Composite Perovskites of Cesium Lead Bromide for Optimized Photoluminescence

High-Color-Rendition White QLEDs by Balancing Red, Green and Blue Centres in Eco-Friendly ZnCuGaS:In@ZnS Quantum Dots

White light-emitting diodes (WLEDs) are the key components in the next-generation lighting and display devices. The inherent toxicity of Cd/Pb-based quantum dots (QDs) limits the further application in WLEDs. Recently, more attention is focused on eco-friendly QDs and their WLEDs, especially the phosphor-free WLEDs based on mono-component, which profits from bias-insensitive color stability. However, the imbalanced carrier distribution between red-green-blue luminescent centers, even the absence of a certain luminescent center, hinders their balanced and stable photoluminescence/electroluminescence (PL/EL). Here, an In3+-doped strategy in Zn-Cu-Ga-S@ZnS QDs is first proposed, and the balanced carrier distribution is realized by non-equivalent substitution and In3+ doping concentration modulation. The alleviation of the green emitter by the In3+-related red emitter and the compensation of blue emitter by the Zn-related electronic states contribute to the balanced red-green-blue emitting with high PL quantum yield (PLQY) of 95.3% and long lifetime (T90) of over 1100 h in atmospheric conditions. Thus, the In3+-doped WLEDs can achieve exceedingly slight proportional variations between red-green-blue EL intensity over time (∆CIE = (0.007, 0.009)), and high champion CRI of 94.9. This study proposes a single-component QD with balanced and stable red-green-blue PL/EL spectrum, meeting the requirements of lighting and display.

High-Performance All-Inorganic Architecture Perovskite Light-Emitting Diodes Based on Tens-of-Nanometers-Sized CsPbBr3 Emitters in a Carrier-Confined Heterostructure

Developing green perovskite light-emitting diodes (PeLEDs) with a high external quantum efficiency (EQE) and low efficiency roll-off at high brightness remains a critical challenge. Nanostructured emitter-based devices have shown high efficiency but restricted ascending luminance at high current densities, while devices based on large-sized crystals exhibit low efficiency roll-off but face great challenges to high efficiency. Herein, we develop an all-inorganic device architecture combined with utilizing tens-of-nanometers-sized CsPbBr3 (TNS-CsPbBr3) emitters in a carrier-confined heterostructure to realize green PeLEDs that exhibit high EQEs and low efficiency roll-off. A typical type-I heterojunction containing TNS-CsPbBr3 crystals and wide-bandgap Cs4PbBr6 within a grain is formed by carefully controlling the precursor ratio. These heterostructured TNS-CsPbBr3 emitters simultaneously enhance carrier confinement and retain low Auger recombination under a large injected carrier density. Benefiting from a simple device architecture consisting of an emissive layer and an oxide electron-transporting layer, the PeLEDs exhibit a sub-bandgap turn-on voltage of 2.0 V and steeply rising luminance. In consequence, we achieved green PeLEDs demonstrating a peak EQE of 17.0% at the brightness of 36,000 cd m-2, and the EQE remained at 15.7% and 12.6% at the brightness of 100,000 and 200,000 cd m-2, respectively. In addition, our results underscore the role of interface degradation during device operation as a factor in device failure.

Solution-grown millimeter-scale Mn-doped CsPbBr3/Cs4PbBr6 crystals with enhanced photoluminescence and stability for light-emitting applications

Metal halide perovskites are particularly emerging for optoelectronic applications in light-emitting diodes, photodetectors, and solar cells due to their flourishing photophysical properties. However, the poor stability of three-dimensional (3D) lead halide perovskite nanocrystals (NCs) significantly hampers their optoelectronics and photovoltaics applications. Embedding 3D perovskites into zero-dimensional (0D) perovskite crystals and doping ions of appropriate elements into host lattices provide effective approaches to improve the stability and optical-electronic performance. In this study, millimeter-scale Mn-doped and undoped CsPbBr3/Cs4PbBr6 perovskite crystals were successfully fabricated by a one-step slow cooling method. We systematically investigated the effects of Mn2+ ion doping on the PL performance and stability of CsPbBr3/Cs4PbBr6 crystals. Compared with undoped crystals, the existence of Mn2+ ions not only blue-shifted the PL peak but also improved the luminescence performance and stability of the prepared millimeter-sized crystals. Moreover, doping Mn2+ ions can increase the proportion of radiative recombination at low temperature, which may be because Mn2+ ions can effectively accelerate the decay of a dark exciton by the magnetic mixing of bright and dark excitons. In addition, green LED devices with high efficiency packaged as-grown crystals are explored, which promises further application in display backlights.

Eco-Friendly Zn-Ag-In-Ga-S Quantum Dots: Amorphous Indium Sulfide Passivated Silver/Sulfur Vacancies Achieving Efficient Red Light-Emitting Diodes

I-III-VI quantum dots (QDs) and derivatives (I, III, and VI are Ag+/Cu+, Ga3+/In3+, and S2-/Se2-, respectively) are the ideal candidates to replace II-VI (e.g., CdSe) and perovskite QDs due to their nontoxicity, pure color, high photoluminescence quantum yield (PLQY), and full visible coverage. However, the chaotic cation alignment in multielement systems can easily lead to the formation of multiple surface vacancies, highlighted as VI and VVI, leading to nonradiative recombination and nonequilibrium carrier distribution, which severely limit the performance improvement of materials and devices. Here, based on Zn-Ag-In-Ga-S QDs, we construct an ultrathin indium sulfide shell that can passivate electron vacancies and convert donor/acceptor level concentrations. The optimized In-rich 2-layer indium sulfide structure not only enhances the radiative recombination rate by preventing further VS formation but also achieves the typical DAP emission enhancement, achieving a significant increase in PLQY to 86.2% at 628 nm. Moreover, the optimized structure can mitigate the lattice distortion and make the carrier distribution in the interior of the QDs more balanced. On this basis, red QD light-emitting diodes (QLEDs) with the highest external quantum efficiency (EQE; 5.32%) to date were obtained, providing a novel scheme for improving I-III-VI QD-based QLED efficiency.

