Zero-dimensional Perovskite Research Articles

Unexpected red emission from Cs4PbI6 nanocrystals

The red emission of Cs4PbI6 zero-dimensional perovskite is found heterogeneous between individual particles, yet exhibits an enhanced stability towards both anion exchange reaction and photo radiation than CsPbI3.

The effects of hydroxyl by water addition on the photoluminescence of zero-dimensional perovskites Cs4PbBr6 nanocrystals

To investigate the effect of hydroxyl on the photoluminescence (PL) of zero-dimensional perovskite Cs4PbBr6, the Cs4PbBr6 nanocrystals (NCs) were prepared by solution method, and the influence of hydroxyl on the green emission of Cs4PbBr6 NCs was considered. The experiment results show that the green emission of Cs4PbBr6 displays a certain change by adding different amounts of water, NaOH water solution, and absolute ethyl alcohol. The pure Cs4PbBr6 NCs do not show green emission. After water added, CsPbBr3 NCs were observed and not considered to be the main reason for the green emission. Moreover, the hydroxyl of different degrees polarization has an apparent influence on the PL of Cs4PbBr6, which is believed the origin of the green emission. This effect can be explained by hydroxyl caused defect energy level in Cs4PbBr6.

Room Temperature Synthesis of All Inorganic Lead-Free Zero-Dimensional Cs4SnBr6 and Cs3KSnBr6 Perovskites.

Lead halide perovskites are excellent candidates for photoelectronic and photovoltaic applications, but the toxicity from lead is extremely concerning. Recently, Sn-based zero-dimensional lead-free perovskites synthesized using solid-state reaction techniques have become a new focus in the field. Here, we report a simple room temperature antisolvent method for the synthesis of all inorganic lead-free green emissive Cs4SnBr6 (emission at 524 nm) and cyan emissive Cs3KSnBr6 (emission at 500 nm) zero-dimensional perovskites. Their photoluminescence quantum yields reach 20% and 35%, respectively. In addition, they maintain their emission for 46 and 55 h in the air, respectively, compared to only 5 min of CsSnBr3. This method provides a convenient way to do the research and apply these highly emissive perovskites.

Understanding the Origin of Ultrasharp Sub-bandgap Luminescence from Zero-Dimensional Inorganic Perovskite Cs4PbBr6

Inorganic zero-dimensional perovskites, such as Cs4PbBr6, offer an underexplored opportunity to achieve efficient exciton formation and radiative recombination. In particular, the origin of sub-ban...

Photoluminescence Origin of Zero-Dimensional Cs4PbBr6 Perovskite

Green-emitting zero-dimensional perovskite Cs4PbBr6, consisting of an array of isolated [PbBr6]4– octahedra, has drawn a magnitude of interest due to its peculiar yet robust photoluminescence prope...

Critical Roles of High- and Low-Frequency Optical Phonons in Photodynamics of Zero-Dimensional Perovskite-like (C6H22N4Cl3)SnCl3 Crystals.

The zero-dimensional perovskites composed of isolated polyhedrons have unique and distinct physical properties compared with three-dimensional perovskites composed of interconnected polyhedrons. Here, we study the photodynamics of the zero-dimensional perovskite-like (C6H22N4Cl3)SnCl3 single crystals composed of isolated [SnCl3]- tetrahedrons. They exhibit red luminescence with huge Stokes shift (2.49 eV), large spectral broadening (416 meV), and long lifetime (6.9 μs). The experiments in conjunction with the ab initio calculations reveal the special roles of high- and low-frequency phonons in the photodynamics of the (C6H22N4Cl3)SnCl3 crystals. The resonance between the organic-cation-related high-frequency optical phonons and the singlet-to-triplet state transition induces strong intersystem crossing and resultant spin-forbidden luminescence. The strong electron-tetrahedron-related low-frequency optical-phonon coupling revealed by the low-temperature spectral characterization causes large spectral broadening. The strong lattice relaxation owing to localization of the electronic orbitals along with intersystem crossing accounts for the large Stokes shift.

Lasing from Zero-Dimensional Perovskite and Optical Imaging Applications

Owing to quantum confinement of optical and electrical transitions within isolated [PbBr6]4– octahedral units, zero-dimensional perovskite Cs4PbBr6 exhibits appealing molecular-like quantum optoele...

Delayed Photoluminescence and Modified Blinking Statistics in Alumina-Encapsulated Zero-Dimensional Inorganic Perovskite Nanocrystals.

