Tunable Coloration in Core-Shell Plasmonic Nanopixels Based on Organic Conductive Polymers: A First-Principles and FDTD Study
Md. Shariful Islam, Ahmed Zubair
TL;DR
The paper addresses tunable color generation in plasmonic nanopixels by leveraging four organic electrochromic polymers (PANI, PEDOT, PPy, PTh) in core-shell NPoMs on a mirror. It combines DFT-derived permittivity with FDTD simulations to map spectral shifts and local-field enhancement across redox states, nanoparticle shapes, shell thickness, and a TiN spacer. Key contributions include quantitative spectral tunability up to ~100 nm for some polymers, substantial color-difference metrics in CIE/CIELAB space, and demonstration that bow-tie/gear shapes and TiN spacers widen the color-dynamic range, enabling RGB-capable, low-power nanoscale pixels. The work integrates first-principles optics with nanoscale design to propose a practical route toward fast, tunable plasmonic displays using organic electrochromic materials.
Abstract
From raindrops to planets, the scattering of electromagnetic fields introduces exciting phenomena that can be utilized for display devices. Here, we designed an electrochromic nanoparticle on mirror (eNPoM) structure with core-shell geometries for low-power nanoscale pixels with rapid coloration abilities based on four electrochromic organic conducting polymers utilizing the first-principles calculations based on density functional theory (DFT) and the finite-difference time-domain (FDTD) simulations. Au nanoparticles are coated with electrochromic conductive polymers (such as PANI, PEDOT, PPy, and PTh) and positioned on the metal mirror. The electric field enhancement and the impact of shell thickness are analyzed. Dielectric properties of all polymers resulting from atomistic calculation were utilized for FDTD simulation, which helps to correlate the direct relationship between polymer structure and optical properties. Notably, the study reveals significant wavelength tunability of 100nm, 40nm, 70nm, and over 40nm using PANI, PEDOT, PPy, and PTh shells, respectively. Additionally, the potential for RGB color production using a TiN layer on the mirror is explored. For the first time, complex structures such as bow tie and gear were utilized to model the nanopixels studied and a significant absorption peak shift was observed. Chromaticity coordinates in the CIE 1931 color space and CIELAB2000 color difference quantify color change capabilities during the redox cycle, and a comparative analysis of organic and inorganic materials highlights the prospects of the proposed plasmonic nanopixels.