High stability and strong luminescence CsPbBr3-Cs4PbBr6 thin films for all-inorganic perovskite light-emitting diodes

All-inorganic lead halide perovskite, characterized by its exceptional optical and electrical properties, is burgeoning as a potential optoelectronic material. However, the standalone CsPbBr3 component encounters several challenges including small exciton binding energy (≈40 meV) and long charge diffusion length, giving rise to low photo-luminescence quantum-yield (PLQY); ion migration leads to instability in device operation, hindering device operation and potential development. To circumvent these limitations, our research endeavors to construct a novel core-shell structure that transforms the continuous [PbX6]4- octahedron into an isolated octahedral structure. We introduce the Cs4PbBr6 phase with 0D structure to passivate the vacancy defects in CsPbBr3, thereby suppressing ion migration and enhancing the luminescence intensity and stability. Our methodology involves fabricating dense CsPbBr3-Cs4PbBr6 composite films using a co-evaporation method, wherein the molar ratio of CsBr and PbBr2 is precisely adjusted. The films are subsequently rapidly annealed under ambient air conditions, and the effects of different annealing temperatures and annealing times on the CsPbBr3-Cs4PbBr6 films were investigated. Our results demonstrate significantly improved stability of the annealed films, with a mere 15% decrease in PL intensity after 100 days of storage under ambient air conditions at 48% relative humidity (RH). Based on this thin film, we fabricated all-inorganic structure Ag/N-Si/CsPbBr3-Cs4PbBr6/NiO/ITO light emitting diodes (LEDs), the devices have a low turn-on voltage VT ∼3 V and under unencapsulated, ambient air conditions, it can operate continuously for 12 hours under DC drive with only 10% attenuation. The results we obtained open up the possibility of designing and developing air-stable perovskite LEDs.

Circularly Polarized Luminescence in Zero-Dimensional Antimony Halides: Structural Distortion Controlled Luminescence Thermometer

Materials emitting circularly polarized luminescence (CPL) have been intensively studied for their promising applications in various fields. However, developing tunable and responsive CPL materials in a wide wavelength range remains a great challenge. Here, a pair of chiral (R,R/S,S-DCDA)₃Sb₂Cl₁₂ (DCDA = dimethyl-1,2-cyclohexanediamine divalent cation) shows efficient broadband yellow emission with a photoluminescence (PL) quantum yield of 27.6% with a CPL asymmetry factor of 3 × 10^-3. The associated chiroptical activity is attributed to the efficient chiral transfer as well as the self-trapped exciton emission originating from the large distortion of the inorganic blocks. Notably, (R,R/S,S-DCDA)₃Sb₂Cl₁₂ exhibits a large red-shift emission exceeding 100 nm upon lowering temperature. An excellent linear correlation of the PL wavelength on temperature indicates that the compounds can be used as PL thermometers, which originates from a temperature-dependent linear structural distortion of the [SbCl₆] emitter. This work inspires the potential utilization of CPL-emitting materials as responsive light sources.

Vacuum-Deposited Inorganic Perovskite Light-Emitting Diodes with External Quantum Efficiency Exceeding 10% via Composition and Crystallinity Manipulation of Emission Layer under High Vacuum

Although vacuum-deposited metal halide perovskite light-emitting diodes (PeLEDs) have great promise for use in large-area high-color-gamut displays, the efficiency of vacuum-sublimed PeLEDs currently lags that of solution-processed counterparts. In this study, highly efficient vacuum-deposited PeLEDs are prepared through a process of optimizing the stoichiometric ratio of the sublimed precursors under high vacuum and incorporating ultrathin under- and upper-layers for the perovskite emission layer (EML). In contrast to the situation in most vacuum-deposited organic light-emitting devices, the properties of these perovskite EMLs are highly influenced by the presence and nature of the upper- and presublimed materials, thereby allowing us to enhance the performance of the resulting devices. By eliminating Pb° formation and passivating defects in the perovskite EMLs, the PeLEDs achieve an outstanding external quantum efficiency (EQE) of 10.9% when applying a very smooth and flat geometry; it reaches an extraordinarily high value of 21.1% when integrating a light out-coupling structure, breaking through the 10% EQE milestone of vacuum-deposited PeLEDs.

The Synergy of the Buried Interface Surface Energy and Temperature for Thermal Evaporated Perovskite Light-Emitting Diodes

Multisource coevaporation is such a promising method for the preparation of perovskite films. However, there is limited research about the effects of the buried interface on thermal-evaporated perovskite light-emitting diodes (PeLEDs). In this study, the effects of buried interfaces on thermal-evaporated all-inorganic perovskite films are systematically investigated. It is found that the low-surface-energy buried interface promotes the formation of columnar grain by suppressing heterogeneous nucleation, and functional groups on the high-surface-energy interface have a significant effect on the actual element ratio of the film. The substrate temperature can affect the nucleation and film-formation kinetics of the columnar grains. As a result of the synergistic strategy, a peak external quantum efficiency (EQE) of 8.6% is achieved in the green PeLEDs with a stable emission peak at 516 nm, which is among the best thermal-evaporated PeLEDs reported. This work provides an insight into the preparation of perovskites by thermal evaporation and builds the groundwork for future studies.

Citric acid tuned negative thermal quenching of all inorganic copper-based perovskites

Copper-based perovskites, with lower electronic dimensions and high photoluminescence quantum yields (PLQY), which are non-toxic and thermally stable, have been reported since 2019 and have immediately attracted great attention. So far, only a few studies have researched the temperature-dependent photoluminescence properties, posing a challenge in ensuring the stability of the material. In this paper, the temperature-dependent photoluminescence properties have been investigated in detail, and a negative thermal quenching of all-inorganic CsCu₂I₃ perovskites has been studied. Moreover, the negative thermal quenching property can be tuned with the assistance of citric acid, which has not been reported before. The Huang-Rhys factors are calculated to be 46.32/38.31, which is higher than for many semiconductors and perovskites.

