Metal Halide Perovskite Nanocrystals Research Articles

CaCl2 doping effect on optical and structural properties of halide perovskites under ligand assisted reprecipitation synthesis

The high potential of metal halide perovskite (MHP) nanocrystals with the general formula CsPbX3 (X = Cl, Br, and I) has led to the development of easy and cost-effective methods on a daily basis. The room temperature (RT) and open atmosphere ligand-assisted reprecipitation (LARP) methods were utilized to synthesize CsPbBr3 and CsPbBr2I nanocrystals (NCs). CaCl2 was used as a dopant in four different concentrations (0.25, 0.5, 0.75, and 1 % molar) to optimize the optical and electrical properties and to enhance the stability of NCs. The most optimal results were observed with 0.25 % doping for CsPbBr2I and 0.75 % doping for CsPbBr3. XRD and FE-SEM analyses revealed a cubic crystal structure for the synthesized nanocrystals. Dynamic light scattering (DLS) analysis indicated an average size of was 35–70 nm. The introduction of Ca2+ impurity, resulted in increased sizes for 0.75 % doped CsPbBr3 NCs; and increased intensity for 0.25 % doped CsPbBr2I NCs. Optical studies, including UV–vis, Fourier Transform Infrared (FTIR), and photoluminescence spectroscopies were conducted. The bandgap of CsPbBr2I and CsPbBr3 was estimated at 2.60 and 2.75 eV, respectively. The FTIR spectra suggested the effective involvement of the ligand agents oleic acid (OA) and oleylamine (OLA) in synthesis of metal halide perovskite nanocrystals. Photoluminescence spectroscopy demonstrated that the photoluminescence intensity of CsPbBr2I and CsPbBr3 varied with impurity doping, indicating an enhancement of semiconductor electronic properties under Ca2+ doping.

Enhanced Photodetection Performance of an In Situ Core/Shell Perovskite-MoS2 Phototransistor.

While two-dimensional transition metal dichalcogenides (TMDCs)-based photodetectors offer prospects for high integration density and flexibility, their thinness poses a challenge regarding low light absorption, impacting photodetection sensitivity. Although the integration of TMDCs with metal halide perovskite nanocrystals (PNCs) has been known to be promising for photodetection with a high absorption coefficient of PNCs, the low charge mobility of PNCs delays efficient photocarrier injection into TMDCs. In this study, we integrated MoS2 with in situ formed core/shell PNCs with short ligands that minimize surface defects and enhance photocarrier injection. The PNCs/MoS2 heterostructure efficiently separates electrons and holes by establishing type II band alignment and consequently inducing a photogating effect. The synergistic interplay between photoconductive and photogating effects yields a high responsivity of 2.2 × 106 A/W and a specific detectivity of 9.0 × 1011 Jones. Our findings offer a promising pathway for developing low-cost, high-performance phototransistors leveraging the advantages of two-dimensional (2D) materials.

Ultranarrow Deep-Blue Luminescence of Perovskite Nanocrystals by A-Site Cation Control.

Metal-halide perovskite nanocrystals (NCs) are one of the most promising emitters for the application of display and nanolight sources. The full width at half-maximum (FWHM) of photoluminescence (PL) emission is essential for color purity, which however remains a difficulty to further reduce the FWHM of the perovskite NCs at room temperature. Here, we show the quasi-sphere perovskite NCs with narrow PL emission at a deep-blue wavelength of ∼430 nm; its PL FWHM reaches ∼11 nm at room temperature, owing to the monodispersion in size distribution as well as the symmetric quasi-sphere morphology of NCs releasing the fine structure splitting-induced inhomogeneous broadening. Through regulating A cations with respect to the ratio of FA (or MA)-to-Cs and Cs-to-Pb, the PL emission of the NCs could be tuned from ∼505 to ∼430 nm combined with varied morphologies from large cube to small quasi-sphere. Such spectroscopic and morphological discrepancies are supposed to be attributed to the different crystalline kinetics that is strongly dependent on the synthetic condition. To be specific, in the case of increasing FA (or MA)-to-Cs, the growth rate of CsPbBr3 and FAPbBr3 (or MAPbBr3) perovskites is determined by the reactivity of transient species, while in the case of decreasing the Cs-to-Pb ratio, the growth rate of perovskites is slowed down by the serious reduction of Cs+ in the precursor. This study provides an effective strategy to adjust the emission across from green to deep-blue color and promotes the perovskite NCs with a narrow FWHM, and tunable PL emission facilitates in application of optoelectronic devices.

Near-Infrared Circularly Polarized Luminescent Physical Unclonable Functions.

