All-inorganic Cesium Lead Halide Perovskite Research Articles

In Situ Annealing Effect on Thermally Co-Evaporated CsPbI2Br Thin Films Studied via Spectroscopic Ellipsometry.

All-inorganic cesium lead halide perovskites possess excellent thermal stability, a feature that renders them highly favorable for optoelectronic applications with an elevated thermal budget. Employing a coevaporation approach for their deposition holds promise for manufacturing at an industrial level, owing to improvements in device scalability and reproducibility. For unlocking the full potential of vacuum-evaporated perovskite thin films, it is crucial to delve deeper into their crystallization process, which, as a solid-state reaction, has been less investigated compared to the crystallization process of, most commonly used, solution-based methods. In this work, we employ spectroscopic ellipsometry, a nondestructive, high speed, and high accuracy characterization method, to study the real time annealing effect on thermally coevaporated CsPbI2Br thin films in a temperature range between 25 and 300 °C. We achieve this by developing a singular dynamic model that can be fitted in real time as a function of temperature, providing insights into how thermal annealing influences the perovskite film's morphology and optical constants. Based on the latter, we derive the temperature dependence of the thermo-optic coefficient and Urbach energy as well as analyze the interband transition energies via critical point analysis. We demonstrate that the γ- to β-phase transition can be identified through a pronounced shift in the bandgap energy, whereas the β- to α-phase transition can be discerned by a sharp increase in the film's roughness. We corroborate the obtained fit results with additional in- and ex situ measurements, such as in situ grazing incidence wide-angle X-ray scattering, atomic force microscopy, reflectance/transmittance, and profilometry.

Efficiently green-emitting and ultra-stable CsPbBr3@SiO2 nanocomposites for white light-emitting diodes

Inorganic oxide especially SiO2 encapsulation strategy is an effective way to improve the stability of all-inorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) nanocrystals (NCs). However, when CsPbX3 NCs are encapsulated in SiO2 by in situ tetraethyl orthosilicate (TEOS) hydrolysis, the unavoidable by-products (water and ethanol) of TEOS hydrolysis commonly damage the structural and optical properties of the CsPbX3 NCs. Herein, TDPA-CsPbBr3 NCs with the dense tetradecylphosphonic acid (TDPA) passivation were pre-prepared and subsequently encapsulated into SiO2 via in situ TEOS hydrolysis. Benefitting from the dense phosphonic passivation layer capable of resisting the erosion of polar by-products generated by TEOS hydrolysis, the obtained TDPA-CsPbBr3@SiO2 nanocomposites maintain the excellent optical properties of the colloidal CsPbBr3 NCs, showing near-unity photoluminescence quantum yield (PLQY) and ultra-narrow full width at half maximum (FWHM). Furthermore, the TDPA-CsPbBr3@SiO2 nanocomposites exhibit outstanding stability against ethanol, UV light, and heating treatment due to the dual protection of dense phosphonate ligand layers and inorganic SiO2 matrix. The white light-emitting diodes (WLED) device was fabricated by sequentially depositing green-emitting TDPA-CsPbBr3@SiO2 nanocomposites and red-emitting K2SiF6:Mn on blue-emitting GaN LED chip. The obtained WLED exhibits excellent luminous performances with standard white emission of CIE Coordinates (0.33, 0.33), a color gamut 138 % of the NTSC and 103 % of Rec. 2020, respectively. This study demonstrates that TDPA-CsPbBr3@SiO2 nanocomposites have a potential application in solid-state lighting and backlight displays.

