From Nonluminescent Cs4PbX6 (X = Cl, Br, I) Nanocrystals to Highly Luminescent CsPbX3 Nanocrystals: Water-Triggered Transformation through a CsX-Stripping Mechanism

Rationalizing and Controlling the Surface Structure and Electronic Passivation of Cesium Lead Halide Nanocrystals

Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and luminescent properties are challenged by the lability of their surfaces, i.e., the interface of the NC core and the ligand shell. On the example of CsPbBr₃ NCs, we model the nanocrystal surface structure and its effect on the emergence of trap states using density functional theory. We rationalize the typical observation of a degraded luminescence upon aging or the luminescence recovery upon postsynthesis surface treatments. The conclusions are corroborated by the elemental analysis. We then propose a strategy for healing the surface trap states and for improving the colloidal stability by the combined treatment with didodecyldimethylammonium bromide and lead bromide and validate this approach experimentally. This simple procedure results in robust colloids, which are highly pure and exhibit high photoluminescence quantum yields of up to 95-98%, retained even after three to four rounds of washing.

An overview on enhancing the stability of lead halide perovskite quantum dots and their applications in phosphor-converted LEDs

Beyond the unprecedented success achieved in photovoltaics (PVs), lead halide perovskites (LHPs) have shown great potential in other optoelectronic devices. Among them, nanometer-scale perovskite quantum dots (PQDs) with fascinating optical properties including high brightness, tunable emission wavelength, high color purity, and high defect tolerance have been regarded as promising alternative down-conversion materials in phosphor-converted light-emitting diodes (pc-LEDs) for lighting and next-generation of display technology. Despite the promising applications of perovskite materials in various fields, they have received strong criticism for the lack of stability. The poor stability has also attracted much attention. Within a few years, numerous strategies towards enhancing the stability have been developed. This review summarizes the mechanisms of intrinsic- and extrinsic-environment-induced decomposition of PQDs. Simultaneously, the strategies for improving the stability of PQDs are reviewed in detail, which can be classified into four types: (1) compositional engineering; (2) surface engineering; (3) matrix encapsulation; (4) device encapsulation. Finally, the challenges for applying PQDs in pc-LEDs are highlighted, and some possible solutions to improve the stability of PQDs together with suggestions for further improving the performance of pc-LEDs as well as the device lifetime are provided.

Tin-assisted growth of all-inorganic perovskite nanoplatelets with controllable morphologies and complementary emissions

The Sn⁴⁺-assisted growth of CsPbBr₃ nanoplatelets with the quantum confinement effect enables controllable morphologies and formation of dual photoluminescence emission.

Improved photoelectric performance of all-inorganic perovskite through different additives for green light-emitting diodes

Improving the performance of all-inorganic CsPbBr₃–PEO–PVP-based LEDs with the structure of ITO/PEDOT:PSS/Perovskite/TPBI/LiF/Al.

Blue-Emitting CsPbCl3 Nanocrystals: Impact of Surface Passivation for Unprecedented Enhancement and Loss of Optical Emission

High-energy-emitting CsPbCl₃ nanocrystals have shown significant loss and enhancement of their emission intensity (∼40-50 folds) during purification and surface treatments, respectively. This confirms that the surfaces of these nanocrystals are very sensitive. In this Letter, physical insights of the interface bindings on the surface of these blue-emitting CsPbCl₃ nanocrystals with different passivating agents and their consequential impact on purification are investigated. Using various metal chlorides irrespective of the charge and size of the metal ions, metal acetates, and nonmetal chloride, the predominant influence of chloride ions in helping retrieve/intensify the blue emission is established. The purification processes are observed to be very delicate, and successive purifications with introduction of polar nonsolvents led to the transformation of an emitting cubic CsPbCl₃ phase to nonemitting tetragonal CsPb₂Cl₅ phase nanocrystals irreversibly. The impact of various salt additions only temporarily helped in enhancing the emission, but the phase change remained inevitable upon successive purification. However, as a remedy, by in situ use of alkylammonium chloride salt in high-temperature reactions, the surface binding was improved, and significant emission as well as the phase could be retained with successive purifications.

