Impact of Molecular Ligands in the Synthesis and Transformation between Metal Halide Perovskite Quantum Dots and Magic Sized Clusters

Microwave-Mediated Synthesis of Lead-Free Cesium Titanium Bromide Double Perovskite: A Sustainable Approach

Theoretical studies have identified cesium titanium bromide (Cs2TiBr6), a vacancy-ordered double perovskite, as a promising lead-free and earth-abundant candidate to replace Pb-based perovskites in photovoltaics. Our research is focused on overcoming the limitations associated with the current Cs2TiBr6 syntheses, which often involve high-vacuum and high-temperature evaporation techniques, high-energy milling, or intricate multistep solution processes conducted under an inert atmosphere, constraints that hinder industrial scalability. This study presents a straightforward, low-energy, and scalable solution procedure using microwave radiation to induce the formation of highly crystalline Cs2TiBr6 in a polar solvent. This methodology, where the choice of the solvent plays a crucial role, not only reduces the energy costs associated with perovskite production but also imparts exceptional stability to the resulting solid, in comparison with previous reports. This is a critical prerequisite for any technological advancement. The low-defective material demonstrates unprecedented structural stability under various stimuli such as moisture, oxygen, elevated temperatures (over 130 °C), and continuous exposure to white light illumination. In summary, our study represents an important step forward in the efficient and cost-effective synthesis of Cs2TiBr6, offering a compelling solution for the development of eco-friendly, earth-abundant Pb-free perovskite materials.

Metal Clusters Based Multifunctional Materials for Solar Cells

As a multifunctional material, metal clusters have recently received some attention for their application in solar cells.This review delves into the multifaceted role of metal clusters in advancing solar cell technologies, covering diverse aspects from electron transport and interface modification to serving as molecular precursors for inorganic materials and acting as photosensitizers in metal-cluster sensitized solar cells (MCSSCs). The studies conducted by various researchers illustrate the crucial impact of metal clusters, such as gold nanoclusters (Au NCs), on enhancing solar cell efficiency through size-dependent effects, distinct interface behaviors, and tailored interface engineering. From optimizing charge transfer rates to improving light absorption and reducing carrier recombination, metal clusters prove instrumental in shaping the landscape of solar energy conversion.The promising performance of metal-cluster sensitized solar cells, coupled with their scalability and flexibility, positions them as a exciting avenue for future clean energy applications. The article concludes by emphasizing the need for continued interdisciplinary research and technological innovation to unlock the full potential of metal clusters in contributing to sustainable and high-performance solar cells.

Ultrafast Study of Excited State Dynamics of Amino Metal Halide Molecular Clusters

The excited state dynamics of ligand-passivated PbBr2 molecular clusters (MCs) in solution have been investigated for the first time using femtosecond transient absorption spectroscopy. The results uncover a transient bleach (TB) feature peaked around 404 nm, matching the ground state electronic absorption band peaked at 404 nm. The TB recovery signal can be fitted with a triple exponential with fast (10 ps), medium (350 ps), and long (1.8 ns) time constants. The medium and long time constants are very similar to those observed in the time-resolved photoluminescence (TRPL) decay monitored at 412 nm. The TB fast component is attributed to vibrational relaxation in the excited electronic state while the medium component with dominant amplitude is attributed to recombination between the relaxed electron and hole. The small amplitude slow component is assigned to electrons in a relatively long-lived excited electronic state, e.g., triplet state, or shallow trap state due to defects. This study provides new insights into the excited state dynamics of metal halide MCs.

Molecularly imprinted fluorescence assay based on lead halide perovskite quantum dots for determination of benzo(a)pyrene

Molecularly imprinted polymers with methylammonium lead halide perovskite quantum dots (MIP@MAPbBr3 PQDs) have been prepared and applied to the determination of benzo(a)pyrene (BaP) for the first time. The photoluminescence (PL) of MIP@MAPbBr3 PQDs was enhanced due to the surface passivation of defects by BaP. PL excitation and emission spectra, X-ray diffraction, Fourier transform infrared, and time-resolved PL studies suggest that the interaction between MIP@MAPbBr3 PQDs and BaP is a dynamic process. After MIP@MAPbBr3 PQDs were incubated with BaP, the benzene ring in the molecular structure of BaP can interact with MIP@MAPbBr3 PQDs through π electrons, which reduces non-radiative recombination of MIP@MAPbBr3 PQDs and lengthens excited state lifetime. The PL intensity of the MIP@MAPbBr3 PQDs-BaP system was monitored at 520 nm with 375 nm excitation. Under optimized conditions, the PL intensity of MIP@MAPbBr3 PQDs is linear with the concentration of BaP in the 10 to 100 ng·mL-1 range, with a detection limit of 1.6 ng·mL-1. The imprinting factor was 3.9, indicating excellent specificity of MIP@MAPbBr3 PQDs for BaP. The MIP@MAPbBr3 PQDs were subsequently applied to the PL analysis of BaP in sunflower seed oil, cured meat, and grilled fish samples, achieving recoveries from 79.3 to 107%, and relative standard deviations below 10%. This molecularly imprinted fluorescence assay improves the selectivity of BaP in complex mixtures and could be extended to other analytes.

