Methylammonium Iodide Research Articles

Nucleophilic Radiofluorination Using Tri-tert-Butanol Ammonium as a Bifunctional Organocatalyst: Mechanism and Energetics.

We present a quantum chemical analysis of the 18F-fluorination of 1,3-ditosylpropane, promoted by a quaternary ammonium salt (tri-(tert-butanol)-methylammonium iodide (TBMA-I) with moderate to good radiochemical yields (RCYs), experimentally observed by Shinde et al. We obtained the mechanism of the SN2 process, focusing on the role of the –OH functional groups facilitating the reactions. We found that the counter-cation TBMA+ acts as a bifunctional promoter: the –OH groups function as a bidentate ‘anchor’ bridging the nucleophile [18F]F− and the –OTs leaving group or the third –OH. These electrostatic interactions cooperate for the formation of the transition states of a very compact configuration for facile SN2 18F-fluorination.

Surface Passivation of MAPbBr3 Perovskite Single Crystals to Suppress Ion Migration and Enhance Photoelectronic Performance.

Recently, organometal halide perovskites (OHPs) have achieved significant advancement in photovoltaics, light-emitting diodes, X-ray detectors, and transistors. However, commercialization and practical applications were hindered by the notorious ion migration issue of OHPs. Here, we report a simple solvent-based surface passivation strategy with organic halide salts (methylammonium bromide (MABr) and phenylethylammonium bromide (PEABr)) to suppress the ion migration of MAPbBr3 single crystals. The surface passivation effect is evidenced by the stronger photoluminescence (PL) intensity and extended PL lifetime. Using the pulse voltage and continuous voltage current-voltage measurements, we found that single crystals with surface passivation showed negligible hysteresis on the surface due to the suppression of ion migration. As a result, the dark current stability of coplanar structure devices was significantly improved. Moreover, the vertical structure X-ray detectors with PEABr treatment exhibited a high sensitivity of 15 280 μC Gyair-1 cm-2 and a low detection limit of 87 nGyair s-1 under 5 V bias. The proposed technology would be a versatile tool to improve the performance of perovskite photoelectronic devices.

Self-Assembled Donor-Acceptor Dyad Molecules Stabilize the Heterojunction of Inverted Perovskite Solar Cells and Modules.

The heterointerface between a semiconducting metal oxide and a perovskite critically impacts on the overall performance of perovskite solar cells (PVSCs). Herein, we report a feasible yet effective strategy to suppress the interfacial reaction between nickel oxide and the perovskite via chemical passivation with self-assembled dyad molecules, which leads to the simultaneous improvement of the power conversion efficiencies (PCEs) and operational lifetimes of inverted PVSCs. As a result, inverted PVSCs consisting of simple methylammonium iodide perovskites have achieved an excellent PCE of 20.94% and decent photostability with 93% of the initial value after 600 h of 1 sun equivalent illumination. Moreover, this strategy can be readily translated into slot-die fabrication of perovskite modules, achieving a high PCE of 14.90% with an area of 19.16 cm2 (no shade in the interconnecting area) and a geometrical fill factor of 93%. Overall, this work provides an effective strategy to stabilize the vulnerable heterointerface in PVSCs.

Overcoming Nanoscale Inhomogeneities in Thin-Film Perovskites via Exceptional Post-annealing Grain Growth for Enhanced Photodetection.

Antisolvent-assisted spin coating has been widely used for fabricating metal halide perovskite films with smooth and compact morphology. However, localized nanoscale inhomogeneities exist in these films owing to rapid crystallization, undermining their overall optoelectronic performance. Here, we show that by relaxing the requirement for film smoothness, outstanding film quality can be obtained simply through a post-annealing grain growth process without passivation agents. The morphological changes, driven by a vaporized methylammonium chloride (MACl)–dimethylformamide (DMF) solution, lead to comprehensive defect elimination. Our nanoscale characterization visualizes the local defective clusters in the as-deposited film and their elimination following treatment, which couples with the observation of emissive grain boundaries and excellent inter- and intragrain optoelectronic uniformity in the polycrystalline film. Overcoming these performance-limiting inhomogeneities results in the enhancement of the photoresponse to low-light (<0.1 mW cm–2) illumination by up to 40-fold, yielding high-performance photodiodes with superior low-light detection.

Methylammonium Compensation Effects in MAPbI3 Perovskite Solar Cells for High-Quality Inorganic CuSCN Hole Transport Layers.

