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 photothermalconversionefficiency (PCE) in the near-infrared II region and a relevant photophysicalmechanism is helpful for practical applications. Here, we measurethe femtosecond transient absorption spectra of Cu2-x S nanochains (PAA-chains-8.9 and PSS-chains-7.3)and nanoparticles (PSS-particles-8.2) to track the excited carrierdecay dynamics. The ultrafast carrier-phonon scattering (similar to 0.33ps) in PAA-chains-8.9 depletes a vast majority of the excited-statepopulation (>90%). Moreover, the particles have longer decay timefor phonon-phonon scattering than the chains. The Fermi levelof nanochains is higher than that of nanoparitcles, which affectsthe attenuation dynamic process of the excited carriers. The PSS-chains-7.3exhibit higher PCE (88.0%) than PSS-particles-8.2 (82.1%) with a slowerphonon-phonon scattering. A remarkable PCE of 90.5% is achievedin PAA-chains-8.9, which represents the highest value in plasmonicphotothermal agents. This research indicates strong carrier-phononscattering and short phonon-phonon scattering processes havegreat contribution in boosting the PCE.