Methylammonium Lead Bromide Perovskite Research Articles

Ultrasmall 2D Sn‐Doped MAPbBr3 Nanoplatelets Enable Bright Pure‐Blue Emission

AbstractSynthesis of perovskites that exhibit pure‐blue emission with high photoluminescence quantum yield (PLQY) in both nanocrystal solutions and nanocrystal‐only films presents a significant challenge. In this work, a room‐temperature method is developed to synthesize ultrasmall, monodispersed, Sn‐doped methylammonium lead bromide (MAPb1‐xSnxBr3) perovskite nanoplatelets (NPLs) in which the strong quantum confinement effect endows pure blue emission (460 nm) and a high quantum yield (87%). Post‐treatment using n‐hexylammonium bromide (HABr) repaired surface defects and thus substantially increased the stability and PLQY (80%) of the NPL films. Concurrently, high‐precision patterned films (200‐µm linewidth) are successfully fabricated by using cost‐effective spray‐coating technology. This research provides a novel perspective for the preparation of high PLQY, highly stable, and easily processable perovskite nanomaterials.

Continuous-wave quasi-single-mode random lasing in CH3NH3PbBr3 perovskite films on patterned sapphire substrates.

We report intriguing continuous-wave quasi-single-mode random lasing in methylammonium lead bromide (CH3NH3PbBr3) perovskite films synthesized on a patterned sapphire substrate (PSS) under excitation of a 532-nm laser diode. The random laser emission evolves from a typical multi-mode to a quasi-single-mode with increasing pump fluences. The full width at half-maximum of the lasing peak is as narrow as 0.06 nm at ∼547.8 nm, corresponding to a high Q-factor of ∼9000. Such excellent random lasing performance is plausibly ascribed to the exciton resonance in optical absorption at 532 nm and the enhanced optical resonance due to the increased likelihood for randomly scattered light to re-enter the optical loops formed among the perovskite grains by multi-reflection at the perovskite/PSS interfaces. This work demonstrates the promise of single-mode perovskite random lasers by introducing the exciton resonance effect and ingeniously designed periodic nano/micro optical structure.

Flexible water-resistant bamboo-like perovskite-embedded polymer nano/microfibers exhibiting Fabry–Pérot lasing

Methylammonium lead bromide perovskite (MAPbBr3)-embedded nano- and micro-fibers are successfully fabricated by using the uniaxial electrospinning technique. Through the study of solidification and coordination between perovskite with hybrid polymers, polymethyl methacrylate, and polyacrylonitrile, the bamboo-like perovskite-embedded polymer nano/microfibers are unpredictably formed. Encapsulated in polymer, the passive perovskite-embedded polymer fibers exhibit a long-term fluorescence performance when simultaneously exposed to both water immersion and short-wavelength laser irradiation. Notably, due to the efficient gain media, the perovskite-rich region of the electrospun fiber can act as an optical microcavity. Multi-mode and single-mode lasing behaviors can be achieved via different cavity lengths. The mechanism of a microlaser within this perovskite fiber is confirmed through a Fabry–Pérot cavity, which provides an opportunity for optical components in lasers.

The impact of bi-doped on MAPb(IxBr1–x)3 mixed halide perovskite films

Perovskite solar cells have attracted considerable attention from researchers owing to their cost-effective manufacturing processes, facilitating their suitability for commercialization. Halide perovskite such as methylammonium lead iodide (MAPbI3), methylammonium lead bromide (MAPbBr3) and other mixed halide perovskite are intensively studied as light absorber for solar cells. In order to adjust the properties of the perovskite, doping with heterovalent metal ions such as bismuth iodide, BiI3, has demonstrated notable impact on both crystal structure and optical properties. Traditionally, Bi3+ doping has been conducted primarily in single halide perovskite. However, our study explored the possibility of Bi3+ doping at a concentrations of 5% in mixed halide perovskite, specifically the mixed iodide-bromide perovskite, MAPb(IxBr1–x)3 at x = 0.2, 0.4, 0.6 and 0.8. The XRD results revealed a decrease in lattice constant upon Bi3+ doping which likely attributed to the smaller ionic radius of Bi3+ compared to Pb2+. The light absorption spectra of Bi3+ doping perovskites exhibited a significant red shift compared to the undoped samples. The presences of the key elements are confirmed by photoemission spectroscopy results. Moreover, our investigation found no notable effect on the valence band maximum upon doping. The observed red-shift presents a potential advantage for precisely adjusting the absorption edge in tandem solar cells, particularly when specific energy gaps are required.