Recent studies have demonstrated that copper (I) thiocyanate (CuSCN) has huge potential as a hole extraction material (HEM) for perovskite solar cells. Here, we used CuSCN as a HEM and analyzed its relationships with a methylammonium lead iodide (MAPbI3) perovskite layer. The CuSCN dissolved in diethyl sulfide (DES) was spin-coated on the MAPbI3 layer. For high-quality and dense CuSCN layers, post-annealing was carried out at various temperatures and times. However, the unwanted dissociation of MAPbI3 to PbI2 was observed due to the post-annealing for a long time at elevated temperatures. In addition, DES, which is used as a CuSCN solvent, is a polar solvent that damages the surface of MAPbI3 perovskites and causes poor interfacial properties between the perovskite layer and HEM. To solve this problem, the effect of the molar ratio of methylammonium iodide (MAI) and PbI2 in the MAPbI3 precursor solution was investigated. The excess MAI molar ratio in the MAPbI3 precursor solution reduced MAPbI3 surface damage despite using DES polar solvent for CuSCN solution. In addition, dissociation of MAPbI3 to PbI2 following an adequate post-annealing process was well suppressed. The excess MAI molar ratio in the MAPbI3 precursor could be compensated for the MA loss and effectively suppress phase separation from MAPbI3 to MAI + PbI2 during post-annealing. The efficiency based on the normal planar structure of CuSCN/MAPbI3 (using excess MAI)/TiO2 was approximately 17%. The CuSCN-based MAPbI3 device shows more optimized stability than the conventional spiro-OMeTAD under damp heat (85 °C and 85% relative humidity) conditions because of the robust inorganic HEM.

Surface interface structural studies of CH3NH3PbI3 thin films using synchrotron source X-ray diffraction for solar cell application

Presently, Organic-inorganic hybrid-based Perovskite material research is gaining attraction in the solar energy field, with efficiencies reaching upwards of 25.7 percent. Even though various efforts have been made to increase the shelf life and to reduce the degradation of perovskite material, still several complicated processes are required to achieve better structural properties and chemical stability. In this paper, Perovskite material is prepared with an optimized molar ratio (PbI2/MAI) = 1.0/1.0, this combination of PbI2 (Lead Iodide) and MAI (Methyl Ammonium Iodide) provides the best inter-diffusion (as noticed) and structural ordering. The above-stated ratio of PbI2 (Lead Iodide) and MAI (Methyl Ammonium Iodide) is suggested to be one of the best molar ratios in the literature. Except of this, there is still a lack of studies found in literature like the optimized structure properties for better device performance, as well as the thickness dependence structural properties variation and the role of inter-diffusion of MAI and PbI2. The present studies focused on the Synchrotron source-based X-ray Diffraction measurements to understand the structural properties of such films at the three different angles of incidence supported by SEM and AFM data. Finally, the present study of this perovskite material paves a way to understand the diffusion of MAI into the PbI2 along with the film thickness of 350 ± 50 nm of the Perovskite layer for one molar ratio in detail. Last but not the least, together with the Synchrotron source-based GIXRD measurements SEM, AFM, and UV–Vis spectroscopy helped to understand the distribution of PbI2 after MAI gets diffused into it and a little amount of un-used PbI2 leftover along with the entire film after the PbI2 and MAI Interaction.

THE SYNTHESIS OF METHYLAMMONIUM LEAD IODIDE ON MESOPORE TiO2 THIN FILM APPLYING OSTWALD RIPENING PROCESS UNDER AMBIENT CONDITION

Organometallic halide-based perovskite solar cells have played a significant role in the development of photovoltaic technology. The synthesis of the perovskite usually needs specific atmospheres, especially controlled humidity. Here, we demonstrate the synthesis of compact methylammonium lead iodide perovskite (MAPbI3) on TiO2 under ambient conditions through one and two-step spin-coating deposition methods, which both resulted in an unconverted PbI2 on the films. The two-step method provided a higher amount of PbI2 regarding the reaction of methyl ammonium iodide (MAI) with an outer layer of the first bonded PbI2 hindered the inner layer to interact with MAI. The Ostwald ripening (OR) process that was applied to the thin film resulted through one-step deposition synthesis has successfully converted the unformed PbI2 to MAPbI3 with a more uniform, lower void, and higher crystal size as confirmed by XRD and SEM analysis results. The application of MAPbI3 prepared using OR treatment in the solar cell resulted in higher efficiency (7.64%) than the one synthesized without OR (4.91%).

Ferroelectricity driven by orbital resonance of protons in CH3NH3Cl and CH3NH3Br

The β and γ phases of methylammonium chloride CH3NH3Cl and methylammonium bromide CH3NH3Br are identified to be ferroelectric via pyroelectric current and dielectric constant measurements.

