Flexible bidirectional self-powered photodetector with significantly reduced volume and accelerated response speed based on hydrogel and lift-off GaN-based nanowires

Due to the wide range of potential applications for next-generation multi-functional devices, the flexible self-powered photodetector (PD) with polarity-switchable behavior is essential but very challenging to be realized. Herein, a wearable bidirectional self-powered PD based on detached (Al,Ga)N and (In,Ga)N nanowires has been proposed and demonstrated successfully. Arising from the photovoltage-competing dynamics across (Al,Ga)N and (In,Ga)N nanowire photoelectrodes, such PD can generate the positive (33.3 mA W−1) and negative (-0.019 mA W−1) photo-responsivity under ultraviolet (UV) and visible illumination, respectively, leading to the bidirectional photocurrent behavior. Thanks to the introduction of quasi solid-state hydrogel, the PD can work without the liquid-electrolyte, thus remarkably reducing the volume from about 482 cm3 to only 0.18 cm3. Furthermore, the use of hydrogel is found to enhance response speed in the UV range by reducing the response time for more than 95%, which is mainly attributed to the increased open circuit potential and reduced ion transport distance. As the GaN connecting segment is pretty thin, the piezoelectric charges generated by stress are proposed to have only a limited effect on the photocurrent density. Therefore, both the stable on-off switching characteristics and photocurrent densities can still be achieved after being bent 400 times. With an excellent flexibility, this work creates opportunities for technological applications of bidirectional photocurrent PDs in flexible optoelectronic devices, e.g., wearable intelligent sensors.