Halide Precursors Research Articles

Air‐Processed Perovskite Films with Inner‐to‐Outside Passivation for High‐Efficiency Solar Cells

Metallic halide perovskite films are usually fabricated in inert environment due to their high sensitivity to moisture and oxygen. However, the fabrication process in the strictly controlled environment is not economical for mass production. Therefore, the fabrication of high‐quality perovskite films in ambient air is more practical for optoelectronic devices. Herein, a spinning–bathing–spinning (SBS) method is demonstrated to deposit pinhole‐free perovskite films with large grains in ambient air for solar cells. The effect of moisture on the rapid crystallization and grain coarsening can be suppressed using this SBS method. Furthermore, the moisture is found to encourage the halogen separation in the perovskite films when using PbI2–PbCl2 as the lead halide precursor, resulting in the formation of I‐dominant perovskite grains and Cl‐enriched boundaries and surface in the films. The Cl‐enriched grain boundaries and film surface, which mainly originate from the confined methylammonium chloride (MACl), can passivate defects and prevent further damage from moisture and oxygen. This spontaneous inner‐to‐outside passivation enables the air‐processed perovskite solar cells with the high power conversion efficiencies of more than 20% and improved stability.

Adsorption of Titanium Halides on Nitride and Oxide Surfaces during Atomic Layer Deposition: A DFT Study

Various processes based on atomic layer deposition (ALD) have been reported for growing Ti-based thin films such as TiN and TiO2. To improve the uniformity and conformity of thin films grown via ALD, fundamental understanding of the precursor–substrate surface reactions is required. Herein, we present a density functional theory (DFT) study of the initial nucleation process of some titanium halide precursors (TiCl4, TiBr4, and TiI4) on Si surfaces having –OH or –NH2 functional groups. We consider the most favorable adsorption site in the reaction between the precursor and functional group of the surface, based on the thermodynamics and kinetics of the reaction. Sequential dissociation reaction mechanisms of halide ligands were systematically investigated. The exothermicity of the dissociative adsorption was found to be in the order of: TiI4 > TiBr4 > TiCl4. In addition, the precursors were observed to be more exothermic and show higher reaction rate constant when adsorbed on the –OH–terminated surface than on the –NH2–terminated surface. These observations reveal the selectivity of deposition by surface functional groups.

Synthesis and Characterization of a Magnesium Boryl and a Beryllium-Substituted Diazaborole.

Reaction of a lithium boryl, [(THF)2 Li{B(DAB)}] (DAB=[(DipNCH)2 ]2- , Dip=2,6-diisopropylphenyl), with a dinuclear magnesium(I) compound [{(Mes Nacnac)Mg}2 ] (Mes Nacnac=[HC(MeCNMes)2 ]- , Mes=mesityl) unexpectedly afforded a rare example of a terminal magnesium boryl species, [(Mes Nacnac)(THF)Mg{B(DAB)}]. Attempts to prepare the magnesium boryl via a salt metathesis reaction between the lithium boryl and a β-diketiminato magnesium iodide compound, instead led to an intractable mixture of products. Similarly, reaction of the lithium boryl with a β-diketiminato beryllium bromide precursor, [(Dep Nacnac)BeBr] (Dep=2,6-diethylphenyl) did not give a beryllium boryl, but instead afforded an unprecedented example of a beryllium substituted diazaborole heterocycle, [{(Dep Nacnac)Be(4-DAB-H )}BBr]. For sake of comparison, the same group 2 halide precursor compounds were treated with a potassium gallyl analogue of the lithium boryl, viz. [(tmeda)K{:Ga(DAB)}] (tmeda=N,N,N',N'-tetramethylethylenediamine), but no reactions were observed.

