Moth-eye effect in hierarchical carbon nanotube anti-reflective coatings

Optical anti-reflection is achieved in natural surfaces by exploiting hierarchical surface morphology. Here, we show that single-walled carbon nanotube (SWCNT) coatings deposited on silicon (Si) realize a broad-band, omnidirectional, and nearly polarization-independent suppression of Si optical reflection, with an increase of film absorption. This is attributed to a biomimetic, hierarchical surface morphology, which introduces a graded refractive index-the so-called moth-eye effect. Moreover, the anti-reflective behavior can be tuned by varying the SWCNT film thickness. The SWCNT random networks are realized by a simple, rapid, reproducible, and inexpensive solution-processing technique and deposited on Si by a dry-transfer printing method, at room temperature. The technology may be used to coat arbitrary substrates such as optical instruments, radiometric applications, light and thermal sensors, solar cells, and light emitting diodes; thus improving the device absorption or emission of light, due to the film optical properties. (C) 2016 Elsevier Ltd. All rights reserved.