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Metal halide perovskites are difficult to be prepared entirely in water due to their ionic nature. Aqueous synthesis routes of methylammonium lead bromide (CH3NH3PbBr3) perovskite were reported previously, but those methods failed to produce uniform perovskite nanocrystals. Here, monodisperse CH3NH3PbBr3 nanocrystals with an average size of 8.0 nm were directly obtained in an aqueous solution through adopting the hydrophilic polymer polyvinylpyrrolidone (PVP) as a capping ligand. It was revealed from the X-ray photoelectron and Fourier transform infrared spectra that strong chemical interactions occurred between the polymer lactam groups and the perovskite ions, which resulted in the restriction on crystal growth and the production of monodisperse nanocrystals. In addition, both the passivation and the protection of CH3NH3PbBr3 nanocrystals were effectively reached by the PVP macromolecules, endowing the perovskite nanocrystals with a high photoluminescence quantum yield and a long stability. This work presents an important progress in the pursuit of the environment-friendly and economical route for the synthesis of halide perovskite nanocrystals. [ABSTRACT FROM AUTHOR]

Reprecipitation synthesis has been demonstrated to be a simple and convenient route to fabricate high quality perovskite quantum dots toward display applications, whereas the limited chemical yields (< 10%) and difficulty of purification limited its further application. In order to overcome this issue, we here report a modified emulsion synthesis by introducing phase transfer strategy, which achieving effective extraction of newly formed perovskite quantum dots into non-polar solvent and avoiding the degradation of perovskite quantum dots to a large extent. Based on this strategy, gram-scale CH3NH3PbBr3 quantum dots were fabricated in 10 mL (~0.02 mol/L) colloidal solution with chemical yields larger than 70%. The as fabricated CH3NH3PbBr3 quantum dots exhibit an emission peak of 453 nm and a full width at half maximum of only 14 nm. Moreover, electroluminescent devices based on blue emitting CH3NH3PbBr3 quantum dots were also explored with a maximum luminance of 32 cd/m2, showing potential applications in blue light emitting devices.

Lead-based organic–inorganic hybrid perovskite single crystals (OIHP SCs) offer promising opportunity for X-ray detection and imaging owing to their high X-ray attenuation coefficient, excellent optoelectronic properties, and simple fabrication processes. Nevertheless, it remains a key challenge to reduce its dark current and meanwhile maintain a high sensitivity. Herein, we developed an on-substrate method for growing methylamine lead bromide (MAPbBr3) SCs on aluminum oxide (Al2O3) layer coated indium tin oxide (ITO) glass. The photodiode based on this approach exhibits an ultralow-dark-current density of 1 nA cm−2 at an operative voltage of −5 V, a signal-to-noise ratio (SNR) more than 80 dB, and meanwhile retaining a high X-ray sensitivity of 2.02 $\times 10^{{3}}\,\, \mu \text{C}\cdot $ ${\mathrm {Gy}}_{\text {air}}^{-1} \cdot $ cm−2. Our further investigation reveals that the dark current was reduced due to two beneficial effects of the Al2O3 layer in tandem, including the interfacial defect passivation and blocking of hole injection by increased interfacial energy barrier. Our approach sheds light on advancing the fabrication of high-performance OIHP SCs-based X-ray sensors that can be potentially integrated with large-area readout panel at low temperature. [ABSTRACT FROM AUTHOR]

