Thin‐Film MoS ₂ Phototransistor‐Integrated Piezo‐Transmittance Sensor for Wearable Electronics

ABSTRACT Soft and stretchable wearable sensors are increasingly critical for healthcare diagnostics, sports performance monitoring, and virtual/augmented reality. Piezo transmittance sensors offer several key advantages, including fast response time, high sensitivity, long‐term durability, and self‐powered operation through ambient light. However, they are often limited by their bulkiness and the difficulty of fabrication of flexible optical components, hindering their stretchability. We introduce a design strategy to miniaturize and ensure stretchability to piezo‐transmittance strain sensors. The MoS ₂ ‐based phototransistor, fabricated on a flexible polyimide substrate, offers mechanically compliant visible light detection, yielding a fully flexible optical sensing element. By integrating serpentine‐patterned electrodes with a nanocomposite piezo transmittance layer, we developed a highly conformable wearable sensor platform. This sensor exhibits stable optical responsiveness up to 20% strain and leverages ambient light. The sensor was successfully integrated onto the wearable platform and demonstrates its effectiveness of tracking the sports performance during weighted workout, such as seated bench presses and arm curls.