices and delineate the strategies in stretchable electronics. We first introduce the emission mechanisms that have been successfully demonstrated on stretchable EL devices. Limitations and advantages of the different mechanisms for stretchable EL devices are also discussed. Representative reports are reviewed based on different structural and material strategies. Unprecedented applications that have been enabled by the stretchable EL devices are reviewed. Finally, we summarize with our perspectives on the approaches for the stretchable EL devices and our proposals on the future development in these devices.

Recent Progress of Fiber Shaped Lighting Devices for Smart Display Applications—A Fibertronic Perspective

“…Emission brightness using phosphor power that depends on voltage can be described in following relation where L is the brightness of the device, L 0 and β are parameters depending on the ACEL device, and V is the voltage applied to the device. The constants L 0 and β are characterized by material properties, such as the different ratios of the electroluminescence powers in the dielectric materials, the particle size of the phosphors, the thickness of the device and embedding medium . In the ACEL device, emissions behavior is mainly driven by the applied bias voltage in the above equation.…”

“…The efforts of Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura who were awarded the Nobel Prize in Physics for the invention of efficient blue LEDs, accelerated research and development of white LEDs along with their high efficient blue LEDs, and characteristics such as low power consumption and high stability based on high efficiency and cost reduction through mass production have allowed LEDs to replace incandescent and fluorescent lamps, which were previously the dominantly used light bulbs. With their unquestionable advantages, these EL devices have become indispensable, not only in backlight units of displays but also in decorative lighting and phototherapy for ecofriendly treatment . Presently, beyond previous rigid substrate‐based LEDs, numerous scientists have attempted to fabricate and apply LEDs on versatile substrates used in daily life .…”

“…With their unquestionable advantages, these EL devices have become indispensable, not only in backlight units of displays but also in decorative lighting and phototherapy for ecofriendly treatment . Presently, beyond previous rigid substrate‐based LEDs, numerous scientists have attempted to fabricate and apply LEDs on versatile substrates used in daily life . Accordingly, we summarize the basic theory and principle of LEDs and introduce some recent research associated with stretchable, fabric and fiber‐based LEDs in this section.…”

“…The radiative principle of electroluminescent LEDs is initiated from p–n junction structure comprising a p‐type semiconductor and an n‐type semiconductor . When the p–n junction is employed, the electrons of the conduction band in the n‐type semiconductor and the holes of the valence band in the p‐type semiconductor flow into the opposite side counterparts, and thus a depletion region is formed at the junction with an equilibrium state.…”

“…Inorganic‐based LEDs are usually rigid and require an advanced crystal growth technique with a high temperature process, making them generally unsuitable for applications such as flexible, stretchable, and wearable electronics, which generally are heat sensitive generally . However, the wide range of LED applications such as lighting, displays, and biomedicine have resulted in a number of efforts to combine the high efficient LEDs with stretchable and wearable substrates while maintaining their inherent soft properties .…”