Stability Of Lead Halide Perovskites Research Articles

Stability and photocatalytic performance enhancement of sodium-doped CsPbBr3/Cs4PbBr6 nanocomposites for dye wastewater degradation

The extremely poor stability of lead halide perovskites has always been a challenge. In this paper, CsPbBr3 nanocrystals, CsPbBr3/Cs4PbBr6 nanocomposites and Na-CsPbBr3/Cs4PbBr6 nanocomposites were prepared by thermal injection and ligand-assisted reprecipitation method. The photocatalytic effect and stability of CsPbBr3 in aqueous systems were significantly improved by sodium ions doping and complexation with Cs4PbBr6. The results showed that the photocatalytic degradation rate of 5% Na-CsPbBr3 for Sudan red (III) was 57.8% within 180 min, while that of pure CsPbBr3 was only 14.47%. In the CsPbBr3/Cs4PbBr6 nanocomposites, Na-CsPbBr3/Cs4PbBr6 nanocomposites photocatalyzed nearly 94% of Sudan red (III) in 120 min, while CsPbBr3/Cs4PbBr6 photocatalyzed only 56% of organic dyes in the same time. Cs4PbBr6 can passivate CsPbBr3 in situ to enhance the stability of the perovskite material. In the four cyclic degradation experimental tests in aqueous systems, the nanocomposites maintained good stability performance. This study provides a new way to improve the catalytic performance and stability of perovskite materials.

Bromine Incorporation Affects Phase Transformations and Thermal Stability of Lead Halide Perovskites.

Mixed-cation and mixed-halide lead halide perovskites show great potential for their application in photovoltaics. Many of the high-performance compositions are made of cesium, formamidinium, lead, iodine, and bromine. However, incorporating bromine in iodine-rich compositions and its effects on the thermal stability of the perovskite structure has not been thoroughly studied. In this work, we study how replacing iodine with bromine in the state-of-the-art Cs0.17FA0.83PbI3 perovskite composition leads to different dynamics in the phase transformations as a function of temperature. Through a combination of structural characterization, cathodoluminescence mapping, X-ray photoelectron spectroscopy, and first-principles calculations, we reveal that the incorporation of bromine reduces the thermodynamic phase stability of the films and shifts the products of phase transformations. Our results suggest that bromine-driven vacancy formation during high temperature exposure leads to irreversible transformations into PbI2, whereas materials with only iodine go through transformations into hexagonal polytypes, such as the 4H-FAPbI3 phase. This work sheds light on the structural impacts of adding bromine on thermodynamic phase stability and provides new insights into the importance of understanding the complexity of phase transformations and secondary phases in mixed-cation and mixed-halide systems.

Stability of Cesium-Based Lead Halide Perovskites under UV Radiation.

Lead halide perovskites have been extensively studied for their potential applications, including photodetectors, solar cells, and high-energy radiation detection. These applications are possible because of their unique optoelectronic properties, such as tunable band gap, high optical absorption coefficient, and unique defect self-healing properties, which result in high defect tolerance. Despite these advantages, the long-term stability remains a critical issue that could hinder commercial applications of these materials. Reports on the stability of lead halide perovskites for optoelectronic applications have normally focused on methylammonium (MA)/formamidinium (FA), with very limited information for other systems, in particular, Cs-containing perovskites. In this paper, we report the stability of thick CsPbBr3-x Cl x polycrystalline thin films (∼8 μm) with several halide Br-Cl ratios after exposure to deep UV radiation. The chemical, crystal structure, optical, and electrical properties are analyzed, and the results are used to propose a degradation mechanism. The chemical analysis on the surface and bulk of the films indicates the formation of cesium oxide after UV exposure, with no significant change in the crystalline structure. The proposed mechanism explains the formation of cesium oxides during UV exposure. The I-V characteristics of diode structures also showed significant degradation after UV exposure, primarily at lower diode rectification ratios. The mechanism proposed in this paper can contribute to developing strategies to enhance the long-term stability of inorganic lead halide perovskites under UV exposure.

