CH NH Research Articles

Lead-Free, Water-Stable A3 Bi2 I9 Perovskites: Crystal Growth and Blue-Emitting Quantum Dots [A=CH3 NH3 + , Cs+ , and (Rb0.05 Cs2.95 )+

Despite the great success in the increase in the power conversion efficiency of lead halide perovskite solar cells, the toxicity of lead and the unstable nature of the materials are still major concerns for their wider implementation at the industrial level. Herein, large-size single crystals (SCs) are developed in HI solution by using a temperature lowering method and nanocrystals (NCs) of A3 Bi2 I9 perovskites [where A=CH3 NH3 + (MA)+ , Cs+ , and (Rb0.05 Cs2.95 )+ ] are formed in ethanol (EtOH) and toluene (TOL). The stability of A3 Bi2 I9 perovskite is investigated by immersing the SCs for 24 h and pellets for 12 h in water. Moreover, the A3 Bi2 I9 perovskite NCs displays a promising photoluminescence quantum yield of 17.63 % and a long lifetime of 8.20 ns.

Electronic-Grade High-Quality Perovskite Single Crystals by a Steady Self-Supply Solution Growth for High-Performance X-ray Detectors.

High-quality perovskite single crystals with large size are highly desirable for the fundamental research and high energy detection application. Here, a simple and convenient solution method, featuring continuous-mass transport process (CMTP) by a steady self-supply way, is shown to keep the growth of semiconductor single crystals continuously stable at a constant growth rate until an expected crystal size is achieved. A significantly reduced full width at half-maximum (36 arcsec) of the (400) plane from the X-ray rocking curve indicates a low angular dislocation of 6.8 × 106 cm-2 and hence a higher crystalline quality for the CH3 NH3 PbI3 (MAPbI3 ) single crystals grown by CMTP as compared to the conventional inverse temperature crystallization (ITC) method. Furthermore, the CMTP-based single crystals have lower trap density, reduced by nearly 200% to 4.5 × 109 cm-3 , higher mobility increased by 187% to 150.2 cm2 V-1 s-1 , and higher mobility-lifetime product increased by around 450% to 1.6 × 10-3 cm2 V-1 , as compared with the ITC-grown reference sample. The high performance of the CMTP-based MAPbI3 X-ray detector is comparable to that of a traditional high-quality CdZnTe device, indicating the CMTP method as being a cost-efficient strategy for high-quality electronic-grade semiconductor single crystals.

Self-Repairing Tin-Based Perovskite Solar Cells with a Breakthrough Efficiency Over 11.

The development of tin (Sn)-based perovskite solar cells (PSCs) is hindered by their lower power conversion efficiency and poorer stability compared to the lead-based ones, which arise from the easy oxidation of Sn2+ to Sn4+ . Herein, phenylhydrazine hydrochloride (PHCl) is introduced into FASnI3 (FA = NH2 CH  NH2 + ) perovskite films to reduce the existing Sn4+ and prevent the further degradation of FASnI3 , since PHCl has a reductive hydrazino group and a hydrophobic phenyl group. Consequently, the device achieves a record power conversion efficiency of 11.4% for lead-free PSCs. Besides, the unencapsulated device displays almost no efficiency reduction in a glove box over 110 days and shows efficiency recovery after being exposed to air, due to a proposed self-repairing trap state passivation process.

Room-Temperature Ferroelectric Material Composed of a Two-Dimensional Metal Halide Double Perovskite for X-ray Detection.

Although two-dimensional (2D) metal-halide double perovskites display versatile physical properties due to their huge structural compatibility, room-temperature ferroelectric behavior has not yet been reported for this fascinating family. Here, we designed a room-temperature ferroelectric material composed of 2D halide double perovskites, (chloropropylammonium)4 AgBiBr8 , using an organic asymmetric dipolar ligand. It exhibits concrete ferroelectricity, including a Curie temperature of 305 K and a notable spontaneous polarization of ≈3.2 μC cm-2 , triggered by dynamic ordering of the organic cation and the tilting motion of heterometallic AgBr6 /BiBr6 octahedra. Besides, the alternating array of inorganic perovskite sheets and organic cations endows large mobility-lifetime product (μτ=1.0×10-3 cm2 V-1 ) for detecting X-ray photons, which is almost tenfold higher than that of CH3 NH3 PbI3 wafers. As far as we know, this is the first study on an X-ray-sensitive ferroelectric material composed of 2D halide double perovskites. Our findings afford a promising platform for exploring new ferroelectric materials toward further device applications.