Solvent modification to suppress halide segregation in mixed halide perovskite solar cells

Mixed halide perovskite is essential to construct highly efficient tandem solar cells, whereas halide segregation is a main issue hindering their device efficiency for this kind of perovskite materials. Herein, we modify the solvents for the mixed halide precursor solution to suppress halide segregation during fabrication process. An alternative solvent, N-Methyl pyrrolidone (NMP), is used to replace commonly used solvent, dimethyl sulfoxide (DMSO). It is shown that the halide segregation and the resultant carrier recombination are notably suppressed. The improvements brought by NMP may correlate with its moderate Lewis base property, which modifies the crystallization process of the mixed halide perovskite film. Consequently, the device performance is greatly improved by using NMP. The device efficiency is increased from less than 10% for DMSO solvent to approach 14% for NMP solvent. This work provides a facile way to improve the device efficiency, which also highlights on the importance of the solvents on halide segregation.

All-vacuum-deposited inorganic cesium lead halide perovskite light-emitting diodes

Polycrystalline CsPbBr3 thin films are deposited by vacuum co-evaporation of cesium halide and lead halide precursors, leading to uniform pinhole-free morphology and precise control over the film thickness and precursor stoichiometry. By utilizing the organic hole and electron transport layers, all-vacuum-deposited perovskite LEDs are fabricated. The resulting devices exhibit a maximum luminance of 1800 cd/m2, a 531 nm emission wavelength peak with a spectral linewidth of 21 nm, and an external quantum efficiency of 1.1%.

Nanowire crystals of tantalum nitride grown in ammonium halide fluxes at high pressures

Nanowire crystals of a tantalum nitride phase have been grown from epsilon-tantalum nitride and ammonium halide precursors at high pressures exceeding several gigapascals. Synchrotron x-ray diffraction and Transmission Electron Microscopy (TEM) observations revealed that they had crystallized in an unreported hexagonal structure with lattice parameters of a = 3.050(1) Å and c = 2.909(2) Å. The one-dimensional growth orientation was along the crystallographic [001] direction. Scanning TEM–EDX elemental analyses showed that the nanowire crystals were composed of tantalum and nitrogen with small amounts of oxygen. The presence of the melted ammonium halides combined with supercritical ammonia acting as a reactive flux at high pressure and temperature played a significant role in the nanowire crystal growth. Raman spectroscopy performed on several single crystal nanowires pointed toward metallic properties, and the temperature dependence of the magnetization measured by Superconducting Quantum Interference Device magnetometry suggested a superconducting transition about 6.2 K. The analysis of the compression behavior revealed an incompressible nature, and the bulk modulus was determined to be 363(6) GPa.

Remote Tuning of Bandgap and Emission of Lead Perovskites by Spatially Controlled Halide Exchange Reactions

Local halide exchange reactions enable one to fabricate heterojunction perovskites; however, it is particularly challenging to deliver reactive halide precursors at the desired position. Here, we r...

Impact of Perovskite Composition on Film Formation Quality and Photophysical Properties for Flexible Perovskite Solar Cells.

In recent years, flexible perovskite solar cells have drawn tremendous attention in the field of wearable devices, and optimization of perovskite composition plays an important role in improving film quality and photophysical properties. At present, some researchers have only studied A-site organic cations mixing or X-site halide anions mixing in the ABX3 structure of perovskite, but there are few reports on co-mixing of A-site and X-site ions in flexible perovskite solar cells. In this paper, we mainly try to study the effects of different concentrations of mixed formamidine methylamine halide (FAxMA1-xBrxClyI1-x-y) precursor solutions on the quality and photophysical properties of perovskite films under low temperature process. We conclude that the film quality and photophysical properties reached the best results when the optimized precursor solution concentration was 60:6:6. The investigation on composition optimization in this experiment laid the foundation for the improvement of the performance of flexible perovskite solar cells. We also use the results of this experiment to prepare flexible perovskite solar cells based on carbon electrodes, which are expected to be applied in other flexible optoelectronic or electro-optical devices.

Revealing the perovskite formation kinetics during chemical vapour deposition

High control chemical vapour deposition of (Cs,FA)PbI3 perovskite provides insights into CVD kinetics and perovskite phase evolution.

