The molecular and ionic sublimation of neodymium, dysprosium, holmium, and erbium triiodides was studied by Knudsen effusion mass spectrometry. The monomer LnI3, dimer Ln2I6, and trimer Ln3I9 ...molecules and the ions LnI4– and Ln2I7– were found to be constituents of the saturated vapors in each case. The partial pressures of the vapor species and the equilibrium constants of the ion-molecular reactions were calculated. On the basis of a joint analysis of all literature data, the sublimation enthalpies ΔsHo(298.15 K)/(kJ mol−1) are recommended as 293 ± 3 (NdI3), 387 ± 30 (Nd2I6), 281 ± 3 (DyI3), 353 ± 12 (Dy2I6), 281 ± 3 (HoI3), 352 ± 6 (Ho2I6), 278 ± 4 (ErI3), and 350 ± 30 (Er2I6). The standard formation enthalpies ΔfHo(298.15 K)/(kJ mol−1) of the molecules and ions were determined to be −346 ± 5 (NdI3), −891 ± 30 (Nd2I6), −815 ± 23 (NdI4–), −1379 ± 46 (Nd2I7–), −336 ± 4 (DyI3), −880 ± 12 (Dy2I6), −811 ± 23 (DyI4–), −1360 ± 46 (Dy2I7–), −342 ± 4 (HoI3), −894 ± 7 (Ho2I6), −814 ± 23 (HoI4–), −1372 ± 46 (Ho2I7–), −341 ± 5 (ErI3), −888 ± 30 (Er2I6), −819 ± 23 (ErI4–), and −1377 ± 46 (Er2I7–).
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•Molecular and ionic sublimation of LnI3 (Ln = Nd, Dy, Ho, Er) was studied by KEMS.•The monomer and dimer molecules were found to be the primary vapor species.•Negative ions LnI4– and Ln2I7− predominate among the charged vapor constituents.•Molecular and ion-molecular equilibria were investigated.•Thermochemical parameters of the molecules and ions were determined.
Organometal lead halides perovskites are promising solar cells material due to their outstanding properties such as tuneable bandgap, impressive tolerance to defects, long exciton diffusion length, ...high carrier mobility and absorption coefficient. Up to now, the organometal lead halides based solar cells (PSCs) have demonstrated impressive power conversion efficiency reaching 25.2% (not stabilised). However, their operating life-times are limited due to degradation of the organic components under some environmental conditions. Therefore, researchers have focused their interest on the all inorganic perovskite; especially on the caesium lead triiodide perovskite (CsPbI3) which exhibits a better compositional and chemical stability. Nevertheless, the phase instability of the black phase of this material constitutes its main limitation for its use in the solar cell devices production. This review aims to present the most impactful research giving insights on the factors that may cause the instability of all-inorganic lead halide perovskite materials, as well as the instability of the whole device. In addition to deposition methods, the composition, structure and optical properties of inorganic perovskite materials have also been presented. Furthermore, this review highlights the different strategies used in order to improve the phase stability of caesium lead halide perovskite material through either engineering on the material structure or the fabrication method.
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•The most relevant studies on the stability of all-inorganic PSCs materials and preparation methods are reviewed.•The effects of different engineering/modifications methods on the phase stability of CsPbI3 are reviewed.•The influence of the different layers on the device efficiency and stability are pointed out.