Optical spin hall effect in exciton-polariton condensates in lead halide perovskite microcavities.

An exciton-polariton condensate is a hybrid light-matter state in the quantum fluid phase. The photonic component endows it with characters of spin, as represented by circular polarization. Spin-polarization can form stochastically for quasi-equilibrium exciton-polariton condensates at parallel momentum vector k|| ∼ 0 from bifurcation or deterministically for propagating condensates at k|| > 0 from the optical spin-Hall effect (OSHE). Here, we report deterministic spin-polarization in exciton-polariton condensates at k|| ∼ 0 in microcavities containing methylammonium lead bromide perovskite (CH3NH3PbBr3) single crystals under non-resonant and linearly polarized excitation. We observe two energetically split condensates with opposite circular polarizations and attribute this observation to the presence of strong birefringence, which introduces a large OSHE at k|| ∼ 0 and pins the condensates in a particular spin state. Such spin-polarized exciton-polariton condensates may serve not only as circularly polarized laser sources but also as effective alternatives to ultracold atom Bose-Einstein condensates in quantum simulators of many-body spin-orbit coupling processes.

Polymer Backbone Stabilized Methylammonium Lead Bromide Perovskite Nano Islands.

Organic-inorganic hybrid perovskite materials continue to attract significant interest due to their optoelectronic application. However, the degradation phenomenon associated with hybrid structures remains a challenging aspect of commercialization. To overcome the stability issue, we have assembled the methylammonium lead bromide nano islands (MNIs) on the backbone of poly-3-dodecyl-thiophene (PDT) for the first time. The structural and morphological properties of the MNI-PDT composite were confirmed with the aid of X-ray diffraction (XRD) studies, Field emission scanning electron microscope (FESEM), and X-ray photoelectron spectroscopy (XPS). The optical properties, namely absorption studies, were carried out by ultraviolet-visible spectroscopy. The fluorescent behavior is determined by photoluminescence (PL) spectroscopy. The emission peak for the MNI-PDT was observed at 536 nm. The morphology studies supported by FESEM indicated that the nano islands are completely covered on the surface of the polymer backbone, making the hybrid (MNI-PDT) stable under environmental conditions for three months. The interfacial interaction strategy developed in the present work will provide a new approach for the stabilization of hybrids for a longer time duration.

Surface Engineering of Methylammonium Lead Bromide Perovskite Crystals for Enhanced X-ray Detection.

The surface quality of lead halide perovskite crystals can extremely influence their optoelectronic properties and device performance. Here, we report a surface engineering crystallization technique in which we in situ grow a polycrystalline methylammonium lead tribromide (MAPbBr3) film on top of bulk mm-sized single crystals. Such MAPbBr3 crystals with a MAPbBr3 passivating film display intense green emission under UV light. X-ray photoelectron spectroscopy demonstrates that these crystals with emissive surfaces are compositionally different from typical MAPbBr3 crystals that show no emission under UV light. Time-resolved photoluminescence and electrical measurements indicate that the MAPbBr3 film/MAPbBr3 crystals possess less surface defects compared to the bare MAPbBr3 crystals. Therefore, X-ray detectors fabricated using the surface-engineered MAPbBr3 crystals provide an almost 5 times improved sensitivity to X-rays and a more stable baseline drift with respect to the typical MAPbBr3 crystals.

Temperature-Dependent Intensity Modulated Two-Photon Excited Fluorescence Microscopy for High Resolution Mapping of Charge Carrier Dynamics.