Controllable and facile synthesis of CsPbBr3-Cs4PbBr6 perovskite composites in pure polar solvent

Here, we present a single atomic supersaturated recrystallization method to synthesize the green-emitting CsPbBr₃-Cs₄PbBr₆ perovskite composites in solid state with the highest PLQY of 40.8% in pure polar solvent. The component, morphology, and optical properties of the microcrystals can be tuned by varying growth time, the content of ammonium bromide, and bromine source. The developed method provides a new route to large-scale synthesize high quality perovskite composites emitters for light-emitting diodes.

CsBr-Induced Stable CsPbI3- xBr x ( x < 1) Perovskite Films at Low Temperature for Highly Efficient Planar Heterojunction Solar Cells

All-inorganic cesium lead perovskites have emerged as alternative absorbing layers in solar cells owing to their superb thermal stability compared with the organic-inorganic hybrid perovskites. However, the desired cubic CsPbI₃ phase forms at a high temperature and suffers from a phase transition to the orthorhombic yellow phase at room temperature. A developed nonstoichiometric method is applied to fabricate CsPbI_{3- x}Br _x ( x < 1) films by adding excess CsBr into the precursor solution. The excess CsBr in the precursor solution helps to produce a microstrain in the lattice to stabilize the cubic CsPbI₃ phase at low temperature and incorporate a small part of Br^- into the CsPbI₃ lattice. At the optimal CsBr concentration (0.5 M), the corresponding solar cell achieves a power conversion efficiency of 10.92%. This work provides an effective way to stabilize the cubic CsPbI_{3- x}Br _x ( x < 1) phase at low temperature to further improve the performance of all-inorganic perovskite solar cells.

Self-Assembly of Perovskite Crystals Anchored Al2 O3 -La2 O3 Nanofibrous Membranes with Robust Flexibility and Luminescence

Inorganic luminescent materials as one of the important high-performance materials are widely used for industry and scientific research, mainly owing to their outstanding luminescence properties. However, inorganic luminescent materials are typically brittle and inelastic, which greatly limit their use in practical applications, particularly in flexible optoelectronic devices. In this work, it is shown that "plum-pudding" like CsPbBr₃ /Cs₄ PbBr₆ perovskite crystals anchor onto Al₂ O₃ -La₂ O₃ (CCAL) nanofibrous membranes, which are synthesized via a facile electrospinning and subsequent supersaturated recrystallization process. The as-synthesized CCAL membranes exhibit outstanding mechanical flexibility and luminescence properties. Meanwhile, the crystal structure and luminous performance of the CCAL membranes are regulated by different molar ratios of CsBr/PbBr₂ . The photoluminescence reaches a maximum value for the CCAL membranes produced with a CsBr/PbBr₂ ratio of 1, and shows a narrow emission line-width of 18 nm. Furthermore, the potential applications of the CCAL nanofibrous membranes in green light devices through a remote nanofibrous membranes packaging approach are demonstrated. A pure green emission is achieved with the Commission Internationale de L'Eclairage color coordinates of (0.28, 0.65). This facile strategy would open a new avenue to flexible inorganic luminescent materials for the lighting and backlight display industries.

Pressure-induced emission of cesium lead halide perovskite nanocrystals

Metal halide perovskites (MHPs) are of great interest for optoelectronics because of their high quantum efficiency in solar cells and light-emitting devices. However, exploring an effective strategy to further improve their optical activities remains a considerable challenge. Here, we report that nanocrystals (NCs) of the initially nonfluorescent zero-dimensional (0D) cesium lead halide perovskite Cs₄PbBr₆ exhibit a distinct emission under a high pressure of 3.01 GPa. Subsequently, the emission intensity of Cs₄PbBr₆ NCs experiences a significant increase upon further compression. Joint experimental and theoretical analyses indicate that such pressure-induced emission (PIE) may be ascribed to the enhanced optical activity and the increased binding energy of self-trapped excitons upon compression. This phenomenon is a result of the large distortion of [PbBr₆]^4- octahedral motifs resulting from a structural phase transition. Our findings demonstrate that high pressure can be a robust tool to boost the photoluminescence efficiency and provide insights into the relationship between the structure and optical properties of 0D MHPs under extreme conditions.

