All-inorganic Lead Halide Perovskite Research Articles

Ambient processed and stable all-inorganic lead halide perovskite solar cells with efficiencies nearing 20% using a spray coated Zn1−xCsxO electron transport layer

Achieving ambient-processed and stable all-inorganic halide perovskite solar cells with high conversion efficiencies is a well-established goal within the halide perovskite research community. In striving for this, electron transporting layers based on common TiO2 and SnO2 nanoparticles have been widely deployed, however, can stifle device performance due to their requirement for high temperature processing and non-uniform layer deposition. Using a low-temperature processed Cs-doped ZnO nanocrystalline electron transport layer and a narrow-bandgap (~1.70 eV) all-inorganic absorber (Cd-doped CsPbI2.5Br0.5), we report ambient-processed solar cells which exhibit high conversion efficiencies (>19.75%) and stable performance under ambient condition (>300 h). A smooth interface is established by combining spray-deposition of the electron transport layer and injection of hot-air during the perovskite deposition, which crystallizes smooth, compact perovskite thin films directly from solution. The high performance is attributed to preserving a solar-friendly and phase-stable perovskite layer, along with improved charge carrier management.

Investigation of the Role of Cations during Anion Exchange in All-Inorganic Halide Perovskite Nanocrystals

All-inorganic lead halide perovskite nanocrystals (PeNCs) exhibit tunable optical bandgap energies by adjusting their compositions. PeNC-based optical or optoelectronic devices have been developed using the anion exchange strategy, which can replace the X-site anion with the target halide without phase transition. Thus, various methods for adjusting the anions in PeNCs have been developed; however, the cation effect on anion exchange has rarely been discussed. Here, we investigated the effect of cations on the optical bandgap energy and stability of CsPbX3 (X = Cl, Br, and I) PeNCs by analyzing as cation candidates NH4 +, Na+, K+, and TBA+. Among them, NH4Cl and NaI are efficient anion-exchanging chemicals because they effectively provide Cl− or I−, respectively, to PeNCs without structural deformation. The halide sources allow exchange in the composition of PeNCs under benign conditions, such as atmospheric conditions and 298 K. This phenomenon is explained using the hard-soft acid-base (HSAB) theory. We believe that these findings will contribute to the improvement of optoelectronic devices, such as solar cells, displays, and light-emitting diodes (LEDs).

Resonantly Pumped Bright-Triplet Exciton Lasing in Cesium Lead Bromide Perovskites.

The surprising recent observation of highly emissive triplet-states in lead halide perovskites accounts for their orders-of-magnitude brighter optical signals and high quantum efficiencies compared to other semiconductors. This makes them attractive for future optoelectronic applications, especially in bright low-threshold nanolasers. While nonresonantly pumped lasing from all-inorganic lead-halide perovskites is now well-established as an attractive pathway to scalable low-power laser sources for nano-optoelectronics, here we showcase a resonant optical pumping scheme on a fast triplet-state in CsPbBr3 nanocrystals. The scheme allows us to realize a polarized triplet-laser source that dramatically enhances the coherent signal by 1 order of magnitude while suppressing noncoherent contributions. The result is a source with highly attractive technological characteristics, including a bright and polarized signal and a high stimulated-to-spontaneous emission signal contrast that can be filtered to enhance spectral purity. The emission is generated by pumping selectively on a weakly confined excitonic state with a Bohr radius ∼10 nm in the nanocrystals. The exciton fine-structure is revealed by the energy-splitting resulting from confinement in nanocrystals with tetragonal symmetry. We use a linear polarizer to resolve 2-fold nondegenerate sublevels in the triplet exciton and use photoluminescence excitation spectroscopy to determine the energy of the state before pumping it resonantly.

