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Structures and Properties of Higher-Degree Aggregates of Methylammonium Iodide toward Halide Perovskite Solar Cells
摘要： Organic–inorganic halide perovskite solar cells have been in the limelight in recent years due to their outstanding power conversion efficiency (PCE) and facile synthesis. Despite of the ever increasing PCE that astonishes the solar cell community, many fundamental structural and theoretical aspects remain elusive, which inhibit our understanding on this fascinating material. Methylammonium iodide (MAI) is one important precursor to fabricate the halide perovskite materials based on the prototypical CH3NH3PbI3. Some MAI might remain in the CH3NH3PbI3 layer, forming a MAI-rich layer that is considered strongly affecting the perovskite solar cell performance. Therefore it is helpful to take one step back to re-evaluate the structures of MAI that is overlooked in many perovskite solar cell studies. In this manuscript, we identify the alternative structures of MAI aggregates via the ab-initio calculations, including the monomeric, dimeric, trimeric, tetrameric, pentameric, hexameric, heptameric, octameric and decameric structures of MAI. These aggregate structures are proposed to act as a simplified, yet efficient model to represent the MAI-rich region in perovskite solar cells that are usually simulated using the computationally expensive slab model. We find that the aggregates of MAI are universally stabilized by the hydrogen bonds. We further evaluate these MAI aggregate structures via studying the interactions between the MAI aggregates and an experimentally-proven additive iodopentafluorobenzene (IPFB) as an example, and show that the iodine atoms in the MAI aggregates acting as potential charge traps could be passivated by the additive molecule. The present study provides an efficient modeling platform for the MAI-rich halide perovskite materials without high computational cost.
关键词： aggregates,perovskite solar cell,methylammonium iodide,ab initio
更新于2025-09-12 10:27:22
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Exploiting supramolecular assemblies for filterless ultra-narrowband organic photodetectors with inkjet fabrication capability
摘要： Narrowband photodetectors are useful for a myriad of applications involving color discrimination as well as biological imaging and machine vision. Prevalent devices use broadband light absorbing materials in conjunction with electric (charge collection narrowing, photo multiplication) and optical strategies (optical cavity) to narrow down the spectral response of the detector. Here we exploit the intrinsic narrow absorption width of B13–50 nm peculiar to J-aggregates of strongly coupled cyanine dye molecules for narrowband photodetectors. Albeit using ultrathin J-aggregate films (10 nm) unparalleled optical aggregate properties lead to high external quantum efficiency (15%) and response speed (15 kHz) at low bias voltage ((cid:2)1 V). We show that the self-assembly process and device architecture used permit the incorporation of J-aggregates of various cyanine dyes with photodetection maxima ranging from the visible to the near-infrared region up to 1000 nm. Narrow bandwidth (o50 nm) photodetectors fabricated by inkjet printing the active device layers including the J-aggregate film perform on par with spin-coated devices, thus underlining their industrial potential.
关键词： J-aggregates,organic photodetectors,cyanine dyes,narrowband photodetectors,inkjet printing
更新于2025-09-12 10:27:22
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Scanning acoustic microscopy of quantum dot aggregates
摘要： Quantum dot (QD) aggregate formation is essential, especially, in nanoparticle-based drug delivery systems. Imaging of these targeted QD aggregates exposes information about the the treatment of many diseases including cancer. Scanning Acoustic Microscopy (SAM) is a non-invasive and rapid imaging modality, which can obtain qualitative and quantitative features simultaneously. In our study, acoustic impedance microscopy of QD aggregates was performed by SAM for evaluating the potential of SAM in the detection of lead-sulphide (PbS), graphene and cadmium-telluride/cadmium sulphide (CdTe/CdS) quantum dot aggregates for the first time. Absorption spectra of QDs, obtained with an ultraviolet-visible spectrometer, and fluorescence spectra of QD aggregates, obtained with an inverted fluorescence microscope, are also demonstrated. The success of imaging quantum dot aggregates by SAM indicated the potential of SAM in monitoring the micro-environment of the disease and also the therapeutic effect of the drug-loaded QD aggregates.
