Metal Halide Perovskite Quantum Dots Research Articles

Atomically Contacted Cs3Bi2Br9 QDs@UiO-66 Composite for Photocatalytic CO2 Reduction.

Metal halide perovskite quantum dots (QDs) are widely studied in the field of photocatalytic CO2 due to their strong light absorption and long carrier migration length. However, it can not exhibit high catalytic performance because of the radiative recombination and the lack of effective catalytic sites. Metal organic frameworks (MOFs) encapsulated QDs can not only solve the aforementioned problems, but also maintain their own unique characteristics with ultra-high specific surfaces area and abundant metal sites. In this work, lead-free bismuth-based halide perovskite QDs are encapsulated into Zr-based MOF (UiO-66), which combines the advantages with high power conversion efficiency of QDs and the high surface area and porosity of UiO-66. In addition, benefiting from the close contact between the Cs3Bi2Br9 QDs and the UiO-66 enables the photogenerated electrons in the QDs to be rapidly transferred to the MOF. As a result, the Cs3Bi2Br9@UiO-66 composite exhibits a higher yield for photocatalytic CO2 reduction than that of the prepared large-sized composite of Cs3Bi2Br9 and UiO-66.

Highly luminescent CsPbX3/PMMA (X=Br, I) composites with improved stability for full-color Micro-LED displays

Inorganic metal halide perovskite quantum dots (PQDs) have recently emerged as promising candidates for color conversion materials in Micro-LED displays, due to their outstanding color purity, high absorption coefficient, tunable emission wavelength. However the inferior stability and undesirable photoluminescence quantum yield (PLQY) restrict their particle applications. Herein, CsPbX3/PMMA (X = Br, I) composites with improved stability and optical performance were successfully prepared by a general and mild in-situ polymerization strategy. The ester carbonyl (CO) group in MMA formed complexes with Pb2+, leading to the in-situ thermal polymerization of polymethyl methacrylate (PMMA) under the action of the initiator. The multifunctional PMMA can efficiently passivate halogen vacancies while acting as a barrier against the degradation caused by heat, water, and oxygen. As a result, the PLQYs and stability of PMMA-coated CsPbX3 PQDs have been significantly improved. When implementing CsPbX3/PMMA/PDMS composites as color conversion layers in Micro-LEDs, they achieve an impressive color gamut of 127.23% with excellent stability. We believe our work will stimulate the exploration of perovskite/polymer composites for industrial Micro-LED applications.

Reversible hydrochromic CsPbBr3/Cs4PbBr6@MCM-41 to enable organic solvent polarity detection

Hydrochromic materials have received much attention in anticounterfeiting due to their reversible photoemission properties toward water. However, existing hydrochromic materials usually suffer from slow hydrochromic response and limited stability, repeatability, and color tunability. This paper found for the first time that CsPbBr3/Cs4PbBr6 composites with quantum-limited domain effects had reversible hydrochromism. CsPbBr3/Cs4PbBr6 composites were successfully synthesized in molecular sieve MCM-41 using an improved mechanochemical method. The composites underwent a reversible phase transition from Cs4PbBr6/CsPbBr3 to CsPbBr3 upon treatment with a trace amount of water, the photoluminescence colors underwent a change from blue to green, and reversion occurred due to heating. Mechanistic investigation revealed that quantum dots underwent soft agglomeration due to van der Waals forces in polar solvent environments, affecting the action of quantum domain-limiting effects. Therefore, organic solvents with different polarities can cause different degrees of reversible discoloration of the material. This study provides new ideas for understanding the phase transition and agglomeration of metal halide perovskite quantum dots in polar solvent environments. Additionally, it offered new options for aqueous color-changing materials and organic solvent polar detection materials.

Enhanced Hot-Phonon Bottleneck Effect on Slowing Hot Carrier Cooling in Metal Halide Perovskite Quantum Dots With Alloyed A-Site.

A deep understanding of the effect of the A-site cation cross-exchange on the hot-carrier relaxation dynamics in perovskite quantum dots (PQDs) has profound implications on the further development of disruptive photovoltaic technologies. In this study, we investigated the hot carrier cooling kinetics of pure FAPbI3 , MAPbI3 , CsPbI3 and alloyed FA0.5 MA0.5 PbI3 , FA0.5 Cs0.5 PbI3 , and MA0.5 Cs0.5 PbI3 QDs using ultrafast transient absorption (TA) spectroscopy. The lifetimes of the initial fast cooling stage (<1ps) of all the organic cation-containing PQDs were shorter than those of the CsPbI3 QDs, as verified by the electron-phonon coupling strength extracted from the temperature-dependent photoluminescence spectra. The lifetimes of the slow cooling stage of the alloyed PQDs were longer under illumination greater than 1 sun, which was ascribed to the introduction of co-vibrational optical phonon modes in the alloyed PQDs. This facilitated efficient acoustic phonon upconversion and enhanced the hot-phonon bottleneck effect, as demonstrated by first-principles calculations. This article is protected by copyright. All rights reserved.