Near Unity PLQY and High Stability of Barium Thiocyanate Based All-Inorganic Perovskites and Their Applications in White Light-Emitting Diodes

All-inorganic lead halide perovskite (CsPbX3) nanocrystals (NCs) have emerged as a highly promising new generation of light emitters due to their extraordinary photophysical properties. However, the performance of these semiconducting NCs is undermined due to the inherent toxicity of lead and long-term environmental stability. Here, we report the addition of B-site cation and X-site anion (pseudo-halide) concurrently using Ba(SCN)2 (≤50%) in CsPbX3 NCs to reduce the lead and improve the photophysical properties and stability. The as-grown particles demonstrated an analogous structure with an almost identical lattice constant and a fluctuation of particle size without altering the morphology of particles. Photoluminescence quantum yield is enhanced up to near unity (~98%) by taking advantage of concomitant doping at the B- and X-site of the structure. Benefitted from the defect reductions and stronger bonding interaction between Pb2+ and SCN− ions, Ba(SCN)2-based NCs exhibit improved stability towards air and moisture compared to the host NCs. The doped NCs retain higher PLQY (as high as seven times) compared to the host NCs) when stored in an ambient atmosphere for more than 176 days. A novel 3D-printed multiplex color conversion layer was used to fabricate a white light-emitting diode (LED). The obtained white light shows a correlated color temperature of 6764 K, a color rendering index of 87, and luminous efficacy of radiation of 333 lm/W. In summary, this work proposes a facile route to treat sensitive lead halide perovskite NCs and to fabricate LEDs by using a low-cost large-scale 3-D printing method, which would serve as a foundation for fabricating high-quality optoelectronic devices for near future lighting technologies.

Texture Formation in Polycrystalline Thin Films of All-Inorganic Lead Halide Perovskite.

Controlling grain orientations within polycrystalline all-inorganic halide perovskite solar cells can help increase conversion efficiencies toward their thermodynamic limits; however, the forces governing texture formation are ambiguous. Using synchrotron X-ray diffraction, mesostructure formation within polycrystalline CsPbI2.85 Br0.15 powders as they cool from a high-temperature cubic perovskite (α-phase) is reported. Tetragonal distortions (β-phase) trigger preferential crystallographic alignment within polycrystalline ensembles, a feature that is suggested here to be coordinated across multiple neighboring grains via interfacial forces that select for certain lattice distortions over others. External anisotropy is then imposed on polycrystalline thin films of orthorhombic (γ-phase) CsPbI3- x Brx perovskite via substrate clamping, revealing two fundamental uniaxial texture formations; i)I-rich films possess orthorhombic-like texture (<100> out-of-plane; <010> and <001> in-plane), while ii) Br-rich films form tetragonal-like texture (<110> out-of-plane; <110> and <001> in-plane). In contrast to relatively uninfluential factors like the choice of substrate, film thickness, and annealing temperature, Br incorporation modifies the γ-CsPbI3- x Brx crystal structure by reducing the orthorhombic lattice distortion (making it more tetragonal-like) and governs the formation of the different, energetically favored textures within polycrystalline thin films.

Stable CsPbI3-Mesoporous Alumina Composite Thin Film at Ambient Condition: Preparation, Characterization, and Study of Ultrafast Charge-Transfer Dynamics

Among the all-inorganic lead halide perovskites, CsPbI3 has emerged as a competent photovoltaic material because of its enhanced stability and comparable efficiency to that of organic–inorganic hyb...

Laurionite Competes with 2D Ruddlesden-Popper Perovskites During the Saturation Recrystallization Process.

The room-temperature saturation recrystallization (RTSR) method has been extensively used to prepare all-inorganic lead halide perovskite (e.g., CsPbBr3) nanocrystals. Here, we revealed that the composition of the products prepared by the seemingly simple RTSR method could be extremely complex under different experimental parameters. The pH value of the solution and the protonation tendency of the amines influenced by the amounts and types of introduced amines, oleic acid, and water from the environment determined the composition of the final products. PbBr2, 2D Ruddlesden-Popper perovskites (RPPs) formed by perovskite layers separated by intercalating cations, and laurionite Pb(OH)Br would form under acidic, mildly acidic, and alkaline conditions, respectively. Based on the understanding of the formation mechanism, Pb(OH)Br microparticles with well-defined morphologies were prepared, which could be transformed into highly luminescent CH3NH3PbBr3 with the morphology unchanged. The protonated amine behaves as an intercalating layer during the formation of 2D RPPs. Phenylethylamine (PEA) was proven to be an appropriate amine to prepare pure RPP microplates because of its weaker alkalinity compared to aliphatic amines. The prepared (PEA)2PbBr4 RPP microplates showed strong deep-blue light emission with a PL peak at 415 nm, which could be fine-tuned by changing amines. This study proved the complex reaction pathways of the seemingly simple RTSR method and extended the RTSR method into the fabrication of 2D RPPs and laurionite with promising applications in optoelectronic devices.

