Broadband and omnidirectional antireflection from conductive indium-tin-oxide nanocolumns prepared by glancing-angle deposition with nitrogen

Abstract

Characteristic formation of highly oriented indium-tin-oxide (ITO) nanocolumns is demonstrated using electron-beam evaporation with an obliquely incident nitrogen flux. The nanocolumn material exhibits broadband and omnidirectional antireflective characteristics up to an incidence angle of 70° for the 350–900 nm wavelength range for both s- and p-polarizations. Calculations based on a rigorous coupled-wave analysis indicate that the superior antireflection arises from the tapered column profiles which collectively function as a gradient-index layer. Since the nanocolumns have a preferential growth direction which follows the incident vapor flux, the azimuthal and polarization dependence of reflectivities are also investigated. The single ITO nanocolumn layer can function as antireflection contacts for light emitting diodes and solar cells.

Structure of Glancing Incidence Deposited TiO2 Thin Films as Revealed by Grazing Incidence Small‐Angle X‐ray Scattering

“…The angle between the columns and the substrate surface is around 508, which is in good agreement with that estimated by employing the simple models proposed to describe the microstructure of this kind of thin films. [5] A close look at this cross-section view also reveals that the diameter of the columns and the distance between them increase towards the surface. This feature is in agreement with the fact that the growth process is dominated by shadow effects.…”

“…The greater characteristic length (*), which is not observed for the thinnest film (45 nm), presents values in the range of 39-160 nm, increasing with film thickness. This suggests the development of a second population of wider and/or more separated columns that, due to the shadowing effects controlling the growth mechanism of GLAD films, [4,5] grow in length and width at the expense of the initially deposited columns as the thickness of the films increases. This general phenomenology revealed by GISAXS is in agreement with the evolution of the thickness of the columnar microstructure as revealed by the SEM micrographs in Figure 1.…”

“…This feature is in agreement with the fact that the growth process is dominated by shadow effects. [4,5] Moreover, a high number of short, thinner columns appear in contact with the substrate at the initial stages of the film growth. The increase in the column width with the film thickness is well supported by the top-view images in Figure 1.…”

“…[2,3] Among the various methods available to produce nanostructured thin films a very versatile procedure is the use of glancing angle physical vapor deposition (GLAD). [4,5] This method produces porous thin films formed by columns tilted by a certain angle with respect to the substrate. Although different methods of characterization have been used to ascertain the morphology of this type of thin films, to our knowledge grazing incidence small-angle Xray scattering (GISAXS) [6,7] has not yet been applied.…”

General Design Procedures for Airport-Based Solar Photovoltaic Systems

“…It would thus be expected that for a given angle reflection from a PV front glass surface without any antireflecting (AR) coating is less intense than that of water. Now, with the current progress in solar module technology and development in anti-reflection materials such as materials with an index of refraction of 1.05 [91,92], it is safe to assume that solar PV module will have reflection off their surface dropped further with future technologies [93][94][95][96]. However, even today with the refractive index off PV with AR coating dropping below 1.33 to 1.20-1.30 [97], PV poses no (or presents tolerable/safe) hazards from reflection for airport solar PV projects.…”