Distinguished from traditional physical unclonable functions (PUFs), optical PUFs derive their encoded information from the optical properties of materials, offering distinct advantages, including solution processability, material versatility, and tunable luminescence performance. However, existing research on optical PUFs has predominantly centered on visible photoluminescence, while advanced optical PUFs based on higher-level covert light remain unexplored. In this study, we present optical PUFs based on the utilization of the covert light of near-infrared circularly polarized luminescence (NIR-CPL). This interesting property is achieved by incorporating Yb-doped metal halide perovskite nanocrystals (Yb-PeNCs) possessing NIR emission property into chiral imprinted photonic (CIP) films. By employing a solvent immersion method, we successfully integrated Yb-PeNCs into these CIP films, thereby creating an optically unclonable surface. The resulting NIR-CPL emission adds a layer of advanced security to the optical PUF systems. These findings underscore the potential of solution-processable chiral films to play a pivotal role in advancing the next generation of PUFs.

Harnessing Multi‐Modal Exciton Migration in Hybrid Halide Perovskite for Photocatalytic Amplification of Nitric Oxide and Hydroxyl Radicals toward Bacterial Killing and Biofilm Disruption

AbstractAntimicrobial resistance is a multifaceted phenomenon and a serious threat to the prevailing global healthcare options. Photocatalytic therapy using nanotherapeutics is a promising alternative as this enables redox‐tuning of substrates inside biofilm while forming cytotoxic reactive oxygen species at hypoxic conditions. Herein, a new paradigm using the heterostructure of metal halide perovskite (PeV) nanocrystals is introduced by in situ capping with a nitric oxide (NO) releasing derivative (NTFA) and a •OH releasing phenothiazine ligand (BA‐PTZ) to yield NTFA@PeV@BA‐PTZ heterostructure. Material characterization, along with the mechanistic insights for the sunlight‐induced exciton formation, separation, and migration into respective molecular ligands inducing the catalytic generation of cytotoxic •OH/NO species are supported by in situ spectroscopic/microscopic studies. Encapsulation of NTFA@PeV@BA‐PTZ NCs with silica results NTFA@PeV@BA‐PTZ@SiO2, ensures its physiological stability and biologically benign nature. The efficacy of heterostructure toward biofilm inactivation and bactericidal activity are established through appropriate in vitro and in vivo biocompatibility, biodistribution, and assessment of antibacterial activity. The results also confirm the minimal toxicity and effective excretion of NTFA@PeV@BA‐PTZ@SiO2 from orally administered Balb/c mice. Together, based on manipulating the redox gradient omnipresent in bacterial/biofilm microenvironments and by catapulting the exciton‐mediated redox process, a proof‐of‐concept for an efficient multimodal photocatalytic nanotherapeutics is demonstrated.

Growth of CsPbX3 nanocrystals using sol–gel SiO2 solid powders as reactors without capping agents towards anomalous stable emission membranes

To overcome the poor stability of metal halide perovskite nanocrystals (NCs) prepared in organic solvents, a solid reaction method at high temperature was developed using sol–gel porous SiO2 as a reactor. Sol-gel SiO2 powders were used to encapsulate CsPbX3 NCs at high temperatures (600–800 °C) in air to get SiO2/CsPbX3 glass by dispersing growth cites in advance and no ligands added. After NaOH etching, a thin dense SiO2 shell was remained on the surface of CsPbX3 NCs (named as CsPbX3@SiO2).The photoluminescence (PL) quantum yield of the CsPbX3@SiO2 was 86.7 %, in which their PL peak wavelengths were adjusted from 410-707 nm by changing halogen components. The dense SiO2 shell on CsPbX3 NCs blocked the connection of CsPbX3 cores with water and oxygen in the external environment, resulting in CsPbX3@SiO2 revealed extraordinary high stability. After immersing in water for half year, the PL intensity of CsPbX3@SiO2 composites was remained unchanged and the composites still revealed bright PL after heat-treating in boiling water for 14 h. These highly stable composites were used to fabricate a white light-emitting diode, in which the color coordinates are located at (0.36, 0.33), and the color temperature reaches 5169 K which belongs to the warm white light range.