We present a temperature-dependent intensity modulated two-photon excited fluorescence microscopy technique that enables high-resolution quantitative mapping of charge carrier dynamics in perovskite microcrystal film. By disentangling the emission into harmonics of the excitation modulation frequency, we analyze the first and second order charge carrier recombination processes, including potential accumulation effects. Our approach allows for a quantitative comparison of different emission channels at a micrometer resolution. To demonstrate the effectiveness of the method, we applied it to a methylammonium lead bromide perovskite microcrystal film. We investigated the temperature-dependent modulated imaging, encompassing the exciton dissociation-association and charge carrier trapping-detrapping equilibrium. Additionally, we explored the potential freezing out of traps and the phase transition occurring at low temperatures.

Enhanced stability of methylammonium lead bromide perovskite interlaced on cellulose nanofiber

The interest in highly luminescent organic-inorganic hybrid perovskite, methylammonium lead bromide (MLB) nanocrystals (NCs) has grown significantly due to their many applications in optoelectronics. However, the biggest hurdle has been the effective use of the materials in large optoelectronic applications and their poor stability in various environmental conditions. To address the problem of the poor stability of highly luminescent MLB nanostructures, we synthesized MLB NCs on the surface of cellulose nanofibers (CNF) for the first time. The synthesized (MLB@CNF) composite shows green emission peak at 529 nm. The scanning electron microscopy images confirm that perovskite NCs are well attached to the surface of cellulose nanofiber. These composite materials offer improved stability and luminescent features in moist environments for over six months. The developed interfacial interaction strategy will provide a novel approach to obtain durable nanocrystals using cellulose-based materials.

Pressure-Induced Phase Transition versus Amorphization in Hybrid Methylammonium Lead Bromide Perovskite.

The crystal structure of the CH3NH3PbBr3 perovskite has been investigated under high-pressure conditions by synchrotron-based powder X-ray diffraction. We found that after the previously reported phase transitions in CH3NH3PbBr3 (Pm3̅m→Im3̅→Pmn21), which occur below 2 GPa, there is a third transition to a crystalline phase at 4.6 GPa. This transition is reported here for the first time contradicting previous studies, which reported amorphization of CH3NH3PbBr3 between 2.3 and 4.6 GPa. Our X-ray diffraction measurements show that CH3NH3PbBr3 remains crystalline up to at least 7.6 GPa, the highest pressure covered by experiments. The new high-pressure phase is also described by the space group Pmn21; however, the transition involves abrupt changes in the unit-cell parameters and a 3% decrease of the unit-cell volume. Our conclusions are confirmed by optical-absorption experiments, by visual observations, and by the fact that pressure-induced changes up to 10 GPa are reversible. The optical studies also allow for the determination of the pressure dependence of the band-gap energy, which is discussed using the structural information obtained from X-ray diffraction.

Separation of 2D Ruddlesden-Popper phase methylammonium lead bromide perovskite layers through hydrogen bonding of 5-aminovaleric acid organic spacer cations by colloidal solution method

2D Ruddlesden-Popper (RP) phase methylammonium lead bromide perovskites with different layers (n = 1, 2, and 3) were successfully synthesized through hydrogen bonding between 5-aminovaleric acid (5-AVA) organic cations using colloidal solution method. XRD patterns confirmed the formation of 2D perovskites with their layer thickness. Further, UV–vis absorption and PL spectra revealed the tuning of optical properties could be achieved by changing the layer thickness of 2D perovskites. The outcomes of our research might assist in the development of various layered 2D perovskites with carboxylic group-based organic spacers that may find applications in the field of optoelectronics.

Boosting the stability and growth of methylammonium lead bromide perovskites film doped with FA for solar cells

In this work, we investigated the lead methylammonium bromide with different contents of formamidinium (0%, 2%, 4%, 6%, 8%, and 10%) deposited by a one-step spin coating method. The effect of FA in MA1-xFAxPbBr3 films was investigated. The crystal structures and morphology, and the optical properties were analysed by X-ray diffraction (XRD), using a scanning electron microscope (SEM) as well as a UV–visible spectrometer, and the surface morphology and optical properties were characterized respectively. From the XRD results, it is found that the crystal structure exhibits 1 crystallographic orientation along the (001) and (002) planes at diffraction angles 2Ɵ = 15.70° and 30.91° respectively. The different layers show perovskite structures with rough surfaces without pinholes although the grain size appearance is different in each case. Optical analysis revealed an increase in the absorbance of the films with FA contents of 6%, 8% and 10% with increasing percentages. For the 2% and 4% contents, the absorbance decreases compared to that of 0% FA. We find that the band gaps are between 1.92 eV and 2.33 eV, the lowest corresponding to the 6% FA layer (1.92 eV). From the results obtained, we can say that the incorporation of FA in MAPbBr3 films is a good candidate for photovoltaic application.For the degradation study, we observed a decrease in the different peaks from XRD and absorption of the samples after 4 weeks in the ambient environment. This decrease is attenuated for some films such as thin films with 0% FA, 4% FA and 8% FA. The different morphological surfaces also experienced degradation. In general, we can say that some films are more or less resistant to the elements of the ambient atmosphere.