Vacuum-Vapor-Deposited 0D/3D All-Inorganic Perovskite Composite Films toward Low-Threshold Amplified Spontaneous Emission and Lasing

Vacuum vapor deposition (VVD) is a promising way to advancing the commercialization of perovskite light sources owing to its convenience for wafer-scale mass production and compatibility with silicon photonics manufacturing infrastructure. However, the light emission performance of VVD-grown perovskites still lags far behind that of the conventional solution-processed counterparts due to their inferior luminescence properties. Here, a 0D/3D cesium-lead-bromide perovskite composite film is prepared on Si/SiO₂ substrates through composition modulation with the VVD method, which exhibits an ultralow amplified spontaneous emission (ASE) threshold down to 14.3 µJ cm^-2 in the optimal films, which is on par with that of the solution-processed counterparts. Meanwhile, they also display intriguing operational stability with negligible emission intensity decay under continuous excitation above ASE threshold for 4 h in the air. The outstanding ASE performance mainly originates from the reduced trap density and weakened electron-phonon coupling in the 3D CsPbBr₃ phase enabled by the incorporation of the 0D Cs₄ PbBr₆ phase. Finally, by integrating the composite film with the distributed feedback (DFB) cavity, DFB lasing is achieved with a low threshold of 18.2 µJ cm^-2 under nanosecond-pulsed laser pumping, which highlights the potential of VVD-processed perovskites for developing high-performance lasers.

Stable and Bright Electroluminescent Devices utilizing Emissive 0D Perovskite Nanocrystals Incorporated in a 3D CsPbBr3 Matrix

The 0D cesium lead halide perovskite Cs₄ PbBr₆ has drawn remarkable interest due to its highly efficient robust green emission compared to its 3D CsPbBr₃ counterpart. However, seizing the advantages of the superior photoluminescence properties for practical light-emitting devices remains elusive. To date, Cs₄ PbBr₆ has been employed only as a higher-bandgap nonluminescent matrix to passivate or provide quantum/dielectric confinement to CsPbBr₃ in light-emitting devices and to enhance its photo-/thermal/environmental stability. To resolve this disparity, a novel solvent engineering method to incorporate highly luminescent 0D Cs₄ PbBr₆ nanocrystals (perovskite nanocrystals (PNCs)) into a 3D CsPbBr₃ film, forming the active emissive layer in single-layer perovskite light-emitting electrochemical cells (PeLECs) is designed. A dramatic increase of the maximum external quantum efficiency and luminance from 2.7% and 6050 cd m^-2 for a 3D-only PeLEC to 8.3% and 11 200 cd m^-2 for a 3D-0D PNC device with only 7% by weight of 0D PNCs is observed. The majority of this increase is driven by the efficient inherent emission of the 0D PNCs, while the concomitant morphology improvement also contributes to reduced leakage current, reduced hysteresis, and enhanced operational lifetime (half-life of 129 h), making this one of the best-performing LECs reported to date.

Efficient and large-area all vacuum-deposited perovskite light-emitting diodes via spatial confinement

With rapid advances of perovskite light-emitting diodes (PeLEDs), the large-scale fabrication of patterned PeLEDs towards display panels is of increasing importance. However, most state-of-the-art PeLEDs are fabricated by solution-processed techniques, which are difficult to simultaneously achieve high-resolution pixels and large-scale production. To this end, we construct efficient CsPbBr3 PeLEDs employing a vacuum deposition technique, which has been demonstrated as the most successful route for commercial organic LED displays. By carefully controlling the strength of the spatial confinement in CsPbBr3 film, its radiative recombination is greatly enhanced while the nonradiative recombination is suppressed. As a result, the external quantum efficiency (EQE) of thermally evaporated PeLED reaches 8.0%, a record for vacuum processed PeLEDs. Benefitting from the excellent uniformity and scalability of the thermal evaporation, we demonstrate PeLED with a functional area up to 40.2 cm2 and a peak EQE of 7.1%, representing one of the most efficient large-area PeLEDs. We further achieve high-resolution patterned perovskite film with 100 μm pixels using fine metal masks, laying the foundation for potential display applications. We believe the strategy of confinement strength regulation in thermally evaporated perovskites provides an effective way to process high-efficiency and large-area PeLEDs towards commercial display panels.

Efficient and Stable Blue Perovskite Light-Emitting Devices Based on Inorganic Cs4PbBr6 Spaced Low-Dimensional CsPbBr3 through Synergistic Control of Amino Alcohols and Polymer Additives

Perovskite light-emitting devices (PeLEDs) have drawn a great deal of attention because of their exceptional optical and electrical properties. However, as for the blue PeLEDs based on low-dimensional (LD) CsPbBr₃, the low conductivity of the widely used organic spacers as well as the difficulty of forming pure and uniform LD CsPbBr₃ phase have severely inhibited the device performance such as stability and efficiency. In this work, we report an effective strategy to obtain high-quality LD CsPbBr₃ by using a novel spacer of inorganic Cs₄PbBr₆ instead of the common long-chain ammonium halides. We found that a 3-amino-1-propanol (3AP)-modified PEDOT:PSS was helpful to stimulate the formation of the LD blue emissive CsPbBr₃:Cs₄PbBr₆ composite. We also revealed that an additive of poly(vinylpyrrolidone) (PVP) in the precursor can limit further growth of LD perovskite phase into 3D perovskite phase upon annealing, thus resulting in a uniformly distributed LD perovskite with high color stability. Consequently, efficient blue PeLEDs @ 485 nm with a brightness of 2192 cd/m², current efficiency of 2.68 cd/A, and external quantum efficiency of 2.3% was successfully achieved. More importantly, the device showed much improved working stability compared to those with the spacer of organic ammonium halides. Our results provide some helpful insights into developing efficient and stable blue PeLEDs.

