Optimization of Effective Absorption Enhancement of Paired-Strips Gold Nanoantennas in a P3HT:PCBM Thin-Film
Zih-Ying Yang1*, Chen-Wei Su2, Kuo-Ping Chen3
1College of Photonics, Institute of Lighting and Energy Photonics, National Chiao Tung University, Tainan, Taiwan
2College of Photonics, Institute of Photonic System, National Chiao Tung University, Tainan, Taiwan
3College of Photonics, Institute of Imaging and Biomedical Photonics, National Chiao Tung University, Tainan, Taiwan
* presenting author:Zih-Ying Yang, email:yanggene010@gmail.com
When metallic nanostructures are embedded within absorber layers, the effective absorption of a absorber layer can be achieved by optimizing the thickness of the active and spacer layers [1], as well as the dimensions of the nanostructures [2]. The width/period ratio of nano-gratings and the aspect ratio of spheroids have been discussed with regard to plasmonic thin-film solar cells, particularly in applications associated with energy harvesting [3]. However, little research has been conducted into optimizing the dimension of nanostructures with gaps embedded within a given volume, in which the period and thickness of the absorber layer are fixed. Considering not only a tradeoff between the size of the nanostructures and the volume of the absorber layer, but also the appropriate gaps, to maximize the effective absorption.
In this study, the solutions from the commercially available finite element method (FEM) software package COMSOL (version 4.3) are used to approach the near-field behavior by integral analysis. Absorption integral equation was used to obtain the effective absorption of paired-strip nanoantennas embedded within a thin-film. At first, the correlation between far- and near-field characteristics in the air is discussed. Then, based on the two-dimensional maps of average absorption, the discussion would focus on comparing the optimized dimension of paired-strips nanoantennas embedded in a dielectric thin-film, and in air. Finally, from the average absorption two-dimensional maps, the optimized dimension of paired-strips nanoantennas could be realized.
This study sought to optimize the dimensional characteristics of paired-strips gold nanoantennas embedded in a P3HT:PCBM thin-film by taking into account the tradeoff between the size of the nanostructures and absorber layer as well as the gaps between nanoparticles, to maximize the effective absorption enhancement. By comparing the resonance bands in two-dimensional maps tuning the width, height, and gaps between nanoparticles, an optimized dimension could be determined. Fixing the period (400 nm) of paired-strips nanoantennas embedded in P3HT:PCBM thin-films (120 nm in thickness) enhanced absorption by 9.2 times.

1. J. Zuloaga, and P. Nordlander, Nano letters 11, 1280-1283 (2011).
2. Z.-Y. Yang, and K.-P. Chen, Optics Express 22, 12737-12749 (2014).
3. E. Kazuma, and T. Tatsuma, The Journal of Physical Chemistry C 117, 2435-2441 (2012).

Keywords: Plasmonics, Nanoantennas, Near-field analysis