Overcoming Charge Confinement in Perovskite Nanocrystal Solar Cells.

The small nanoparticle size and long-chain ligands in colloidal metal halide perovskite quantum dots (PeQDs) cause charge confinement, which impedes exciton dissociation and carrier extraction in PeQD solar cells, so they have low short-circuit current density Jsc , which impedes further increases in their power conversion efficiency (PCE). Here, a re-assembling process (RP) is developed for perovskite nanocrystalline (PeNC) films made of colloidal perovskite nanocrystals to increase Jsc in PeNC solar cells. The RP of PeNC films increases their crystallite size and eliminates long-chain ligands, and thereby overcomes the charge confinement in PeNC films. These changes facilitate exciton dissociation and increase carrier extraction in PeNC solar cells. By use of this method, the gradient-bandgap PeNC solar cells achieve a Jsc = 19.30mA cm-2 without compromising the photovoltage, and yield a high PCE of 16.46% with negligible hysteresis and good stability. This work provides a new strategy to process PeNC films and pave the way for high performance PeNC optoelectronic devices.

Dual-function ligand surface control to achieve high efficiency and brightness perovskite quantum dots LED devices

Metal halide perovskite quantum dots (QDs) have significant potential for application in light-emitting diodes (LED) owing to their superior optical properties. However, the dynamic instability of traditional oleic acid/amine ligands has a considerable impact on the optical and chemical properties of the surface. Additionally, one of its insulating qualities restricts the practical application of electroluminescent devices. In this case, the dual-function ligand DDA-MeS can passivate surface defects while also stabilizing chelation on QDs surface. As a result, the electrical performance of green QDs-LED devices is greatly enhanced, the external quantum efficiency is raised to 10.18%, the maximum brightness is also boosted to 8025 cd/m2, and the turn-on voltage is decreased to 2.5 V. This work also provides a novel strategy for the development of green LED devices with dual-function ligands that can be highly effective and bright.

Improved performance of CsPbBr3 light-emitting diodes based on zinc bromide passivated quantum dots

Metal halide perovskite quantum dots (Pe QDs) have aroused tremendous interest in the past several years for their promising applications in display and lighting. However, an inevitable precipitation and purification process has to be conducted to clear away redundant uncoordinated organic ligands during the synthesis of QDs, leading to the formation of surface vacancy defects. Herein, an ion replenishment process has been demonstrated to passivate cesium lead bromide QDs (CsPbBr3 QDs) with zinc bromide (ZnBr2) without cosolvent. This technology does not introduce any more process of QDs synthesis, ZnBr2 has been utilized as the inorganic additive dispersed in antisolvent ethyl acetate during the precipitation and purification. The formation of both lead ions (Pb2+) and bromide ions (Br−) vacancy defects could be suppressed. Improved radiative recombination and stability were achieved. As a result, light-emitting diodes (LEDs) based on the CsPbBr3 QDs with ZnBr2 exhibited an maximum luminance of 96392 cd m−2, current efficiency of 21.1 cd A−1 and external quantum efficiency (EQE) of. Compared with the devices fabricated from Pe QDs without passivation, the enhancement of maximum luminance and EQE is up to 200% and 100%. This work provides a simple and effective strategy to passivate the surface vacancy defects of CsPbBr3 QDs.

A fluorescent probe of CH3NH3PbBr3 perovskite quantum dots on polystyrene nanofibres for the detection of copper ions

Recently, metal halide perovskite quantum dots (MHPQDs) have attracted considerable interest in sensing activities due to their excellent optoelectronic properties and high surface activity. Here, aiming for heavy metal detection, we proposed an ultrasensitive turn-off fluorescent probe based on MAPbBr3 MHPQDs for the measurement of copper ions in an organic solvent. A low limit of detection (LOD) of 5.6nM was achieved and the test range was recorded from 0nM to 100nM. In order to achieve this high sensitivity, a thin film layer of electrospun polystyrene(PS) nanofibre was introduced for the structural support of MHPQDs, by which the sensitivity increased two orders of magnitude. The quenching mechanism is also discussed in the paper. We believe the electron transfer effect between Cu2+ and perovskite QDs made the main contribution for turn off sensing in our prototype device.

