A super-flexible and transparent wood film/silver nanowire electrode for optical and capacitive dual-mode sensing wood-based electronic skin

Flexible electronic skin (e-skin) with multimode broad-range pressure sensing and high sensitivity is highly desirable for robotics, artificial intelligence and human-machine interaction applications. Most research on e-skin has focused on improving the sensitivity of sensing layers interfaced with an electronic output device, with only a limited number of studies focused on user interfaces based on a human-readable output. Moreover, naturally degradable materials are receiving increasing attention for e-skin. Herein, inspired by a bioluminescent noctiluca, a wood-based e-skin with instrument- and naked eye-readable characteristics was sandwich assembled using silver nanowires and a super-flexible transparent wood (STW) film as an electrode and a pyramidal microstructure polydimethlysiloxane film as a stimuli-responsive layer. The electrode was prepared by depositing silver nanowires on the surface of the STW film through a Meyer rod coating method. The film demonstrated outstanding performance with high transmittance (91.4%), a small curvature radius (2 mm) and excellent sheet resistance stability even after greater than 1500 bending cycles. The e-skin showed notable changes in electroluminescence from 0 to 150 kPa (where humans feel pain) and the sensitivity remains larger than 0.15 kPa(-1) over the broad pressure range. The sensitivity in capacitance exhibited high sensitivity at 1.01 kPa(-1) in the low-pressure regime, meanwhile, the luminescence exhibited a maximum value at 1.28 kPa(-1) at medium pressure. Furthermore, the e-skin accurately mapped the spatial distribution of static and dynamic pressures through optical sensing. This work not only improves the sustainable development of materials in electrodes but also illustrates the potential of utilizing natural wood in high value-added e-skin.