Tuning the fluorescence emission of water-stable CsPb(Br/I)3 perovskite nanocrystal probes for naked-eye visual detection of mercury ion

All-inorganic cesium lead halide perovskite nanocrystals (PNCs) have rarely been reported in analytical chemistry, especially in water environment analysis, due to their high susceptibility to environmental conditions. Herein, we investigate and report a method of visual detection of Hg2+ concentration in aqueous solution using CsPb(Br/I)3 PNCs. In this strategy, three kinds of CsPb(Br/I)3 PNCs with FL emission peaks of 551 nm, 591 nm, and 617 nm were used to detect Hg2+, and it was found that Hg2+ can quench the fluorescence of CsPb(Br/I)3 PNCs and blue-shift the maximum FL emission peak. We also found that the Hg2+ concentration has a good linear relationship with the fluorescence quenching rate (I0/I) and FL emission peak shift (Δλ) of CsPb(Br/I)3 PNCs. With the red-shift of the probe FL emission peak, the detected concentration range of Hg2+ gradually expanded. Therefore, the possibility of detecting Hg2+ concentration without huge equipment was detailed by examining the red (R), green (G), and blue (B) values of photographs of CsPb(Br/I)3 PNCs with Hg2+. Under a 365 nm ultraviolet (UV) lamp, the solution color of CsPb(Br/I)3 PNCs emission peaks at 591 nm gradually changes from orange to green with the increase of Hg2+ concentration, which has an excellent visualization effect. The method presented here has the potential to establish a new analytical method for the visual detection of Hg2+ in aqueous environments, and may also facilitate the application of all-inorganic cesium lead halide perovskite nanocrystals for analytical detection in aqueous environments.

Facile synthesis of phase-adjustable CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> composite nanocrystals and <i>in-situ</i> study of phase transformation process

All-inorganic cesium lead halide perovskites have shown great potential applications in optoelectronic field due to their fascinating optical properties. Although perovskite materials have achieved great success in various fields, their inherent ionic properties and high dynamic surface properties have led to their poor stability, hindering their applications. The preparation of CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals has proven to be an effective strategy to enhance their photoluminescence properties and stability. Herein, we report an easy synthesis of CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> nanocrystals with a diphase structure at room temperature by using Cs-OA, Pb-OA and TOABr as precursors in toluene. It is found that the phase transformation and the relative composition between CsPbBr<sub>3</sub> and Cs<sub>4</sub>PbBr<sub>6</sub> are dependent on the concentration of TOABr and the ratio of Cs/Pb. The <i>in-situ</i> PL experiments reveal that the formation of ~12 nm CsPbBr<sub>3</sub> nanocubes experiences the fast nucleation, the focusing growth of size-distribution in early growth stage and Ostwald ripening growth in the later stage at a TOABr concentration of 0.16 mmol. With the increase of concentration of TOABr or molar ratio of Cs/Pb > 1 (Cs/Pb < 1), [PbBr<sub>4</sub>]<sup>2–</sup> complex and [PbBr<sub>3</sub>]<sup>–</sup> complex can coexist and compete with each other in toluene, and the CsPbBr<sub>3</sub> nucleations dominate in the early stage, then CsPbBr<sub>3-</sub>Cs<sub>4</sub>PbBr<sub>6</sub> nanocomposites are gradually formed on CsPbBr<sub>3</sub> nucleations as photoluminescence centers due to the continuous generation of [PbBr<sub>4</sub>]<sup>2–</sup> complex between TOABr and Pb<sup>2+</sup>. The relative composition of Cs<sub>4</sub>PbBr<sub>6</sub> in CsPbBr<sub>3-</sub>Cs<sub>4</sub>PbBr<sub>6</sub> nanocomposites can be improved from 4% to 85% with the concentration of TOABr increasing or Cs/Pb < 1. The optimized CsPbBr<sub>3</sub>-Cs<sub>4</sub>PbBr<sub>6</sub> composite nanocrystals possess high PLQY and stability. Our work provides an understanding of the mechanism of phase transformation in cesium lead halide perovskite materials.

Turn-on fluorescence humidity sensing based on Cs4PbBr6 nanocrystal array

A nanocrystal array composed of Cs4PbBr6 has been prepared and employed for turn-on fluorescence humidity sensing. This nanoarray assures a low detection limit, rapid response times, and the incorporation of statistical data acquisition.

Linearly Manipulating Color Emission via Anion Exchange Technology for High Performance Amplified Spontaneous Emission of Perovskites.