Synthesis of two-dimensional phenylethylamine tin-lead halide perovskites with bandgap bending behavior

Recently, two-dimensional (2D) metal halide perovskite materials with wide application in perovskite-based solar cells have attracted significant attention. Among them, 2D mixed lead-tin perovskites have not been systematically explored. Herein, we synthesize a 2D phenethylammonium (PEA) tin-lead bromide perovskite, PEA₂Sn _x Pb_1-x Br₄, via a simple solution-phase approach without toxic reagents and high temperatures. By tuning the ratio of Sn and Pb, the UV-vis absorption spectra showed unique bandgap bending behaviors. DFT calculations indicate the key effects of spin-orbital coupling (SOC) without the interference of lattice distortion. Moreover, we provided the standard equation with a correction term to introduce the influence of SOC. These results not only provide a step forward towards the bandgap engineering of perovskites, but also help to expand the application of 2D perovskite materials.

Coherent Spin Precession and Lifetime-Limited Spin Dephasing in CsPbBr3 Perovskite Nanocrystals

Carrier spins in semiconductor nanocrystals are promising candidates for quantum information processing. Using a combination of time-resolved Faraday rotation and photoluminescence spectroscopies, we demonstrate optical spin polarization and coherent spin precession in colloidal CsPbBr₃ nanocrystals that persists up to room temperature. By suppressing the influence of inhomogeneous hyperfine fields with a small applied magnetic field, we demonstrate inhomogeneous hole transverse spin-dephasing times (T₂^*) that approach the nanocrystal photoluminescence lifetime, such that nearly all emitted photons derive from coherent hole spins. Thermally activated LO phonons drive additional spin dephasing at elevated temperatures, but coherent spin precession is still observed at room temperature. These data reveal several major distinctions between spins in nanocrystalline and bulk CsPbBr₃ and open the door for using metal-halide perovskite nanocrystals in spin-based quantum technologies.

Highly efficient radiative recombination in intrinsically zero-dimensional perovskite micro-crystals prepared by thermally-assisted solution-phase synthesis

Zero-dimensional (0D) quantum confinement can be achieved in perovskite materials by the confinement of electron and hole states to single PbX₆⁴⁻ perovskite octahedra. In this work, 0D perovskite (Cs₄PbBr₆) micro-crystals were prepared by a simple thermally-assisted solution method and thoroughly characterized. The micro-crystals show a high level of crystallinity and a high photoluminescence quantum yield of 45%. The radiative recombination coefficient of the 0D perovskite micro-crystals, 1.5 × 10⁻⁸ s⁻¹ cm³, is two orders of magnitude higher than that of typical three-dimensional perovskite and is likely a strong contributing factor to the high emission efficiency of 0D perovskite materials. Temperature dependent luminescence measurements provide insight into the role of thermally-activated trap states. Spatially resolved measurements on single 0D perovskite micro-crystals reveal uniform photoluminescence intensity and emission decay behaviour suggesting the solution-based fabrication method yields a high-quality and homogenous single-crystal material. Such uniform emission reflects the intrinsic 0D nature of the material, which may be beneficial to device applications.

0D Cs₄PbBr₆ perovskite microcrystals exhibit a radiative recombination coefficient two orders of magnitude higher than typical 3D perovskite.

Fluorescence-enhanced Cs4 PbBr6 /CsPbBr3 composites films synthesized by double-films solid phase reaction method

Due to indispensable ligands, polluted organic solution, or complex vapour deposition, stable CsPbBr₃ film is hard to be prepared directly using a simple and environmentally friendly method. To improve the stability of CsPbBr₃ film and its synthesis methods, the double-films solid phase reaction was developed, and Cs₄ PbBr₆ /CsPbBr₃ composites were designed. Although the synthesized particle had a size of 2-5 μm, much larger than that of quantum dots, in ambient conditions the composites films still showed good photoluminescence properties, with the highest photoluminescence quantum yield of 80%. It had good stability against air, temperature and humidity, and even had interesting fluorescence-enhanced phenomenon after about 4 days.

Efficient Luminescence from CsPbBr3 Nanoparticles Embedded in Cs4PbBr6

Cs₄PbBr₆ is regarded as an outstanding luminescent material with good thermal stability and optical performance. However, the mechanism of green emission from Cs₄PbBr₆ has been controversial. Here we show that isolated CsPbBr₃ nanoparticles embedded within a Cs₄PbBr₆ matrix give rise to a "normal" green luminescence while superfluorescence at longer wavelengths is suppressed. High-resolution transmission electron microscopy shows that the embedded CsPbBr₃ nanoparticles are around 3.8 nm in diameter and are well-separated from each other, perhaps by a strain-driven mechanism. This mechanism may enable other efficient luminescent composites to be developed by embedding optically active nanoparticles epitaxially within inert host lattices.

Improved Performance for Thermally Evaporated Perovskite Light-Emitting Devices via Defect Passivation and Carrier Regulation

Efficient inorganic perovskite light-emitting devices (PeLEDs) with a vacuum-deposited CsPbBr₃ emission layer were realized by introducing an ultrathin 2-phenylethanamine bromide interlayer. The PEA⁺ cations not only passivated the nonradiative defects by terminating on the CsPbBr₃ surface but also regulated the charge transport to balance the hole and electron transport. Consequently, the PeLEDs exhibit significantly promoted performance with a turn-on voltage of 3 V, a maximum current efficiency of 14.64 cd A^-1, and an external quantum efficiency of 4.10%. Our work would provide instructive guidance for realizing efficient PeLEDs based on a vacuum processing method via focusing on the interface modification between the perovskite layer and the carrier transport layer.