Partial Substitution of Pb2+ in CsPbI3 as an Efficient Strategy To Design Fairly Stable All-Inorganic Perovskite Formulations.

All-inorganic lead halide perovskites, for example, CsPbI3, are becoming more attractive for applications as light absorbers in perovskite solar cells because of higher thermal and photochemical stability as compared to their hybrid analogues. However, a specific drawback of the CsPbI3 absorber consists of the rapid phase transition from black to yellow nonphotoactive phase at low temperatures (e.g., <100 °C), which is accelerated under exposure to light. Herein, an experimental screening of an unprecedently large series (>30) of metal cations in a wide range of concentration has allowed us to establish a set of Pb2+ substitutes, facilitating the crystallization of the photoactive black CsPbI3 phase at low temperatures. Importantly, the appropriate Pb2+ substitution with Ca2+, Sr2+, Ce3+, Nd3+, Gd3+, Tb3+, Dy2+, Er3+, Yb2+, Lu3+, and Pt2+ cations has led to a spectacular enhancement of the film stability under realistic solar cell operation conditions (∼1 sun equivalent light exposure, 50 °C). Optoelectronic, structural, and morphological effects of partial Pb2+ substitution were investigated, providing a deeper insight into the processes underlying the stabilization of the CsPbI3 films. Several CsPb1-xMxI∼3 systems were evaluated as absorber materials in perovskite solar cells, demonstrating encouraging light power conversion efficiency of 11.4% in preliminary experiments. The obtained results feature the potential of designing efficient and stable all-inorganic perovskite solar cells using novel absorber materials rationally designed via compositional engineering.

Large-Area Synthesis and Patterning of All-Inorganic Lead Halide Perovskite Thin Films and Heterostructures.

All-inorganic lead halide perovskites have attracted tremendous interest for their excellent stability when compared with hybrid perovskites. Here we report a large-area growth of monocrystalline all-inorganic perovskite thin films and further patterning them into heterostructure arrays. We show that highly oriented CsPbBr3 microcrystal domains can be readily grown on muscovite mica substrates with a well-defined epitaxial relationship, which can further expand and eventually merge into large-area monocrystalline CsPbBr3 thin films with an excellent optical quality. Taking a step further, we show the large-area CsPbBr3 thin film can be further patterned and selectively transformed into CsPbI3 using a selective anion-exchange process to produce CsPbBr3-CsPbI3 lateral heterostructure arrays with spatially modulated photoluminescence emission and an apparent current rectification behavior. The capability to grow large-area CsPbBr3 monocrystalline thin films and heterostructure arrays defines a robust material platform for both the fundamental investigations and potential applications in optoelectronics.

Reducing the leakage current for a CsPbBr3 detector via asymmetric area electrodes and heterostructures

As a typical representative of all-inorganic lead halide perovskites, cesium lead bromine (CsPbBr3) has been regarded as the workhorse of next-generation room temperature X-ray detectors in recent years.

Hierarchical Metal-Organic Framework-Confined CsPbBr3 Quantum Dots and Aminated Carbon Dots: A New Self-Sustaining Suprastructure for Electrochemiluminescence Bioanalysis.

All-inorganic lead halide perovskites have become promising alternatives to traditional semiconductor electrochemiluminescence (ECL) emitters because of their appealing optoelectronic attributes, but major challenges remain in improving their stability and enhancing charge injection/transfer capacities. Herein, a self-sustaining suprastructure was constructed by successively loading aminated carbon dots (NCDs) and CsPbBr3 perovskite quantum dots (PeQDs) in situ into hierarchical zeolite imidazole framework-8 (HZIF-8). The elaborated architecture guarantees not only improved stability via the peripheral HZIF-8 protective barrier but also accelerated charge transport and efficient self-enhanced ECL between PeQDs and the surrounding NCDs in a confined structure. As a result, the ternary nanocomposite is endowed with greatly improved stability and ECL efficiency. Based on this ternary nanocomposite as an electrode substrate, a novel ECL sensing strategy is further proposed for the first time to evaluate T4 polynucleotide kinase activity and screen its inhibitors. This work opens an avenue for the advancement of perovskite-based ECL emitters as well as the development of corresponding applications in the ECL domain.