Dry Mechanochemical Synthesis of Highly Luminescent, Blue and Green Hybrid Perovskite Solids

AbstractA simple method to obtain bright photoluminescent wide bandgap mixed‐halide 3D perovskites is reported. The materials are prepared by dry mechanochemical synthesis (ball‐milling) starting from neat binary precursors, and show enhanced photoluminescence upon the addition of an adamantane derivative in the precursors' mixture. The structural characterization suggests that the additive does not participate in the crystal structure of the perovskite, which remains unvaried even with high loading of amantadine hydrochloride. By simple stoichiometric control of the halide precursors, the photoluminescence can be finely tuned from the UV to the green part of the visible spectrum. Photoluminescence quantum yields as high as 29% and 5% have been obtained for green‐ and blue‐emitting perovskite solids, even at very low excitation densities.

Synthetic Control of the Photoluminescence Stability of Organolead Halide Perovskites

An optimized synthetic procedure for preparing photostable nanocrystalline methylammonium lead halide materials is reported. The procedure was developed by adjusting the lead halide to methylammonium/octylammonium halide precursor ratio. At a high precursor ratio (1:3), a blue-shifted photoinduced luminescence peak is measured at 642 nm for CH3NH3PbI3 with 0.01 to 12 mJ pulsed-laser irradiation. The appearance of this peak is reversible over 300 min upon blocking the irradiation. In order to determine if the peak is the result of a phase change, in situ x-ray diffraction measurements were performed. No phase change was measured with an irradiance that causes the appearance of the photoinduced luminescence peak. Luminescence microscpectroscopy measurements showed that the use of a lower precursor ratio (1:1.5) produces CH3NH3PbI3 and CH3NH3PbBr3 perovskites that are stable over 4 min of illumination. Given the lack of a measured phase change, and the dependence on the precursor ratio, the photoinduced luminesce peak may derive from surface trap states. The enhanced photostability of the resulting perovskite nanocrystals produced with the optimized synthetic procedure supports their use in stable optoelectronic devices.

Assessment for Anion-Exchange Reaction in CsPbX3 (X = Cl, Br, I) Nanocrystals from Bond Strength of Inorganic Salt

Anion exchange via inorganic halide precursors is a highly efficient protocol to tune the chemical composition and optoelectronic properties of colloidal cesium lead halide perovskite (CsPbX3, X = ...

Isolation and Computational Studies of a Series of Terphenyl Substituted Diplumbynes with Ligand Dependent Lead-Lead Multiple-Bonding Character.

A series of formally triply bonded diplumbyne analogues of alkynes of the general formula ArPbPbAr (Ar = terphenyl ligand with different steric properties) was synthesized by two routes. All diplumbyne products were synthesized by a simple reduction of the corresponding Pb(II) halide precursor ArPb(Br) by DIBAL-H with yields in the range 8-48%. For one of the diplumbynes ArPri4PbPbArPri4 (ArPri4 = C6H3-2,6-(C6H3-2,6-Pri2)2) it was shown that reduction of ArPri4Pb(Br) using a magnesium(I) beta-diketiminate afforded a much improved yield in comparison (29 vs 8%) to that obtained by reduction with DIBAL-H. The more sterically crowded diplumbyne ArPri8PbPbArPri8 (ArPri8 = C6H-3,5-Pri2-2,6-(C6H2-2,4,6-Pri3)2) displayed a shortened Pb-Pb bond with a length of 3.0382(5) Å and wide Pb-Pb-C angles of 114.73(7)° and 116.02(6)° consistent with multiple-bond character with a bond order of up to 1.5. The others displayed longer metal-metal distances and narrower Pb-Pb-C angles that were consistent with a lower bond order that approached one. Computational studies of the diplumbynes yielded detailed insight of the unusual bonding and explained their similar electronic spectra arising from the flexibility of the C-Pb-Pb-C core in solution. Furthermore, the importance of London dispersion interactions for the stabilization of the diplumbynes was demonstrated.