Strong Viscosity Increase in Aqueous Solutions of Cationic C22-Tailed Surfactant Wormlike Micelles

The viscoelastic properties and structure parameters have been investigated for aqueous solutions of wormlike micelles of cationic surfactant erucyl bis(hydroxyethyl) methylammonium chloride with long C22 tail in the presence inorganic salt KCl. The salt content has been varied to estimate linear to branched transition conditions due to screening of the electrostatic interaction in the networks. The local cylindrical structure and low electrostatic repulsion was obtained by SANS data. The drastic power law dependencies of rheological properties on surfactant concentrations were obtained at intermediate salt content. Two power law regions of viscosity dependence were detected in semi-dilute solutions related to “unbreakable” and “living” micellar chains. The fast contour length growth with surfactant concentration demonstrated that is in good agreement with theoretical predictions.

Ambient environment induced synergetic improvement in morphology and iodine vacancy passivation by MAI surface engineering in mixed-cation lead mixed-halide (FA0.85MA0.15PbI0.55Br0.45) perovskite solar cells

Perovskite solar cells (PSCs), have made tremendous progress but are still far away from theoretically estimated power conversion efficiencies (PCEs) and commercialization. Defects present in the perovskite materials and at various interfaces (between ETL/HTL and perovskite) in devices are inhibiting the performance to get closer to the theoretical limits, whereas the controlled atmosphere fabrication is creating a bottleneck in large scale production. Therefore, meticulous attention is required to overcome these problems. In this work, we report a very simple, facile and efficient post-synthesis surface treatment with methyl ammonium iodide (MAI) for surface and grain boundary defect passivation in the PSCs processed in fully ambient atmosphere. Ambient atmosphere, MAI surface treatment showed synergetic improvement, firstly it healed the defects (iodine trap states) existing on the surface/interface and grain boundaries and secondly increased the grain size, thereby reducing the defect sites. The improved crystallinity, morphology and decreased defects, reduced the trap density and non-radiative recombination losses leading to fast charge extraction. As a result, planar (n-i-p) PSCs, passivated with optimum MAI concentration, showed significantly higher boost (14%) in the power conversion efficiency (PCE) compared to previous MAI surface treatments, where no morphological changes were observed.

Improved Performance of Perovskite Solar Cells by Suppressing the Energy-Level Shift of the PEDOT:PSS Hole Transport Layer

In inverted architectures of perovskite solar cells (PSCs), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used as the hole transport layer (HTL). An issue occurring in such PSCs is that the hole transport level of PEDOT:PSS shifts upward since methylammonium iodide (MAI) used for the perovskite structure organization interacts with the underlying PEDOT:PSS HTL as a reducing agent, which impedes hole extraction and therefore lowers the performance of PSCs. To overcome this issue, we demonstrate a way of adding tetraethoxysilane (TEOS) into a water-based PEDOT:PSS solution. The HTL spin-coated from the solution contains PEDOT:PSS, which is blended with siloxanes because the polymerization of TEOS takes place via the hydrolysis reaction. This siloxane blending suppresses the MAI-induced reducing reaction and upward energy-level shift of PEDOT:PSS. Using the siloxane-blended PEDOT:PSS HTL in PSCs leads a ∼1.3-fold increase in power conversion efficiencies of iodide-based PSCs from the original ∼10.58% to ∼13.65%.

Influence of molar ratio of MAI and PbI2 on synthesis of perovskite film

This study explores the influence of molar ratio of the synthetic solution of methylammonium iodide (MAI) and PbI2 on perovskite solar cells. The complete perovskite crystals must be produced in a low-humidity environment. The substrate is spin-coated in the adjusted MAPbI3 synthesis solution and annealed by using a nitrogen furnace tube to form perovskite crystals. During the crystallization of MAPbI3, some of the PbI2 remains, which improves the efficiency of the perovskite solar cell. Therefore, we adjust the molar concentration of MAI to find the appropriate amount of the PbI2 residual. We fix the MAI molar concentration at 1 M and adjust the PbI2 molar concentration from 0.8 M to 1.4 M. The molar ratios of MAI and PbI2 are, then, 1:0.8, 1:1, 1:1.2, and 1:1.4, respectively. Then, we use UV–vis, FE-SEM, and photoelectric conversion efficiency (PCE) measurements for comparing the growth of perovskite crystals and their photoelectric characteristics. The results show that 1.2 M of PbI2 is the most appropriate concentration for perovskite solar cells among the adjusted concentrations.