Synergistically enhanced water-resistive perovskite nanocrystals for cell nucleus imaging and acid phosphatase detection

Despite the impressive success of metal halide perovskite nanocrystals (NCs) in diverse fields, such as solar cells, light-emitting diodes, photodetectors, and so forth, their intrinsic sensitivity to water limits the extending applications in aqueous systems. Herein, enhanced water stability is achieved for NH2-PEG-COOH capped Mn2+-doped CsPbCl3/CsPb2Cl5 core/shell NCs through the synergistic effect of ion doping, core/shell construction and polymer encapsulation. The NH2-PEG-COOH encapsulation is validated crucial for the formation of CsPbCl3/CsPb2Cl5 core/shell structure, since it retains contact for CsPbCl3 NCs with trace water, and guarantees a slow water-etching process, triggering the CsPbCl3 to CsPb2Cl5 transformation. Thanks to the high formation energy induced by Mn2+ doping, CsPbCl3/CsPb2Cl5 hetero core/shell construction and NH2-PEG-COOH protective barrier, the obtained NCs exhibit unattenuated photoluminescence quantum yield after dipped in water for 15 days. Based on the robust water stability, the NH2-PEG-COOH capped Mn2+-doped CsPbCl3/CsPb2Cl5 NCs work well in cell nucleus imaging and acid phosphatase detection. This work not only produces a novel perovskite fluorescence probe in aqueous systems but also provides a general and effective combination strategy to enhance the water stability of perovskite materials.

Luminescent Perovskite-Cross-Linked Polymer with Low Shrinkage and Excellent Stability.

When organic cross-linked polymers are combined with metal halide perovskite nanocrystals (PNCs) for realizing luminescent perovskite-polymer display materials, the stability of PNCs is enhanced and their shrinkage is suppressed. This work presents a feasible strategy for preparing CsPbBr3 nanocrystals (NCs) within a polydicyclopentadiene (PDCPD) thermosetting cross-linked resin matrix simultaneously via a one-step reaction. The obtained PDCPD@PNCs composite exhibits narrow peak half-widths (15-20 nm), high light transmittance (80%), low curing volume shrinkage (1.4%), tunable tensile properties, excellent stability, and a photoluminescence quantum yield (PLQY) of 44.3%. The composite material exhibits long-term stability in water, acid, and base solutions for over 90 days, with the PL intensity being maintained at over 90%. Furthermore, the composite is highly resistant to polar organic solvents owing to the insolubility imparted by cross-linking. White LEDs (WLED) fabricated using the as-prepared composite demonstrate excellent potential as light sources in optical devices.

Preparation of CsPbBr3@Fe2O3 heterojunction nanocrystals for ppb-level H2S sensing

Metal-halide perovskite (MHP) nanocrystals (NCs) have unique advantages in the gas sensing field, but the poor stability restricts their widespread applications. In this work, the CsPbBr3@Fe2O3 heterojunction NCs were synthesized successfully by simple solution process and subsequent surface modification strategy for constructing a gas sensor. The Fe2O3 shell layer was obtained through thermal decomposition of acetylacetone iron (AAI) at 400 °C. The resulting CsPbBr3@Fe2O3 heterostructured NCs exhibit a higher gas-sensing performance to H2S than pure CsPbBr3 and Fe2O3, respectively. Upon exposure to 10 ppm H2S, the response value of 4.12 was obtained at a moderate working temperature of 350 °C, while the response was fast both in terms of response time and recovery time, i.e., 1.84 s and 24.20 s, respectively. This might be the best performance for MHP sensors, to the best of our knowledge. The excellent gas-sensitive response might be attributed to the formation of a heterojunction which promotes the electron migration from CsPbBr3 to Fe2O3.

Engineering Metal Halide Perovskite Nanocrystals with BODIPY Dyes for Photosensitization and Photocatalytic Applications.

The sensitization of surface-anchored organic dyes on semiconductor nanocrystals through energy transfer mechanisms has received increasing attention owing to their potential applications in photodynamic therapy, photocatalysis, and photon upconversion. Here, we investigate the sensitization mechanisms through visible-light excitation of two nanohybrids based on CsPbBr3 perovskite nanocrystals (NC) functionalized with borondipyrromethene (BODIPY) dyes, specifically 8-(4-carboxyphenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) and 8-(4-carboxyphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (I2-BDP), named as NC@BDP and NC@I2-BDP, respectively. The ability of I2-BDP dyes to extract hot hole carriers from the perovskite nanocrystals is comprehensively investigated by combining steady-state and time-resolved fluorescence as well as femtosecond transient absorption spectroscopy with spectroelectrochemistry and quantum chemical theoretical calculations, which together provide a complete overview of the phenomena that take place in the nanohybrid. Förster resonance energy transfer (FRET) dominates (82%) the photosensitization of the singlet excited state of BDP in the NC@BDP nanohybrid with a rate constant of 3.8 ± 0.2 × 1010 s-1, while charge transfer (64%) mediated by an ultrafast charge transfer rate constant of 1.00 ± 0.08 × 1012 s-1 from hot states and hole transfer from the band edge is found to be mainly responsible for the photosensitization of the triplet excited state of I2-BDP in the NC@I2-BDP nanohybrid. These findings suggest that the NC@I2-BDP nanohybrid is a unique energy transfer photocatalyst for oxidizing α-terpinene to ascaridole through singlet oxygen formation.

