Boosting Carrier-Phonon Scattering in Cu 2- x S Nanochains for 90.5% Photothermal Conversion Efficiency in Near-Infrared II Region.

For plasmonic systems, pursuit of higher photothermal conversion efficiency (PCE) in the near-infrared II region and a relevant photophysical mechanism is helpful for practical applications. Here, we measure the femtosecond transient absorption spectra of Cu 2- x S nanochains (PAA-chains-8.9 and PSS-chains-7.3) and nanoparticles (PSS-particles-8.2) to track the excited carrier decay dynamics. The ultrafast carrier-phonon scattering (∼0.33 ps) in PAA-chains-8.9 depletes a vast majority of the excited-state population (>90%). Moreover, the particles have longer decay time for phonon-phonon scattering than the chains. The Fermi level of nanochains is higher than that of nanoparitcles, which affects the attenuation dynamic process of the excited carriers. The PSS-chains-7.3 exhibit higher PCE (88.0%) than PSS-particles-8.2 (82.1%) with a slower phonon-phonon scattering. A remarkable PCE of 90.5% is achieved in PAA-chains-8.9, which represents the highest value in plasmonic photothermal agents. This research indicates strong carrier-phonon scattering and short phonon-phonon scattering processes have great contribution in boosting the PCE.