A simple multiple centrifugation method for large-area homogeneous perovskite CsPbBr3 films with optical lasing

Large scale cesium lead-halide (CsPbX₃, X = Cl, Br, and I) perovskite films have become the basis of laser applications.

Hydraulic shear-induced rapid mass production of CsPbBr3/Cs4PbBr6 perovskite composites

Pure green CsPbBr₃/Cs₄PbBr₆ perovskite composites were synthesized by generating hydraulic shear as a rapid mass synthesis strategy.

CsPbBr3-Cs4PbBr6 composite nanocrystals for highly efficient pure green light emission

All-inorganic perovskite CsPbBr₃-Cs₄PbBr₆ composite nanocrystals (NCs) were synthesized via a convenient solution process without inert gas protection and systematically studied as green phosphors for light emitting diode (LED) applications. While colloidal composite NCs emit green color with an emission peak at around 515 nm, their thin films on top of blue GaN chips exhibit a redshift of ∼15-20 nm due to subsequential aggregation in solid state. The Commission Internationale De I'eclairage (CIE) chromaticity coordinates of the green LEDs assembled by composite NCs reached (0.201, 0.746) with nearly 100% green ratio. Moreover, the pure green LED displayed a luminous efficiency of 45 lm W^-1 under 10 mA driving current. The colloidal CsPbBr₃-Cs₄PbBr₆ composite NCs have the photoluminescence quantum yield (PLQY) as high as 74%. The high PLQY originates from cubic CsPbBr₃ NCs well passivated by the zero-dimensional Cs₄PbBr₆ matrix, substantially suppressing the nonradiative recombination. The comparison between the green LEDs fabricated with pure and composite perovskites imply that the CsPbBr₃-Cs₄PbBr₆ composites with higher quantum yield could be an effective way to get the brightness and the stability of pure green LEDs.

Vacuum-Deposited Blue Inorganic Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have drawn great research attention because of their outstanding electroluminescence performance by solution processing. PeLEDs made by thermal evaporation are relatively rarely explored but are compatible to existing organic light-emitting diode industrial lines. Blue-emitting PeLEDs are all based on organic-containing perovskites, rather than more stable all-inorganic perovskites because of their poor solubility, too fast crystallization, uneven discrete films, and unattainable pure blue emission. Here, we report all-inorganic, vacuum-processed blue PeLEDs. High-throughput combinatorial approaches are employed to optimize Cs-Pb-Br-Cl composition in our dual-source co-evaporation system to achieve the balance between film photoluminescence and injection efficiency. The as-deposited perovskite films demonstrated excellent intrinsic stability against heat, UV-light, and humidity attack. A series of PeLEDs were obtained covering the standard blue spectral region with a best luminance of 121 cd/m² and an external quantum efficiency of 0.38%. We believe that the vacuum processing strategy demonstrated here provides a very promising alternative way to produce efficient and stable all-inorganic blue-emitting PeLEDs.

Highly stable hetero-structured green-emitting cesium lead bromide nanocrystals via ligand-mediated phase control

Green-emissive Cs₄PbBr₆ shows promise for light-emitting diode devices superior to that of CsPbBr₃ NCs owing to their stability and high photoluminescence efficiency. Nevertheless, there is still no consensus regarding the basis of their green emission, which decelerates their advance in light-emitting applications. Herein, a systematic investigation on the concentration of capping ligands (oleylamine and oleic acid), which determines the predominant phase between CsPbBr₃ and Cs₄PbBr₆ for a given Cs to Pb feed ratio, is conducted. This study deduces that oleylamine to oleic acid ratio plays a crucial role in obtaining either green-emissive or non-emissive Cs₄PbBr₆ NCs. Scrutiny of Cs₄PbBr₆ microscopic and optical data in addition to their emission quenching study with a hole-withdrawing molecule reveals that the green emission originates from the CsPbBr₃ impurity phase. Furthermore, stable green emission is observed for CsPbBr₃/Cs₄PbBr₆ nanocrystals when CsPbBr₃ particles are well protected by the Cs₄PbBr₆ matrix. These CsPbBr₃/Cs₄PbBr₆ films remained highly luminescent even after UV exposure for hours or annealing at ∼150 °C for days in addition to their long-term stability under an ambient atmosphere, which are the desirable properties for various practical applications.

Microcarrier-Assisted Inorganic Shelling of Lead Halide Perovskite Nanocrystals

The conventional strategy of synthetic colloidal chemistry for bright and stable quantum dots has been the production of epitaxially matched core/shell heterostructures to mitigate the presence of deep trap states. This mindset has been shown to be incompatible with lead halide perovskite nanocrystals (LHP NCs) due to their dynamic surface and low melting point. Nevertheless, enhancements to their chemical stability are still in great demand for the deployment of LHP NCs in light-emitting devices. Rather than contend with their attributes, we propose a method in which we can utilize their dynamic, ionic lattice and uniquely defect-tolerant band structure to prepare non-epitaxial salt-shelled heterostructures that are able to stabilize these materials against their environment, while maintaining their excellent optical properties and increasing scattering to improve out-coupling efficiency. To do so, anchored LHP NCs are first synthesized through the heterogeneous nucleation of LHPs onto the surface of microcrystalline carriers, such as alkali halides. This first step stabilizes the LHP NCs against further merging, and this allows them to be coated with an additional inorganic shell through the surface-mediated reaction of amphiphilic Na and Br precursors in apolar media. These inorganically shelled NC@carrier composites offer significantly improved chemical stability toward polar organic solvents, such as γ-butyrolactone, acetonitrile, N-methylpyrrolidone, and trimethylamine, demonstrate high thermal stability with photoluminescence intensity reversibly dropping by no more than 40% at temperatures up to 120 °C, and improve compatibility with various UV-curable resins. This mindset for LHP NCs creates opportunities for their successful integration into next-generation light-emitting devices.