Reactions of 3-arylpropenenitriles with arenes under superelectrophilic activation conditions: Hydroarylation of the carbon-carbon double bond followed by cyclization into 3-arylindanones

Reactions of 3-arylpropenenitriles [ArCHCHCN] with arenes [Ar’H] under the superelectrophilic activation conditions with Brønsted superacid TfOH (CF3SO3H) or strong Lewis acid AlBr3 result, first, in the formation of products of hydroarylation of the carbon-carbon double bond, 3,3-diarylpropanenitriles [Ar(Ar’)CHCH2CN]. Reactions may go further in TfOH leading to 3-arylindanones, as products of intramolecular aromatic acylation by the electrophilically activated nitrile group. Intermediate cationic species, derived at the protonation of the starting 3-arylpropenenitriles onto the carbon of CC bond and the nitrile nitrogen, have been studied by DFT calculation. A plausible reaction mechanism including the formation of highly reactive dications [(Ar)HC+–CH2C+ = NH] has been proposed. The obtained 3,3-diarylpropanenitriles have been transformed into pharmaceutically valuable 5-(2,2-diarylethyl)-1H-tetrazoles [Ar(Ar’)CHCH2Tetr] and 3-diarylpropylamines [Ar(Ar’)CH(CH2)2NH2] by the reactions with NaN3 and LiAlH4 correspondingly.

General Decomposition Pathway of Organic-Inorganic Hybrid Perovskites through an Intermediate Superstructure and its Suppression Mechanism.

Organic-inorganic hybrid perovskites (OIHPs) have generated considerable excitement due to their promising photovoltaic performance. However, the commercialization of perovskite solar cells (PSCs) is still plagued by the structural degradation of the OIHPs. Here, the decomposition mechanism of OIHPs under electron beam irradiation is investigated via transmission electron microscopy, and a general decomposition pathway for both tetragonal CH3 NH3 PbI3 and cubic CH3 NH3 PbBr3 is uncovered through an intermediate superstructure state of CH3 NH3 PbX2.5 , X = I, Br, with ordered vacancies into final lead halides. Such decomposition can be suppressed via carbon coating by stabilization of the perovskite structure framework. These findings reveal the general degradation pathway of OIHPs and suggest an effective strategy to suppress it, and the atomistic insight learnt may be useful for improving the stability of PSCs.

An Electrically Modulated Single-Color/Dual-Color Imaging Photodetector.

An electrically modulated single-/dual-color imaging photodetector with fast response speed is developed based on a small molecule (COi 8DFIC)/perovskite (CH3 NH3 PbBr3 ) hybrid film. Owing to the type-I heterojunction, the device can facilely transform dual-color images to single-color images by applying a small bias voltage. The photodetector exhibits two distinct cut-off wavelengths at ≈544 nm (visible region) and ≈920 nm (near-infrared region), respectively, without any power supply. Its two peak responsivities are 0.16 A W-1 at ≈525 nm and 0.041 A W-1 at ≈860 nm with a fast response speed (≈102 ns). Under 0.6 V bias, the photodetector can operate in a single-color mode with a peak responsivity of 0.09 A W-1 at ≈475 nm, showing a fast response speed (≈102 ns). A physical model based on band energy theory is developed to illustrate the origin of the tunable single-/dual-color photodetection. This work will stimulate new approaches for developing solution-processed multifunctional photodetectors for imaging photodetection in complex circumstances.