Electronic properties of individual CsPbI2Br nanocrystals investigated by LT-STM

Solution-processed metal halide perovskite nanocrystals show promise for various potential optoelectronic applications and the exploration of the fundamental physics underlying them. However, the electronic properties of individual nanocrystals have not been thoroughly studied. Here, we applied low-temperature scanning tunneling microscopy to investigate the properties of metal halide perovskite CsPbI2Br nanocrystals with a diameter in the range of 10–20 nm. Sub-monolayer dispersions of the nanocrystal on highly oriented pyrolytic graphite and gold thin film substrates were achieved. Using scanning tunneling microscopy, we resolved topographies of individual nanocrystals on the gold film, and their electronic properties were probed by scanning tunneling spectroscopy. In our experiment, no obvious dependence of the extracted energy gap on the nanocrystal size and shape was found, which is consistent with the reported small exciton Bohr radius in metal halide perovskite materials. Additionally, we observed that the energy gaps of some nanocrystals are smaller than that of the bulk, suggesting the influence of factors such as deep-level defects/traps, ion migration, etc. on the electronic structure.

Localized Temperature Engineering Enables Writing of Heterostructures in Glass for Polarized Photoluminescence of Perovskites.

Metal halide perovskite (MHP) structures that exhibit polarized photoluminescence (PL) have attracted significant interest in fabricating light field regulation elements for display, imaging, and information storage applications. We report a three-dimensional direct lithography of heterostructures for controllable polarized PL inside glass by laser-induced localized temperature engineering. The heterostructures consisted of oriented periodic structures (OPSs) and MHP nanocrystals, and the mechanism for hierarchical distribution of heterostructures was illustrated. The patterning of heterostructures for manipulable polarized PL can be used for information encryption, wave-plate, and polarized micro-LEDs.

Autonomous nanomanufacturing of lead-free metal halide perovskite nanocrystals using a self-driving fluidic lab.

Lead-based metal halide perovskite (MHP) nanocrystals (NCs) have emerged as a promising class of semiconducting nanomaterials for a wide range of optoelectronic and photoelectronic applications. However, the intrinsic lead toxicity of MHP NCs has significantly hampered their large-scale device applications. Copper-base MHP NCs with composition-tunable optical properties have emerged as a prominent lead-free MHP NC candidate. However, comprehensive synthesis space exploration, development, and synthesis science studies of copper-based MHP NCs have been limited by the manual nature of flask-based synthesis and characterization methods. In this study, we present an autonomous approach for the development of lead-free MHP NCs via seamless integration of a modular microfluidic platform with machine learning-assisted NC synthesis modeling and experiment selection to establish a self-driving fluidic lab for accelerated NC synthesis science studies. For the first time, a successful and reproducible in-flow synthesis of Cs3Cu2I5 NCs is presented. Autonomous experimentation is then employed for rapid in-flow synthesis science studies of Cs3Cu2I5 NCs. The autonomously generated experimental NC synthesis dataset is then utilized for fast-tracked synthetic route optimization of high-performing Cs3Cu2I5 NCs.

Harnessing laser technology to create stable metal halide perovskite-rGO conjugates as promising electrodes for Zn-ion capacitors.

We report that the direct conjugation of metal halide perovskite nanocrystals on rGO sheets can provide high performance and stable electrodes for Zn-ion capacitors. It is the first time that metal halide nanocrystals have been used to enhance the energy storage of 2D materials in capacitors by introducing an additional pseudocapacitance mechanism. In particular, we present a simple, rapid and room temperature laser-induced method to anchor CsPbBr3 nanocrystals on rGO sheets without affecting the initial morphology and crystal structure of the two components. The flexible and high surface area of the rGO sheets enables the conjugation of individual metal halide perovskite nanocrystals, giving rise to new synergetic functionalities. As a result, the specific capacitance of the perovskite-rGO conjugated electrodes can be enhanced by 178- and 152-times compared to those of the plain rGO and perovskite electrodes respectively.

Long live(d) CsPbBr3 superlattices: colloidal atomic layer deposition for structural stability.