Green-Emitting Powders of Zero-Dimensional Cs4PbBr6: Delineating the Intricacies of the Synthesis and the Origin of Photoluminescence

A detailed investigation into the synthesis of green-emitting powders of Cs₄PbBr₆ and CsPbBr₃ materials by antisolvent precipitation from CsBr-PbBr₂ precursor solutions in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is reported. Various solvated lead bromide and polybromide species (PbBr₂, [PbBr₃]^-, [PbBr₄]^2-, and possibly [PbBr₅]^3-or [PbBr₆]^4-) are detected in the precursor solutions by optical absorbance and emission spectroscopies. The solvodynamic size of the species in solution is strongly solvent-dependent: ~1 nm species were detected in DMSO, while significantly larger species were observed in DMF by dynamic light scattering. The solvodynamic size of the lead bromide species plays a critical role in determining the Cs-Pb-Br composition of the precipitated powders: smaller species favor the precipitation of Cs₄PbBr₆, while larger species template the formation of CsPbBr₃ under identical experimental conditions. The powders have been characterized by ¹³³Cs and ²⁰⁷Pb solid-state nuclear magnetic resonance, and ¹³³Cs sensitivity toward the different Cs environments within Cs₄PbBr₆ is demonstrated. Finally, the possible origins of green emission in Cs₄PbBr₆ samples are discussed. It is proposed that a two-dimensional Cs₂PbBr₄ inclusion may be responsible for green emission at ~520 nm in addition to the widely acknowledged CsPbBr₃ impurity, although we found no conclusive experimental evidence supporting such claims.

Highly efficient nanocrystalline CsxMA1-xPbBrx perovskite layers for white light generation

Perovskite light converting layers optimization for cost-efficient white light emitting diodes (LED) was demonstrated. High excitation independent internal quantum efficiency (IQE) of 80% and weakly excitation dependent PL spectra suitable for white light generation were obtained in the mixed cation Cs_xMA_1-xPbBr₃ perovskite nanocrystal layers with optimal x = 0.3 being determined by effective surface passivation and phase mixing as revealed by x-ray diffraction. Enhancement of the PL homogeneity and the external quantum efficiency (EQE) were secured when using 2,2',2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole (TPBi) additive in the layer preparation process. Excitation dependent PL intensity, decay time, and IQE revealed that the high emission efficiency of the layers originates from a dominant radiative localized exciton recombination (130 ns) weakly influenced by the nonradiative free carrier recombination (750 ns). Warm and cool white LEDs with correlated color temperature 3000 K and 5600 K, and color rendering index 82 and 74, respectively, were realized by using the optimized perovskite layers, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) red emitter and a blue LED.

The optical properties of Cs4PbBr6-CsPbBr3 perovskite composites

Although the optoelectronic applications of metal halide perovskites have been intensively investigated in recent years, the fundamental carrier dynamics of zero-dimensional (0D) Cs4PbBr6 perovskites has been relatively underexplored; in particular, the nature of the green fluorescence is highly debated. Nevertheless, the unique photophysical properties are of immense interest for a variety of potential applications. In this work, the green emission of the CsPbBr3-Cs4PbBr6 perovskite composites is studied using temperature dependent photoluminescence (PL). The PL spectra at different temperatures simultaneously contain two sub-peaks (520 nm and 550 nm), which are ascribed to the emissions of the band-edge and the defect trapped exciton of CsPbBr3. This finding will help to understand the controversial photoluminescence currently observed in different 0D Cs4PbBr6 perovskites.

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties

Metal halide perovskites represent a flourishing area of research, which is driven by both their potential application in photovoltaics and optoelectronics and by the fundamental science behind their unique optoelectronic properties. The emergence of new colloidal methods for the synthesis of halide perovskite nanocrystals, as well as the interesting characteristics of this new type of material, has attracted the attention of many researchers. This review aims to provide an up-to-date survey of this fast-moving field and will mainly focus on the different colloidal synthesis approaches that have been developed. We will examine the chemistry and the capability of different colloidal synthetic routes with regard to controlling the shape, size, and optical properties of the resulting nanocrystals. We will also provide an up-to-date overview of their postsynthesis transformations, and summarize the various solution processes that are aimed at fabricating halide perovskite-based nanocomposites. Furthermore, we will review the fundamental optical properties of halide perovskite nanocrystals by focusing on their linear optical properties, on the effects of quantum confinement, and on the current knowledge of their exciton binding energies. We will also discuss the emergence of nonlinear phenomena such as multiphoton absorption, biexcitons, and carrier multiplication. Finally, we will discuss open questions and possible future directions.

A systematic study of the synthesis of cesium lead halide nanocrystals: does Cs4PbBr6 or CsPbBr3 form?

Cs4PbBr6 nanocrystals (NCs) have been recently studied as they can enhance the light emitting efficiency and stability of CsPbBr3 NCs. However, the synthesis of Cs4PbBr6 NCs is often accompanied by the generation of CsPbBr3 NCs, and less attention has been paid to how to exactly control their formation. Here, we investigated the key factors in deciding the final products in the hot-injection synthesis by a modified amine-free method. We found that the molarity ratio of Cs/Pb dominated the final products, while the amount of bromine had a relatively small effect. In addition, introducing a certain amount of oleylamine into the amine-free reaction leads to the formation of Cs4PbBr6, instead of CsPbBr3 NCs. This clearly shows that the protection ligand oleylamine also plays an important role in the formation of Cs4PbBr6 NCs. This well understood and fine control of the synthesis may inspire a new CsPbBr3@Cs4PbBr6 core-shell structure, with the same chemical elements but a different crystal phase in the core and the shell. This nanostructure would open a new avenue for enhancing the stability of perovskite nanocrystals.

