NOVELTY - A thin-film broadband antireflection layer for use with an optical element or an optoelectronic device, comprises at least a thin-film dielectric layer; at least one array of nanoparticles disposed onto or in the thin-film dielectric layer, where the dielectric constant of the nanoparticles is distinct from the dielectric constant of the dielectric layer.    USE - As thin-film broadband antireflection layer used in multilayer structure, optical element (preferably optical lens or display screen), optoelectronic device (preferably a light-receiving or a light-emitting device); as part of an antireflective coating (claimed). The optoelectronic device includes solar cells, light emitting diodes, lasers, and displays.    ADVANTAGE - The layer provides effective broadband antireflection properties over a wide range of incident angles and broad range of wavelength. Also provides broadband AC coatings which are simple to fabricate. The nanostructure of the metal particles, and their assembly in regular arrays or random geometries, leads to efficient anti-reflective properties. The layer uses the scattering properties of light, which depend on the optical constants of the nanoparticles, the optical constants of the surrounding dielectric and the optical constants of the substrate. Light is preferentially scattered by the nanoparticles into the high-refractive index substrate material, thus rendering the metal nanoparticle arrays effective anti-reflective coatings. The scattered light acquires an angular spread in the substrate, which leads to more effective absorption of light in the solar cell. This is a particularly important for thin-film solar cells.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) optoelectronic device, where the antireflection layer is deposited onto a thin-film light absorbing or light-emitting layer;    (2) use of an array of dielectric nanoparticles, preferably metallic nanoparticles, as part of an antireflective coating.