Molecular Intercalation and Electronic Two Dimensionality in Layered Hybrid Perovskites

In layered hybrid perovskites, such as (BA)2 PbI4 (BA=C4 H9 NH3 ), electrons and holes are considered to be confined in atomically thin two dimensional (2D) Pb-I inorganic layers. These inorganic layers are electronically isolated from each other in the third dimension by the insulating organic layers. Herein we report our experimental findings that suggest the presence of electronic interaction between the inorganic layers in some parts of the single crystals. The extent of this interaction is reversibly tuned by intercalation of organic and inorganic molecules in the layered perovskite single crystals. Consequently, optical absorption and emission properties switch reversibly with intercalation. Furthermore, increasing the distance between inorganic layers by increasing the length of the organic spacer cations systematically decreases these electronic interactions. This finding that the parts of the layered hybrid perovskites are not strictly electronically 2D is critical for understanding the electronic, optical, and optoelectronic properties of these technologically important materials.

Structural Diversity and Magnetic Properties of Hybrid Ruthenium Halide Perovskites and Related Compounds.

There has been a great deal of recent interest in extended compounds containing Ru3+ and Ru4+ in light of their range of unusual physical properties. Many of these properties are displayed in compounds with the perovskite and related structures. Here we report an array of structurally diverse hybrid ruthenium halide perovskites and related compounds: MA2 RuX6 (X=Cl or Br), MA2 MRuX6 (M=Na, K or Ag; X=Cl or Br) and MA3 Ru2 X9 (X=Br) based upon the use of methylammonium (MA=CH3 NH3 + ) on the perovskite A site. The compounds MA2 RuX6 with Ru4+ crystallize in the trigonal space group and can be described as vacancy-ordered double-perovskites. The ordered compounds MA2 MRuX6 with M+ and Ru3+ crystallize in a structure related to BaNiO3 with alternating MX6 and RuX6 face-shared octahedra forming linear chains in the trigonal space group. The compound MA3 Ru2 Br9 crystallizes in the orthorhombic Cmcm space group and displays pairs of face-sharing octahedra forming isolated Ru2 Br9 moieties with very short Ru-Ru contacts of 2.789 Å. The structural details, including the role of hydrogen bonding and dimensionality, as well as the optical and magnetic properties of these compounds are described. The magnetic behavior of all three classes of compounds is influenced by spin-orbit coupling and their temperature-dependent behavior has been compared with the predictions of the appropriate Kotani models.

Light-Emitting Nanophotonic Designs Enabled by Ultrafast Laser Processing of Halide Perovskites.

Nanophotonics based on resonant nanostructures and metasurfaces made of halide perovskites have become a prospective direction for efficient light manipulation at the subwavelength scale in advanced photonic designs. One of the main challenges in this field is the lack of large-scale low-cost technique for subwavelength perovskite structures fabrication preserving highly efficient luminescence. Here, unique properties of halide perovskites addressed to their extremely low thermal conductivity (lower than that of silica glass) and high defect tolerance to apply projection femtosecond laser lithography for nanofabrication with precise spatial control in all three dimensions preserving the material luminescence efficiency are employed. Namely, with CH3 NH3 PbI3 perovskite highly ordered nanoholes and nanostripes of width as small as 250 nm, metasurfaces with periods less than 400 nm, and nanowire lasers as thin as 500 nm, corresponding to the state-of-the-art in multistage expensive lithographical methods are created. Remarkable performance of the developed approach allows to demonstrate a number of advanced optical applications, including morphology-controlled photoluminescence yield, structural coloring, optical- information encryption, and lasing.

Rigid Amine-Induced Pseudo-3 D Lead-Free Bismuth Halide Perovskite with an Improved Band Edge for Visible-Light Absorption.

