A Comprehensive Review on Self-Powered Wearable Photonic Sensors: Materials, Photophysics, and System Integration.

Self-powered wearable photonic sensors enable energy-autonomous operation by integrating optical sensing, energy harvesting, and signal transduction within a unified platform. These systems exploit photophysical mechanisms such as photovoltaic, photogating, and triboelectric effects to convert ambient or body-derived energy into electrical signals while simultaneously performing sensing. Advances in hybrid semiconductors, two-dimensional materials, and nanocomposites have significantly improved light absorption, carrier transport, and mechanical compliance, enabling integration into flexible and textile-based wearable formats. Device architectures have evolved from simple junctions to heterostructured and tandem configurations that enhance spectral selectivity and energy utilization under variable illumination. However, reliable operation under low-intensity and dynamically changing conditions remains a key challenge, particularly in balancing sensing performance with energy autonomy. This review analyzes the interplay between materials, photophysical mechanisms, device architectures, and system-level design, with emphasis on energy harvesting-sensing co-optimization. Challenges related to mechanical stability, signal reliability, and real-world deployment are discussed, alongside emerging solutions based on adaptive photonic systems and intelligent data processing. These insights provide a framework for next-generation wearable photonic platforms for healthcare, environmental monitoring, and human-machine interfaces.