Synthesis of two-dimensional MoS2/graphene heterostructure by atomic layer deposition using MoF6 precursor

The effective synthesis of two-dimensional (2D) heterostructures is essential for their use in electronic devices. In this study, by using atomic layer deposition (ALD), 2D transition metal dichalcogenide (TMD) heterostructures were grown by a halide precursor. This study shows the growth characteristics of the fluoride precursor compared to the chloride precursor used for the synthesis of the TMD on the graphene layer and the other TMD layer. Additionally, a carbonyl precursor was used for comparison with the halide precursor in terms of the thermal stability. From these experiments, the fluoride precursor was adequate for synthesizing on the graphene, however, was inappropriate for the TMD/TMD heterostructure because of its etching characteristic. Meanwhile, the chloride precursor was appropriate for the TMD/TMD heterostructure, even for a low binding energy with the substrate, but was inadequate in forming the TMD/graphene heterostructure, even if the ALD cycle increased. Through our experiments, we show, for the first time, that there exists a suitable halide precursor for a 2D layer for a substrate.

Probing the surface composition effect of silver-gold alloy in SERS efficiency

Ag-Au alloy microflower substrates with tunable surface compositions are prepared through simple thermolysis of metal-alkyl ammonium halide precursors for probing the role of surface composition in SERS. The bulk and surface composition of the microflowers are characterized using ED-XRF and XPS analyses, respectively. For alloys, the ED-XRF studies show that the bulk compositions are in tune with the feed ratio, while the surface compositions are found to be rich in silver, as revealed by XPS studies. Efficiency studies on these substrates using the analyte molecule Rhodamine 6 G (R6 G) evidence 30 fold enhancements in SERS spectra with 90:10 Ag-Au alloy microflowers as opposed to the pure Ag ones. Raman mapping studies performed on individual microflowers clearly show increase in the density of hot spots, in addition to the enhancement, with increase in concentration of gold in the alloys. It is critically observed that, the surface needs to be rich in Ag in the alloy substrates for obtaining maximum SERS enhancement. The optimized Ag-Au alloy substrate also finds applicability for mercury sensing in water via quantitative loss of SERS enhancement of R6 G.

Improved Open-Circuit Voltage and Repeatability of Perovskite Cells Based on Double-Layer Lead Halide Precursors Fabricated by a Vapor-Assisted Method.

Highly repeatable fabrication of compact perovskite films is crucial for large-area perovskite cells (PSCs) in commercial applications. In this work, a vapor-assisted method with the combination of spin-coating and thermal evaporation is employed to fabricate the double-layer PbI2/PbIxBr(2-x) precursor. It is found that surface morphologies of perovskite films could be tailored through tuning the spin-coating speed (the first precursor layer) and chemical compositions (the second precursor layer). The continuous pinhole-free perovskite films are successfully fabricated by double-layer PbI2/PbBr2 precursors. The open-circuit voltages of all the corresponding cells exceed 1.00 V, showing an average value of 1.02 V. The high mean voltage and small variation reveals high repeatability of this method. This work provides a potential method to achieve large-area and high-efficiency PSCs.

The Removal of Organic Halide Precursors by Preozonation and Alum Coagulation

Journal AWWAVolume 111, Issue 6 p. 62-67 Pages From the Past The Removal of Organic Halide Precursors by Preozonation and Alum Coagulation David A. Reckhow, David A. ReckhowSearch for more papers by this authorPhilip C. Singer, Philip C. SingerSearch for more papers by this author David A. Reckhow, David A. ReckhowSearch for more papers by this authorPhilip C. Singer, Philip C. SingerSearch for more papers by this author First published: 29 May 2019 https://doi.org/10.1002/awwa.1309Citations: 2Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume111, Issue6June 2019Pages 62-67 RelatedInformation

Scandium-Promoted Direct Conversion of Dinitrogen into Hydrazine Derivatives via N-C Bond Formation.

