Quantification of Efficient Plasmonic Hot-Electron Injection in Gold Nanoparticle-TiO₂ Films

Area of Science:

• Materials Science
• Nanotechnology
• Photovoltaics
• Photocatalysis

Background:

• Localized surface plasmons in metal nanostructures generate hot electrons.
• Hot electron transfer to semiconductors enhances light-harvesting devices.
• Current external quantum efficiency in hot-electron devices is impractically low (<1%), with unclear underlying physics.

Purpose of the Study:

• To quantify the efficiency of initial electron transfer in model plasmonic systems.
• To investigate the factors limiting hot-electron device performance.
• To understand achievable injection efficiencies for hot-electron plasmonic devices.

Main Methods:

• Utilized transient absorption spectroscopy to measure electron transfer efficiency.
• Employed model systems with gold nanoparticles (Au NPs) embedded in TiO₂ or Al₂O₃ films.
• Measured free carrier absorption and electron-phonon decay independently.

Main Results:

• Determined electron-injection efficiency from Au NPs to TiO₂ to be between 25% and 45%.
• This measured efficiency is significantly higher than some previous estimates.
• The results align with upper-bound estimates based on gold hot-electron energy distribution.

Conclusions:

• High electron injection efficiencies are achievable for hot-electron plasmonic devices.
• Embedding gold nanoparticles within a semiconductor (like TiO₂) enhances efficiency.
• Optimal performance is observed when nanoparticle dimensions are less than the electron mean free path.