In situ growth strategy to construct perovskite quantum dot@covalent organic framework composites with enhanced water stability

Metal halide perovskite quantum dots (QDs) have excellent optoelectronic properties; however, their poor stability under water or thermal conditions remains an obstacle to commercialization. Here, we used a carboxyl functional group (−COOH) to enhance the ability of a covalent organic framework (COF) to adsorb lead ions and grow CH3NH3PbBr3 (MAPbBr3) QDs in situ into a mesoporous carboxyl-functionalized COF to construct MAPbBr3 QDs@COF core–shell-like composites to improve the stability of perovskites. Owing to the protection of the COF, the as-prepared composites exhibited enhanced water stability, and the characteristic fluorescence was maintained for more than 15 d. These MAPbBr3 QDs@COF composites can be used to fabricate white light-emitting diodes with a color comparable to natural white emission. This work demonstrates the importance of functional groups for the in situ growth of perovskite QDs, and coating with a porous structure is an effective way to improve the stability of metal halide perovskites.

Electrohydrodynamic Printing of PCL@CsPbBr3 Composite Fibers with High Luminescence for Flexible Displays

Metal halide perovskite quantum dots (PQDs) are widely used in the display field due to their excellent photoelectric properties, such as ultra-narrow half-peak widths and ultra-pure luminescence color purity. Inkjet printing, laser direct writing and electrospinning are all common methods for PQDs printing to prepare micropattern displays. In order to produce large-scale and high-resolution PQDs micropatterns, electrohydrodynamic (EHD) printing technology is capable of large-scale deposition of highly oriented nanofibers on rigid or pliable, flat or bent substrates with the advantages of real-time regulation and single control. Therefore, it has a lot of potential in the fabrication of pliable electronic devices for one-dimensional ordered light-emitting fibers. Polycaprolactone (PCL) as an EHD printing technology polymer material has the advantages of superior biocompatibility, a low melting point, saving energy and easy degradation. By synthesizing CsPbBr3 quantum dots (QDs) and PCL composite spinning stock solution, we used the self-built EHD printing platform to prepare the PCL@CsPbBr3 composite light-emitting optical fiber and realized the flexible display of high-resolution micropatterns in polydimethylsiloxane (PDMS) packaging. An x-ray diffractometer (XRD), scanning electron microscope (SEM) and photoluminescence (PL) were used to characterize and analyze the fiber’s morphology, phase and spectral characteristics. EHD printing technology may open up interesting possibilities for flexible display applications based on metal halide PQDs.

In situ passivation and thiol-mediated anchoring of perovskite quantum dots in mesoporous covalent-organic frameworks

Metal halide perovskite quantum dots (PQDs) are considered as promising candidate for the next generation optoelectronic applications. However, their development is severely restricted by their poor stability. Here, we demonstrate the in situ growth of PQDs in the ordered channels of functionalized covalent-organic frameworks (COFs). The strong S-Pb chemical binding firmly anchors the PQDs in COF matrix, which prevent the aggregation of PQDs and eliminate the nonradiative trap centers of PQDs, leading to the high photoluminescence quantum yield (81.5 %) and remarkable stability. Femtosecond transient absorption spectroscopy reveal the elimination of nonradiative trap centers in PQD@COFs. Theoretical simulation results demonstrate the strong waveguide effect in PQD@COFs, which reduces the reabsorption loss. Further, the obtained white light-emitting diode exhibits ultrahigh luminous efficiency of 89.6 lm/W and excellent operating stability, which paves the way for the commercial application of PQDs.

In-Situ Anchoring Pb-Free Cs3 Bi2 Br9 @BiOBr Quantum Dots on NHx -Rich Silica with Enhanced Blue Emission and Satisfactory Stability for Photocatalytic Toluene Oxidation.

