Flexible, Self-Powered Humidity Sensor Based on Silicon Nanoparticle Composites for Moisture Monitoring in Wearables

Abstract

Moisture monitoring in wearables with humidity sensors is essential for safeguarding health and enhancing living comfort. For this purpose, a flexible, self-powered humidity sensor was fabricated by using silicon nanoparticle (SiNP) films as the active layer. Poly(vinyl alcohol) (PVA) was introduced to form SiNP/PVA composites enhancing the adhesiveness between SiNPs as well as the quality and stability of the SiNP film. The optimal composition of 67% SiNPs and 33% PVA was identified through morphological and electrical characterization, demonstrating superior film quality, electrical conductivity, and hydrovoltaic performance. After optimization, the sensor exhibited an obvious response to moisture, generating a hydrovoltaic voltage of up to 100 mV, with reversibility and repeatability under wet–dry cycles. The sensing mechanism of the hydrovoltaic effect was validated through controlled experiments, highlighting the decisive role of directional water flow through the nanopores between SiNPs in electricity generation. Further investigation into device size revealed that the active layer can be reduced to a minimum length of 1 cm and width of 0.2 cm without downgrading output voltage, while the integration of multiple sensors enabled signal amplification. Finally, practical applications of the sensor in respiratory monitoring and diaper moisture sensing were demonstrated. The flexible, self-powered humidity sensor based on SiNP composites offers a low-cost, scalable, and versatile solution for moisture detection in wearables.