Photoinduced Charge Carrier Dynamics and Electron Injection Efficiencies in Au Nanoparticle-Sensitized TiO2 Determined with Picosecond Time-Resolved X-ray Photoelectron Spectroscopy.

Progress in the development of plasmon-enabled light-harvesting technologies requires a better understanding of their fundamental operating principles and current limitations. Here, we employ picosecond time-resolved X-ray photoemission spectroscopy to investigate photoinduced electron transfer in a plasmonic model system composed of 20 nm sized gold nanoparticles (NPs) attached to a nanoporous film of TiO2. The measurement provides direct, quantitative access to transient local charge distributions from the perspectives of the electron donor (AuNP) and the electron acceptor (TiO2). On average, approximately two electrons are injected per NP, corresponding to an electron injection yield per absorbed photon of 0.1%. Back electron transfer from the perspective of the electron donor is dominated by a fast recombination channel proceeding on a time scale of 60 ± 10 ps and a minor contribution that is completed after ∼1 ns. The findings provide a detailed picture of photoinduced charge carrier generation in this NP-semiconductor junction, with important implications for understanding achievable overall photon-to-charge conversion efficiencies