We demonstrate enhancement of the photoluminescence (PL) properties of individual zero-dimensional (0D) Cs4PbBr6 perovskite nanocrystals (PNCs) upon encapsulation by alumina using an appropriately modified atomic layer deposition method. In addition to the increased PL intensity and improved long-term stability of encapsulated PNCs, our single-particle studies reveal substantial changes in the PL blinking statistics and the persistent appearance of the long-lived, "delayed" PL components. The blinking patterns exhibit a modification from the fast switching between fluorescent ON and OFF states found in bare PNCs to a behavior with longer ON states and more isolated OFF states in alumina-encapsulated PNCs. Controlled exposure of 0D nanocrystals to moisture suggests that the observed PL lifetime changes may be related to water-induced "reservoir" states that allow for longer-lived charge storage with subsequent back-feeding into the emissive states. Viable encapsulation of PNCs with metal oxides that can preserve and even enhance their PL properties can be utilized in the fabrication of extended structures on their basis for optoelectronic and photonic applications.

Revealing the Origin of Luminescence Center in 0D Cs4PbBr6 Perovskite

Zero dimensional perovskite Cs4PbBr6 has attracted considerable attention recently not only because of its highly efficient green photoluminescence (PL), but also its two highly debated opposing mechanisms of the luminescence: embedded CsPbBr3 nanocrystals versus intrinsic Br vacancy states. After a brief discussion on the root cause of the controversy, we provide sensitive but non-invasive methods that can not only directly correlate luminescence with the underlying structure, but also distinguish point defects from embedded nanostructures. We first synthesized both emissive and non-emissive Cs4PbBr6 crystals, obtained the complete Raman spectrum of Cs4PbBr6 and assigned all Raman bands based on density functional theory simulations. We then used correlated Raman-PL as a passive structure-property method to identify the difference between emissive and non-emissive Cs4PbBr6 crystals and revealed the existence of CsPbBr3 nanocrystals in emissive Cs4PbBr6. We finally employed a diamond anvil cell to probe the response of luminescence centers to hydrostatic pressure. The observations of fast red-shifting, diminishing and eventual disappearance of both green emission and Raman below Cs4PbBr6 phase transition pressure of ~3 GPa is compatible with CsPbBr3 nanocrystal inclusions as green PL emitters and cannot be explained by Br vacancies. The resolution of this long-lasting controversy paves the way for further device applications of low dimensional perovskites, and our comprehensive optical technique integrating structure-property with dynamic pressure response is generic and can be applied to other emerging optical materials to understand the nature of their luminescent centers.

Outstanding Challenges of Zero-Dimensional Perovskite Materials.

Outstanding Challenges of Zero-Dimensional Perovskite Materials.

Controlled synthesis of zero-dimensional phase-pure Cs4PbBr6 perovskites crystals with high photoluminescence quantum yield

Cesium lead halide perovskites have been arise as a new promising materials for optoelectronic applications. On this basis, zero-dimensional inorganic perovskites, Cs4PbBr6 can be an important candidate because of the excellent stability. However, obtaining the high photoluminescence quantum yield (PLQY) of phase-pure Cs4PbBr6 Perovskites still remains a challenge. Here, we synthesized the phase-pure Cs4PbBr6 crystals through a simple ligand-assisted, reprecipitation strategy under room-temperature. We altered the assisted ligands that used in the experiment synthesis, such as substitute dodecylamine for oleylamine, and obtained high near PLQY (95.1%) of phase-pure Cs4PbBr6 Perovskites. We revealed the extra oleic acid (OA), such as the ratio of OA and dodecylamine for 10:1, would improve their PLQY. Most importantly, we demonstrated the short lifetime decay is caused by the recombination of trapped exciton inside the crystal but the long lifetime decay is attributed to the recombination of the surface energy states, and provided a great comprehension in photophysical of Cs4PbBr6 Perovskite materials.

Air-Stable, Lead-Free Zero-Dimensional Mixed Bismuth-Antimony Perovskite Single Crystals with Ultra-broadband Emission.