Amino acid modified melamine foam as solid-state proton donor for CsPbBr3-based S-scheme heterojunction driven photocatalytic CO2 reduction

H2O as a proton source affects the stability of lead halide perovskites, restricting the photocatalytic CO2 reduction reaction (CO2RR). In this paper, l-lysine modified melamine foam (L-MF) is designed as an efficient solid-state proton donor to participate in CO2RR of CsPbBr3-based S-scheme heterojunction. On the one hand, abundant –COOH and –NH2 groups of l-lysine would break easily compared with H2O, which provides adequate protons for CO2RR. Moreover, the functionalized –COOH and –NH2 groups of l-lysine as Lewis base could coordinate with unsaturated Pb2+ of CsPbBr3, which could decrease the defect density of perovskite and improve the charge migration of catalyst. On the other hand, three-dimensional and porous melamine foam as a supporter could achieve gas-solid bi-phase CO2RR system, which contributes to mass transfer efficiency between CO2 gas and catalyst, accelerating CO2 conversion into high value-added fuels. Under sunlight irradiation, product yield of CO2RR reaches 73.47 μmol/g/h for L-MF/CsPbBr3/Bi2WO6, which is 2.8- and 72.7-fold of MF/CsPbBr3/Bi2WO6 (25.93 μmol/g/h) and CsPbBr3/Bi2WO6 powder (1.01 μmol/g/h) with H2O as proton source, suggesting the efficient proton supply for CO2RR from solid-state proton donor. This work could open a new avenue to utilize lead halide perovskites-based catalysts for energy conversion.

Investigation of the stability of organic-inorganic halide perovskite thin films: Insight from experimental and simulation

Herein, we investigated the stability of lead halide perovskites under ambient conditions after mixing the two cations Formamidinium (FA) and Cesium (Cs). The CsxFA1-xPbI3 perovskites solutions were prepared with different contents of x (0.0, 0.3, 0.5, 0.7 and 1.0) and deposited on substrates by spin-coating technique. The CsxFA1-xPbI3 films were, afterwards, characterized using the X-ray diffraction (XRD), UV–visible spectroscopy, photoluminescence (PL) spectra and scanning electron microscopy (SEM) to figure out their crystallinity, morphology, and optical properties. We noticed a stable perovskite structure for the mixed compounds unalike the pure FA and Cs films. The XRD analysis revealed, even after two weeks, the growth and good stability after two weeks of the desired black cubic α-phase perovskite structure in opposite to FAPbI3 and CsPbI3 which, respectively, showed faster degradation and transition into non-perovskite δ-phase and ɣ-phase no perovskite phases. The mixed perovskites Cs-FA also displayed a high absorbance especially for the ones with 30% of Cs and 70% of FA or 50% of each, with an excellent band gap energy ranging between 1.52 and 1.7 eV where FAPbI3 and CsPbI3 were showing a bandgap between 1.5 and 1.9 eV respectively. Moreover, the performance of the CsxFA1-xPbI3 based solar cells were simulated with SCAPS by using the band gaps obtained from the experimental study and after by varying the band gap, the thickness of the absorber layers and then different types of Electron Transport Layer (ETL). The simulation results revealed that the Cs0.3FA0.7PbI3 based solar cells had the highest higher efficiency around 22.36%.

Enhanced Phase, Thermal and Aqueous Stability of the Embedded the CsPbI3 Ncs in Cs4PbI6 Ncs

Increasing the stability of lead halide perovskites (LHPs) is required for integrating them into light-emitting devices. To date, most studies toward this direction have primarily concentrated on improving the chemical stability of green-emitting LHPs. In this work, red-emitting CsPbI3–Cs4PbI6 hybrid nanocrystals (NCs) were synthesized with a high photoluminescence (PL) quantum yield of ∼90%. Their hybrid structure was examined via structural (Rietveld) refinement analysis and transmission electron microscopy. Rietveld refinement also revealed that the black polymorph of CsPbI3 NCs is an orthorhombic perovskite rather than a cubic one. The thermodynamic stability of the CsPbI3 NCs in Cs4PbI6 matrices is enhanced in both solutions and films for up to several weeks. The enhanced stability of the embedded CsPbI3 NCs is attributed to the lowering of their Gibbs free energy, as determined on the basis of experimental data. Additionally, the hybrid NCs exhibit unprecedented emission stability—maintaining 65% of their original PL efficiency at 150 °C—and improved aqueous stability.