Bismuth organometal halide perovskites have recently been investigated as potential substitutes for lead perovskite solar-cell absorbers because of their lower toxicity. However, the narrowing of the band gap remains a crucial challenge for their practical application. All known Bi-based perovskites have large band gaps, thereby affording weak visible-light absorption. This study concerns a novel, lead-free, pseudo-3 D perovskite optoelectronic material, (MV)BiI5 (MV2+ =methyl viologen). The pseudo-3 D metal-halogen perovskite-like structure is constructed by connecting [BiI5 ] 2+ units via I⋅⋅⋅I contacts. MV, as a rigid organic amine, is located at the center of each parallelepiped to balance the charge and stabilize the structure. (MV)BiI5 has a narrow band gap of 1.48 eV and a better photoresponse than (MV)BiCl5 with a 1 D structure. (MV)BiI5 is the first Bi-based perovskite compound with a band gap energy comparable with (CH3 NH3 )PbI3 , which is encouraging for optoelectronic applications. This research will open a potential pathway for the design of pseudo-3 D Bi-based perovskites with performances comparable with APbX3 absorbers.

In Situ Growth of MAPbBr3 Nanocrystals on Few-Layer MXene Nanosheets with Efficient Energy Transfer.

The performance of perovskite nanocrystals (NCs) in optoelectronics and photocatalysis is severely limited by the presence of large amounts of crystal boundaries in NCs film that greatly restricts energy transfer. Creating heterostructures based on perovskite NCs and 2D materials is a common approach to improve the energy transport at the perovskite/2D materials interface. Herein, methylamine lead bromide (MAPbBr3 , MA: CH3 NH3 + ) perovskite NCs are homogeneously deposited on highly conductive few-layer MXene (Ti3 C2 Tx ) nanosheets to form heterostructures through an in situ solution growth method. An optimal mixed solvent ratio is essential to realize the growth of perovskite NCs on Ti3 C2 Tx nanosheets. Time-resolved photoluminescence spectroscopy, transient absorption spectroscopy, and the photoresponse of electron- and hole-only photoelectric conversion devices reveal the interfacial energy transfer behavior within MAPbBr3 /Ti3 C2 Tx heterostructures. The present investigation may provide a useful guide toward use of halide perovskite/2D material heterostructures in applications such as photocatalysis as well as optoelectronics.

Efficient Generation of Permutationally Invariant Potential Energy Surfaces for Large Molecules

An efficient method is described for generating a fragmented, permutationally invariant polynomial basis to fit electronic energies and, if available, gradients for large molecules. The method presented rests on the fragmentation of a large molecule into any number of fragments while maintaining the permutational invariance and uniqueness of the polynomials. The new approach improves on a previous one reported by Qu and Bowman by avoiding repetition of polynomials in the fitting basis set and speeding up gradient evaluations while keeping the accuracy of the PES. The method is demonstrated for CH3–NH–CO–CH3 (N-methylacetamide) and NH2–CH2–COOH (glycine).

Graphdiyne: A Brilliant Hole Accumulator for Stable and Efficient Planar Perovskite Solar Cells.

Traditional carbon materials have demonstrated immense potential in perovskite solar cells (PSCs) owing to their superior electrical properties and environmental stability. Graphdiyne (GDY), as an emerging carbon allotrope, features uniformly distributed pores, endless design flexibility, and unique electronic character compared with traditional carbon materials. Herein, graphdiyne is introduced into the upper part of the perovskite (CH3 NH3 PbI3 ) layer by utilizing a GDY-containing antisolvent during the one-step synthesis of perovskite. Intriguingly, GDY plays an essential role in hole accumulation and transportation because of its higher Fermi level than perovskite. As a result, the automatic separation of photogenerated carriers inside the perovskite film is achieved. Furthermore, the Schottky barrier formed on the interface between perovskite and GDY guarantees the unidirectional hole transport from perovskite to GDY, thereby benefiting further extraction to the hole transport layer. Consequently, GDY-modified perovskite-based planar PSCs exhibit a boosted Jsc of 24.21 mA cm-2 and up to 19.6% power conversion efficiency owing to the increased efficient light utilization and charge extraction. The device with GDY modification exhibits less than 10% shrinkage after a month in ambience. Overall, this work demonstrates an easy method for the utilization of GDY to boost the charge extraction and environmental stability in PSCs.