Cs4PbX6 (X = Cl, Br, I) Nanocrystals: Preparation, Water-Triggered Transformation Behavior, and Anti-Counterfeiting Application

As a promising material, Cs₄PbX₆ (X = Cl, Br, I) nanocrystals (NCs) have attracted much attention. However, their luminescent property is still under debate. In this work, we first systematically studied the colloidal preparation of Cs₄PbX₆ NCs. It is found that the critical parameter for the formation of Cs₄PbX₆ NCs is the ratio between Cs and Pb. Pure Cs₄PbX₆ NCs are nonluminescent. The luminescence property of previous reported Cs₄PbX₆ NCs may come from the impurity of luminescent CsPbX₃ NCs. No coexistence of both Cs₄PbX₆ and CsPbX₃ phase has been found in one single nanoparticle. The water-triggered transformation from nonluminescent Cs₄PbX₆ NCs to luminescent CsPbX₃ NCs has been quantitatively studied. The potential application of Cs₄PbX₆ NCs in humidity sensor and anticounterfeiting have been demonstrated. This work is important because it not only confirmed the nonluminescent nature of Cs₄PbX₆ NCs but also demonstrated the potential application of such NCs.

One-Pot Synthesis of Highly Stable CsPbBr3@SiO2 Core-Shell Nanoparticles

The practical applications of CsPbX₃ nanocrystals (NCs) have been limited by their poor stability. Although much effort has been devoted to making core-shell nanostructures to enhance the stability of CsPbX₃ NCs, it is still very difficult to coat CsPbX₃ NCs with another material on a single-particle level. In this work, we report a facile one-pot approach to synthesize CsPbBr₃@SiO₂ core-shell nanoparticles (NPs), in which each core-shell NP has only one CsPbBr₃ NC. The formation process has been carefully monitored. It has been found that the formation rates, determined by reaction temperature, precursor species, pH value, etc., of both CsPbBr₃ and SiO₂ are critical for the successful preparation of core-shell NPs. Thanks to the protection of SiO₂ shell, the product shows much higher long-term stability in humid air and enhanced stability against ultrasonication treatment in water than that of naked CsPbBr₃ NCs. This work not only provides a robust method for the preparation of core-shell nanostructures but also sheds some light on the stabilization and applications of CsPbX₃ NCs.

All-Inorganic Metal Halide Perovskite Nanocrystals: Opportunities and Challenges

The past decade has witnessed the growing interest in metal halide perovskites as driven by their promising applications in diverse fields. The low intrinsic stability of the early developed organic versions has however hampered their widespread applications. Very recently, all-inorganic perovskite nanocrystals have emerged as a new class of materials that hold great promise for the practical applications in solar cells, photodetectors, light-emitting diodes, and lasers, among others. In this Outlook, we first discuss the recent developments in the preparation, properties, and applications of all-inorganic metal halide perovskite nanocrystals, with a particular focus on CsPbX₃, and then provide our view of current challenges and future directions in this emerging area. Our goal is to introduce the current status of this type of new materials to researchers from different areas and motivate them to explore all the potentials.

Tuning the Optical Properties of CsPbBr3 Nanocrystals by Anion Exchange Reactions with CsX Aqueous Solution

Topotactic anion exchange has been developed to tune the composition and band gap energies of cesium lead halide (CsPbX₃) perovskite nanocrystals (NCs). However, current anion exchange methods either require harsh conditions or take a long time to realize substantial substitution. Here, we present a method to modulate the composition of colloidal CsPbBr₃ NCs through ultrasonication-assisted anion exchange with CsX (X = Cl, I) solution. Efficient anion exchange of CsPbBr₃ NCs with Cl^- or I^- is realized with substitution ratio up to 93% and preservation of the pristine shape and structure of CsPbBr₃ NCs. This anion exchange results in tunable emission, covering the whole visible spectral range, with relatively high photoluminescence quantum yield, narrow emission bandwidths, and good stability. This work provides a facile and efficient way to engineer the properties of halide perovskite NCs and has great potential for large-scale production of compositionally diverse perovskite NCs.

Reversible modulation of CsPbBr3 perovskite nanocrystal/gold nanoparticle heterostructures

A facile strategy is illustrated to reversibly modulate CsPbBr3 perovskite nanocrystal/Au nanoparticle heterostructures with the reversible formation and fragmentation of gold nanoparticles anchored to the corners and surface of CsPbBr3 perovskite nanocrystals. The modulation process was performed under ambient conditions and could be conducted for cycles.

