Solvent-Assisted Self-Assembly of CsPbBr₃ 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 CsPbBr₃ perovskite nanocrystals (NCs) in one-dimensional (1D) superlattice chains mediated by ligand–solvent interactions. CsPbBr₃ 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⁺ and Br^– 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 CsPbBr₃ into 1D chains. In polar solvents, the minimization of repulsive forces between the solvent and the ligands drives proximal CsPbBr₃ 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@SiO₂ nanocubes) embedded in the photoanodes of DSSCs had a power conversion efficiency of 7.8% relative to 5.8% of reference (TiO₂ 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@SiO₂ 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/SiO₂ 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/SiO₂ 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/SiO₂ 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 TiO₂

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 Au³⁺, 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>_a 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