Fabrication of an imperceptible liquid metal electrode for triboelectric nanogenerator based on gallium alloys by contact printing

A simple method for fabricating a liquid metal (LM) pattern on a polydimethylsiloxane substrate through the process of contact printing is introduced in this paper. This material is easily oxidized when it is exposed to air; consequently, it is difficult to manipulate. Contact printing is a fabrication process based on an adhesive force between interfaces. Adhesion is enhanced by forming a new oxide layer; thus, the LM film on a flat mold is transferred to another mold by contact printing. Electrical conductivity of the transferred LM is 1.93 × 106 S/m, which is sufficiently high for its usage as an electrode in electric circuits. The resolution of the LM pattern can be controlled at ~20 μm and a complex pattern can be fabricated. Furthermore, the LM is semi-transparent and it is visually imperceptible when observed from a distance. Using the semi-transparent LM electrode, a LM triboelectric nanogenerator is fabricated. The device demonstrates normal performance as an energy harvesting system; consequently, the LM patterned by contact printing can be applied to wearable self-powered electronics.