Photoemission Enhancement of Plasmonic Hot Electrons by Au Antenna-Sensitizer Complexes

The photoemission of surface plasmon decay-produced hot electrons is usually of very low efficiencies, hindering the practical utilization of such nonequilibrium charge carriers in harvesting photons with less energy than the semiconductor band gap for more efficient solar energy collection and photodetection. However, it has been demonstrated that the photoemission efficiency of small metal clusters increases as the particle size decreases. Recent studies have also shown that the photoemission efficiency of surface plasmon-yielded hot carriers can be intrinsically improved through proper material construction. In this paper, we report that the photoemission efficiency of hot electrons on the Au nanodisk-cluster complex/TiO2 interface can be dramatically enhanced under optical nanoantenna-sensitizer design. Such an enhancement is dominantly attributed to three factors. First, the large plasmonic nanodisk antennas provide a significantly enhanced optical near field, which largely increases light absorption in the small Au clusters that are acting as hot electron injection sensitizers. Second, the sub-3 nm size of the Au clusters facilitates the collection of delocalized spreading charges by the semiconductor. Third, the hybrid interface and molecule-like energy level of the Au cluster result in a much longer lifetime of excited electrons. Our results provide a promising approach for the effective harvesting of solar energy with plasmonic antenna-sensitizer complexes.