The most attractive advantages of all-inorganic cesium lead halide perovskites are their optical gain over broad spectral ranges through the visible spectrum, so are well suited to use in tunable lasers or broadband amplifiers. Most reported anion exchange reactions face a challenge to achieve the desired halogen-variable perovskites due to rapid and uncontrollable reactions and difficulty to synthesize directly. In this study, a simple vapor/solid anion exchange strategy is demonstrated for controlling the reaction process and realizing a wide range tuning of band gap and amplified spontaneous emission (ASE) wavelength, which exhibits a temperature-dependent anion exchange rate. By optimizing the reaction temperature at 90°C, the ASE wavelength can be linearly manipulated by just controlling the reaction time. A clear quantitative relationship between ASE peak position and reaction time is achieved. Compares with the CsPbClBr2 film obtained via the liquid phase anion exchange method, the fabricated perovskite films obtained by vapor/solid anion exchange technology exhibit superior film quality and enhanced ASE performance. This work may have applications in the future using facile and controllable techniques to develop high-quality full-color visible lasers.

In Situ Real-Time Observation of Formation and Self-Assembly of Perovskite Nanocrystals at High Temperature.

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have received much attention due to their outstanding optical and electronic properties, but the underlying growth mechanism remains elusive due to their rapid formation process. Here, we report an in situ real-time study of the growth of Cs4PbBr6 NCs under practical synthesis conditions in a custom-made reactor. Through the synchrotron-based small-angle X-ray scattering technique, we find that the formation of Cs4PbBr6 NCs is accomplished in three steps: the fast nucleation process accompanied by self-focusing growth, the subsequent diffusion-limited Ostwald ripening, and the self-assembly of NCs into the face-centered cubic (fcc) superlattices at high temperature and the termination of growth. The simultaneously collected wide-angle X-ray scattering signals further corroborate the three-step growth model. The influence of superlattice formation is also elucidated, which improves the uniformity of the final NCs.

Multi-Functional Ethylene-vinyl Acetate Copolymer Flexible Composite Film Embedded with Indium Acetate-Passivated Perovskite Quantum Dots.

In recent years, all-inorganic cesium lead halide perovskite quantum dots have emerged as promising candidates for various optoelectronic applications, including sensors, light-emitting diodes, and solar cells, owing to their exceptional photoelectric properties. However, their commercial utilization has been limited by stability issues. In this study, we addressed this challenge by passivating the surface defects of CsPbBr3 quantum dots using indium acetate, a metal-organic compound. The resulting CsPbBr3 quantum dots exhibited not only high photoluminescence intensity, but also a remarkably narrow half-peak width of 19 nm. Furthermore, by embedding the CsPbBr3 quantum dots in ethylene-vinyl acetate, we achieved stretchability and significantly enhanced stability while preserving the original luminous intensity. The resulting composite film demonstrated the potential to improve the power conversion efficiency of crystalline silicon solar cells and enabled the creation of excellent white light-emitting diodes with coordinates of (0.33, 0.31). This co-passivation strategy, involving surface passivation and polymer packaging, provides a new idea for the practical application of CsPbBr3 quantum dots.

Perovskite quantum dot one-dimensional topological laser

Various topological laser concepts have recently enabled the demonstration of robust light-emitting devices that are immune to structural deformations and tolerant to fabrication imperfections. Current realizations of photonic cavities with topological boundaries are often limited by outcoupling issues or poor directionality and require complex design and fabrication that hinder operation at small wavelengths. Here we propose a topological cavity design based on interface states between two one-dimensional photonic crystals with distinct Zak phases. Using a few monolayers of solution-processed all-inorganic cesium lead halide perovskite quantum dots as the ultrathin gain medium, we demonstrate a lithography-free, vertical-emitting, low-threshold, and single-mode laser emitting in the green. We show that the topological laser, akin to vertical-cavity surface-emitting lasers (VCSELs), is robust against local perturbations of the multilayer structure. We argue that the design simplicity and reduction of the gain medium thickness enabled by the topological cavity make this architecture suitable for low-cost and efficient quantum dot vertical emitting lasers operating across the visible spectral region.

Patterning Perovskite Quantum Dots Using Photopolymerization.

