Plasmonic and Conductive Structures of TCO Films with Embedded Cu Nanoparticles

Abstract

Cu nanoparticles were produced by using solid-state dewetting (dry) of a 1.3 nm Cu layer or laser ablation of a Cu solid target (wet) in acetone and methanol. The morphology and chemical composition of the nanoparticles were investigated as a function of the synthesis methods and their key parameters of the annealing temperature (200–500 °C) and the liquid environment during the ablation. Cu nanoparticles were then embedded in transparent conductive oxide (TCO) films as aluminum-doped zinc oxide (AZO) or zirconium-doped indium oxide (IZrO); the TCObott/Cu nanoparticle/TCOtop structures were synthesized with all combinations of AZO and IZrO as the top and bottom layers. The goal was to achieve a plasmonic and conductive structure for photovoltaic applications via a comparison of the involved methods and all fabricated structures. In particular, solid-state dewetting produced faceted or spherical (depending on the annealing temperature) nanoparticles with an average size below 150 nm while laser ablation produced spherical nanoparticles below 250 nm. Dry and wet plasmonic conductive structures as a function of the TCOs employed and the temperature of annealing could reach a sheet resistance of 86 Ω/sq. The energy band-gap Egap, absorbance, transmittance, and reflectance of the plasmonic conductive structures were investigated in the UV–vis–NIR range. They showed a dependence on the sequence of the top and bottom TCO, with best transmittances of 89.4% for the dry plasmonic conductive structure and 84.7% for the wet plasmonic conductive structure. The latter showed a higher diffused transmittance of between 10–20% in the visible range.

Monte Carlo Approach to the Evaluation of Nanoparticles Size Distribution from the Analysis of UV-Vis-NIR Spectra

“…In Refs. [20,31], the same NPs are produced with slightly the same process parameters and analyzed with TEM, resulting in µ 1 = 2.1 nm, w 1 = 0.62 for Cu NPs in methanol, µ 1 = 3.3 nm, w 1 = 0.52 for Cu NPs in ethanol and µ 1 = 2.6 nm, w 1 = 0.14 for Cu NPs in acetone. For NPs dispersion produced with PLAL, the mean radius value is strongly dependent on the laser fluence, and some casual fluctuations may occur; in fact, the algorithm finds very similar values.…”

“…In particular, copper and gold NPs are widely used in plasmonic devices due to their optical properties in the visible light range. The UV-Vis-NIR spectra of Cu and Au NPs present a typical peak, called plasmonic peak, in a specific wavelength range, depending on the material, that can be used for various devices and applications [1][2][3][4][5][6][7][8][9][10].…”