Influence of the Substrate on the Morphology of Self-Assembled Silver Nanoparticles by Rapid Thermal Annealing

Abstract

Metal nanoparticles are of great interest for light trapping in photovoltaics. They are usually incorporated in the rear electrode of solar cells, providing strong light scattering at their surface plasmon resonances.In most cases, the nanoparticles are self-assembled by solid-state dewetting over a transparent conductive oxide (TCO) layer incorporated in the cell's rear electrode. Up to now, this process has been optimized mainly by tuning the thermal annealing parameters responsible for dewetting, or the thickness of the precursor metallic layer; but little attention has been paid to the influence of the underlying TCO layer properties on the morphology of the nanoparticles formed, which is the focus of the present article. This work investigates Ag nanoparticles structures produced on distinct surfaces by a simple, fast and highly reproducible method employing rapid thermal annealing. The results indicate that both the thermal conductivity and surface roughness of the TCO layer play a determinant role on the morphology of the nanostructures formed. This is of particular relevance, since we show in the study performed that the parasitic absorption of these Ag nanostructures is reduced, while the scattering is enhanced when the Ag nanostructures are formed on TCO layers with the highest conductivity and the lowest surface roughness (∼1 nm). These results unveil novel possibilities for the improvement of plasmonic nanostructures fabricated by thermal dewetting, via the careful adjustment of the physical properties of the underlying surface.

Ag-AgO nanostructures on glass substrates by solid-state dewetting: From extended to localized surface plasmons

“…Annealing in air induces the formation of holes, their percolation, and appearance of elongated islands that finally achieve rounded shape, in agreement with the previous studies. [17][18][19][20][21][22]29 The process is completed at a temperature that depends on the initial film thickness: the thicker the initial film, the larger the annealing temperature required to complete the process. A representative scheme of the solidstate dewetting mechanism for a Ag film depending on the annealing temperature and the film thickness is presented in Figs.…”

“…Noble metal thin films grown on oxide substrates exhibit a Volmer-Weber growth, and their morphological modifications upon annealing have been studied for a long time. 21,[29][30][31][32] When increasing the temperature, the difference in the thermal expansion coefficient between the substrate and the metallic film induces mechanical interface stress that increases the surface and interfacial energies. These energies are relieved by the activation of the dewetting process.…”

Deposition of gold nanoparticles upon bare and indium tin oxide film coated glass based on annealing process

“…At the same conditions, the size of AuNPs deposited on bare glass was lower than that on ITO substrate. This may be ascribed to the difference of thermal conductivity between ITO thin film and bare glass surface [39]. The ITO surface with high thermal conductivity can transfer heat efficiently to the Au particles, which leads to its high mobility on the ITO surface.…”

Enhancing the Performance of Textured Silicon Solar Cells by Combining Up-Conversion with Plasmonic Scattering

“…The resonance wavelength is sensitive to the size and shape of the NPs as well as the surrounding material [11]. Nanoparticles of gold (Au NPs) [12][13][14], silver (Ag NPs) [15][16][17][18][19], and aluminum (Al NPs) [20][21][22] are widely used to induce light scattering, with the aim of trapping more of the light energy in order to create solar cells of greater efficiency. The maximum theoretical efficiency of a single-junction (single bandgap) crystalline silicon solar cell is approximately 31% under one sun AM 1.5G illumination [23,24].…”