Zero-Dimensional Cesium Lead Halides: History, Properties, and Challenges

Over the past decade, lead halide perovskites (LHPs) have emerged as new promising materials in the fields of photovoltaics and light emission due to their facile syntheses and exciting optical properties. The enthusiasm generated by LHPs has inspired research in perovskite-related materials, including the so-called "zero-dimensional cesium lead halides", which will be the focus of this Perspective. The structure of these materials is formed of disconnected lead halide octahedra that are stabilized by cesium ions. Their optical properties are dominated by optical transitions that are localized within the individual octahedra, hence the title "'zero-dimensional perovskites". Controversial results on their physical properties have recently been reported, and the true nature of their photoluminescence is still unclear. In this Perspective, we will take a close look at these materials, both as nanocrystals and as bulk crystals/thin films, discuss the contrasting opinions on their properties, propose potential applications, and provide an outlook on future experiments.

Inter-Conversion between Different Compounds of Ternary Cs-Pb-Br System

The perovskite CsPbBr₃ attracts great attention due to its potential in optoelectronics. However, stability remains a major obstacle to achieving its effecting application. In this work, we prepared CsPbBr₃ solids through a simple reaction and investigated reversible conversion between CsPbBr₃, Cs₄PbBr₆, and CsPb₂Br₅. We found that CsPbBr₃ can be respectively converted to Cs₄PbBr₆ or CsPb₂Br₅ by reacting with CsBr or PbBr₂. Thermodynamic analysis demonstrated that the chemical reactions above were exothermic and occurred spontaneously. Moreover, the formed Cs₄PbBr₆ could be converted to CsPbBr₃ reversely, and then progressively converted to Cs-deficient CsPb₂Br₅ by extraction of CsBr with water. The CsPb₂Br₅ was converted to CsPbBr₃ reversely under thermal annealing at 400 °C. The thermodynamic processes of these conversions between the three compounds above were clarified. Our findings regarding the conversions not only provide a new method for controlled synthesis of the ternary Cs-Pb-Br materials but also clarify the underlying mechanism for the instability of perovskites CsPbBr₃.

Genesis, challenges and opportunities for colloidal lead halide perovskite nanocrystals

Lead halide perovskites (LHPs) in the form of nanometre-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same experimental mindset and theoretical framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.

Ligand-mediated synthesis of compositionally related cesium lead halide CsPb2X5 nanowires with improved stability

Compositionally related cesium lead halide materials, such as CsPb2X5, have attracted great interest due to their considerable optoelectronic/optical properties as well as improved stability. Currently, CsPb2Br5 nanocrystals can be well-designed by tuning the ligands or precursor ratio, whereas, CsPb2X5 (with Cl- or I-) nanocrystals can only be obtained by the anion exchange method. Herein, we report a method to directly synthesize CsPb2X5 facilitated by thiol ligands. The morphology of CsPb2X5 can be designed as a nanowire. Importantly, the stability of directly synthesized CsPb2X5 nanowires is much improved when compared with the stabilities of the materials obtained by the anion-exchange method. We believe that this method will promote the application of 1D tetragonal CsPb2X5 in optoelectronics, optics and other fields.

Enhancing Hybrid Perovskite Detectability in the Deep Ultraviolet Region with Down-Conversion Dual-Phase (CsPbBr3-Cs4PbBr6) Films

Hybrid perovskite photodetectors (PDs) exhibit outstanding performance in the ultraviolet-visible (UV-vis) spectrum but have poor detectability in the deep ultraviolet (DUV) region (200-350 nm). In this work, a novel inorganic-hybrid architecture that incorporates a dual-phase (CsPbBr₃-Cs₄PbBr₆) inorganic perovskite material as a down-conversion window layer and a hybrid perovskite as a light capture layer was prepared to achieve faster, highly sensitive photodetection in the DUV spectrum. A dual-phase inorganic perovskite film coated on the back surface of the photodetector enables strong light absorption and tunes the incident energy into emission bands that are optimized for the perovskite photodetector. The presence of Cs₄PbBr₆ enhances the capture and down-conversion of the incident DUV light. Due to the down-conversion and transport of the DUV photons, a self-driven perovskite photodetector with this composite structure exhibits a fast response time of 7.8/33.6 μs and a high responsivity of 49.4 mA W^-1 at 254 nm without extra power supply.