All-inorganic cesium lead halide perovskite quantum dots (QDs) have several potential applications, owing to their unique optical and electronic properties. However, patterning perovskite QDs using conventional methods is difficult because of the ionic nature of QDs. Here, we demonstrate a unique approach, in which perovskite QDs are patterned in polymer films through the photocuring of monomers under patterned light illumination. The pattern illumination creates the transient polymer concentration difference, which drives the QDs to form patterns; hence controlling polymerization kinetics is essential for the generation of the QD pattern. For the patterning mechanism, a light projection system equipped with a digital micromirror device (DMD) is developed; thus, light intensity, an important factor to determine polymerization kinetics, is precisely controlled per position on the photocurable solution, resulting in the understanding of the mechanism and the formation of distinct QD patterns. The demonstrated approach assisted by the DMD-equipped projection system can form desired perovskite QD patterns solely by patterned light illumination, paving the way for the development of patterning methods for perovskite QDs and other nanocrystals.

CsPbBr3@PbBrOH 3D/1D molecular matrix for a high-performance scintillator

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have become highly sought-after materials for X-ray detection and imaging because of their outstanding intrinsic electronic and optical properties. However, because of their highly ionic crystal structure, perovskite materials suffer severe moisture, thermal, and photo instability problems, which hinder their commercialization. To resolve this annoying problem, three-dimensional (3D)/1D CsPbBr3@PbBrOH composite structures in terms of molecular structure are designed by incorporating highly luminescent 3D CsPbBr3 NCs into a 1D PbBrOH matrix to form an “emitter-in-matrix”. The prepared CsPbBr3@PbBrOH exhibits excellent stability without sacrificing photoluminescence quantum yield. Meanwhile, 1D PbBrOH can be considered a perfect host, and the presence of heavy atom Pb in its matrix enhances X-ray absorption. The luminescent CsPbBr3 NCs embedded in an inert PbBrOH host are subjected to X-ray detection and imaging. The CsPbBr3@PbBrOH scintillator shows bright radiation luminescence and sensitive response to X-ray signals. In addition, the scintillator is made into a thin film screen for imaging, obtaining a clear image of the transmission electron microscopy grid hidden inside the capsule, and the resolution of CsPbBr3@PbBrOH film is calculated to be as high as 50 lp mm−1. This property of CsPbBr3@PbBrOH scintillators demonstrates their promising application prospects for ionizing radiation detection, particularly for X-ray imaging.

Polystyrene-based Macromolecular Ammonium Halides for Tuning Color and Exchange Kinetics of Perovskite Nanocrystals.

Post-synthesis anion exchange of all-inorganic cesium lead halide perovskite nanocrystals (CsPbX3 NCs, where X=Cl, Br, and/or I) provides a rapid and simple means of tuning their band gap and photoluminescence emission wavelengths. Here we report color-shifting of CsPbX3 nanocrystals induced by a macromolecular source of halide ions, specifically using polystyrene with ammonium halides as pendent groups. This strategy for introducing new halides to the perovskite nanocrystals gave access to perovskite-polymer hybrid materials as solutions, thin films, or free-flowing powders. Spectroscopic measurements of the halide-exchanged nanocrystal products revealed high photoluminescence quantum yields across the visible spectrum, with exchange kinetics that were tunable based on the solution environment, suggesting an aggregation-inhibited exchange process that affords access to multi-colored solutions and films.

Improving inorganic perovskite photovoltaic performance via organic cation addition for efficient solar energy utilization

Organic cations help in executing better crystal growth of halide perovskites. Herein, we have realized improved all-inorganic cesium lead halide perovskite film quality with reduced pinholes and high crystallinity in phenylethylammonium (PEA+) assisted perovskite. Additionally, PEA+ cation acts as an additive to control intermediate perovskite phase and executes pure phase perovskite crystal growth as compared to MA+ and FA+ cations assisted perovskite films. X-ray photoelectron and UV–vis spectroscopy results revealed that adding PEA+ in the perovskite helps in almost uniform distribution of Br− ion after post-annealing process. Furthermore, depth profiling analysis reveals that PEA+ in the intermediate phase perovskite interacts more with the ZnO layer beneath perovskite, which helps in the fabrication of compact film. PEA+ sublimates after post-annealing treatment of 300 °C, as no evidence of PEA+ existence was found in characterizations for post-annealed perovskite films. This brings multiple benefits to inorganic mixed halide perovskite film formation. The best performing perovskite solar cell (PSC) exhibits a high conversion efficiency of 14.75% as well as enhanced stability of maintaining almost 83% of its initial efficiency for 400 h. Electrochemical impedance spectroscopy and space-charge-limited current results suggests reduced recombination loss and defect densities in PEA+ assisted PSC.