Electronic aspects of hydrogen bond patterns of P=O···H in crystal structures of phosphoramido acid derivatives: QSAR study of anti-urease activity, Hirshfeld surface analysis, and DFT calculations

New derivatives of phosphoramido acid with the formula(C6H11NCH3)(NHCOCF3)P(O)(O−)(CH3–+NH2–C6H11)(1) (amidophosphoricacid), (C6H5)2P(O)(O−)(+NH3–C6H4–NH2)(2) (phosphonicacid), (C6H5O)2P(O)(O−)(+NH3–C6H4–NH2) (3) (phosphoricacidester) were synthesized and characterized by X-ray crystallography. The asymmetric unit of compounds 1–3 consists of one molecule with the P atom in a tetrahedral environment. The X-ray structural analysis showed that the H-bond patterns depend on the kind of atoms linked to the P atom. In the crystal packing of compound 1, P(O)···H–N and C(O)···H–N hydrogen bonds in 3 and P(O)···H–N distances in compounds 2 and 3 led to a one-dimensional arrangement. The energy of P–O···H–N hydrogen bond (EHB) model and stabilizing energies (E2) were calculated. Hirshfeld surface analysis demonstrated that the C···H contact is attributed to CH···π contact in the 2 and 3 compounds and the F···H contact is referred to hydrogen bond in one O···H counterion interaction. Quantitative structure–activity relationship (QSAR) was used to comprehend the relationship between molecular structural features and the inhibitory of investigated compounds. The use of density functional theory along with the QSAR model for enzymes revealed the importance of QH parameter in describing the anti-AChE and anti-urease activities of monophosphoramidates including P(O)–NH2 moiety.

Negative-to-Positive Thermal Conductivity Temperature Coefficient Transition Induced by Dynamic Fluctuations of the Alkyl Chains in the Layered Complex (C4 H9 NH3 )2 CuCl4.

A negative-to-positive transition of the temperature coefficients of thermal conductivity was found in the two-dimensional organic-inorganic layered complex (C4 H9 NH3 )2 CuCl4 (C4CuCl4) over the three structural phase transitions in the range 176-218 K. The coefficients of the low-temperature phases (85-200 K, α and β phases) were negative, as is typical for insulating crystals, whereas those of the high-temperature phases (200-300 K, γ and δ phases) were positive, as is typical for glasses and liquids. Single-crystal X-ray structure analyses revealed that the tilted C4 H9 NH3 + chains in the α and β phases were fully outstretched in the δ phase, and the interlayer distances between the CuCl4 2- planes increased significantly. The γ phase was an intermediate phase that crystallized with an incommensurate structure, in which the CuCl4 2- sheets formed wave-like structures consisting of connected alternating regions of β-like and δ-like moieties. In the γ and δ phases, thermal fluctuations of the C4 H9 NH3 + chains were found in the electron density maps; however, powder X-ray diffraction (PXRD) data indicated that the thermal expansion of the C4 H9 NH3 + layers was restricted by the rigid CuCl4 2- layers. This situation was considered to induce glass-like thermal conducting properties in the material, such as a positive temperature coefficient. The mean free path of the phonons estimated by using the thermal conductivities and heat capacities was a function of T-1 in the range 85-200 K, as would be expected for crystals, whereas it was approximately constant in the range 200-300 K, which is typical of glasses. In addition, the existence of soft vibration modes in the two-dimensional perovskite CuCl4 2- sheets was revealed by analysis of the incommensurate crystal structure of the γ phase. These low-energy vibration modes were believed to induce the cooperative phase transitions, along with the thermal fluctuations and van der Waals interactions in the C4 H9 NH3 + layers.

Reversible Ultra-Slow Crystal Growth of Mixed Lead Bismuth Perovskite Nanocrystals: The Presence of Dynamic Capping.

An ultra-slow crystal growth over a period of 24 h of a newly synthesized CH3 NH3 Pb1/2 Bi1/3 I3 perovskite (MPBI) nanocrystal in non-polar toluene medium is reported here. From several spectroscopic techniques as well as from TEM analysis we found that the size of nanocrystals changes continuously with time, in spite of being capped by the ligands. Using a single molecular spectroscopic technique, we also found that this size change is not due to the stacking of nanocrystals but due to crystal growth. The notable temperature dependence and reversible nature of the nanocrystals growth is explained by the dynamic nature of the capping. The observed temperature-dependent ultra-slow growth is believed to be a pragmatic step towards controlling the size of perovskite NC in a systematic manner.