Superlattice formation afforded by metal halide perovskite nanocrystals has been a phenomenon of interest due to the high structural order induced in these self-assemblies, an order that is influenced by the surface chemistry and particle morphology of the starting building block material. In this work, we report on the formation of superlattices from aluminum oxide shelled CsPbBr3 perovskite nanocrystals where the oxide shell is grown by colloidal atomic layer deposition. We demonstrate that the structural stability of these superlattices is preserved over 25 days in an inert atmosphere and that colloidal atomic layer deposition on colloidal perovskite nanocrystals yields structural protection and an enhancement in photoluminescence quantum yields and radiative lifetimes as opposed to gas phase atomic layer deposition on pre-assembled superlattices or excess capping group addition. Structural analyses found that shelling resulted in smaller nanocrystals that form uniform supercrystals. These effects are in addition to the increasingly static capping group chemistry initiated where oleic acid is installed as a capping ligand directly on aluminum oxide. Together, these factors lead to fundamental observations that may influence future superlattice assembly design.

Shape-controlled synthesis of CsPbBr3 nanorods with bright pure blue emission and high stability

CsPbBr3 NRs synthesized at 80 °C show bright blue emission at 462 nm and exhibit a high PLQY of 62.65%. The 1 : 1 mixed anti-solvents of EAC and IPA can change the state of NR surface ligands and improve the stability of NRs.

Green-route manufacturing towards future industrialization of metal halide perovskite nanocrystals.

Perovskite nanocrystals (PeNCs) with excellent optical properties have attracted tremendous research interests and have been considered as promising candidates for new-generation optoelectronic devices. Over the past few years, numerous efforts have been made to overcome the challenges in terms of sustainable manufacturing of PeNCs and related devices and systems, including the solvents used in precursor preparation, antisolvents and perovskite materials for the fabrication of devices and systems, and remarkable progress has been made. However, the usage of toxic, organic solvents in the synthesis of PeNCs poses a threat to the ecosystem and human health, which has hindered the progress in the commercialization and industrialization of PeNCs. This has promoted the development of green solvents for the sustainable manufacturing of PeNCs. In this Feature Article, a state-of-the-art green method for the synthesis of PeNCs is presented, in which the solvents of low toxicities are underlined in contrast to the reported Reviews which focus on toxic solvents for the preparation of precursor solutions. We then focus on green, aqueous methods for the preparation of PeNCs, including conventional perovskite and double PeNCs, by summarizing our previous research efforts and studies. In particular, pure water as the greenest solvent is introduced for the preparation of PeNCs, and the parameters affecting the size and optical characteristics of PeNCs, such as sonication time and ligands for post-treatment, are discussed. The strategies of using a passivation layer to improve the aqueous stability of PeNCs are reviewed, which are grouped into organic polymers and inorganic semiconductors. We highlight the challenges and possible solutions in the green manufacturing and applications of PeNCs. The green routes discussed in this article for the synthesis of PeNCs are expected to be a major step forward for the commercialization and industrialization of the fabrication of PeNCs. It is anticipated that green manufacturing will continue to be the mainstream in the synthesis and fabrication of PeNCs.

Metal halide perovskite nanocrystals for plant-growth lighting applications: strategies for boosting stability

This review article provides a comprehensive overview of the advantages and latest progress of MHP materials for plant lighting. Efforts to enhance stability for plant lighting applications are explored.

Facets in metal halide perovskite nanocrystals for photoinduced electron transfer annulation reaction

Facets in metal halide perovskite nanocrystals for photoinduced electron transfer annulation reaction

Near-infrared two-photon excited photoluminescence from Yb3+-doped CsPbClxBr3-x perovskite nanocrystals embedded into amphiphilic silica microspheres.

Nonlinear absorption of metal-halide perovskite nanocrystals (NCs) makes them an ideal candidate for applications which require multiphoton-excited photoluminescence. By doping perovskite NCs with lanthanides, their emission can be extended into the near-infrared (NIR) spectral region. We demonstrate how the combination of Yb3+ doping and bandgap engineering of cesium lead halide perovskite NCs performed by anion exchange (from Cl- to Br-) leads to efficient and tunable emitters that operate under two-photon excitation in the NIR spectral region. By optimizing the anion composition, Yb3+-doped CsPbClxBr3-x NCs exhibited high values of two-photon absorption cross-section reaching 2.3 × 105 GM, and displayed dual-band emission located both in the visible (407-493 nm) and NIR (985 nm). With a view of practical applications of bio-visualisation in the NIR spectral range, these NCs were embedded into silica microspheres which were further wrapped with amphiphilic polymer shells to ensure their water-compatibility. The resulting microspheres with embedded NCs could be easily dispersed in both toluene and water, while still exhibiting a dual-band emission in visible and NIR under both one- and two-photon excitation conditions.