Hot Carrier extraction with plasmonic broadband absorbers (1601.03119v1)

Abstract: Hot charge carrier extraction from metallic nanostructures is a very promising approach for applications in photo-catalysis, photovoltaics and photodetection. One limitation is that many metallic nanostructures support a single plasmon resonance thus restricting the light-to-charge-carrier activity to a spectral band. Here we demonstrate that a monolayer of plasmonic nanoparticles can be assembled on a multi-stack layered configuration to achieve broad-band, near-unit light absorption, which is spatially localised on the nanoparticle layer. We show that this enhanced light absorbance leads to $\sim$ 40-fold increases in the photon-to-electron conversion efficiency by the plasmonic nanostructures. We developed a model that successfully captures the essential physics of the plasmonic hot-electron charge generation and separation in these structures. This model also allowed us to establish that efficient hot carrier extraction is limited to spectral regions where the photons possessing energies higher than the Schottky junctions and the localised light absorption of the metal nanoparticles overlap.

Hot Carrier Extraction with Plasmonic Broadband Absorbers

The paper "Hot carrier extraction with plasmonic broadband absorbers" investigates the potential of plasmonic nanostructures composed of gold nanoparticles (AuNPs) integrated within a multi-layer architecture to enhance the efficiency of hot carrier generation and extraction. This promising approach has implications for applications in areas such as photocatalysis, photovoltaic energy conversion, and photodetection. Traditional metallic nanostructures limit absorption to a narrow spectral band due to their support of a single plasmon resonance. The research addresses this limitation by demonstrating the broadening of absorption spectra through a strategic configuration involving a metal-semiconductor-metal (MSM) design.

Mechanism and Results

The paper constructs a plasmonic broadband absorber by sandwiching a TiO$_2$ dielectric layer between an Au mirror and a monolayer of Au nanoparticles. A remarkable finding is that such MSM structures enable absorption of up to 90% of incident sunlight across a wide spectral range from 600 nm to 1000 nm. This configuration leads to a substantial increase in the photon-to-electron conversion efficiency, up to 40-fold, relative to conventional designs. The enhanced efficiency is attributed to the concentrated absorption on the nanoparticle layer, which was corroborated by numerical modeling using Maxwell's equations.

Key photoelectrochemical measurements reveal significant differences among configurations: the complete MSM structure, just AuNPs on TiO$_2$, and TiO$_2$ supported on Au alone. The MSM structure demonstrated superior performance, generating higher photocurrents and internal quantum efficiencies (IPCE) when tested in photoelectrochemical cells. The observed enhancements are further supported by the broadband absorption characteristics of the MSM design.

The IPCE measurements confirm that the plasmon-induced hot electron generation in the MSM structure is maximized in regions where photon energy exceeds the Schottky barrier between the Au nanoparticles and the TiO$_2$ layer, yet does not extend to energy ranges where absorption is predominantly by the mirror.

Implications

The findings suggest that optimizing plasmonic nanostructures in terms of broadband absorption capabilities can substantially heighten the efficiency of devices dependent on hot carrier processes. Such configurations can potentially drive improvements in solar energy conversion technologies through more effective harnessing of the electromagnetic spectrum. Furthermore, the research integrates theoretical modeling to delineate the mechanisms underlying the transport and extraction of hot carriers, offering insights for future tuning of these processes.

Future Directions

The experiment illustrates that further enhancements are achievable by adjusting structural parameters such as the thickness of the semiconductor layer and the choice of reflective material. Additional investigations aiming to refine these parameters and explore alternative materials could further improve device performance. Moreover, exploring how chemical environments affect $\eta_{ed}$—the efficiency of electron donation by sacrificial reagents—provides another avenue to enhance practical applicability.

This paper lays a foundation for advancing plasmonic technologies in optoelectronic systems. By fostering an understanding of the interaction between physical design and device efficiency, it encourages developments in materials science, paving the way for innovative applications boosted by plasmonically driven phenomena.