关键词： scanning acoustic microscopy,quantum dot aggregates,fluorescence microscopy
更新于2025-09-12 10:27:22
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Unraveling the origin of chirality from plasmonic nanoparticle-protein complexes
摘要： Plasmon-coupled circular dichroism has emerged as a promising approach for ultrasensitive detection of biomolecular conformations through coupling between molecular chirality and surface plasmons. Chiral nanoparticle assemblies without chiral molecules present also have large optical activities. We apply single-particle circular differential scattering spectroscopy coupled with electron imaging and simulations to identify both structural chirality of plasmonic aggregates and plasmon-coupled circular dichroism induced by chiral proteins. We establish that both chiral aggregates and just a few proteins in interparticle gaps of achiral assemblies are responsible for the ensemble signal, but single nanoparticles do not contribute. We furthermore find that the protein plays two roles: It transfers chirality to both chiral and achiral plasmonic substrates, and it is also responsible for the chiral three-dimensional assembly of nanorods. Understanding these underlying factors paves the way toward sensing the chirality of single biomolecules.
关键词： chiral nanoparticle assemblies,single-particle circular differential scattering spectroscopy,plasmonic aggregates,biomolecular conformations,chiral proteins,Plasmon-coupled circular dichroism
更新于2025-09-12 10:27:22
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Ultrafast coherent exciton dynamics in size-controlled perylene bisimide aggregates
摘要： For H-aggregates of perylene bisimide (PBI), it has been reported that upon photoexcitation, an initially delocalized Frenkel exciton is localized by excimer formation. However, in recent studies, the beforehand exciton dynamics preceding the excimer formation was suggested in larger aggregates consisting of at least more than 10-PBI subunits, which was not observed in small aggregates comprising less than four-PBI subunits. This feature implies that the size of molecular aggregates plays a crucial role in the initial exciton dynamics. In this regard, we have tried to unveil the initial exciton dynamics in PBI H-aggregates by tracking down the transient reorientations of electronic transition dipoles formed by interactions between the PBI subunits in systematically size-controlled PBI H-aggregates. The ultrafast coherent exciton dynamics depending on the molecular aggregate sizes can be distinguished using polarization-dependent femtosecond-transient absorption anisotropy spectroscopic measurements with a time resolution of ~40 fs. The ultrafast decay profiles of the anisotropy values are unaffected by vibrational relaxation and rotational diffusion processes; hence, the coherent exciton dynamics of the PBI H-aggregates prior to the excimer formation can be directly revealed as the energy migration processes along the PBI H-aggregates.
关键词： exciton dynamics,femtosecond-transient absorption anisotropy,perylene bisimide,coherent exciton dynamics,H-aggregates
更新于2025-09-12 10:27:22
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Double Rabi Splitting in a Strongly Coupled System of Core-Shell Au@Ag Nanorods and J-Aggregates of Multiple Fluorophores
摘要： The interaction of several components in the strong coupling regime yielding multiple Rabi splittings opens up remarkable possibilities for studies of multimode hybridization and energy transfer, which is of considerable interest in both fundamental and applied science. Here we demonstrate that three different components such as core-shell Au@Ag nanorods and J-aggregates of two different dyes, can be integrated into a single hybrid structure, which leads to strong collective exciton-plasmon coupling and double-mode Rabi splitting totaling 338 meV. We demonstrate strong coupling in these multicomponent plexitonic nanostructures by means of magnetic circular dichroism spectroscopy, and demonstrate strong magneto-optical activity for the three hybridized states resulting from this coupling. The J-aggregates of two different non-magnetic dyes interact with metal nanoparticles effectively, achieving magnetic properties due to the hybridization of electronic excitations in the three-component system.