Scalable synthesis of highly luminescent and stable thiocyanate based CsPbX3 perovskite nanocrystals for efficient white light-emitting diodes

All-inorganic lead halide perovskites have attracted considerable attention as promising materials for optoelectronic devices because of their excellent photophysical properties. However, the stability issue of halide perovskites precludes their practical applications. For the first time, this work exhibits that the optical properties and stability of CsPbX3 perovskite nanocrystals (NCs), prepared by the saponification precipitation method, can be improved using thiocyanate (SCN−). Besides, this work offers a simple and economical synthesis method operable at room temperature and ambient atmosphere. Specifically, an increasing concentration of SCN− induces an increase in quantum yield almost by 10% and stability against air and moisture over several days due to the better passivation of trap states, irrespective of size and shape variation of NCs. The demonstration of tunable emission (454–645 nm) across the visible spectrum and the design of 3-D printed thin layers facilitate the preparation of green, yellow, and red-emitting color conversion layers. Benefitted from the decreased photon loss in as-synthesized conversion layers, the application of these color conversion layers results in a bright neutral white light (5184 K) with remarkable optical properties. Hence, this experimental study offers a low-temperature synthetic path for the scalable preparation of high-quality CsPbX3 NCs processed with SCN− and reveals the practical applications of such NCs.

Controllable synthesis and performance research of CsPbBr&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;@CsPb&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;Br&amp;lt;sub&amp;gt;5&amp;lt;/sub&amp;gt; nanocrystals with high stability and quantum yield

In the past decade, all-inorganic lead halide perovskite nanocrystals have emerged as promising active materials for optoelectronics, such as photovoltaics, lasers, and photodetectors, owing to their size-tunable optical bandgaps, attractive light absorption, and extraordinary charge-transport properties. Besides these photoelectric applications, nanostructured lead halide perovskites have shown good wavelength tunability, high photoluminescence quantum yields (PLQYs), and high color purity with narrow full width at half maximum (FWHM), rendering them potential candidates for high-performance light-emitting diodes (LEDs). Unfortunately, despite the remarkable advancements of all-inorganic lead halide perovskite, the problem of their unsolved stability upon exposure to thermal and humid environments has greatly hampered their further practical and commercial applications. Thus, many researchers have been bent their mind to improve the water stability of perovskites from moist air or solutions, such as moisture-impermeable polymer embedding, water proof organic ligand coating, inorganic encapsulation, and superhydrophobic framework structures. CsPb2Br5, which has an indirect band gap of 3.87 eV and a two-dimensional structure with [Pb2Br5]– layers spaced by Cs+ cations, has been reported to modify the stability of CsPbBr3. However, the arrangement of CsPbBr3 and CsPb2Br5 phases, which is significant for both the improvement of the stability and the investigation of the mechanism, is still a bottleneck. In order to improve the stability of the all-inorganic lead halide perovskite, an innovative method—Pseudo-peritectic method, that is a peritectic reaction in the solution, was proposed to achieve the same element surface modification of the CsPbBr3 perovskite by reasonably controlling the ratio of reactants. In our experiment, the CsPbBr3 nanocrystals were synthesized by solvothermal method first, and then injected into the PbBr2 solution. The peritectic reaction between CsPbBr3 and PbBr2 occurred in the solution. The synthesized CsPb2Br5 phase is excepted to disperse on the surface of the as-prepared CsPbBr3 phase. The study of the crystal structure, morphology, composition and photoluminescence of the prepared composite perovskite CsPbBr3@CsPb2Br5 were carried out. The X-ray diffraction (XRD) pattern and morphologies of the samples synthesized by the pseudo-peritectic method indicated that the composite perovskite CsPbBr3@CsPb2Br5 with uniformly distributed CsPb2Br5 phase on the surface can be prepared by controlling the ratio of reactants. With the ratio of CsPbBr3: PbBr2 changing from 1:1 to 2.5:1, the CsPb2Br5 phase increased. When the ratio of CsPbBr3:PbBr2 was 2.5:1, the CsPb2Br5 phase well dispersed on the surface of the as-prepared CsPbBr3 phase. However, when the ratio increased to 3:1, even 5:1, the synthesized CsPb2Br5 phase decreased. The photoluminescence spectroscopy and fluorescence quantum yield of the composite material showed that the presence of the same element phase CsPb2Br5 greatly improved the stability and the photoluminescence (PL) properties. The uniformly distributed CsPb2Br5 phase on the surface of the composite material reduced the surface defect concentration of CsPbBr3, and protected the CsPbBr3 phase to a certain extent, that improved the luminescence and stability of the CsPbBr3 perovskite. The method for synthesizing composites provides a new pathway to ensure a controllable surface modification structure, which would dramatically enhance the stability of CsPbBr3 nanocrystals in highly polar solvents such as water. The water-stable enhanced nanocrystals make it possible for long-term stable electronic applications in the atmosphere.