Mixed‐dimensional (2D/3D) van der Waals (vdW) heterostructures made with complementary materials hold a lot of promise in the field of optoelectronic devices. Beyond simple mechanical stacking, directly growing the single‐crystal perovskite on 2D materials to construct a high‐quality vdW heterojunction can better promote carrier transport. In this work, a monolithic integrated graphene/perovskite heterojunction device is fabricated by directly growing a single‐crystal hybrid perovskite on monolayer graphene. Due to the strong interface coupling, the hybrid device achieves self‐powering behavior and exhibits prominent photoresponse properties with a fast response speed of up to 2.05 μs. Moreover, the responsivity and detectivity can be boosted to up to 10.41 A W−1 and 4.65 × 1012 Jones under the actuation of −3 V bias. This technique not only improves the device performance, but also provides an effective guideline for the development of next‐generation directly integrated vdW optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract Mixed‐dimensional (2D/3D) van der Waals (vdW) heterostructures made with complementary materials hold a lot of promise in the field of optoelectronic devices. Beyond simple mechanical stacking, directly growing the single‐crystal perovskite on 2D materials to construct a high‐quality vdW heterojunction can better promote carrier transport. In this work, a monolithic integrated graphene/perovskite heterojunction device is fabricated by directly growing a single‐crystal hybrid perovskite on monolayer graphene. Due to the strong interface coupling, the hybrid device achieves self‐powering behavior and exhibits prominent photoresponse properties with a fast response speed of up to 2.05 μs. Moreover, the responsivity and detectivity can be boosted to up to 10.41 A W−1 and 4.65 × 1012 Jones under the actuation of −3 V bias. This technique not only improves the device performance, but also provides an effective guideline for the development of next‐generation directly integrated vdW optoelectronic devices.

• Variuos hole-transport layers are used independently. • Ohmic contact region is identified by tuning electrode work functions. • Based on our results, an alternate to Au, low-cost contact materials are suggested. • Commonly used expensive hole-transport layer can be replaced. • Current density depends on reflectance from hole-transport layer. Metal halide perovskites are promising absorber materials for solar cell applications due to (i) low-cost processing methods, and (ii) cell efficiency is comparable to the standard silicon solar cells. Methylammonium lead bromide (CH 3 NH 3 PbBr 3) is a metal halide perovskite having wide band gap suitable for high open-circuit voltage (V oc) solar cell. Here we report the performance of CH 3 NH 3 PbBr 3 based solar cells by using various hole-transport layers (HTLs) independently with titanium dioxide (TiO 2) as electron transport layer (ETL). Spiro-OMeTAD was used as HTL in the control device. Absorbance study indicates the band gap of CH 3 NH 3 PbBr 3 is around 2.25 eV. Energy band alignment shows the superior band alignment across the device when copper thiocyanate (CuSCN) is used. Short-circuit current density (J sc) is independent of electrode work functions. However, J sc depends upon internal reflection at the absorber/HTL interface and reflection is high for CuSCN and low for nickel oxide (NiO). Our result shows that fill factor and efficiency depends on absorber thickness, top and bottom electrode work functions. For Ohmic contact, top electrode and bottom electrode work functions must be between −4.0 eV to −4.4 eV and −4.9 eV to −5.26 eV respectively and device performs excellent in these regimes. For the control device, V oc , J sc , fill factor, and efficiency of 2.10 V, 9.64 mA/cm2, 0.90, and 18.42% were obtained. Whereas for the cell having CuSCN as HTL, a high efficiency of 23.39% with V oc of 2.10 V, J sc of 13.04 mA/cm2, and fill factor of 0.85 were obtained. [ABSTRACT FROM AUTHOR]

Herein, the aspects of ion migration in polycrystalline CH3NH3PbBr3 thin film and their phenomenal influences on the output performance of perovskite light‐emitting diodes (PeLEDs) are reported. The physical insight of bias‐induced migration of mobile ions in the perovskite active layer effectuating the observed non‐linearity in the increased magnitude of electroluminescence (EL) and luminous efficiency (LE) as a function of current density for PeLEDs is directly evidenced using the capacitance spectroscopy. Adding the zwitterion molecule, Choline chloride (Ch.Cl), in CH3NH3PbBr3 precursor solution for preparing polycrystalline perovskite film effectively passivates the charged defects, either positively or negatively, in organic‐inorganic halide perovskite and most importantly interferes the migration of ions crossing the grains in PeLEDs as verified by the higher calculated magnitude of the activation energy for the migration of mobile ions. As a result, the Ch.Cl‐additive devices exhibit the rather stable EL and LE magnitude under the electric bias. EL magnitude increases linearly as a function of current density, revealing the epitome of output characteristics for decent light‐emitting diodes. To suppress the influence of the migrating ions on operating PeLEDs is a key issue before it is stepped further to advance the efficiencies and the operational stabilities of perovskite devices. [ABSTRACT FROM AUTHOR]