Lead-free zero-dimensional (0D) organic-inorganic metal halide perovskites have recently attracted increasing attention for their excellent photoluminescence properties and chemical stability. Here, we report the synthesis and characterization of an air-stable 0D mixed metal halide perovskite (C8 NH12 )4 Bi0.57 Sb0.43 Br7 ⋅H2 O, in which individual [BiBr6 ]3- and [SbBr6 ]3- octahedral units are completely isolated and surrounded by the large organic cation C8 H12 N+ . Upon photoexcitation, the bulk crystals exhibit ultra-broadband emission ranging from 400 to 850 nm, which originates from both free excitons and self-trapped excitons. This is the first example of 0D perovskites with broadband emission spanning the entire visible spectrum. In addition, (C8 NH12 )4 Bi0.57 Sb0.43 Br7 ⋅H2 O exhibits excellent humidity and light stability. These findings present a new direction towards the design of environmentally-friendly, high-performance 0D perovskite light emitters.

On the origins of the green luminescence in the "zero-dimensional perovskite" Cs4PbBr6: conclusive results from cathodoluminescence imaging.

There is great interest in the use of highly-efficient all-inorganic halide perovskites CsnPbBr2+n for optoelectronic applications. There however remains considerable debate as to the origins of the green luminescence in the zero-dimensional phase of the perovskite Cs4PbBr6, with theories suggesting it originates either from defects in the Cs4PbBr6 lattice or CsPbBr3 impurities/inclusions. The confusion has arisen due to the two phases being miscible and typically co-existing. Moreover, low impurity levels of CsPbBr3 in Cs4PbBr6 are difficult to detect by XRD measurements, yet have much stronger photoluminescence than bulk CsPbBr3 that exhibits quenching, further contributing to the confusion as to the origins of the green photoluminescence. With the rise of significant debate and misconceptions, we provide conclusive evidence that the green emission from Cs4PbBr6 is indeed due to nanocrystalline CsPbBr3 impurities. This is demonstrated by undertaking cathodoluminescence and EDX measurements on samples prepared mechanochemically by ball-milling. Cathodoluminescence imaging clearly shows the presence of small crystals embedded in/or between larger crystallites of Cs4PbBr6 and they emit around 520 nm. EDX shows that the smaller crystal inclusions have a Pb : Br ratio that is approximately 2 times higher, confirming the CsPbBr3 phase, which has the expected size-dependent shift to shorter wavelengths (about 528 to 515 nm). These studies make significant inroads into understanding these lead halide perovskites for their use in a variety of optoelectronic and photovoltaic applications.

Performance and stability gain in zero-dimensional perovskite solar cells after >2 years when hybridized with silicon nanocrystals.

We report highly stable zero-dimensional (CH3NH3)3Bi2I9 photovoltaic cells which demonstrate a 33% increase in performance after 2 years when hybridized with silicon nanocrystals (SiNCs). The natural oxidation of SiNCs is expected to consume radical species and improve the SiNC/(CH3NH3)3Bi2I9 interface and electronic coupling whilst also inhibiting defect-induced degradation.

Probing molecule-like isolated octahedra via phase stabilization of zero-dimensional cesium lead halide nanocrystals

Zero-dimensional (0D) inorganic perovskites have recently emerged as an interesting class of material owing to their intrinsic Pb2+ emission, polaron formation, and large exciton binding energy. They have a unique quantum-confined structure, originating from the complete isolation of octahedra exhibiting single-molecule behavior. Herein, we probe the optical behavior of single-molecule-like isolated octahedra in 0D Cesium lead halide (Cs4PbX6, X = Cl, Br/Cl, Br) nanocrystals through isovalent manganese doping at lead sites. The incorporation of manganese induced phase stabilization of 0D Cs4PbX6 over CsPbX3 by lowering the symmetry of PbX6 via enhanced octahedral distortion. This approach enables the synthesis of CsPbX3 free Cs4PbX6 nanocrystals. A high photoluminescence quantum yield for manganese emission was obtained in colloidal (29%) and solid (21%, powder) forms. These performances can be attributed to structure-induced confinement effects, which enhance the energy transfer from localized host exciton states to Mn2+ dopant within the isolated octahedra.

Quantum confinement luminescence of trigonal cesium lead bromide quantum dots

Cesium lead halides are novel and superior optoelectronic materials. Unlike the cases of the widely investigated cubic CsPbXr3 (X = Cl, Br, or I) nanocrystals, people know little about the optical properties of the “zero-dimensional perovskite” Cs4PbX6 nanocrystals. We study the photoluminescence properties of the Cs4PbBr6 quantum dots (QDs) with sizes of only a few nanometers. They exhibit stable wavelength-tunable (from 340 to 378 nm) luminescence stemming from quasi-self-trapped excitons. The spectral characterizations in conjunction with first-principles calculations reveal there is remarkable quantum confinement effect in the Cs4PbBr6 QDs. The large exciton binding energy obtained from both calculation and experiment explains why the trigonal Cs4PbX6 QDs have strong exciton-related absorption and emission at room temperature. This family of wide-gap trigonal cesium lead halide QDs with intrinsic near-UV luminescence have potential applications in short-wavelength photonic nanodevices.

