Iontronic Transparent Triboelectric Charge Pump and Charge Reservoir for Skin‐Mountable Touch‐Driven Direct‐Current Generation

ABSTRACT Skin‐mountable devices require flexible, durable, and transparent power sources capable of providing stable electrical energy during repeated interactions. Triboelectric nanogenerators (TENGs), which harvest touch‐induced mechanical energy, are promising candidates for meeting these requirements. However, conventional TENGs generate intrinsically pulsed AC output, limiting their use as sustained DC power sources for on‐body operation. Here, we report an iontronic direct‐current triboelectric nanogenerator (iDC‐TENG) that monolithically integrates a charge pump with a capacitive charge reservoir to convert intermittent touch into sustained DC voltage while preserving transparency and deformability. In this system, triboelectric charges generated during repeated touch are progressively accumulated in the charge reservoir, inducing stable DC voltage output. Furthermore, we derive a quantitative voltage‐evolution model that describes this process by coupling repeated charge transfer with RC decay. The model is validated through finite‐element analysis, enabling prediction of DC voltage evolution. Consistent with this model, the iDC‐TENG exhibited tunable DC output governed by charge‐reservoir capacitance, contact area, and input frequency. To highlight its potential as an on‐body power source, the iDC‐TENG enabled continuous illumination of 64 LEDs under repeated hand touch. This work establishes a strategy for converting intermittent biomechanical energy into predictable and sustained DC power for soft and skin‐conformable devices.