Ag ₂ Se‐Modified Carbon Nanotube Film with Efficient Photothermoelectric Conversion for Flexible Non‐Contact Detectors

ABSTRACT Simultaneously achieving high photothermal and thermoelectric conversion efficiencies in flexible thin films remains challenging, limiting the performance of ultra‐broadband photothermoelectric (PTE) detectors. This study introduces a two‐step approach involving silver pre‐deposition and vapor‐phase selenization, based on a solid‐vapor diffusion mechanism, to fabricate a flexible carbon nanotube (CNT) film modified with Ag 2 Se nanoparticles (CNT@Ag 2 Se), synergistically enhancing its light absorption and thermoelectric properties. By optimizing the selenization time, the carrier transport behavior was effectively modulated, yielding a maximum power factor of 84.35 µW·m −1 ·K −2 at room‐temperature after 20 min of treatment. The incorporation of Ag 2 Se nanoparticles also significantly improved light absorption and photothermal conversion, enabling broad‐spectrum absorption across 200–2500 nm with a 47% enhancement in photothermal performance. As a result, the CNT@Ag 2 Se film exhibited a doubled voltage output compared to pristine CNT films, along with ultra‐broadband detection capability. Laser position‐dependent measurements and synchronized infrared thermal imaging confirm that the photovoltage originates from a light‐induced temperature gradient driving directional carrier diffusion, illustrating a photothermal‐thermoelectric coupling mechanism. Systematic characterization and simulation further reveal the underlying mechanisms for the performance improvement. Furthermore, the film demonstrates excellent flexibility, retaining a stable output under multiple bending cycles and demonstrating outstanding non‐contact sensing capabilities.