Septuple‐Layer ABi 2 Te 4 Topological Insulators for Flexible Self‑Powered Mid‑ and Long‑Wave Infrared Detection toward Non‐Contact Human Thermal‐Radiation Sensing

Room‐temperature, self‐powered and mechanically flexible infrared detectors are highly desirable for wearable health monitoring and non‐contact human–machine interaction, yet achieving efficient detection of weak human‐body thermal radiation is particularly challenging. Photothermoelectric (PTE) detection, which converts photoinduced temperature gradients into electrical signals through the Seebeck effect, provides an effective route for weak infrared sensing. To establish a material‐level guideline for material selection, we introduce a wavelength‐dependent PTE response factor, PRF = , which integrates the key material‐dependent attributes associated with PTE response. Guided by this criterion, we explored septuple‐layer ABi 2 Te 4 (A = Ge, Sn, or Pb) topological insulators for mid‐ and long‐wave infrared detectors, among which SnBi 2 Te 4 delivers the best performance, achieving a responsivity of 47.5 mA W −1 and a detectivity of 1.40 × 10 9 Jones at 8.47 µm. Importantly, a comparative analysis of representative PTE materials reveals a positive correlation between PRF and experimentally measured voltage responsivity, supporting the use of PRF as a practical descriptor for screening PTE materials. Benefiting from their stable response to weak human‐body thermal radiation, the devices further enable non‐contact gesture recognition and real‐time respiration monitoring.