Flexible, stretchable, and transparent InGaN/GaN multiple quantum wells/polyacrylamide hydrogel-based light emitting diodes

Visualization is a direct, efficient, and simple interface method to realize the interaction between human and machine, whereas the flexible display unit, as the major bottleneck, still deeply hinders the advances of wearable and virtual reality devices. To obtain flexible optoelectronic devices, one of the effective methods is to transfer a high-efficient and long-lifetime inorganic optoelectronic film from its rigid epitaxial substrate to a foreign flexible/soft substrate. Additionally, piezo-phototronic effect is a fundamental theory for guiding the design of flexible optoelectronic devices. Herein, we demonstrate a flexible, stretchable, and transparent InGaN/GaN multiple quantum wells (MQWs)/polyacrylamide (PAAM) hydrogel-based light emitting diode coupling with the piezo-phototronic effect. The quantum well energy band and integrated luminous intensity (increased by more than 31.3%) are significantly modulated by external mechanical stimuli in the device. Benefiting from the small Young's modulus of hydrogel and weak Van der Waals force, the composite film can endure an extreme tensile condition of about 21.1% stretching with negligible tensile strains transmitted to the InGaN/GaN MQWs. And the stable photoluminescence characteristics can be observed. Moreover, the hydrogen-bond adsorption and excellent transparency of the hydrogel substrate greatly facilitate the packaging and luminescence of the optoelectronic device. And thus, such a novel integration scheme of inorganic semiconductor materials and organic hydrogel materials would help to guide the robust stretchable optoelectronic devices, and show great potential in emerging wearable devices and virtual reality applications.