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Haihua Xu1 Qingqing Zhu1

1, Shenzhen University, Shenzhen, , China

Wearable electronics are essential for continuous monitoring of physiological.However, commercial wearable devices such as smart watches, bracelets and glasses, are poorly skin-mountable and bulky since their sensors are fabricated by rigid inorganic semiconductor materials. Thus, there exist obvious motion-relative disturbances on sensing information obtained from these sensors. One practicable solution is to adopt flexible electronics especially epidermal electronics that can be ultrathin, lightweight and stretchable. Although great progress has been made on epidermal electronics, it is evident that these availble epidermal electronics still have drawbacks such as high power consumption, sophisticated process and high cost To address these issues, solution-processable electrolyte-gated organic transistors which have low-voltage, easy-process and high sensitivity, are developed as promising wearable electronics devices. Here, we develop flexible and highly photodetectors based on electrolyte-gated organic transistors with ionogel/silver nanowire membranes. Random network of silver nanowire (AgNW), which is used as a transparent and flexible electrode, exhibits high conductivityand excellent mechanical flexibility. The ionogel/AgNW nanocomposite membrane, in which AgNW was directly embedded into an ionogel-type gate dielectric layer, shows a large capacitance (~2µF/cm2),low sheet resistance and ultra-high optical transparency (T > 90%). In the electrolyte-gated organic transistor device, we chose a heterojunction active layer formed by blending a high hole mobility and narrow-bandgap polymer semiconductor (PSC) with an inorganic quantum dots (QDs) and silver nanoparticles(AgNPs) . Thanks to the large mobility difference between PSC and QDs as well as large carrier trapping effects of AgNPs, the device exhibits high responsivity of 7.5×105 AW-1 and ultrahigh sensitivity (~7.5×105). Transient photocurrent response at different light intensitiesreveals the device has shorter photoresponse time at lower light intensity, contrary to that of traditional phototransistors with oxide gate dielectrics. We suggest this difference is originated from the existing strong interactions between photogenerated hole carriers and anions that can induce extra long-lived trap states. It is noting that our device presents a large 3dB bandwidth of ~100 Hz. Therefore, our device is capable of detecting low-frequency pulse signals.To evaluate the utility for flexible electronic applications, we carried out bend-radius dependent measurements. It is noteworthy that the sensitivity remains in the level of 105 when bending device to a radius as small as 2 mm. Owing to fast and air-stable operations, we believe the device can be taken as a very promising photosensing module for constructing smart wearable devices in the future.

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