Hydroxyl terminated mesoporous silica-assisted dispersion of ligand-free CsPbBr3/Cs4PbBr6 nanocrystals in polymer for stable white LED

Composite nanocrystals of CsPbBr3/Cs4PbBr6 have gained significant attention because of their high stability and unique photoelectronic property. However, their dispersion within polymers is rather difficult due to the absence of ligands, which limits further enhancement of stability and practical applications. Herein, a feasible, effective, and general method was developed to assist the dispersion of CsPbBr3/Cs4PbBr6 nanocrystals in polymer by using -OH terminated mesoporous silica as a micro-container. The composite film obtained is employed as the light emitter for the fabrication of white LEDs. It was found that silica loaded with composite nanocrystals disperse uniformly in the composite film which shows excellent stability with a half-life of 400 hours under the illumination with optical power density of 1.7 × 103 mW cm-2 and peak wavelength of 457 nm. The inner pore of the micro-container attracts precursors and confines the crystallization, leading to the incorporation of CsPbBr3/Cs4PbBr6 nanocrystals. Meanwhile, the hydrogen bonding of the outer surface with poly(methyl methacrylate) (PMMA) enables good dispersion of the loaded micro-containers in PMMA as evidenced by the optical microscopy characterization and water resistance test. Moreover, this strategy can also be applied to other kinds of polymers since the outside -OH group can react with siliane coupling agents. On the basis of stability tests associated with silica and polymer encapsulation, a possible mechanism is proposed for the enhancement of the stability of composite films under working condition.

Cs4PbBr6/CsPbBr3 perovskite composites for WLEDs: pure white, high luminous efficiency and tunable color temperature

Cs₄PbBr₆/CsPbBr₃ perovskite composites are fabricated by room-temperature one-pot mixing synthesis, which is short in time, free from inert gases and delivers a high product yield. Temperature-dependent photoluminescence shows that a larger exciton binding energy of 291.1 meV exhibits better thermal stability compared with that of pure Cs₄PbBr₆ and CsPbBr₃ materials. The CIE chromaticity coordinates (0.1380, 0.7236) of green LEDs designed with Cs₄PbBr₆/CsPbBr₃ perovskite composites show almost no variation under driving current changing from 5 to 30 mA. Furthermore, the ground Cs₄PbBr₆/CsPbBr₃ perovskite composites mixed with red emitting K₂SiF₆:Mn⁴⁺ phosphor are dropped and casted on a blue-emitting InGaN chip. The white light emitting diodes (WLEDs) are presented, which have good luminous efficiency of 65.33 lm W⁻¹ at 20 mA, a correlated color temperature of 5190 K, and the white gamut with chromaticity coordinate of (0.3392, 0.3336). According to the state of art, these excellent characteristics observed are much superior to the reported results of conventional perovskite-based WLEDs, which demonstrate the immense potential and great prospect of Cs₄PbBr₆/CsPbBr₃ perovskite composites to replace conventional phosphors in lighting devices.

WLED devices are designed with high luminous efficiency of 65.33 lm W⁻¹ and excellent CIE chromaticity coordinates of (0.3392, 0.3336). The properties of material and the luminous performance of device are calculated and discussed comprehensively.

One-Step Co-Evaporation of All-Inorganic Perovskite Thin Films with Room-Temperature Ultralow Amplified Spontaneous Emission Threshold and Air Stability

Inorganic cesium lead halide perovskite has been successfully applied in the optoelectronic field due to its remarkable optical gain properties. Unfortunately, conventional solution-processed CsPbX₃ films suffer unavoidable pinhole defects and poor surface morphology, severely limiting their performance on amplified spontaneous emission (ASE) and lasing applications. Herein, a dual-source thermal evaporation approach is explored to achieve a uniform and high-coverage CsPbX₃ polycrystalline thin film. It was found that one-step co-evaporated CsPbBr₃ (OC-CsPbBr₃) thin films without post-annealing exhibit an ultralow ASE threshold of ∼3.3 μJ/cm² and a gain coefficient above 300 cm^-1. The coexistence of cubic and orthorhombic phases in these materials naturally form an energy cascade for the exciton transfer process, which enables rapid accumulation of excitons. Stable ASE intensity without degradation for at least 7 h is also realized from OC-CsPbBr₃ thin films under continuous excitation, which is superior to that in the solution-processed CsPbBr₃ thin films. Notably, a Fabry-Pérot cavity laser based on the OC-CsPbBr₃ thin film is first achieved, featuring an ultralow lasing threshold (1.7 μJ/cm²) and directional output (a beam divergence of ∼3.8°). This work highlights the noteworthy optical properties of OC-CsPbBr₃ thin films, leading to potential available applications in integrated optoelectronic chips.

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.

Room temperature precipitated dual phase CsPbBr3-CsPb2Br5 nanocrystals for stable perovskite light emitting diodes

Although the efficiency of metal halide perovskite light emitting diodes (PeLEDs) has been improved to an attractive level, the poor stability of perovskite emitting layers is a major concern for the application of PeLEDs. Herein, we report a facile ligand-assisted precipitation synthesis of stable dual-phase CsPbBr₃-CsPb₂Br₅ nanocrystals (NCs) for improving the stability of PeLEDs. In our synthetic process, the bromide-rich circumstance is beneficial to generate high quality dual-phase perovskite NCs with PLQY as high as 92% and a narrow emission linewidth (19 nm). More importantly, as-synthesized dual phase perovskite NCs exhibit extremely high thermal stability in heating tests in air with a considerable humidity of 30%-55% in comparison with previously reported single phase CsPbBr₃ NCs. The aforementioned advantages of our synthesized dual-phase CsPbBr₃-CsPb₂Br₅ NCs allow for the fabrication of light emitting layers of PeLEDs under ambient conditions. The fabricated green PeLED based on CsPbBr₃-CsPb₂Br₅ NCs shows a low turn-on voltage of 2.5 V and a high brightness of 8383 cd m^-2 at 8 V. Owing to the high stability of dual-phase CsPbBr₃-CsPb₂Br₅ NCs, the fabricated PeLED also exhibits better operational stability in comparison with those PeLEDs based on single phase CsPbBr₃ NCs. Our work presents a new route to fabricate stable perovskite light-emitting diodes using room temperature precipitated dual-phase CsPbBr₃-CsPb₂Br₅ NCs as emitting layer materials.

