Broadband Solar Absorption Enhancement in a Silver–Epoxy Nanocomposite for Use as Selective Coating

Abstract

This paper reports the optical properties of a black silver–epoxy nanocomposite deposited on copper substrate for use as selective solar absorber. The silver nanoparticles at 3 wt% have been formed in situ in an epoxy resin in presence of organic solvent at room temperature. The nanocomposite exhibited a strong broadband light absorption in the entire visible spectrum. Atomic force microscopy images showed mixtures of spherical and elongated nanoparticles very close together (spacing much smaller than light wavelength) and predominantly clusters of them. The origin of the wide-band absorption is due to the superposition of all excitations of dipole and high-order modes coming from nanoparticles of different diameters (of 10–80 nm) and elongations (length of 80–500 nm). In order to evaluate the solar optical properties, the black silver–epoxy nanocomposite was deposited on copper substrate by the roll coating method and subsequently thermocured in air at 100 °C. The spectral data of the thermocured coatings in air showed significant decrease of the reflectance (< 13%) in the wavelength region from 200 to 1300 nm. The reduction in reflectance is explained in terms of the light trapping by forward scattering in the nanoparticles. The silver–epoxy nanocomposite deposited on a metal substrate for use as solar selective absorber is very attractive due to the easiness of its deposition, very good adherence, low-cost processing, high thermal stability, and low weight of coating per square meter of substrate (1.4 g/m2), and finally, it can be applied over large substrate areas.