关键词： magnetic circular dichroism,double Rabi splitting,J-aggregates,plexciton,Strong coupling,magneto-optical activity
更新于2025-09-12 10:27:22
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Ultra‐Stable Plasmonic Colloidal Aggregates for Accurate and Reproducible Quantitative SE(R)RS in Protein‐Rich Biomedia
摘要： Au/Ag colloids aggregated with simple salts are amongst the most commonly used substrates in surface-enhanced (resonance) Raman spectroscopy (SE(R)RS). However, salt-induced aggregation is a dynamic process, which means that SE(R)RS enhancements vary with time and that measurements therefore need to be taken at a fixed time point, normally within a short time-window of a few minutes. Here, we present an emulsion templated method which allows formation of densely-packed quasi-spherical Au/Ag colloidal aggregates. Since the particles in the product aggregates retain their weakly adsorbed charged ligands and the ionic strength remains low these charged aggregates resist further aggregation while still providing intense SE(R)RS enhancement which remains stable for days. This eliminates a major source of irreproducibility in conventional colloidal SE(R)RS measurements and paves the way for SE(R)RS analysis in complex systems, such as protein-rich bio-solutions where conventional aggregated colloids fail.
关键词： self-assembly,colloidosomes,SE(R)RS,interfaces,aggregates
更新于2025-09-11 14:15:04
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Controlling the Morphologies of Silver Aggregates by Laser-Induced Synthesis for Optimal SERS Detection
摘要： Controlling the synthesis of metallic nanostructures for high quality surface-enhanced Raman scattering (SERS) materials has long been a central task of nanoscience and nanotechnology. In this work, silver aggregates with different surface morphologies were controllably synthesized on a glass–solution interface via a facile laser-induced reduction method. By correlating the surface morphologies with their SERS abilities, optimal parameters (laser power and irradiation time) for SERS aggregates synthesis were obtained. Importantly, the characteristics for largest near-field enhancement were identified, which are closely packed nanorice and flake structures with abundant surface roughness. These can generate numerous hot spots with huge enhancement in nanogaps and rough surface. These results provide an understanding of the correlation between morphologies and SERS performance, and could be helpful for developing optimal and applicable SERS materials.
关键词： laser-induced synthesis,silver aggregates,surface-enhanced Raman scattering,hot spots
更新于2025-09-11 14:15:04
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Augmenting nitrogen removal by periphytic biofilm strengthened via upconversion phosphors (UCPs)
摘要： The application of periphytic biofilm in removing nitrogen from water is limited by the fluctuating nitrogen concentration. Here, we delineate a novel approach to enhance periphytic biofilm performance in nitrogen removal via upconversion luminescence of upconversion phosphors (UCPs). Nitrogen removal rates (14 d) in high nitrogen wastewater (26 mg/L) were significantly improved to 58.6% and 61.4% by UCPs doped with Pr3+ and Li+ and UCPs doped with Pr3+, respectively, and to 95.1% and 95.9% in low nitrogen surface water (2 mg/L), respectively. The stimulation of UCPs optimized the microbial community structure in the periphytic biofilms, and also resulted in good acclimation to use different carbon sources. The enhanced synergic action of cyanobacterial biomass, ratio of Gram +ve to Gram -ve bacteria and carbon source metabolic capacity contributed to the improved nitrogen removal. This novel approach is promising in nitrogen removal from wastewater and surface water with fluctuating initial nitrogen concentration.
关键词： Nitrogen removal,Microbial aggregates,Upconversion luminescence,Microbial community structure,Periphytic biofilm
更新于2025-09-10 09:29:36
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Photoluminescence of Squaraine Thin Films: Spatial Homogeneity and Temperature Dependence
摘要： Temperature-dependent and spatially resolved photoluminescence (PL) spectroscopy is employed to probe the optical properties of spin-cast squaraine thin films annealed to different temperatures. SQIB, a squaraine derivative with donor-acceptor-donor configuration, crystallizes in monoclinic and orthorhombic structures at low and high temperatures, respectively. The former is characterized by an optical response typical for H-aggregates, while the latter shows J-type behavior. In temperature-dependent PL spectra, the two polymorphs are identified via their specific vibrational signature. Spatially resolved data taken with 5 μm resolution give insight into the homogeneity of the SQIB films. The high-temperature films are made of uniform J-type crystallites of 50–100 μm size, as also seen in polarization-dependent data. The low-temperature films comprise a mixture of grains with H- and J-character. Their specific spectral fingerprints superimpose to the overall emission response detected in the global PL spectra. The study demonstrates that the optical properties of SQIB thin films can be probed at the level of individual grains and systematically modified by thermal treatment.
关键词： squaraines,thin films,polarization,photoluminescence,J- and H-aggregates
更新于2025-09-10 09:29:36