Solution-processed perovskite light emitting diodes with efficiency exceeding 15% through additive-controlled nanostructure tailoring

Organometal halide perovskites (OHP) are promising materials for low-cost, high-efficiency light-emitting diodes. In films with a distribution of two-dimensional OHP nanosheets and small three-dimensional nanocrystals, an energy funnel can be realized that concentrates the excitations in highly efficient radiative recombination centers. However, this energy funnel is likely to contain inefficient pathways as the size distribution of nanocrystals, the phase separation between the OHP and the organic phase. Here, we demonstrate that the OHP crystallite distribution and phase separation can be precisely controlled by adding a molecule that suppresses crystallization of the organic phase. We use these improved material properties to achieve OHP light-emitting diodes with an external quantum efficiency of 15.5%. Our results demonstrate that through the addition of judiciously selected molecular additives, sufficient carrier confinement with first-order recombination characteristics, and efficient suppression of non-radiative recombination can be achieved while retaining efficient charge transport characteristics.

Crystal sizes play a vital role in pushing up the efficiency of organometal halide perovskites based LEDs. Here Ban et al. incorporate a molecular additive to control the crystallite distribution and phase separation in the perovskite devices, resulting in high external quantum efficiency of 15.5%.

Monodisperse and brightly luminescent CsPbBr3/Cs4PbBr6 perovskite composite nanocrystals

The microscale composite structure strategy of embedding CsPbBr3 nanocrystals (NCs) in the microscale Cs4PbBr6 matrix (CPB113/CPB416) has successfully demonstrated its ability to resolve the fluorescence quenching of perovskite NCs in the solid agglomeration state due to the loss of quantum confinement. Unfortunately, the controllable synthesis of monodisperse nanoscale composites with bright emission in the solid state remains a great challenge. Here, we present for the first time a novel supersaturated recrystallization process to controllably synthesize monodisperse CPB113/CPB416 composite NCs with bright emission in the solid form, where CsPbBr3 NCs were uniformly embedded in the nano hexagonal Cs4PbBr6 matrix. The existence of 2-methylimidazole (MeIm) not only can control the composition rate of CsPbBr3 to Cs4PbBr6, the size and dispersity of CsPbBr3 in the composite NCs but can also help controllably obtain the monodisperse and hexagonal Cs4PbBr6 matrix. The as-prepared composite structure can effectively prevent CsPbBr3 fluorescence quenching and make the composite NCs have a high photoluminescence quantum yield (PLQY) of 83%. In addition, we obtained tunable blue to red emitting composite NCs by varying the halide salts.

Cs4PbBr6/CsPbBr3 Perovskite Composites with Near-Unity Luminescence Quantum Yield: Large-Scale Synthesis, Luminescence and Formation Mechanism, and White Light-Emitting Diode Application

All-inorganic perovskites have emerged as a new class of phosphor materials owing to their outstanding optical properties. Zero-dimensional inorganic perovskites, in particular the Cs₄PbBr₆-related systems, are inspiring intensive research owing to the high photoluminescence quantum yield (PLQY) and good stability. However, synthesizing such perovskites with high PLQYs through an environment-friendly, cost-effective, scalable, and high-yield approach remains challenging, and their luminescence mechanisms has been elusive. Here, we report a simple, scalable, room-temperature self-assembly strategy for the synthesis of Cs₄PbBr₆/CsPbBr₃ perovskite composites with near-unity PLQY (95%), high product yield (71%), and good stability using low-cost, low-toxicity chemicals as precursors. A broad range of experimental and theoretical characterizations suggest that the high-efficiency PL originates from CsPbBr₃ nanocrystals well passivated by the zero-dimensional Cs₄PbBr₆ matrix that forms based on a dissolution-crystallization process. These findings underscore the importance in accurately identifying the phase purity of zero-dimensional perovskites by synchrotron X-ray technique to gain deep insights into the structure-property relationship. Additionally, we demonstrate that green-emitting Cs₄PbBr₆/CsPbBr₃, combined with red-emitting K₂SiF₆:Mn⁴⁺, can be used for the construction of WLEDs. Our work may pave the way for the use of such composite perovskites as highly luminescent emitters in various applications such as lighting, displays, and other optoelectronic and photonic devices.

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.

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.

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.

Luminescent zero-dimensional organic metal halide hybrids with near-unity quantum efficiency

Single crystalline zero-dimensional organic metal halide hybrids have been developed.

Single crystalline zero-dimensional (0D) organic–inorganic hybrid materials with perfect host–guest structures have been developed as a new generation of highly efficient light emitters. Here we report a series of lead-free organic metal halide hybrids with a 0D structure, (C₄N₂H₁₄X)₄SnX₆ (X = Br, I) and (C₉NH₂₀)₂SbX₅ (X = Cl), in which the individual metal halide octahedra (SnX₆^4–) and quadrangular pyramids (SbX₅^2–) are completely isolated from each other and surrounded by the organic ligands C₄N₂H₁₄X⁺ and C₉NH₂₀⁺, respectively. The isolation of the photoactive metal halide species by the wide band gap organic ligands leads to no interaction or electronic band formation between the metal halide species, allowing the bulk materials to exhibit the intrinsic properties of the individual metal halide species. These 0D organic metal halide hybrids can also be considered as perfect host–guest systems, with the metal halide species periodically doped in the wide band gap matrix. Highly luminescent, strongly Stokes shifted broadband emissions with photoluminescence quantum efficiencies (PLQEs) of close to unity were realized, as a result of excited state structural reorganization of the individual metal halide species. Our discovery of highly luminescent single crystalline 0D organic–inorganic hybrid materials as perfect host–guest systems opens up a new paradigm in functional materials design.