4 research outputs found
Solvent-Assisted Self-Assembly of CsPbBr<sub>3</sub> Perovskite Nanocrystals into One-Dimensional Superlattice
The
self-assembly of colloidal nanocrystals into ordered architectures
has attracted significant interest enabling innovative methods of
manipulating physicochemical properties for targeted applications.
This study reports the self-assembly of CsPbBr<sub>3</sub> perovskite
nanocrystals (NCs) in one-dimensional (1D) superlattice chains mediated
by ligand–solvent interactions. CsPbBr<sub>3</sub> NCs synthesized
at ≥170 °C and purified in a nonpolar solvent, hexane,
self-assembled into 1D chains, whereas those purified in polar solvents,
including toluene and ethyl acetate, were disordered or formed short-range
two-dimensional (2D) assemblies. The NCs assembled into 1D chains
showed red shifts in both the absorbance and photoluminescence spectra
relative to those of disordered NCs purified in a 50/50 hexane/ethyl
acetate mixture. Microscopy and X-ray diffraction results confirmed
the formation of polymeric nanostrands in hexane followed by organization
of the NCs into 1D chains along the nanostrands. Our results suggest
that excess aliphatic ligands remaining after purification of the
NCs complex with ionic Cs<sup>+</sup> and Br<sup>–</sup> species
through a hydrophobic effect; further, the alkyl chains of these ligands
interlace with each other through van der Waals forces. Collectively,
these interactions give rise to the nanostrands and subsequent self-assembly
of CsPbBr<sub>3</sub> into 1D chains. In polar solvents, the minimization
of repulsive forces between the solvent and the ligands drives proximal
CsPbBr<sub>3</sub> NCs together into short-range 2D assemblies or
disordered clusters. Our solvent-assisted self-assembly approach provides
a general strategy for designing 1D superlattice chains of nanocrystals
of any geometry, dimension, and composition by simply tuning the ligand–solvent
interactions
Enhanced Efficiency in Dye-Sensitized Solar Cells with Shape-Controlled Plasmonic Nanostructures
In this work, we demonstrate enhanced
light harvesting in dye-sensitized
solar cells (DSSCs) with gold nanocubes of controlled shape. Silica-coated
nanocubes (Au@SiO<sub>2</sub> nanocubes) embedded in the photoanodes
of DSSCs had a power conversion efficiency of 7.8% relative to 5.8%
of reference (TiO<sub>2</sub> only) devices, resulting in a 34% improvement
in DSSC performance. Photocurrent behavior and incident photon to current efficiency spectra revealed
that device performance is controlled by the particle density of Au@SiO<sub>2</sub> nanocubes and monotonically decreases at very high nanocube
concentration. Finite difference time domain simulations suggest that,
at the 45 nm size regime, the nanocubes predominantly absorb incident
light, giving rise to the lightning rod effect, which results in intense
electromagnetic fields at the edges and corners. These intense fields
increase the plasmonic molecular coupling, amplifying the carrier
generation and DSSC efficiency
Improving Light Harvesting in Dye-Sensitized Solar Cells Using Hybrid Bimetallic Nanostructures
In this work we demonstrate improved
light trapping in dye-sensitized
solar cells (DSSCs) with hybrid bimetallic gold core/silver shell
nanostructures. Silica-coated bimetallic nanostructures (Au/Ag/SiO<sub>2</sub> NSs) integrated in the active layer of DSSCs resulted in
7.51% power conversion efficiency relative to 5.97% for reference
DSSCs, giving rise to 26% enhancement in device performance. DSSC
efficiencies were governed by the particle density of Au/Ag/SiO<sub>2</sub> NSs with best performing devices utilizing only 0.44 wt %
of nanostructures. We performed transient absorption spectroscopy
of DSSCs with variable concentrations of Au/Ag/SiO<sub>2</sub> NSs
and observed an increase in amplitude and decrease in lifetime with
increasing particle density relative to reference. We attributed this
trend to plasmon resonant energy transfer and population of the singlet
excited states of the sensitizer molecules at the optimum concentration
of NSs promoting enhanced exciton generation and rapid charge transfer
into TiO<sub>2</sub>
Geometry-Dependent Plasmonic Tunability and Photothermal Characteristics of Multibranched Gold Nanoantennas
Plasmon resonances of anisotropic
multibranched nanostructures
are governed by their geometry, allowing morphology-directed selective
manipulation of the optical properties. In this work, we have synthesized
multibranched gold nanoantennas (MGNs) of variable geometry by a one-step
seedless approach using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic
acid (HEPES) as a capping and reducing agent. This approach enables
us to modulate the MGNs’ geometry by controlling three different
parameters: concentration of HEPES, concentration of Au<sup>3+</sup>, and pH of HEPES buffer. By altering the MGNs morphology with minimal
increase in the overall dimensions, the plasmon resonances were tuned
from the visible to the near-infrared. The MGNs plasmon resonances
demonstrated a nonintuitive blue-shift when pH > p<i>K</i><sub>a</sub> of HEPES which we attributed to emergence of charge
transfer oscillations formed when MGNs cluster to dimers and trimers.
Further, due to the presence of multiple sharp protrusions, the MGNs
demonstrated a refractive index sensitivity of 373 nm/RIU, which is
relatively high for this class of branched nanostructures of similar
size. Finally, the sharp protrusions of MGNs also give rise to intense
photothermal efficiencies; ∼53 °C was achieved within
5 min of laser illumination, demonstrating the efficacy of MGNs in
therapeutic applications. By modulating the mass density of MGNs,
the laser flux, and time of illumination, we provide a detailed analysis
of the photothermal characteristics of MGNs