All-inorganic metal halide perovskite quantum dots (QDs) have attracted attention from researchers with their fascinating optoelectronic properties. However, blue-emitting perovskite QDs typically have low photoluminescence quantum yield (PLQY). For potential commercial applications, it is preferable to replace Pb with an element having low toxicity. Here, Pb-free Cs3 Bi2 Br9 @BiOBr perovskite QDs were anchored on the surface of NHx -rich monodisperse silica (A-SiO2 ) via N-Bi chemical bonding to isolate QDs from each other, thus enhancing efficient surface passivation and suppressing optical decay. Compared to unanchored QDs, Cs3 Bi2 Br9 @BiOBr QDs/A-SiO2 composites exhibited significantly enhanced blue emission performance, the PLQY of which increased from 16.62 % to 77.26 %, in addition to good water and environmental stability. Finally, the novel composites as photocatalysts were used to drive the oxidation of toluene, a template reaction of C(sp3 )-H bond activation and demonstrated astonishing conversion rates (4317 μmol g-1 h-1 ) with high selectivity (around 87 %).

Autonomous Nanocrystal Doping by Self‐Driving Fluidic Micro‐Processors

Self-Driving Fluidic Micro-Processors In article number 2200017, Milad Abolhasani and co-workers present a self-driving lab using artificial intelligence-guided fluidic blocks for accelerated fundamental and applied studies of emerging clean energy materials. Autonomous doping of metal halide perovskite quantum dots is demonstrated as a material testbed of this self-driving lab.

Highly effective surface defect passivation of perovskite quantum dots for excellent optoelectronic properties

Metal halide perovskite quantum dots (QDs) are next-generation materials with excellent optical and electrical properties suitable for display applications. However, their significantly large surface-area-to-volume ratio makes them highly susceptible to surface defects. In this study, we developed an effective passivation strategy that uses various imide derivatives (namely, caffeine, 4-amino-N-methylphthalimide, and 6-amino-1,3-dimethyluracil) to synthesize high-performance perovskite QDs. Caffeine or 6-amino-1,3-dimethyluracil significantly improved the optical properties and thermal stability by passivation of under-coordinated Pb2+ ions of the perovskite QDs. Moreover, these aided the removal of black dots that act as trap states, thereby yielding pure crystals. In contrast, 4-amino-N-methylphthalimide passivation led to deterioration of the optical properties and poor crystal purity because of its intrinsic impurities (black dots). Molecular calculations confirmed that the atomic charge of the carbonyl oxygen of the imide derivatives was proportional to the efficacy of passivation. The caffeine-passivated perovskite QDs were used to fabricate red, green, and blue light-emitting diodes. The current and external quantum efficiencies of these devices were significantly improved compared to those of the devices with pristine perovskite QDs. The color coordinate values of the fabricated devices showed an ultra-wide color gamut of 130% National Television System Committee.

Highly efficient luminescence and enhanced stability of nanocomposites by encapsulating perovskite quantum dots in defect-related luminescent silica nanospheres

The metal-halide perovskite quantum dots (PQDs) have been emerged as new stars of optoelectronic materials with fascinating luminescence properties. However, the poor stability of these materials severely restricts their practical applications. In this work, the novel defect-related luminescent mesoporous silica nanospheres are employed as protective matrix to improve the stability of PQDs for the first time. Firstly, the monodisperse CsPbBr3 and CsPbBr1.5I1.5 PQDs with perfect nanocube morphology and eminent luminescence properties have been prepared respectively by a facile synthesis strategy. Then, the CsPbBr3 and CsPbBr1.5I1.5 PQDs are encapsulated into the non-luminescent (SN) and luminescent silica matrix (DL-SN) respectively, resulting in the PQDs@SN and PQDs@DL-SN nanocomposites. The incorporation of the PQDs and silica matrix can be confirmed by XRD, FT-IR, TEM, XPS, elemental mapping images, N2 adsorption/desorption isotherms, and density functional theory. The as-synthesized silica matrix especially for the DL-SN presents a remarkable enhancement of stability against temperature, storage time, and water for both CsPbBr3 and CsPbBr1.5I1.5 in comparison to the pristine PQDs. Furthermore, the formation mechanism and stability improvement mechanism have been discussed in detail. This work provides a facile and general approach to solve the intrinsic instability of all-inorganic PQDs, which may have a significant impact on their practical applications.

Temperature-Dependent Optical Properties of Perovskite Quantum Dots with Mixed-A-Cations.