Different photocurrent response of Cs4PbBr6 particles.

Zero-dimensional (0D) all-inorganic cesium lead halide perovskites, particularly Cs4PbBr6, have been attracting wide attention due to their excellent optical properties and stability. The research also focuses on the origin of green emission from Cs4PbBr6, which has a bandgap located in the ultraviolet B (UVB) region. So far, both Cs4PbBr6 without visible emission and with green emission have been successfully prepared; however, the origin of green emission remains controversial. Photocurrent response is one of the effective approaches to explore how the photo-excited carriers influence the photo-physical properties of materials. In our study, Cs4PbBr6 particles without visible emission and with green emission were synthesized and their photocurrent response was investigated. The former showed a positive photocurrent response, while the latter showed a negative photocurrent response. The negative response was believed to be due to a built-in electric field constructed by the charged excitons in green-emissive Cs4PbBr6. From our calculations, numerous vacancies of Br are easier to appear in green-emissive Cs4PbBr6 lattices, which could combine the neutral excitons to form charged excitons. This work may contribute to the explanation of the origin of green emission of Cs4PbBr6 to some extent.

Highly luminescent lead bromine perovskite via fast and eco-friendly water-assisted mechanochemical method

All-inorganic cesium lead halide perovskite nanocrystals (CPeNCs) have aroused tremendous research attention due to their excellent photophysical properties. Here, we report an eco-friendly and fast water-assisted mechanochemical synthesis of CsPbBr3 perovskite functionalized by oleic acid (OA) and hydroxyl groups (OH). Owing to the water exfoliation and mechanical shearing force, the CsPbBr3 bulks quickly transformed into rectangular CsPbBr3 particles in 10 min with a bright green emission (λem = 525 nm) and a high photoluminescence quantum yield (PLQY) up to 53%. Impressively, the functionalized CsPbBr3 retains their bright green emission in ethanol after 360 days, showing high ethanol resistance. Thus, an alcohol solubility and easy film-forming transparent polymer of polyvinyl butyral (PVB) is directly employed to encapsulate functionalized CsPbBr3 in ethanol solution. The obtained CsPbBr3/PVB composite film shows excellent water resistance, whose photoluminescence intensity drops only 20% after 60 h in water. The composite film was demonstrated as color converter layers of white light-emitting diodes device with color coordinates of (0.329, 0.321). This work not only offers a green synthesis method for perovskite fluorescent material, but also helps to address their long-term stability in polar solvents towards their various applications.

The phosphorescence emission in undoped lead-halide Cs4PbBr6 single crystals at low temperature

Recently, all-inorganic cesium lead-halide perovskites have shown their promise for light emission applications, due to the excellent optical performance. Herein, we report that the initially nonphosphorescent undoped lead-halide Cs4PbBr6 single crystals (SCs) exhibit an ultralong phosphorescence emission under X-ray excitation at low temperatures. It is shown that the dramatic change has been taken place in radioluminescence spectra and the broad-band emission gradually appeared with the decrease of temperature. Below 210 K, the radioluminescence spectra can be deconvoluted into one narrow peak located at 530 nm and two broad peaks centered at 595 nm and 672 nm respectively. Subsequently, the time-dependent radioluminescence spectra in undoped lead-halide Cs4PbBr6 SCs were investigated. The ultralong phosphorescence emission can persist over 120 min at 70 K. We consider that ultralong phosphorescence originates from defect-related emission. To the best of our knowledge, our finding is the first time that undoped Cs4PbBr6 SCs exhibit the phosphorescence emission, which will offer a paradigm to motivate revolutionary applications on perovskite.

