Flexible and transparent humidity sensors based on hyperbranched poly(ionic liquid)s for wearable sensing

The rapid development of wearable electronics is driving the exploration of flexible and transparent humidity sensors . However, the limited humidity response and mechanical flexibility of sensitive materials hinder the normal operation of the device. In this research, flexible humidity sensors with a fast response time (1 s) were prepared using transparent imidazolium-based hyperbranched poly(ionic liquid)s (HPIL). The sensor performance was improved by regulating the counter anions with different hydrophobicity , such as trifluoromethanesulfonimide ion (TFSI - ). The HPIL-TFSI sensor featured an improved response under low humidity condition (6%∼33% RH) with good linearity, excellent bending humidity response, mechanical stability , and long-term stability over a wide humidity range from 6% to 98% RH. Moreover, accurate sensing was achieved for respiratory monitoring, non-contact sensing, and detecting moisture on patched skin. The HPIL-TFSI sensor paves the way for the production of high-performance wearable sensor platforms.