Reversible light-mediated compositional and structural transitions between CsPbBr3 and CsPb2Br5 nanosheets

This communication describes a new method to achieve reversible light-induced chemical composition and phase structural transitions from polyvinylpyrrolidone-capped orthorhombic CsPbBr₃ to tetragonal CsPb₂Br₅ nanosheets or vice versa. This work will deepen our understanding of the controlled synthesis, post-processing, and decomposition pathway of cesium lead halide perovskite nanocrystals.

All-Ambient Processed Binary CsPbBr3-CsPb2Br5 Perovskites with Synergistic Enhancement for High-Efficiency Cs-Pb-Br-Based Solar Cells

All-inorganic CsPbBr₃ perovskite solar cells display outstanding stability toward moisture, light soaking, and thermal stressing, demonstrating great potential in tandem solar cells and toward commercialization. Unfortunately, it is still challenging to prepare high-performance CsPbBr₃ films at moderate temperatures. Herein, a uniform, compact CsPbBr₃ film was fabricated using its quantum dot (QD)-based ink precursor. The film was then treated using thiocyanate ethyl acetate (EA) solution in all-ambient conditions to produce a superior CsPbBr₃-CsPb₂Br₅ composite film with a larger grain size and minimal defects. The achievement was attributed to the surface dissolution and recrystallization of the existing SCN^- and EA. More specifically, the SCN^- ions were first absorbed on the Pb atoms, leading to the dissolution and stripping of Cs⁺ and Br^- ions from the CsPbBr₃ QDs. On the other hand, the EA solution enhances the diffusion dynamics of surface atoms and the surfactant species. It is found that a small amount of CsPb₂Br₅ in the composite film gives the best surface passivation, while the Br-rich surface decreases Br vacancies (V_Br) for a prolonged carrier lifetime. As a result, the fabricated device gives a higher solar cell efficiency of 6.81% with an outstanding long-term stability.

Exploring Polaronic, Excitonic Structures and Luminescence in Cs4PbBr6/CsPbBr3

Among the important family of halide perovskites, one particular case of all-inorganic, 0-D Cs₄PbBr₆ and 3-D CsPbBr₃-based nanostructures and thin films is witnessing intense activity due to ultrafast luminescence with high quantum yield. To understand their emissive behavior, we use hybrid density functional calculations to first compare the ground-state electronic structure of the two prospective compounds. The dispersive band edges of CsPbBr₃ do not support self-trapped carriers, which agrees with reports of weak exciton binding energy and high photocurrent. The larger gap 0-D material Cs₄PbBr₆, however, reveals polaronic and excitonic features. We show that those lattice-coupled carriers are likely responsible for observed ultraviolet emission around ∼375 nm, reported in bulk Cs₄PbBr₆ and Cs₄PbBr₆/CsPbBr₃ composites. Ionization potential calculations and estimates of type-I band alignment support the notion of quantum confinement leading to fast, green emission from CsPbBr₃ nanostructures embedded in Cs₄PbBr₆.

Fabrication, Characterization, and Biological Activity of Avermectin Nano-delivery Systems with Different Particle Sizes

Nano-delivery systems for the active ingredients of pesticides can improve the utilization rates of pesticides and prolong their control effects. This is due to the nanocarrier envelope and controlled release function. However, particles containing active ingredients in controlled release pesticide formulations are generally large and have wide size distributions. There have been limited studies about the effect of particle size on the controlled release properties and biological activities of pesticide delivery systems. In the current study, avermectin (Av) nano-delivery systems were constructed with different particle sizes and their performances were evaluated. The Av release rate in the nano-delivery system could be effectively controlled by changing the particle size. The biological activity increased with decreasing particle size. These results suggest that Av nano-delivery systems can significantly improve the controllable release, photostability, and biological activity, which will improve efficiency and reduce pesticide residues.

