Plasmon-induced hot-electron generation at nanoparticle/metal-oxide interfaces for photovoltaic and photocatalytic devices

95 The outstanding light-trapping and electromagnetic-fieldconcentrating properties of surface plasmons open up a wide range of applications in the field of plasmonics1. Localized surface plasmon resonance (LSPR) can occur in properly designed nanostructures in which confined free electrons oscillate with the same frequency as the incident radiation and eventually enter resonance, giving rise to intense, highly localized electromagnetic fields. Consequently, such nanostructures have been proposed as efficient light-trapping components that can be integrated in photovoltaic cells to increase the efficiency of conventional architectures considerably2,3. However, recent investigations have shown that plasmonic nanostructures can also directly convert the collected light into electrical energy by generating hot electrons4–13. After light absorption in the nanostructures and LSPR excitation, plasmons can decay, transferring the accumulated energy to electrons in the conduction band of the material. This process produces highly energetic electrons, also known as ‘hot electrons’, which can escape from the plasmonic nanostructures and be collected by, for example, putting the plasmonic nanostructures in contact with a semiconductor, thereby forming a metal–semiconductor Schottky junction6. This new scheme for solar energy conversion opens up a way to realize photovoltaic and photocatalytic devices whose performances may rival, or even exceed, those of conventional devices. However, some difficulties and limitations inherent to the nature of this energy conversion process and to the properties of the materials employed need to be addressed in order to achieve larger efficiencies while keeping fabrication costs low.