Flexible, transparent and conductive wearable electronic skin based on 2D titanium carbide (MXene) ink

Flexible and transparent conductors are essentially required in epidermal wearable devices such as electronicskins (E-skins) that facilitate human interaction and biofeedback. However, due to the "trade-off" effect between high electrical conductivity and optical transparency, it is difficult to obtain transparent E-skins with high electrical conductivity. Furthermore, traditional transparent conductor is bulky and brittle which is not suitable for flexible and wearable applications. Herein, ultrathin two-dimensional (2D) titanium carbide (MXene) nanosheets with metallic conductivity, hydrophilic surface and excellent mechanical flexibility was proposed as a novel high-performance transparent conductor, which was further developed as wearable E-skins. Solutionprocessable MXene conductive ink was obtained by facilely etching Al from MAX phase for large-scale spray coating to obtain flexible transparent conductors. The flexible, transparent, and conductive MXene-based electrodes own a sheet resistance as low as 200 omega/sq, while with high optical transparency of 60% @550 nm, which is sufficient for the applications of E-skins. Moreover, the transparent MXene-based soft E-skins also exhibits outstanding mechanical flexibility which could maintain its high opto-electrical performance even after 1000 cyclic bending tests. In addition, the robust flexible transparent MXene-based E-skins also could accurately identify the movements of human body including approaching, touching and pressing, which is essentially required in various application scenarios such as human-machine interactions, touch panels and healthcare sensors. The solution-processable flexible, transparent and conductive MXene-based E-skins holds tremendous potential in emerging wearable applications.