Next generation high resolution perovskite direct conversion detector: Monte Carlo design optimisation and virtual clinical trial

We implement virtual clinical integration of next-generation perovskite detectors into common x-ray imaging devices. This was achieved by performing Monte Carlo (MC) optimisation of the design and benchmarking of low cost, high spatial resolution, direct conversion perovskite crystal x-ray flat panel imagers for a next generation of breast-, MV-, and kV-cone beam CT detectors. Semiconductor methylammonium lead bromide perovskite crystals energy deposition efficiencies calculated in TOPAS were benchmarked against four common detector materials for twelve detector crystal thicknesses between 40 to 15 mm and ten beam energies ranging from 20 keV to 6 MeV. Based on these simulations, Koning's dedicated breast CT, and Varian's Truebeam kV- and MV-cone beam CT systems were designated as suitable applications for perovskite detectors. System specific Fastcat hybrid MC cone beam CT image simulation was subsequently used to optimise the perovskite detector design and conduct virtual clinical trials. Device-specific optimal perovskite crystal thicknesses were calculated to be 0.30, 0.86, and 1.99 mm for Koning breast CT and Truebeam kV- and MV-cone beam CT systems, respectively. Replacing the current detectors on these machines with low cost perovskite crystal detectors could be advantageous as it would simultaneously yield 12.1%, 9.5% and 86.1% improvements in detective quantum efficiency as well as increases in contrast to noise ratio in brain, lung, and bone tissues.

High-Sensitivity Visualization of Ultrafast Carrier Diffusion by Wide-Field Holographic Microscopy

Ultrafast transient microscopy is a key tool to study the photophysical properties of materials in space and time, but current implementations are limited to ≈1-μm fields of view, offering no statistical information for heterogeneous samples. Recently, we demonstrated wide-field transient imaging based on multiplexed off-axis holography. Here, we perform ultrafast microscopy in parallel around a hundred diffraction-limited excitation spots over a ≈60-μm field of view, which not only automatically samples the photophysical heterogeneity of the sample over a large area but can also be used to obtain a 10-fold increase in signal-to-noise ratio by computing an average spot. We apply our microscope to study the carrier diffusion processes in methylammonium lead bromide perovskites. We observe strong diffusion due to the presence of hot carriers during the first picosecond and slower diffusion afterward. We also describe how many-body kinetics can be misleadingly interpreted as strong diffusion at high excitation densities, while at weak excitation, real diffusion is observed. Therefore, the vast increase in sensitivity offered by this technique benefits the study of carrier transport not only by reducing data acquisition times but also by enabling the measurement of the much smaller signals generated at low carrier densities.

Is the replacement of “Pb” by “Cu” in methylammonium lead bromide possible?

Substitution of hazardous “Lead” by environmentally benign “Copper” in the methylammonium lead bromide perovskite system is investigated in this work. Nanostructured CH3NH3Pb1-xCuxBr3 perovskite thin films exhibiting c-axis growth has been achieved by us. Evidence for c-axis growth in the copper substituted thin films were obtained from HRTEM analysis. Using a two-step process sequence consisting of a non-aqueous emulsion-based technique for nano-power synthesis followed by a drop-cast technique was optimized for thin film growth. Structural and optical characterizations confirmed the formation of copper substituted methylammonium lead bromide in the orthorhombic structure with preferential orientation along the (040) plane. The average grain size was estimated to be ∼20 nm. Optical characterization identified the optical band gap to be ∼2.46 eV with characteristic green photoluminescence at ∼534 nm. Photo response was obtained from a Glass/FTO/CH3NH3Pb1-xCuxBr3/Graphite/FTO/Glass device structure engineered by us. The photosensitivity of the device structure was observed to be 1299 which was nearly an order above the photosensitivity of the pristine counterpart.