Nanomechanical signatures of degradation-free influence of water on halide perovskite mechanics

Humidity is often reported to compromise the stability of lead halide perovskites or of devices based on them. Here we measure the humidity dependence of the elastic modulus and hardness for two series of lead halide perovskite single crystals, varying either by cation or by anion type. The results reveal a dependence on bond length between, hydrogen bonding with, and polarizability/polarization of these ions. The results show an intriguing inverse relation between modulus and hardness, in contrast to their positive correlation for most other materials. This anomaly persists and is strengthened by the effect of humidity. This, and our overall findings are ascribed to the materials’ unique atomic-scale structure and properties, viz nano-polar domains and strong dynamic disorder, yet high-quality average order. Our conclusions are based on comparing results obtained from several different nano-indentation techniques, which separate surface from bulk elastic modulus, and probe different manifestations of the hardness.

X-ray stability and degradation mechanism of lead halide perovskites and lead halides.

Lead halide perovskites have become a leading material in the field of emerging photovoltaics and optoelectronics. Significant progress has been achieved in improving the intrinsic properties and environmental stability of these materials. However, the stability of lead halide perovskites to ionising radiation has not been widely investigated. In this study, we investigated the radiolysis of lead halide perovskites with organic and inorganic cations under X-ray irradiation using synchrotron based hard X-ray photoelectron spectroscopy. We found that fully inorganic perovskites are significantly more stable than those containing organic cations. In general, the degradation occurs through two different, but not mutually exclusive, pathways/mechanisms. One pathway is induced by radiolysis of the lead halide cage into halide salts, halogen gas and metallic lead and appears to be catalysed by defects in the perovskite. The other pathway is induced by the radiolysis of the organic cation which leads to formation of organic degradation products and the collapse of the perovskite structure. In the case of Cs0.17FA0.83PbI3, these reactions result in products with a lead to halide ratio of 1 : 2 and no formation of metallic lead. The radiolysis of the organic cation was shown to be a first order reaction with regards to the FA+ concentration and proportional to the X-ray flux density with a radiolysis rate constant of 1.6 × 10-18 cm2 per photon at 3 keV or 3.3 cm2 mJ-1. These results provide valuable insight for the use of lead halide perovskite based devices in high radiation environments, such as in space environments and X-ray detectors, as well as for investigations of lead halide perovskites using X-ray based techniques.

Simultaneous enhancement of luminescence and stability of lead halide perovskites by a diatomite microcavity for light-emitting diodes

Lead halide perovskite quantum dots (Pe QDs) are revolutionizing the photoelectric field and hold considerable potential for future applications. However, the simultaneous promotion of both high luminescence performance and excellent stability is still a major challenge for its practical application. Herein, we presented a diatomite mineral with naturally optical microcavity is used to construct polyacrylic acid-grafted diatomite (DE-g-PAA) mediate reactors for in-situ crafting CsPbX3 QDs (X = Cl, Br and I). The as-prepared CPB (CsPbBr3) -DE-g-PAA composite emitters not only preserve a higher photoluminescence quantum yield about 76.4% ± 0.7% compared to 33.1% ± 0.5% for CPB but also present outstanding thermal stability and water-resistance property. This luminescence improvement further be confirmed as the electromagnetic field enhancement from resonance effect of cavities with uniform size in the diatomite via electromagnetic field simulations. This study provides new insights for achieving stable and highly efficient CsPbX3 QDs-based multifunctional materials using natural clay minerals with quasi-photonic crystal structure.

Addressing the Stability of Lead Halide Perovskites

The rapid rise in efficiencies of lead halide perovskite solar cells has hastened the case for commercialization. One of the key barriers, however, is stability of devices. In this issue of Joule, Zhou et al. studied the degradation mechanism of a FA-Cs mixed cation perovskite-based solar cell with experimental and modeling techniques to show that phase separation into FA-rich and Cs-rich compositions account for the observed degradation.

Robust, Brighter Red Emission from CsPbI3 Perovskite Nanocrystals via Endotaxial Protection.

