Light-trapping plasmonic nanovoid arrays

Abstract

We consider the suitability of metallic nanovoid arrays for confining incident light and enhancing absorption in an adjacent absorbing material, such as an organic semiconductor. Such nanostructures can facilitate strong coupling of incident light into plasmonic modes localized at the surface of the metal. We investigate this system both experimentally and by performing numerical calculations. To fabricate the samples, we employ a novel imprinting technique to obtain large-area, highly ordered metallic nanovoid arrays. Strong overall absorption enhancements are measured for nanostructured samples compared to planar samples for interfaces between silver and a common organic semiconductor, phenyl-C 61-butyric acid methyl ester. Full-wave, three-dimensional finite element method simulations are employed to investigate the nature of this light trapping, and very good agreement is observed between experimental and simulated absorption spectra. The simulations reveal highly localized surface modes and indicate that the majority of the additional absorption occurs within the organic semiconductor.

Fabrication of Organic Solar Cells with Branched Cauliflower-Like Nano Structures as a Back Electrode Replicated from a Natural Template of Cicada Wing Patterns

“…Also, the enhancement absorption calculated using dividing of the difference between absorption of the nanopatterned and planar devices by that of the planar device [21], can be found in a larger wavelength range between 700-850 nm. These enhanced ranges of absorption spectrum are outside the bulk plasmon resonance of silver [32], but the strong surface plasmon resonance mode can be excited at longer wavelengths than those of bulk plasmon resonances [8,9]. The first reason for improvement of light absorption stems from the especial geometry of the branched nanostructures on the back electrode.…”

“…The light reflected by the branched nanostructures is no longer normal to the substrate plane. Thus, it crosses the absorber layer at a longer angle on the path way back and enhances the optical path length of the incident light, where eventually light absorption is improved in the active layer and the photo-generated current [8,33,34]. Physically, another reason of the enhanced absorption behavior stems from excitation of surface plasmons in silver nanocauliflowers.…”

“…An effective approach to enhance OSCs is to increase the light absorption of the organic active layer without increasing its thickness. Several light trapping strategies have been used to enhance the photon density in OSCs including use of diffraction nano-gratings [3,8], photonic crystals [5], and plasmonic nanostructures [6,7]. Among these approaches, using the plasmonic nanostructures of noble metal materials for light trapping is quite promising.…”

“…Among these approaches, using the plasmonic nanostructures of noble metal materials for light trapping is quite promising. Physically, plasmonic subwavelength structures of noble metal materials interact with incident light and, thus, can modify the incident wave momentum in such a way that the light remains trapped in the solar cell layers [8,9].…”

“…Template-based nanostructuring is one of the most promising nanometer-sized patterning techniques in OSCs [2,3,8,20,21]. Biotemplates have inspired scientists to make use of natural nanostructures and utilize their especial properties [20,22,23].…”