In this work, metal halide perovskite quantum dots (QDs) with Formamidinium (FA) and Cs mixed cations were fabricated using a solution-processed method at room temperature. By controlling Cs doping ratios in a precursor, the optical properties of mixed-cation perovskite QDs were systematically studied. With the increase in Cs ion doping, the photoluminescence (PL) spectra of perovskite QDs were blueshifted, which was mainly due to the smaller radius of Cs ions than those of FA. Temperature-dependent PL spectra were conducted on mixed-cation perovskite QDs. As the temperature gradually increased from 4 K to 300 K, PL peaks were blue shifted, and full-width at half maximum (FWHM) was widened, which was directly related to lattice thermal expansion and the carrier-photon coupling effect under temperature variation. At the same time, excess Cs ion doping had a prominent influence on optical properties at low temperatures, which was mainly due to the introduction of detrimental defects in perovskite crystals. Therefore, it is particularly important to control doping concentration in the preparation of high-quality perovskite QDs and efficient photoelectric devices.

Tough, stable and self-healing luminescent perovskite-polymer matrix applicable to all harsh aquatic environments

Gelatinous underwater invertebrates such as jellyfish have organs that are transparent, luminescent and self-healing, which allow the creatures to navigate, camouflage themselves and, indeed, survive in aquatic environments. Artificial luminescent materials that can mimic such functionality can be used to develop aquatic wearable/stretchable displays and water-resistant devices. Here, a luminescent composite that is simultaneously transparent, tough and can autonomously self-heal in both dry and wet conditions is reported. A tough, self-healable fluorine elastomer with dipole–dipole interactions is synthesized as the polymer matrix. It exhibits excellent compatibility with metal halide perovskite quantum dots. The composite possesses a toughness of 19 MJ m−3, maximum strain of 1300% and capability to autonomously self-heal underwater. Notably, the material can withstand extremely harsh aqueous conditions, such as highly salty, acidic (pH = 1) and basic (pH = 13) environment for more than several months with almost no decay in mechanical performance or optical properties.

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

Metal halide perovskite quantum dots (PQDs) and perovskite magic sized clusters (PMSCs) exhibit interesting size- and composition-dependent optoelectronic properties that are promising for emerging applications including photovoltaic solar cells and light-emitting diodes (LEDs). Much work has focused on developing new synthesis strategies to improve their structural stability and property tunability. In this paper, we review recent progress in the synthesis and characterization of PQDs and PMSCs, with a focus on the impact of different molecular ligands on their surface passivation and interconversion. Moreover, the effect of capping ligands on ion exchange during synthesis and doping is discussed. Finally, we present some perspectives on challenges and opportunities in fundamental studies and potential applications of both PQDs and PMSCs.

One-pot synthesis of novel ligand-free tin(II)-based hybrid metal halide perovskite quantum dots with high anti-water stability for solution-processed UVC photodetectors.

Recently, lead-based halide perovskites have gained extensive attention due to their outstanding optoelectronic properties. However, the toxicity of lead would seriously limit its future application. To address these issues, in this work novel ligand-free organic-inorganic hybrid metal halide TBASnCl3 (C16H36NSnCl3) quantum dots are synthesized by a one-pot method at room temperature, and they showed high anti-water stability and high potential applications for high-performance UVC photodetectors. Our experimental data showed that the responsivity of the lateral photodetectors Au/TBASnCl3/Au, in which the active layer (i.e. TBASnCl3) was synthesized by further introducing SnF2 as a precursor besides SnCl2, reached 7.3 mA W-1 with a specific detectivity of 1.67 × 1011 Jones under 0.36 mW cm-2 254 nm illumination at -5 V, and it showed a long lifetime even in an environment with an air humidity of 60%. Therefore, it laid a solid foundation for further fabricating lead-free metal halide optoelectronic devices.

Surface Chemistry Engineering of Perovskite Quantum Dots: Strategies, Applications, and Perspectives.

The presence of surface ligands not only plays a key role in keeping the colloidal integrity and non-defective surface of metal halide perovskite quantum dots (PQDs), but also serves as a knob to tune their optoelectronic properties for a variety of exciting applications including solar cells and light-emitting diodes. However, these indispensable surface ligands may also deteriorate the stability and key properties of PQDs due to their highly dynamic binding and insulating nature. To address these issues, a number of innovative surface chemistry engineering approaches have been developed in the past few years. Based on an in-depth fundamental understanding of the surface atomistic structure and surface defect formation mechanism in the tiny nanoparticles, a critical overview focusing on the surface chemistry engineering of PQDs including advanced colloidal synthesis, in-situ surface passivation, and solution-phase/solid-state ligand exchange is presented, after which their unprecedented achievements in photovoltaics and other optoelectronics are presented. The practical hurdles and future directions are critically discussed to inspire more rational design of PQD surface chemistry toward practical applications.