Increasing the stability of lead halide perovskites (LHPs) is required for integrating them into light-emitting devices. To date, most studies toward this direction have primarily concentrated on improving the chemical stability of green-emitting LHPs. In this work, red-emitting CsPbI3-Cs4PbI6 hybrid nanocrystals (NCs) were synthesized with a high photoluminescence (PL) quantum yield of ∼90%. Their hybrid structure was examined via structural (Rietveld) refinement analysis and transmission electron microscopy. Rietveld refinement also revealed that the black polymorph of CsPbI3 NCs is an orthorhombic perovskite rather than a cubic one. The thermodynamic stability of the CsPbI3 NCs in Cs4PbI6 matrices is enhanced in both solutions and films for up to several weeks. The enhanced stability of the embedded CsPbI3 NCs is attributed to the lowering of their Gibbs free energy, as determined on the basis of experimental data. Additionally, the hybrid NCs exhibit unprecedented emission stability-maintaining 65% of their original PL efficiency at 150 °C-and improved aqueous stability.

Potassium stabilization of methylammonium lead bromide perovskite for robust photocatalytic H2 generation

AbstractVarious optoelectronic applications of organic inorganic hybrid lead halide perovskites are challenged by their stability. The photocatalytic stability of lead halide perovskites are so low that chemical stabilizer such as H3PO2 are required in their applications. We report a postsynthesis potassium stabilization on methylammonium lead bromide (MAPbBr3) to form K‐MAPbBr3 by doping K cation and depositing KBr layers. In absence of any stabilizer, this stable K‐MAPbBr3 perovskite can exhibit an unprecedented high photostability even after 200 hours continuous photocatalytic H2 generation. Impressively, the K‐MAPbBr3 cocatalyzed with Mo3S132− nanoclusters achieves a high apparent quantum efficiency up to 18.3% at 450 nm for photocatalytic H2 generation. The mechanism study reveals that the photogeneration of Pb0 and Br0 defects are effectively inhibited in K‐MAPbBr3, which makes it a robust photocatalyst for H2 generation. These findings will inspire the development of stable organic‐inorganic hybrid perovskites for photocatalysis and other optoelectronic applications.image

Interfacial crosslinked quasi-2D perovskite with boosted carrier transport and enhanced stability

The fabrication of 2D or quasi-2D perovskite has been a promising strategy to further modulate the electron structure and stability of lead halide perovskites. Here we demonstrate that an interfacial crosslinked 2D perovskite using a bifunctional butanediamine (BDA) cation as BDAPbI4 exhibits similar optical properties as the regular butaneamine (BA) cation based BA2PbI4, but shows a different crystal growth preference and carrier transport properties. More remarkably, once BDAPbI4 and CH3NH3PbI3 (MAPbI3) form a quasi-2D (BDA)(MAn−1)PbnI3n+1 perovskite with crosslinked 2D/3D configuration, superior photovoltaics performance than the regular 2D/3D (BA2) (MAn−1)PbnI3n+1 can be obtained. The conducting atomic force microscopy measurements illustrate the interfacial crosslinked BDA based samples possess higher conductivities than regular ones. Thus, the strategy of cross-linked 2D/3D structure represents a simple and promising approach for designing novel perovskites for optoelectronic applications in future.

Effect of halide ratio and Cs+ addition on the photochemical stability of lead halide perovskites

Visible light-induced changes in mixed-ion perovskites with different compositions are investigated using photoelectron spectroscopy.

Compositional Engineering To Improve the Stability of Lead Halide Perovskites: A Comparative Study of Cationic and Anionic Dopants

The instability of perovskite solar cells is the single greatest barrier to their commercialization. While a number of studies have now looked at the effect of perovskite composition on device stability, many of these have examined only a single compositional variable. With many of these studies having been carried out under different environmental conditions, and still others lacking environmental controls entirely, it is often difficult to compare the relative effect of various cationic or anionic dopants. To address this knowledge gap, we fabricated CH3NH3PbI3-based solar cells where either the methylammonium or iodide ions were replaced with 20 mol % of a dopant ion (ethylammonium, formamidinium, bromide, or chloride). We then assessed their stability either in a controlled 85% relative humidity environment or under 1 sun illumination in air; both conditions have been previously shown to rapidly decompose CH3NH3PbI3. Of the dopants studied, the formamidinium cations imparted the best moisture resistan...