6 research outputs found
Role of Polymer in Hybrid Polymer/PbS Quantum Dot Solar Cells
Hybrid
nanocomposites (HCs) obtained by blend solutions of conjugated
polymers and colloidal semiconductor nanocrystals are among the most
promising materials to be exploited in solution-processed photovoltaic
applications. The comprehension of the operating principles of solar
cells based on HCs thus represents a crucial step toward the rational
engineering of high performing photovoltaic devices. Here we investigate
the effect of conjugated polymers on hybrid solar cell performances
by taking advantage from an optimized morphology of the HCs comprising
lead sulfide quantum dots (PbS QDs). Uncommonly, we find that larger
photocurrent densities are achieved by HCs incorporating wide-bandgap
polymers. A combination of spectroscopic and electro-optical measurements
suggests that wide-bandgap polymers promote efficient charge/exciton
transfer processes and hinder the population of midgap states on PbS
QDs. Our findings underline the key role of the polymer in HC-based
solar cells in the activation/deactivation of charge transfer/loss
pathways
Ultrastrong PlasmonâExciton Coupling by Dynamic Molecular Aggregation
Plasmonâexciton
polaritons arise from the coherent coupling
of the localized plasmon of metal nanoparticles and the exciton of
nearby resonant nanoemitters. The behavior of such systems is strictly
defined by the initial choice of the metallic and excitonic materials,
with only weak control possibilities, essentially limited to polarization-related
effects or photoswitchable molecules. Here we propose a new strategy
to control the plasmonâexciton splitting, based on the number
of excitonic dipoles involved in the interaction. By integrating plasmonic
arrays in a microfluidic device and injecting a dilute near-infrared
cyanine dye solution, we are able to probe in real time the emergence
and evolution of the strong plasmonâexciton coupling regime.
When dye molecules selectively aggregate on silver as a result of
chemical affinity, we observe a continuous increase of the Rabi splitting
up to an exciton energy fraction as high as 35%, compatible with an
ultrastrong coupling regime
Exploring LightâMatter Interaction Phenomena under Ultrastrong Coupling Regime
Exciton-polaritons are bosonic quasiparticles
that arise from the normal mode splitting of photons in a microcavity
and excitons in a semiconductor material. One of the most intriguing
extensions of such a lightâmatter interaction is the so-called
ultrastrong coupling regime. It is achieved when the Rabi frequency
(Ω<sub>R</sub>, the energy exchange rate between the emitter
and the resonant photonic mode) reaches a considerable fraction of
the emitter transition frequency, Ï<sub>0</sub>. Here, we report
a Rabi energy splitting (2âΩ<sub>R</sub>) of 1.12 eV
and record values of the coupling ratio (2Ω<sub>R</sub>/Ï<sub>0</sub>) up to 0.6-fold the material band gap in organic semiconductor
microcavities and up to 0.5-fold in monolithic heterostructure organic
light-emitting diodes working at room temperature. Furthermore, we
show that with such a large coupling strength it is possible to undress
the exciton homogeneous linewidth from its inhomogeneous broadening,
which allows for an unprecedented narrow emission line (below the
cavity finesse) for such organic LEDs. The latter can be exploited
for the realization of novel monochromatic sources and near-IR organic
emitting devices
Ultrastrong PlasmonâExciton Coupling by Dynamic Molecular Aggregation
Plasmonâexciton
polaritons arise from the coherent coupling
of the localized plasmon of metal nanoparticles and the exciton of
nearby resonant nanoemitters. The behavior of such systems is strictly
defined by the initial choice of the metallic and excitonic materials,
with only weak control possibilities, essentially limited to polarization-related
effects or photoswitchable molecules. Here we propose a new strategy
to control the plasmonâexciton splitting, based on the number
of excitonic dipoles involved in the interaction. By integrating plasmonic
arrays in a microfluidic device and injecting a dilute near-infrared
cyanine dye solution, we are able to probe in real time the emergence
and evolution of the strong plasmonâexciton coupling regime.
When dye molecules selectively aggregate on silver as a result of
chemical affinity, we observe a continuous increase of the Rabi splitting
up to an exciton energy fraction as high as 35%, compatible with an
ultrastrong coupling regime
ExcitonâPlasmon Coupling Enhancement <i>via</i> Metal Oxidation
In this paper, we report on the effect of metal oxidation on strong coupling interactions between silver nanostructures and a J-aggregated cyanine dye. We show that metal oxidation can sensibly affect the plexcitonic system, inducing a change in the coupling strength. In particular, we demonstrate that the presence of oxide prevents the appearance of Rabi splitting in the extinction spectra for thick spacers. In contrast, below a threshold percentage, the oxide layer results in an higher coupling strength between the plasmon and the Frenkel exciton. Contrary to common belief, a thin oxide layer seems thus to act, under certain conditions, as a coupling mediator between an emitter and a localized surface plasmon excited in a metallic nanostructure. This suggests that metal oxidation can be exploited as a means to enhance lightâmatter interactions in strong coupling applications
Toward Cavity Quantum Electrodynamics with Hybrid Photon Gap-Plasmon States
Combining
localized surface plasmons (LSPs) and diffractive surface
waves (DSWs) in metallic nanoparticle gratings leads to the emergence
of collective hybrid plasmonicâphotonic modes known as surface
lattice resonances (SLRs). These show reduced losses and therefore
a higher <i>Q</i> factor with respect to pure LSPs, at the
price of larger volumes. Thus, they can constitute a flexible and
efficient platform for lightâmatter interaction. However, it
remains an open question if there is, in terms of the <i>Q</i>/<i>V</i> ratio, a sizable gain with respect to the uncoupled
LSPs or DSWs. This is a fundamental point to shed light upon if such
modes want to be exploited, for instance, for cavity quantum electrodynamic
effects. Here, using aluminum nanoparticle square gratings with unit
cells consisting of narrow-gap disk dimersîža geometry featuring
a very small modal volumeîžwe demonstrate that an enhancement
of the <i>Q</i>/<i>V</i> ratio with respect to
the pure LSP and DSW is obtained for SLRs with a well-defined degree
of plasmon hybridization. Simultaneously, we report a 5Ă increase
of the <i>Q</i>/<i>V</i> ratio for the gap-coupled
LSP with respect to that of the single nanoparticle. These outcomes
are experimentally probed against the Rabi splitting, resulting from
the coupling between the SLR and a J-aggregated molecular dye, showing
an increase of 80% with respect to the DSW-like SLR sustained by the
disk LSP of the dimer. The results of this work open the way toward
more efficient applications for the exploitation of excitonic nonlinearities
in hybrid plasmonic platforms