Highly stable and luminescent silica-coated perovskite quantum dots at nanoscale-particle level via nonpolar solvent synthesis

Currently, unsatisfactory optical stability and toxicity of all-inorganic lead halide perovskite (CsPbX3, X = Cl, Br, and I) quantum dots (QDs) with excellent photoelectric properties is a major obstacle for their practical application. In this work, the CsPbBr3 QDs were assembled into SiO2 shell via nonpolar solvent synthesis, and monodisperse CsPbBr3@SiO2 nanocomposites (NCs) with high photoluminescence quantum yield (PLQY) of ~87% were successfully prepared. Moreover, the introduced hydrophobic and multibranched trioctylphosphine oxide (TOPO) effectively suppressed the hydrolysis rate of tetraethoxysilane (TEOS), resulting in the formation of core@shell NCs at a nanoscale-particle level. Benefiting from the protection of TOPO and SiO2 shell, the CsPbBr3@SiO2 NCs exhibit remarkably improved stability against thermal treatment, UV irradiation and water compared to the bare perovskite-QDs. Notably, the anion-exchange reaction among different perovskite-QDs was completely inhibited. To improve stability of iodide-substituted perovskite-QDs and expand emission wavelength, the CsPbBr0.6I2.4@SiO2 NCs with PLQY of 75% were also successfully prepared by similar strategy. White light-emitting-diodes (WLEDs) were designed by combining CsPbBr3@SiO2 NCs with CsPbBr0.6I2.4@SiO2 NCs onto blue GaN chips. Bright white-light with high color-rendering index of 90 and luminous efficiency of 80 lm W−1 were achieved from these WLEDs, indicating the synthesized perovskite NCs possess huge potentiality in displays and solid-state lighting.

Long-term optical and morphological stability of CsPbBr3 nanocrystal-based films

All-inorganic lead halide perovskite nanocrystals exhibit excellent optical properties, which make them promising for optoelectronic devices. However, the insulating organic ligands at the nanocrystals’ surface represent a major issue in their effective application in devices. To decrease the effect of the ligands on carrier transport in perovskite nanocrystal-based films, several post-synthesis treatment methods have been reported, but in most of the cases the nanocrystals tend to degrade over long term storage. To address these concerns, herein we develop a novel surface treatment procedure based on the combination of ammonium thiocyanate and benzoyl bromide for CsPbBr3 nanocrystals. The morphological, optical and structural characterizations were carried out to investigate the evolution of both as-prepared and surface-treated nanocrystals in spin-coated films, over ageing under ambient conditions. It was found that films based on the treated nanocrystals present higher stability, providing a promising path for fabricating optoelectronic devices based on these materials.

Temperature dependent optical characteristics of all-inorganic CsPbBr3 nanocrystals film

As one of the most promising optoelectronic materials in recent years, colloidal all-inorganic lead halide perovskite nanocrystals (NCs) have become a research focus. An in-depth understanding of electron behavior in the material is essential for advanced device application. Here, temperature-dependent photoluminescence (PL) spectroscopy is employed to study the optical properties of CsPbBr3 NCs film. It is found that the PL intensity decreased with temperature below 200 K, while reverse trend has been observed with temperature above 200 K. The mechanism of the PL unusual quenching phenomenon is attributed to surface states of NCs, which leads to non-radiative recombination of electrons at low temperatures. Above the critical temperature, electrons will escape from the defect level and participate in radiative recombination, which give rise to the enhanced emission. The model is further verified by comparison with nanoplatelets, surface passivation, as well as temperature-dependent PL decay experiments.