The nanowire and nanorod morphology offers great advantages for application in a range of optoelectronic devices, but these high-quality nanorod arrays are typically based on high temperature growth techniques. Here, we demonstrate the successful room temperature growth of a hybrid perovskite (CH3NH3PbBr3) nanorod array, and we also introduce a new low temperature anion exchange technique to convert the CH3NH3PbBr3 nanorod array into a CH3NH3PbI3 nanorod array while preserving morphology. We demonstrate the application of both these hybrid perovskite nanorod arrays for LEDs. This work highlights the potential utility of postsynthetic interconversion of hybrid perovskites for nanostructured optoelectronic devices such as LEDs, which enables new strategies for the application of hybrid perovskites.

Organolead halide perovskites provide tremendous opportunities for ideal radiation detection due to their high atomic numbers, large carrier mobilities, and long lifetimes. Here, we synthesized high-quality single crystal CH3NH3PbBr3 with a high mobility-lifetime product of $\text {4.1} \times \text {10}^{\text {-2}}$ cm2/V by the developed inverse low temperature crystallization method. The sensitive X-ray detector was fabricated by depositing 50 nm of gold on both sides of the perovskite crystal. This device exhibited a high sensitivity up to $259.9~\mu \text{C}$ /Gy $_{\text {air}}$ /cm2 under the 39 keV X-ray exposure at a small electric field of ~0.83 V/mm and yielded a low noise of $\text {3.1} \times \text {10}^{-\text {23}}\,\,\text{A}^{\text {2}}$ /Hz. Additionally, the sensitivity can be further improved by increasing operating voltage. Our results provided a solution for constructing high-performance X-ray detectors. [ABSTRACT FROM AUTHOR]

Fundamental insights into the reaction kinetics of organic–inorganic lead halide perovskite nanocrystals (LHP NCs) are still limited due to their ultrafast formation rate. Herein, we develop a water–oil interfacial synthesis of MAPbBr3 NCs (MA=CH3NH3+), which prolongs the reaction time to tens of minutes. This method makes it possible to monitor in situ the formation process of MAPbBr3 NCs and observe successive spectral evolutions from 438 to 534 nm in a single reaction by extending reaction time. The implementation of this method depends on reducing the formation rate of PbBr64− octahedra and the diffusion rate of MA. The formation of PbBr64− is a rate‐determining step, and the biphasic system offers a favorable reaction condition to control the mass transfer of MA. The effects of temperature and concentration of precursor and ligand are investigated in detail. [ABSTRACT FROM AUTHOR]

Surface plasmons can make highly spatial confinement and near-field enhancement at the metal/dielectric interface and decrease optical loss. Here, we introduced detachable aluminum nanoparticles (Al NPs) substrate to enhance CH 3 NH 3 PbBr 3 perovskite lasing performances, and compared the lasing actions between Al-CH 3 NH 3 PbBr 3 and prime CH 3 NH 3 PbBr 3 microcuboid to understand the mechanism. Based on Al surface plasmons coupled excitation in Al-CH 3 NH 3 PbBr 3 hybrid system, the lasing threshold is dramatically reduced more than 27% and the stimulated emission of CH 3 NH 3 PbBr 3 improved 10 times. • The detachable surface plasmon substrate can minimize the damages to perovskite in fabrication and excitation process. • The lasing performances between pure CH 3 NH 3 PbBr 3 and Al NPs capped hybrid system can be compared more directly. • The lasing threshold is dramatically reduced and the stimulated emission of CH 3 NH 3 PbBr 3 improved 10 times. • This research is helpful to understand the SP coupling effects in Al-CH 3 NH 3 PbBr 3. [ABSTRACT FROM AUTHOR]