Point Defects and Green Emission in Zero-Dimensional Perovskites.

Zero-dimensional (0D) perovskites have recently opened a new frontier in device engineering for light conversion technologies due to their unprecedented high photoluminescence quantum yield as solids. Although many experimental and theoretical efforts have been made to understand their optical behavior, the origin of their green emission is still opaque. Here, we develop a complete experimental and theoretical picture of point defects in Cs-Pb-Br perovskites and demonstrate that bromide vacancies (VBr) in prototype 0D perovskite Cs4PbBr6 have a low formation energy and a relevant defect level to contribute to the midgap radiative state. Moreover, the state-of-the-art characterizations including atomic-resolution electron imaging not only confirm the purity of the 0D phase of Br-deficient green-emissive Cs4PbBr6 nanocrystals (NCs) but also exclude the presence of CsPbBr3 NCs impurities. Our findings provide robust evidence for defect-induced green luminescence in 0D perovskite NCs, which helps extend the scope of the utility of these bulk 0D quantum materials in optoelectronic applications.

Intermediate Bands in Zero-Dimensional Antimony Halide Perovskites

Using density functional theory, the structural and electronic-structure properties of a recently discovered, zero-dimensional antimony halide perovskite are studied. It is found that the herein considered material EtPySbBr6 exhibits very promising electronic-structure properties: a direct band gap close to the peak of the solar spectrum and effective masses allowing for efficient carrier transport of electrons in particular. These results are rationalized by analysis of the electronic structure, which reveals the formation of intermediate bands due to orbital-hybridization effects of the Sb s-states. This study shows that the formation of intermediate bands can lead to highly favorable electronic-structure properties of zero-dimensional perovskites and discusses the possibility of fabricating lead-free halide perovskites with promising optoelectronic properties by targeted substitution of ions and emergence of intermediate bands. These insights are important when understanding and further enhancing the capabilities of antimony and other promising lead-free compounds.

The Benefit and Challenges of Zero-Dimensional Perovskites.

To break free of the limitations imposed by three-dimensional (3D) perovskites, such as their lackluster stability, researchers have opened new frontiers into lower-dimensional perovskite derivatives. Thanks to advances in solvent-based synthesis methods, zero-dimensional (0D) inorganic perovskites, mainly Cs4PbBr6, have recently reemerged in various forms (from single crystals to nanocrystals) as materials with properties that bridge organic molecules and inorganic semiconductors. These properties include intrinsic Pb2+ ion emission, large exciton binding energy, and small polaron formation upon photoexcitation, in addition to anomalous green photoluminescence with improved stability and high quantum yield. Moreover, the demonstration of Cs4PbBr6-based light-emitting diode (LED) devices highlights the accelerating efforts toward their applications and motivates further investigations of these emerging materials. This Perspective summarizes the progress in the field of Cs4PbBr6 perovskites, focusing on their molecular-electronic properties and hotly debated green photoluminescence. We conclude by presenting the implications of the unique findings and suggesting opportunities for the future development and applications of these 0D perovskites.

Synthesis and Optical Properties of Colloidal M3Bi2I9 (M = Cs, Rb) Perovskite Nanocrystals

Bulk Cs3Bi2I9 exhibits zero-dimensional (0-D) perovskite crystal structure at the molecular level, providing scopes for novel optical properties compared to three-dimensional perovskite structures. Here, 0-D refers to the crystal structure irrespective of the size of the crystal. We have prepared colloidal Cs3Bi2I9 nanocrystals and elucidated the unique optical properties arising from their 0-D crystal structure. Absorption spectrum at 10 K confirms that the electronic band gap of Cs3Bi2I9 nanocrystals is at 2.86 eV, along with a sharp excitonic peak at 2.56 eV, resulting in a very high excitonic binding energy, EbX = 300 meV. Interestingly, we observe two peaks in the photoluminescence spectra at room temperature on both sides of the excitonic absorption energy. Because EbX (300 meV) ≫ effective phonon energy (36 meV), the phonon-mediated relaxation of carriers from conduction band minimum to the excitonic state is suppressed to an extent. Consequently, two photoluminescence peaks related to both the bul...