Direct Observation of Size-Dependent Phase Transition in Methylammonium Lead Bromide Perovskite Microcrystals and Nanocrystals.

Methylammonium (MA) lead halide perovskites have been widely studied as active materials for advanced optoelectronics. As crystalline semiconductor materials, their properties are strongly affected by their crystal structure. Depending on their applications, the size of MA lead halide perovskite crystals varies by several orders of magnitude. The particle size can lead to different structural phase transitions and optoelectronic properties. Herein, we investigate the size effect for phase transition of MA lead bromide (MAPbBr3) by comparing the temperature-dependent neutron powder diffraction patterns of microcrystals and nanocrystals. The orthorhombic-to-tetragonal phase transition occurs in MAPbBr3 microcrystals within the temperature range from 100 to 310 K. However, the phase transition is absent in nanocrystals in this temperature range. In this work, we offer a persuasive and direct evidence of the relationship between the particle size and the phase transition in perovskite crystals.

Reassigning the Pressure-Induced Phase Transitions of Methylammonium Lead Bromide Perovskite.

The high-pressure crystal structure evolution of CH3NH3PbBr3 (MAPbBr3) perovskite has been investigated by single-crystal X-ray diffraction and synchrotron-based powder X-ray diffraction. Single-crystal X-ray diffraction reveals that the crystal structure of MAPbBr3 undergoes two phase transitions following the space-group sequence: Pm3̅m → Im3̅ → Pmn21, unveiling the occurrence of a nonpolar/polar transition (Im3̅ → Pmn21). The transitions take place at around 0.8 and 1.8 GPa, respectively. This result contradicts the previously reported phase transition sequence: Pm3̅m → Im3̅ →Pnma. In this work, the crystal structures of each of the three phases are determined from single-crystal X-ray diffraction analysis, which is later supported by Rietveld refinement of powder X-ray diffraction patterns. The pressure dependence of the crystal lattice parameters and unit-cell volumes are determined from the two aforementioned techniques, as well as the bulk moduli for each phase. The bandgap behavior of MAPbBr3 has been studied up to around 4 GPa, by means of single-crystal optical absorption experiments. The evolution of the bandgap has been well explained using the pressure dependence of the Pb-Br bond distance and Pb-Br-Pb angles as determined from single-crystal X-ray diffraction experiments.

Protein-Mediated Aqueous Synthesis of Stable Methylammonium Lead Bromide Perovskite Nanocrystals: Implications for Biological and Environmental Applications

Protein-Mediated Aqueous Synthesis of Stable Methylammonium Lead Bromide Perovskite Nanocrystals: Implications for Biological and Environmental Applications

Tuning between Methylammonium Lead Bromide Perovskite Magic-Sized Clusters and Quantum Dots through Ligand Assisted Reprecipitation at Elevated Temperatures

Tuning between Methylammonium Lead Bromide Perovskite Magic-Sized Clusters and Quantum Dots through Ligand Assisted Reprecipitation at Elevated Temperatures

Mixed-surfactant perovskites with enhanced photostability

Blue and green emitting methylammonium lead bromide perovskite particles with improved UV-light stability have been developed by tuning structure and stabilization with a mixture of different single- and double-tailed surfactants. The ratio of the long alkyl chain surfactants to the methyl ammonium bromide allows for tailoring of the emission color of ready to use perovskite particles without further purification processes. The combination of single and double tailed surfactants exceeds the properties and geometries of the perovskite particles obtainable with a single surfactant. With a mixture of octylammonium bromide and dimethyldioctadecyl bromide, the perovskite particles show a highly anisotropic shape with a layered pyramid structure. The effect of surfactant composition on the perovskite particles’ structure, morphology and light-emitting properties has been elucidated. As these mixed surfactant perovskites are more robust against UV-light than other perovskite particles, they bear great potential for applications in optical devices such as LEDs.