A Broadband Photodetector Based on PbS Quantum Dots and Graphene with High Responsivity and Detectivity

A high-efficiency photodetector consisting of colloidal PbS quantum dots (QDs) and single-layer graphene was prepared in this research. In the early stage, PbS QDs were synthesized and characterized, and the results showed that the product conformed with the characteristics of high-quality PbS QDs. Afterwards, the photodetector was derived through steps, including the photolithography and etching of indium tin oxide (ITO) electrodes and the graphene active region, as well as the spin coating and ligand substitution of the PbS QDs. After application testing, the photodetector, which was prepared in this research, exhibited outstanding properties. Under visible and near-infrared light, the highest responsivities were up to 202 A/W and 183 mA/W, respectively, and the highest detectivities were up to 2.24 × 10¹¹ Jones and 2.47 × 10⁸ Jones, respectively, with light densities of 0.56 mW/cm² and 1.22 W/cm², respectively. In addition to these results, the response of the device and the rise and fall times for the on/off illumination cycles showed its superior performance, and the fastest response times were approximately 0.03 s and 1.0 s for the rise and fall times, respectively. All the results illustrated that the photodetector based on PbS and graphene, which was prepared in this research, possesses the potential to be applied in reality.

Metal Halide Perovskite Nanocrystals for Near-Infrared Circularly Polarized Luminescence with High Photoluminescence Quantum Yield via Chiral Ligand Exchange

Using ligand exchange on FAPbI₃ perovskite nanocrystals (PNCs) surface with chiral tridentate l-cysteine (l-cys) ligand, we successfully prepared chiral FAPbI₃ PNCs that show circularly polarized luminescence (CPL) (dissymmetry factor; g_lum = 2.1 × 10^-3) in the near-infrared (NIR) region from 700 to 850 nm and a photoluminescence quantum yield (PLQY) of 81%. The chiral characteristics of FAPbI₃ PNCs are ascribed to induction by chiral l/d-cys, and the high PLQY is attributed to the passivation of the PNCs defects with l-cys. Also, effective passivation of defects on the surface of FAPbI₃ PNCs by l-cys results in excellent stability toward atmospheric water and oxygen. The conductivity of the l-cys treated FAPbI₃ NC films is improved, which is attributed to the partial substitution of l-cys for the insulating long oleyl ligand. The CPL of the l-cys ligand treated FAPbI₃ PNCs film retains a g_lum of -2.7 × 10^-4. This study demonstrates a facile yet effective approach to generating chiral PNCs with CPL for NIR photonics applications.

Structural water molecules dominated p band intermediate states as a unified model for the origin on the photoluminescence emission of noble metal nanoclusters: from monolayer protected clusters to cage confined nanoclusters

In the past several decades, noble metal nanoclusters (NMNCs) have been developed as an emerging class of luminescent materials due to their superior photo-stability and biocompatibility, but their luminous quantum yield is relatively low and the physical origin of the bright photoluminescence (PL) of NMNCs remain elusive, which limited their practical application. As the well-defined structure and composition of NMNCs have been determined, in this mini-review, the effect of each component (metal core, ligand shell and interfacial water) on their PL properties and corresponded working mechanism were comprehensively introduced, and a model that structural water molecules dominated p band intermediate state was proposed to give a unified understanding on the PL mechanism of NMNCs and a further perspective to the future developments of NMNCs by revisiting the development of our studies on the PL mechanism of NMNCs in the past decade.

Biomolecules incorporated in halide perovskite nanocrystals: synthesis, optical properties, and applications

Halide perovskite nanocrystals (HPNCs) have emerged at the forefront of nanomaterials research over the past two decades. The physicochemical and optoelectronic properties of these inorganic semiconductor nanoparticles can be modulated through the introduction of various ligands. The use of biomolecules as ligands has been demonstrated to improve the stability, luminescence, conductivity and biocompatibility of HPNCs. The rapid advancement of this field relies on a strong understanding of how the structure and properties of biomolecules influences their interactions with HPNCs, as well as their potential to extend applications of HPNCs towards biological applications. This review addresses the role of several classes of biomolecules (amino acids, proteins, carbohydrates, nucleotides, etc.) that have shown promise for improving the performance of HPNCs and their potential applications. Specifically, we have reviewed the recent advances on incorporating biomolecules with HP nanomaterials on the formation, physicochemical properties, and stability of HP compounds. We have also shed light on the potential for using HPs in biological and environmental applications by compiling some recent of proof-of-concept demonstrations. Overall, this review aims to guide the field towards incorporating biomolecules into the next-generation of high-performance HPNCs for biological and environmental applications.

Origin of the near 400 nm Absorption and Emission Band in the Synthesis of Cesium Lead Bromide Nanostructures: Metal Halide Molecular Clusters Rather Than Perovskite Magic-Sized Clusters

In the synthesis of cesium lead bromide (CsPbBr₃) perovskite quantum dots, with an electronic absorption and emission band around 510 nm, and perovskite magic-sized clusters (PMSCs), with an electronic absorption and emission band around 430 nm, another distinct absorption and emission around 400 nm is often observed. While many would attribute this band to small perovskite particles, here we show strong evidence that this band is a result of the formation of lead bromide molecular clusters (PbBr₂ MCs) passivated with ligands, which do not contain the A component of the ABX₃ perovskite structure. This evidence comes from a systematic comparative study of the reaction products with and without the A component under otherwise identical experimental conditions. The results support that the near 400 nm band originates from ligand-passivated PbBr₂ MCs. This observation seems to be quite general and is significant in understanding the nature of the reaction products in the synthesis of metal halide perovskite nanostructures.