Methylammonium Lead Tri-Iodide Perovskite Solar Cells with Varying Equimolar Concentrations of Perovskite Precursors

During recent years, power conversion efficiencies (PCEs) of organic-inorganic halide perovskite solar cells (PSCs) have shown remarkable progress. The emergence of various thin film deposition processes to produce perovskite films, notably using solution processing techniques, can be credited in part for this achievement. The engineering of chemical precursors using solution processing routes is a powerful approach for enabling low-cost and scalable solar fabrication processes. In the present study, we have conducted a systematic study to tune the equimolar precursor ratio of the organic halide (methylammonium iodide; MAI) and metal halide (lead iodide; PbI2) in a fixed solvent mixture of N,N-dimethylformamide (DMF):dimethylsulfoxide (DMSO). The surface morphology, optical characteristics, and crystallinity of the films produced with these four distinct solutions were investigated, and our analysis shows that the MAI:PbI2 (1.5:1.5) film is optimal under the current conditions. The PSCs fabricated from the (1.5:1.5) formulation were then integrated into the n-i-p solar cell architecture on fluorine-doped tin oxide (FTO) substrates, which exhibited a PCE of ~14.56%. Stability testing on this PSC device without encapsulation at 29 °C (ambient temperature) and 60% relative humidity (RH) under one-sun illumination while keeping the device at its maximum power point showed the device retained ~60% of initial PCE value after 10 h of continuous operation. Moreover, the recombination analysis between all four formulations showed that the bimolecular recombination and trap-assisted recombination appeared to be suppressed in the more optimal (1.5:1.5) PSC device when compared to the other formulations used in the n-i-p PSC architecture.

Boric acid improves the stability of perovskite solar cell precursor solution

<p indent=0mm>The stability of perovskite precursor solution which is very important for device efficiency, stability and consistency has been neglected for a long time. In methylamine-formamidine complex perovskite solution, the instability of solution is mainly caused by the deprotonation of methylammonium iodide and its derived side reaction. In order to improve the stability of the solution, we systematically studied the influence of different acid additives on the balance of deprotonation and trans-methylimine reaction, and found that boric acid was the best additive. As a Lewis acid, boric acid has sp² hybrid boron atoms which could accept a lone pair of electrons, thus forming coordination bonds. In the mixed organic cationic perovskite solution, there is a strong coordination interaction between B and I⁻, which can effectively inhibit the deprotonation of methylamine iodide and the transimine reaction of methylamine and formamidine iodide, resulting in a 97.9% reduction in the generated by-products. Perovskite films and devices prepared by the solution with boric acid stabilizer after aging for different times have good repeatability and consistency, which is particularly important for the commercialization of perovskite solar cells.

Luminescence and Structural Characteristics of Lead Halide Perovskite Films Deposited In Situ by a Versatile Multisource Aerosol Assisted Chemical Vapor Deposition (AACVD) Method

AbstractMost solution‐based synthetic routes for perovskite film deposition take place under highly controlled atmospheres and cannot be easily escalated for mass production. Here, the control in situ over luminescent, morphological, and structural characteristics of hybrid and inorganic perovskite films deposited on top of hot glass substrates by multisource AACVD is reported. By simply adjusting the methylammonium chloride (MACl) to lead bromide (PbBr2) molar ratio in the N‐N dimethylformamide (DMF) precursor solution, a gradual transformation from orthorhombic PbBr2 to cubic MAPbBr2Cl hybrid perovskite films is observed, and the generation of highly luminescent MAPbBr3−xClx nanoparticulate domains in a PbBr2 matrix is easily achieved when a specific ratio is used. Additionally, the crystallization of the films is performed in situ modified by the implementation of an antisolvent stream source during deposition which in turn yields films with superior luminescence properties. Finally, an NIR emitting CsPbBr2Cl:Yb inorganic perovskite film is deposited to probe the versatility of the multisource AACVD system, by the simultaneous deposition of separated PbBr2/YbCl3·6H2O/DMF and CsCl/methanol solutions. The high degree of control on the final properties of the films indicates that AACVD could be a breakthrough for low‐cost, scalable, high‐throughput metal‐halide perovskite film deposition.

Coupling Methylammonium and Formamidinium Cations with Halide Anions: Hybrid Orbitals, Hydrogen Bonding, and the Role of Dynamics.