Photoluminescence of Zero-Dimensional Perovskites and Perovskite-Related Materials

Zero-dimensional (0-D) perovskites and perovskite-related materials are an emerging class of optoelectronic materials exhibiting strong excitonic properties and, quite often, high photoluminescence (PL) in the solid state. Here we highlight two different classes of 0-D perovskites with contrasting structural and optical properties, focusing mainly on the less explored but rapidly growing bulk quantum materials termed as 0-D perovskite-related materials (0-D PRMs), whose PL properties are quite intriguing and a topic of recent debate. We attempt to present here a comprehensive picture to rationalize the contrasting properties of the 0-D PRMs and provide an understanding of the mechanism of exciton dynamics and PL of this class of materials. We hope that exciting PL and tunable composition of these systems will help design of new materials with versatile optical properties suited for practical applications.

CsPbX3/Cs4PbX6 core/shell perovskite nanocrystals

The synthesis of 3D/0D core/shell lead halide perovskite nanocrystals has been realized using the seeded growth approach for the first time.

Interfacial Synthesis of Highly Stable CsPbX3/Oxide Janus Nanoparticles

The poor stability of CsPbX₃ (X = Cl, Br, I) nanocrystals (NCs) has severely impeded their practical applications. Although there are some successful examples on encapsulating multiple CsPbX₃ NCs into an oxide or polymer matrix, it has remained a serious challenge for the surface modification/encapsulation using oxides or polymers at a single particle level. In this work, monodisperse CsPbX₃/SiO₂ and CsPbBr₃/Ta₂O₅ Janus nanoparticles were successfully prepared by combining a water-triggered transformation process and a sol-gel method. The CsPbBr₃/SiO₂ NCs exhibited a photoluminescence quantum yield of 80% and a lifetime of 19.8 ns. The product showed dramatically improved stability against destruction by air, water, and light irradiation. Upon continuous irradiation by intense UV light for 10 h, a film of the CsPbBr₃/SiO₂ Janus NCs showed only a slight drop (2%) in the PL intensity, while a control sample of unmodified CsPbBr₃ NCs displayed a 35% drop. We further highlighted the advantageous features of the CsPbBr₃/SiO₂ NCs in practical applications by using them as the green light source for the fabrication of a prototype white light emitting diode, and demonstrated a wide color gamut covering up to 138% of the National Television System Committee standard. This work not only provides a novel approach for the surface modification of individual CsPbX₃ NCs but also helps to address the challenging stability issue; therefore, it has an important implication toward their practical applications.

Improving the Stability and Size Tunability of Cesium Lead Halide Perovskite Nanocrystals Using Trioctylphosphine Oxide as the Capping Ligand

Recently, all-inorganic cesium lead halide (CsPbX₃, X = Cl, Br, and I) nanocrystals (NCs) have drawn wide attention because of their excellent optoelectronic properties and potential applications. However, one of the most significant challenges of such NCs is their low stability against protonic solvents. In this work, we demonstrate that by incorporating a highly branched capping ligand, trioctylphosphine oxide (TOPO), into the traditional oleic acid/oleylamine system, monodisperse CsPbX₃ NCs with excellent optoelectronic properties can be achieved at elevated temperatures (up to 260 °C). The size of such NCs can be varied in a relatively wide range. The capping of TOPO on NCs has been verified through Fourier transform infrared spectroscopy measurement. More importantly, the presence of TOPO can dramatically improve the stability of CsPbX₃ NCs against ethanol treatment. After ethanol treatment for 100 min, the emission intensity of the TOPO-capped sample dropped only 5%, whereas that of non-TOPO-capped NCs dropped up to 86%. This work may shed some light on the preparation and application of CsPbX₃ NCs with higher stability.

Postsynthesis Transformation of Insulating Cs4PbBr6 Nanocrystals into Bright Perovskite CsPbBr3 through Physical and Chemical Extraction of CsBr

Perovskite-related Cs₄PbBr₆ nanocrystals present a "zero-dimensional" crystalline structure where adjacent [PbBr₆]^4- octahedra do not share any corners. We show in this work that these nanocrystals can be converted into "three-dimensional" CsPbBr₃ perovskites by extraction of CsBr. This conversion drastically changes the optoelectronic properties of the nanocrystals that become highly photoluminescent. The extraction of CsBr can be achieved either by thermal annealing (physical approach) or by chemical reaction with Prussian Blue (chemical approach). The former approach can be simply carried out on a dried film without addition of any chemicals but does not yield a full transformation. Instead, reaction with Prussian Blue in solution achieves a full transformation into the perovskite phase. This transformation was also verified on the iodide counterpart (Cs₄PbI₆).