Emission Quenching and Recovery of Illuminated Perovskite Quantum Dots Due to Iodide Ion Migration.

All-inorganic lead halide perovskite quantum dots (PQDs) are well-known to easily lose their luminescence emission under light illumination, which is often attributed to a photoinduced degradation mechanism. Here, we demonstrate that such quenched emission of PQDs can completely recover in the dark at room temperature, which occurs through a spontaneous "self-healing" mechanism. Our findings indicate that the loss of emission under light illumination is not due to the generally accepted photoinduced degradation, as otherwise the complete recovery would not be possible. Instead, we attribute the emission loss and its subsequent recovery to the migration of iodide ions on the PQD surface. Under illumination, the iodide ions migrate out and associate to adjacent lead ions on the PQD surface, leading to halide vacancies, lattice distortions, and fluorescence quenching. During the recovery process, the migrated iodide ions spontaneously migrate back and fill halide vacancies, resulting in fluorescence recovery. The results of this study offer a useful solution on how to improve the emission and photostability of PQDs.

Convenient synthesis of high-quality, all-inorganic lead halide perovskite nanocrystals for high purity monochrome QLED

ABSTRACT In recent years, perovskite quantum dots (QDs) have become a new class of semiconductor materials due to their high monodispersity and adjustable emission spectra. However, there are few studies on perovskite QDs ligands, and there are some problems such as poor stability and low photoluminescence quantum yield (PLQY). Here, we prepared CsPbBr3 QDs with excellent optical properties and crystallinity by using caesium stearate as the precursor. Besides, we systematically studied the effects of different chain length organic amines on the yield, optical properties and stability of CsPbBr3 QDs. The experimental results show that the long-chain organic amin oleylamine and dodecylamine (DOAm) have better encapsulation properties, and the synthesised QDs have better crystallinity and stability. CsPbBr3 QDs with PLQY of 90%were obtained by using oleic acid (OA)/DOAm as a ligand at 140°C. Moreover, a high purity monochrome quantum dot light-emitting diode was prepared.

Tailoring Component Interaction for Air-Processed Efficient and Stable All-Inorganic Perovskite Photovoltaic.

All-inorganic lead halide perovskites are promising candidates for optoelectronic applications. However, fundamental questions remain over the component interaction in the perovskite precursor solution due to the limitation of the most commonly used solvents of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Here, we report an interaction tailoring strategy for all-inorganic CsPbI3-x Brx perovskites by involving the ionic liquid solvent methylammonium acetate (MAAc). C=O shows strong interaction with lead (Pb2+ ) and N-H⋅⋅⋅I hydrogen bond formation is observed. The interactions stabilize the perovskite precursor solution and allow production of the high-quality perovskite films by retarding the crystallization. Without the necessity for antisolvent treatment, the one-step air-processing approach delivers photovoltaic cells regardless of humidity, with a high efficiency of 17.10 % along with long operation stability over 1500 h under continuous light illumination.

Efficient up-conversion photoluminescence in all-inorganic lead halide perovskite nanocrystals

Up-conversion photoluminescence (UCPL) refers to the elementary process where low-energy photons are converted into high-energy ones via consecutive interactions inside a medium. When additional energy is provided by internal thermal energy in the form of lattice vibrations (phonons), the process is called phonon-assisted UCPL. Here, we report the exceptionally large phonon-assisted energy gain of up to ~ 8kBT (kB is Boltzmann constant, T is temperature) on all-inorganic lead halide perovskite semiconductor colloidal nanocrystals that goes beyond the maximum capability of only harvesting optical phonon modes. By systematic optical study in combination with a statistical probability model, we explained the nontrivial phonon-assisted UCPL process in perovskites nanocrystals, where in addition to the strong electron-phonon (light-matter) coupling, other nonlinear processes such as phonon-phonon (matter-matter) interaction also effectively boost the up-conversion efficiency.