Perovskite solar cells with increasingly pure composition of α‐formamidinium lead triiodide (α‐FAPbI3) perovskite are utilized to set more and more record‐breaking efficiencies. However, pure ...α‐FAPbI3 perovskite is unstable and difficult to prepare. Here, a series of bulky alkylammoniums known as the spacer cations (RP cations) of 2D Ruddlesden–Popper perovskites (2D perovskites) are used to prepare α‐FAPbI3 perovskite films. The deprotonation process of RP cations during annealing removes the in situ generated 2D perovskites from the film, which determines the phase and compositional purity, crystallinity, and stability of α‐FAPbI3 perovskite films and depends on the design of RP cations. Only a small number of residual RP cations (0.3–2.3%) are found anchoring at grain boundaries. As a result, α‐FAPbI3 perovskite solar cells prepared from RP cations, especially 2‐thiophenemethylammonium, show higher efficiency and stability than control devices prepared from the most commonly used methylammonium. It is believed that in situ generated 2D perovskites are ideal additives for α‐FAPbI3 perovskite, because a large addition (20%) of 2D perovskites ensures the preparation of high‐quality phase‐pure α‐FAPbI3 perovskite films, while a small number of residual RP cations anchored at grain boundaries guarantee the performance and stability of α‐FAPbI3 perovskite solar cells.
2D perovskites in situ generated from a series of bulky primary alkylammoniums are found to be volatile and are used to prepare phase‐ and compositionally‐pure α‐formamidinium lead triiodide solar cells.
Two kinds of iodine–iodine halogen bonds are the focus of our attention in the crystal structure of the title salt, C12H8ClINO+·I3−, described by X‐ray diffraction. The first kind is a halogen bond, ...reinforced by charges, between the I atom of the heterocyclic cation and the triiodide anion. The second kind is the rare case of a halogen bond between the terminal atoms of neighbouring triiodide anions. The influence of relatively weakly bound iodine inside an asymmetric triiodide anion on the thermal and Raman spectroscopic properties has been demonstrated.
A new dihydrooxazinoquinolinium triiodide has been synthesized and characterized by single‐crystal X‐ray diffraction analysis, Raman spectroscopy and thermal analysis. The iodine–iodine halogen bonds formed between neighbouring triiodide anions and between triiodide anions and iodine‐containing heterocyclic cations are the basis of the noncovalent interactions in the analyzed crystal.
In this paper we report on the influence of light and oxygen on the stability of CH3NH3PbI3 perovskite‐based photoactive layers. When exposed to both light and dry air the mp‐Al2O3/CH3NH3PbI3 ...photoactive layers rapidly decompose yielding methylamine, PbI2, and I2 as products. We show that this degradation is initiated by the reaction of superoxide (O2−) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O2− species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O2− generation is significantly reduced when the mp‐Al2O3 film is replaced with an mp‐TiO2 electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH3NH3PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability.
The influence of light and oxygen on the stability of CH3NH3PbI3 perovskite‐based photoactive layers is investigated. Upon exposure to both light and dry air, the mesoporous (mp) Al2O3/CH3NH3PbI3 layers decompose to methylamine, PbI2, and I2. This degradation is initiated by the reaction of superoxide (O2−) with the methylammonium moiety of the perovskite absorber. MA=methyl ammonium, CB=conduction band, VB=valence band.
Besides widely used surface passivation, engineering the film crystallization is an important and more fundamental route to improve the performance of all‐inorganic perovskite solar cells. Herein, we ...have developed a urea‐ammonium thiocyanate (UAT) molten salt modification strategy to fully release and exploit coordination activities of SCN− to deposit high‐quality CsPbI3 film for efficient and stable all‐inorganic solar cells. The UAT is derived by the hydrogen bond interactions between urea and NH4+ from NH4SCN. With the UAT, the crystal quality of the CsPbI3 film has been significantly improved and a long single‐exponential charge recombination lifetime of over 30 ns has been achieved. With these benefits, the cell efficiency has been promoted to over 20 % (steady‐state efficiency of 19.2 %) with excellent operational stability over 1000 h. These results demonstrate a promising development route of the CsPbI3 related photoelectric devices.
A new urea‐ammonium thiocyanate (UAT) molten salt was introduced as the additive in all‐inorganic cesium lead triiodide solar cell, as a modification strategy to fully release and exploit coordination activities of SCN− to deposit high‐quality CsPbI3 film. Thus, the UAT‐based devices can provide an encouraging PCE up to 20.08 % with excellent operational stability of over 1000 h.
