Abstract
Using a particle swarm optimization algorithm and finite-difference in time-domain simulations, we optimize the coupling strength between excitons in poly(3-hexylthiophene-2,5-diyl) (P3HT) and surface lattice resonances in open cavities defined by arrays of aluminum nanoparticles. Strong light-matter coupling and the formation of exciton-polaritons are demonstrated. Nanoparticle arrays with optimal dimensions have been fabricated and measured, validating the predictions by the numerical method. P3HT is a regioregular semiconducting polymer used as a donor material in acceptor-donor blends for organic photovoltaic applications. Our results demonstrate the efficacy of the proposed method for the optimization of light-matter coupling and its potential application for the enhanced performance of optoelectronic devices.
Highlights
The recent advent of polaritonic devices [optoelectronic devices based on exciton-polaritons (EPs) arising from the strong coupling of excitons in semiconductors and photons in optical cavities] is attracting significant interest due to the remarkable properties of EP states
We investigate the coupling of excitons in regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) semiconducting polymer with optical modes in resonant cavities formed by square arrays of plasmonic nanodisks made of aluminum (Al)
The Rabi splitting is given by the minimum splitting between the lower polariton (LP) and the upper polariton (UP), which is defined at wave vectors in the dispersion relation of zero detuning for the bare states
Summary
The recent advent of polaritonic devices [optoelectronic devices based on exciton-polaritons (EPs) arising from the strong coupling of excitons in semiconductors and photons in optical cavities] is attracting significant interest due to the remarkable properties of EP states. Scitation.org/journal/jcp of EPs, compared to excitons, could be used to reduce the triplet density or enhance reversed intersystem crossing, modify the excited-state life time, or enhance exciton and charge transport.. Scitation.org/journal/jcp of EPs, compared to excitons, could be used to reduce the triplet density or enhance reversed intersystem crossing, modify the excited-state life time, or enhance exciton and charge transport.4–9,33–35 These phenomena could be exploited to solve the problems limiting a more extended utilization of OPV, and the first steps in this direction have been made.. Such a closed geometry limits the application of strong light–matter coupling in OPV, where incident light needs to be absorbed as efficiently as possible in the active material In this manuscript, we investigate the coupling of excitons in regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) semiconducting polymer with optical modes in resonant cavities formed by square arrays of plasmonic nanodisks made of aluminum (Al). These optical modes are known as Surface Lattice Resonances (SLRs). SLRs can have remarkably narrow linewidths (high Q-factors) due to low radiation losses and high field enhancements over large volumes. When the nanoparticle array is covered by a P3HT layer, SLRs can couple to excitons in the organic semiconductor as evidenced by the formation of lower and upper EP states in the absorption spectrum with an associated Rabi splitting. We have used a Particle Swarm Optimization (PSO) algorithm to find the global best sample dimensions for light–matter coupling. We run the PSO algorithm together with FiniteDifference in Time-Domain (FDTD) simulations using 30 stochastic populations with randomly chosen sample parameters that evolve during 100 generations. Samples have been fabricated with the optimized dimensions, and the optical extinction dispersion has been measured, confirming the results obtained by the PSO algorithm
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