Photon–Phonon–Electron Synergy Enables Efficient Photothermoelectric Conversion for Intelligent Fire Warning

ABSTRACT Photothermoelectric (PTE) detectors offer broad‐spectrum response and high sensitivity, but their performance and applications are fundamentally limited by the difficulty of simultaneously controlling photon absorption, phonon propagation, and charge‐carrier dynamics. Here, we report silver selenide/silver secondary phases (Ag 2 Se/Ag‐SPs) nanocomposite films comprising vertically aligned Ag‐SPs within a (00 l )‐oriented Ag 2 Se matrix, fabricated via oriented growth and confined phase separation. This customized architecture suppresses lattice thermal transport through interfacial phonon scattering and regulates carrier transport via shallow‐barrier Ag/Ag 2 Se interfaces, collectively optimizing the thermo‐electric conversion process. Moreover, plasmonic waveguiding within Ag‐SPs domains improves broadband light absorption, thereby promoting photothermal heat generation, enabling a high PTE responsivity of 126 V W −1 at 1550 nm. When integrated with machine‐learning‐based transient signal classification, this detector achieves 100% sensitivity in flame recognition, allowing sub‐second differentiation of combustion events from innocuous thermal sources. This photon–phonon–electron synergistic enhancement mechanism establishes a scalable paradigm for efficient PTE conversion, offering transformative potential for intelligent fire‐warning systems.