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•Active 1T-MoS2 nanosheets are covalently functionalized with n-butyl chains (~4%).•Introduction of n-butyl chains increased the interlayer spacing to 13.8 Å from ...~9 Å.•Functionalization and solvent enrichment process improved the stability of 1T-MoS2.•en-Bu-1T-MoS2 showed superior performance in clean energy (HER & DSSC) applications.
The selective enrichment of a highly active form/phase of material is essential for the development of potential candidates for specific applications. Herein, we demonstrate the first example of the covalent functionalization of a highly active 1T phase of outstanding 2D material, such as MoS2, and its enrichment (>94%) using a solvent extraction technique. Covalent functionalization stabilizes the metastable 1T phase with increased interlayer distance, which makes it a more suitable candidate for energy applications. The enriched functionalized 1T-MoS2 with n-butyl groups (en-Bu-1T-MoS2) shows a lower overpotential of 169 mV (vs. Reversible Hydrogen Electrode, RHE) with the loading mass of 0.9 mg cm−2 toward the hydrogen evolution reaction (HER). The continuous HER of en-Bu-1T-MoS2-based electrode for >200 h showed only <11% increment in the overpotential of HER, which suggests the ultra-long term stability of en-Bu-1T-MoS2 compared to the covalently functionalized 1T-MoS2-based HER electrocatalysts reported thus far. Interestingly, the semi-transparent en-Bu-1T-MoS2 film also served as an excellent counter electrode for dye-sensitized solar cells (DSSCs) with the higher power conversion efficiency (PCE) of 9.11% and 82% of PCE retention even after 200 h. The unprecedented method presented in this work is a unique example, which shows the possibility of improving material properties with the help of a novel approach.
We report the observation of a very large negative magnetoresistance effect in a van der Waals tunnel junction incorporating a thin magnetic semiconductor, CrI3, as the active layer. At constant ...voltage bias, current increases by nearly one million percent upon application of a 2 T field. The effect arises from a change between antiparallel to parallel alignment of spins across the different CrI3 layers. Our results elucidate the nature of the magnetic state in ultrathin CrI3 and present new opportunities for spintronics based on two-dimensional materials.
Formamidinium lead triiodide (FAPbI3) is attractive for photovoltaic devices due to its optimal bandgap at around 1.45 eV and improved thermal stability compared with methylammonium‐based ...perovskites. Crystallization of phase‐pure α‐FAPbI3 conventionally requires high‐temperature thermal annealing at 150 °C whilst the obtained α‐FAPbI3 is metastable at room temperature. Here, aerosol‐assisted crystallization (AAC) is reported, which converts yellow δ‐FAPbI3 into black α‐FAPbI3 at only 100 °C using precursor solutions containing only lead iodide and formamidinium iodide with no chemical additives. The obtained α‐FAPbI3 exhibits remarkably enhanced stability compared to the 150 °C annealed counterparts, in combination with improvements in film crystallinity and photoluminescence yield. Using X‐ray diffraction, X‐ray scattering, and density functional theory simulation, it is identified that relaxation of residual tensile strains, achieved through the lower annealing temperature and post‐crystallization crystal growth during AAC, is the key factor that facilitates the formation of phase‐stable α‐FAPbI3. This overcomes the strain‐induced lattice expansion that is known to cause the metastability of α‐FAPbI3. Accordingly, pure FAPbI3 p–i–n solar cells are reported, facilitated by the low‐temperature (≤100 °C) AAC processing, which demonstrates increases of both power conversion efficiency and operational stability compared to devices fabricated using 150 °C annealed films.
An aerosol‐assisted crystallization method to prepare high‐quality, pure α‐FAPbI3 films at only 100 °C without chemical additives is reported. Remarkably improved phase stability of the α‐FAPbI3 films and their applications in solar cells are demonstrated. The overriding mechanism of stabilizing α‐FAPbI3 is shown to be relaxation of residual tensile strains in the films.
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