In situ siloxane passivation of colloidal lead halide perovskite via hot injection for light-emitting diodes.

All-inorganic cesium lead halide perovskite (CsPbX3; X = Cl, Br) nanocrystals (NCs) are synthesized via a modified hot injection method using 3-mercaptopropyltrimethoxysilane (MPTMS), together with oleic acid and oleylamine, for in situ passivation of the surface defects. The surface chemistry, revealed by Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) techniques, shows an absence of Si-O-Si network and C-O groups on these in situ passivated CsPbX3 NCs, denoted as InMP-CsPbX3, which is in strong contrast to the counterpart NCs obtained via a postsynthesis exchange strategy. The x-ray diffraction (XRD) pattern indicates a lattice structure significantly strained from the cubic structure. The synthesis of these InMP-CsPbX3 NCs is highly reproducible, and the colloids are stable in nonpolar solvents. The emission wavelength of CsPb(Cl/Br)3 mixed halide perovskite NCs is tuned from 405 nm to 508 nm by reducing the nominal Cl/Br ratio, while the photoluminescence quantum yield (PLQY) is greatly enhanced over the whole spectral range. More importantly, the InMP-treatment is among the few strategies that are promising for electroluminescence in light-emitting diodes.

Rapid and facile electrospray preparation of CsPbBr3@PMMA fluorescent microspheres for fluorescent detection of ALP in biological samples

All-inorganic cesium lead halide perovskite quantum dots (QDs) have attracted more attention due to their excellent optoelectronic and photovoltaic properties. However, there are few applications in biochemical detection based on their unique photoluminescence property mainly because of the instability to external stimulus. In this work, we focus on a rapid preparation method of CsPbBr3@poly (methyl methacrylate) (PMMA) fluorescent composite microspheres based on electrospray to protect CsPbBr3 QDs from the external stimuli and stabilize them in aqueous environment. The CsPbBr3@PMMA composite microspheres effectively retained over 70% fluorescence intensity after being immersed in deionized water for 20 days. Based on the effective quenching of CsPbBr3@PMMA composite microspheres by MnO2 nanosheets, we developed a simple, label-free, low-cost, and facile fluorescent detection system for assay of alkaline phosphatase (ALP) in biological samples. The method shows a good linear relationship from 10.0 mU/mL to 100 mU/mL (R2 = 0.998) with the detection limit of 4.85 mU/mL and the recovery range of 95.1–110%. In summary, the PMMA coating can simply and effectively stabilize the CsPbBr3 QDs and preserve the luminescence of the CsPbBr3 QDs. The excellent applicability of the composite microspheres-based fluorescent detection system in human serum samples further demonstrates the potential application in the aqueous phase-based biochemical detection for clinical diagnosis and biomedical research.

On-chip unidirectional micro-nano-light sources based on multi-mode cesium lead halide perovskite nanowires

Unidirectional micro-nano-light sources have been widely applied in integrated photonics and optoelectronic devices. In this study, on-chip all-inorganic cesium lead halide perovskite nanowires are employed and excited as a bright light source to generate unidirectional light. Here, we directly image the angular emission patterns of perovskite nanowires by using fluorescence Fourier microscopy. The extinction ratio for the unidirectional emission is achieved up to 11 dB, and the detected minimum polar divergence angle reaches 8.6° in experiments. The emission direction also can be tuned flexibly within the range of 48° by changing the upper surrounding medium. Detailed calculations based on multi-mode expansion theory are used to reveal the inner physical mechanisms. Further analysis of the far-field emission patterns corresponds well with the experiment results. Our works investigating the perovskite nanowire light source emission from the perspective of Fourier space have potential applications in photon-detection and integrated photonics chips.

Theoretical Study on the Contacting Interface-Dependent Band Alignments of CsPbBr3@MoS2 van der Waals Heterojunctions: Spin–Orbit Coupling Does Matter

Van der Waals heterojunctions formed by all-inorganic cesium lead halide perovskites and two-dimensional transition-metal dichalcogenides (TMDs) have received much attention in recent years due to ...