Crystal structure features of CH3NH3PbI3−xBrx hybrid perovskites prepared by ball milling: a route to more stable materials

Hybrid organic–inorganic perovskites, MAPbX3 (MA: CH3–NH3+; X = halogen), prepared by ball milling are, by far, much more stable towards ambient conditions (air, humidity) than the conventional materials prepared from solution chemistry.

Divalent chromium in the octahedral positions of the novel hybrid perovskites CH3NH3Pb1-xCrx(Br,Cl)3 (x = 0.25, 0.5): Induction of narrow bands inside the bandgap

The hybrid organic-inorganic perovskites, MAPbX3 (MA: methylammonium CH3–NH3+; X = halogen), are the active light absorbing materials in the new generation of solar cells. Previous theoretical quantum calculations indicated that substituting part of the Pb cations by Cr could introduce a partially filled in-gap narrow band, allowing the excitation of electrons from the valence to the conduction band in two steps. This has been realized in this work, where the title compounds were prepared by ball milling from MABr, PbBr2, and CrCl2 in N2 atmosphere. XRD patterns correspond to pure cubic phases, where Cr2+ ions have entered the octahedral sites of this perovskite framework for the first time. The valence state of Cr ions was probed by Cr K-edge X-ray absorption spectroscopy, confirming the 2+ state and possible local octahedral distortion. Magnetic susceptibility measurements indicate for the x = 0.5 compound a conspicuous antiferromagnetic ordering below TN = 38 K and a paramagnetic moment in the high-temperature region of μeff = 3.60 μB, corresponding to high-spin Cr2+ ions, thus confirming the incorporation of this element at the Pb sublattice. Diffuse reflectance spectra indicate, as predicted, that the presence of Cr induces a narrow band inside the bandgap of those perovskites: the new absorption at ca. 1.6 eV corresponds to the electronic transition from the valence band to the empty part of this partially filled in-gap band. Our result here may open a window of opportunity for new tools in band gap engineering, which can be used in other hybrid lead halide perovskites for improvements in solar cell devices depicting high efficiency.

Nonlinear optical properties of single crystal of L-OOMHCL incorporation with Glycine Oxalic Acid (GOA) with high chemical stability for optoelectronic applications

In this report, a good nonlinear optical material with high criteria such as optical nonlinearity, chemical and thermal stability for life time system capability. The crystallographic orientation belongs to monoclinic crystal structure with the non-centrosymmetric space group, the prominent peaks were observed as (101), (112) and (300). The calculated lattice parameter values are, a = 6.21 Å, b = 3.67 Å, c = 12.12 Å, α = 90°, β = 103.21°, γ = 90° monoclinic space group of P21/n. A broad and strong peak at 3427 cm−1 was assigned to NH stretch, the OH and CH stretching of the compound were confirmed by the peaks present at 3043 cm−1 and 2934 cm−1. Moreover, the peaks at 1398 cm−1 represent the tartaric acid, another strong peak at 1261 cm−1 was assigned to CH2 twisting. In addition, the DTA curve shows a sharp endothermic peak at 109 °C, which corresponds to the melting point of the compound at this stage the sample lost its 20% of weights due to dehydration. From TGA curve, the L-OOMHCL crystal has good thermal stability up to melting point as there is no major weight loss below that temperature. However, it shows the more weight loss of 95% after the melting point due to the removal of volatile substances. Thus, it confirms the full degradation around 600 °C. The dielectric constant and the dielectric loss of L-OOMHCL crystal were carried out at three different temperatures 313 K, (40 °C) 333 K (60 °C) and 353 K (80 °C) for frequencies varying from 50 Hz to 5 MHz. Finally, we have calculated the refractive index value at the cutoff wavelength 214 nm and the 2.012 which is larger than unity, this results in greater development of polarization in the presence of dc electrical fields, hence leading to greater mobility.