The electronic structures of four precursors for organic–inorganic hybrid perovskites, namely, methylammonium chloride and iodide, as well as formamidinium bromide and iodide, are investigated by X-ray emission (XE) spectroscopy at the carbon and nitrogen K-edges. The XE spectra are analyzed based on density functional theory calculations. We simulate the XE spectra at the Kohn–Sham level for ground-state geometries and carry out detailed analyses of the molecular orbitals and the electronic density of states to give a thorough understanding of the spectra. Major parts of the spectra can be described by the model of the corresponding isolated organic cation, whereas high-emission energy peaks in the nitrogen K-edge XE spectra arise from electronic transitions involving hybrids of the molecular and atomic orbitals of the cations and halides, respectively. We find that the interaction of the methylammonium cation is stronger with the chlorine than with the iodine anion. Furthermore, our detailed theoretical analysis highlights the strong influence of ultrafast proton dynamics in the core-excited states, which is an intrinsic effect of the XE process. The inclusion of this effect is necessary for an accurate description of the experimental nitrogen K-edge X-ray emission spectra and gives information on the hydrogen-bonding strengths in the different precursor materials.

Facile tuning of PbI2 porosity via additive engineering for humid air processable perovskite solar cells

Fabrication of perovskite solar cells (PSC) in ambient environment or high relative humidity (RH) condition may assist in reducing the production cost and simplifying the fabrication process. However, processing PSC in high-humidity faces major challenges related to degradation of perovskite material and formation of low-quality film. To this end, we focus on improving the perovskite film quality by introducing 4-tert-butylpyridine (TBP) as additive to manipulate the morphology of PbI2 for fabricating efficient PSC in ambient air with RH30–40%. The amount of TBP is varied between 0 and 15 vol%. It is found that increasing the amount of TBP gradually transforms the compact PbI2 layer to porous structure. This allows methylammonium iodide solution to penetrate deep into the layer even after volume expansion of perovskite crystals. As a result, high-quality perovskite layer with low defect and appropriate amount of PbI2 phase passivation layer is produced. Such feature enhances the light absorption, improves the charge separation and reduces the charge recombination. By increasing the TBP content to 10 vol%, a best efficiency of 15.1% has been acquired and the device also exhibits better ambient stability. The additive engineering approach developed in this work may offer a new insight for the development of efficient and stable PSC under humid atmosphere.

Effect of Co‐Solvents on the Crystallization and Phase Distribution of Mixed‐Dimensional Perovskites (Adv. Energy Mater. 42/2021)

Quasi-2D Perovskites The interaction between the co-solvents and the perovskite precursors dictates which quasi-2D perovskite phases are formed during spin coating or thermal annealing. In the cover artwork representing article number 2102144 by René A. J. Janssen and co-workers, methylammonium iodide is depicted in a bubble while interacting with PbI2 and N-methyl-2-pyrrolidone, whereas butylammonium iodide is more available to react and to form a quasi-2D perovskite with n = 2.

A methylammonium iodide healing method for CH3NH3PbI3 perovskite solar cells with high fill factor over 80%

Repressing the thermal decomposition during the process of heat treatment plays an indispensable part in the preparation of perovskite films. Here, a methylammonium iodide healing method was applied to prevent the volatilization of the organic component inside the perovskite structure during the heat treatment. High-quality CH3NH3PbI3 film with a much larger grain size over 800 nm was successfully fabricated via this healing method. Besides, the absorption and photoluminescence intensity were also both improved. Finally, the best power conversion efficiency of 18.89% with a fill factor over 80% was realized in an n–i–p configuration while possessing outstanding stability. This work suggests that methylammonium iodide healing method is a reliable way to promote crystal growth and improve the photovoltaic performance and humidity stability of the CH3NH3PbI3 solar cells.

Probing atomic structure of beam-sensitive energy materials in their native states using cryogenic transmission electron microscopes

SummaryOrganic–inorganic hybrid perovskite nanoplatelets (NPLs) have emerged as promising materials for solar energy. However, the structural instability under electron beam hinders further probing and understanding of its crystalline structures and defects at the atomic scale. Taking methylammonium bromide perovskite methylammonium lead bromide (CH3NH3PbBr3 (MAPbBr3)) perovskite NPLs as model material, we performed atomic-scale characterization of the native state of the hybrid perovskite solar cell material in different states using ultra-low-dose cryo-TEM imaging. With a series of observation at different growth time, we revealed the growth pattern of such MAPbBr3 material from an initially stacked slices with rotational moiré fringes to a perfect single-crystalline structure of NPLs. Our high-resolution cryo-TEM further enabled the atomic-scale investigations of solid electrolyte interphase (SEI) and sodium (Na) dendrite materials, which can largely impact the safety and life of batteries. This study offers insights on the atomic scale characterization of a wide variety of beam-sensitive materials, inspiring us to probe more materials with cryo-transmission electron microscopes (TEM).