Direct conversion of dinitrogen (N2) into organic compounds, not through ammonia (NH3), is of great significance both fundamentally and practically. Here we report a highly efficient scandium-mediated synthetic cycle affording hydrazine derivatives (RMeN-NMeR') directly from N2 and carbon-based electrophiles. The cycle includes three main steps: (i) reduction of a halogen-bridged discandium complex under N2 leading to a (N2)3--bridged discandium complex via a (N2)2- intermediate; (ii) treatment of the (N2)3- complex with methyl triflate (MeOTf), affording a (N2Me2)2--bridged discandium complex; and (iii) further reaction of the (N2Me2)2- complex with the carbon-based electrophile, producing the hydrazine derivative and regenerating the halide precursor. Furthermore, insertion of a CO molecule into one Sc-N bond in the (N2Me2)2--scandium complex was observed. Most notably, this is the first example of rare-earth metal-promoted direct conversion of N2 to organic compounds; the formation of C-N bonds by the reaction of these (N2)3- and (N2Me2)2- complexes with electrophiles represents the first case among all N2-metal complexes reported.

Composition-Controlled Synthesis of Hybrid Perovskite Nanoparticles by Ionic Metathesis: Bandgap Engineering Studies from Experiments and Theoretical Calculations.

Herein a newly discovered non-polar solvent based synthesis of MAPbX3 hybrid perovskite nanoparticles (NPs) is presented, where MA=Methylammonium and X=I, Br and Cl, as well as their mixed halide counterparts. The methodology proposed is simple and uses low-cost commercial precursors. The conventional method of hybrid perovskite preparation requires methylammonium halide precursors and highly polar solvents. Mandatory use of polar solvents and a particular perovskite precursor makes an intermediate compound which then requires a non-polar solvent to recover the NPs. In contrast here, a whole range of mixed halide perovskite NPs is fabricated without using a methylammonium halide precursor and a polar solvent. In this method, a non-polar solvent is used, which provides a better platform for the particle recovery. Organic cations on the nanoparticle surface prevent degradation from water, due to their hydrophobic nature, and hence offer a stable colloidal suspension in toluene for more than three months. Ab-initio calculations within density functional theory (DFT) predict lower formation energies compared to previously reported values, confirming better chemical stability for this synthesis pathway. Through the halide compositional tuning, these NPs exhibit a variety of emission and absorption starting from ultraviolet to near infrared (IR). The absorption spectra of various halide perovskite show a sharp band edge over the visible wavelength with high absorption coefficient. High oscillator strengths due to high excitonic binding energies combined with the simulated finite dipole transition probabilities point towards the observed high absorption. The emission spectra of mixed halide perovskites vary from 400 to 750 nm, which covers the whole range of visible spectra with sharp full-width at half maxima. Different halide perovskite exhibit average recombination lifetime from 5 to 227 ns. Ambient synthesis, chemical robustness and tunability of emission with varying halide compositions make MAPbX3 (X=I, Br and Cl) NPs appealing for the optoelectronic applications.

Formation and Encapsulation of All-Inorganic Lead Halide Perovskites at Room Temperature in Metal-Organic Frameworks.

Improving the stability and tuning the optical properties of semiconducting perovskites are vital for their applications in advanced optoelectronic devices. We present a facile synthetic method for hybrid composites of perovskites and metal-organic frameworks (MOFs). A simple two-step solution-based method without organic surfactants was employed to make all-inorganic lead-halide perovskites (CsPbX3; X = Cl, Br, I, or mixed halide compositions) form directly in the pores of MIL-101 MOF. That is, a polar organic solution of lead halide (PbX2) was impregnated into the MOF pores to give PbX2@MIL-101, which was then subjected to a perovskite-formation reaction with cesium halide (CsX) dissolved in methanol. The compositions of the halogen anions in the perovskites can be modulated with various halide precursors, leading to CsPbX3@MIL-101 composites with X3 = Cl3, Cl2Br, Br2Cl, Br3, Br2I, I2Br, and I3 that exhibit gradual variation of band gap energies and tuned emission wavelengths from 417 to 698 nm.