Perovskite CH 3 NH 3 PbBr 3 single crystals were synthesized by ITC method with DMF as solvent. X-ray diffraction was used to determine the structure of as-grown CH 3 NH 3 PbBr 3 single crystal. The morphology of CH 3 NH 3 PbBr 3 single crystal was measured by HRTEM and SEAD, and the result shows that the grown CH 3 NH 3 PbBr 3 crystal is of good crystallinity. Optical properties were investigated by cathodoluminescence (CL) and photoluminescence (PL). The photoelectric performance of a photodetector based on CH 3 NH 3 PbBr 3 single crystal was studied.The largest responsivity of the device is about 0.67 A/W, and the response time of photocurrent of the detector is 200 ms in the rise time and 250 ms in the fall time. Our results show CH 3 NH 3 PbBr 3 single crystal has great potential for photoelectric device field. • The quality of the CH3NH3PbBr3 crystal grown was investigated by the micromorphology study. • The optical properties of CH3NH3PbBr3 crystal was firstly studied by CL. • Photoelectric properties of the CH3NH3PbBr3 crystal photodetector were studied. [ABSTRACT FROM AUTHOR]

Luminescent lead halide perovskite nanocrystals (LHP NCs) have attracted great attention. This work reports the synthesis of well‐defined core/shell structured CH3NH3PbBr3/β‐cyclodextrin (MAPbBr3/β‐CD) nanodots via host‐guest interaction between β‐cyclodextrin and hexylamine. The MAPbBr3/β‐CD nanodots show high luminescence with photoluminescence quantum yields (PLQYs) of 89.7% in solution and 38.0% in solid state. The MAPbBr3/β‐CD nanodots have superior stability in water, under heat and UV light exposure due to the formation of a β‐CD shell, which gives them great potential for optoelectrical and biological applications. [ABSTRACT FROM AUTHOR]

With the rapid increase of efficiency up to 23% during the past few years, hybrid organic-inorganic metal halide perovskite solar cells (PSCs) have become a research "hot spot" for many solar cell researchers. Hybrid perovskite structures have been obtained from methylammonuim lead bromide solutions deposited by one step spin coating deposition method. In this work, the effects of annealing temperature of the MAPbBr 3 films and devices have been investigated in details. By tuning the variation of the temperature, the properties including photoluminescence, crystallinity and morphology of perovskite films together with device performance have been affected significantly by the annealing temperature. The devices annealed with 70 °C shows the best device performance and exhibit a maximum Fill Factor around 76.5 and a maximum efficiency at 2.89%. Image 10483 • Solar cells based on CH 3 NH 3 PbBr 3 are fabricated by one-step spin coating deposition. • The effect of annealing temperature was investigated. • Standard structure FTO/TiO 2 /MAPbBr 3 /Spiro-OMeTAD/Au was developed. • Optical, structural and electrical properties of the cells have been investigated. [ABSTRACT FROM AUTHOR]

Abstract High-performance CH 3 NH 3 PbBr 3 (MAPbBr 3) room-temperature NO 2 sensors have been developed for the first time based on MAPbBr 3 films prepared directly from perovskite precursor solutions (PSFs) and from surface-capped MAPbBr 3 nanoparticles (NPFs). AFM images of these films revealed that the grain size of MAPbBr 3 crystal in PSFs decreases with the increasing on the concentration of precursor solution, and XRD patterns demonstrate MAPbBr 3 in PSFs packed along with (00 l) crystal orientation. However, MAPbBr 3 NPFs have no preferential crystal orientation despite the good crystallinity of MAPbBr 3 NPs. I-V curves revealed different hysteresis loops for these two kinds of films. Sensors with PSF or NPF as semiconducting layer exhibited remarkable and reversible change when they are exposed to NO 2 gas. Interestingly, NPF sensors show better sensing performance with a lower detection limit (0.1 ppm) and a larger sensitivity. Experiments also revealed that the selectivity of NPF is better than that of PSF sensors. More importantly, NPF sensors are much more stable than PSF sensors due to the protected surface of perovskite NPs. This study opens a new promising application for organometallic halide perovskite materials, especially for the protected perovskite NPs. Graphical abstract Image 1 Highlights • Hybrid perovskite CH 3 NH 3 PbBr 3 films with n-type character have been fabricated in different ways. • Two kinds of CH 3 NH 3 PbBr 3 gas sensors towards toxic NO 2 have been developed for the first time. • The sensor based on CH 3 NH 3 PbBr 3 films from nanoparticles capped by alkyl chain shows superior sensing performance. [ABSTRACT FROM AUTHOR]

An organolead halide (CH3NH3PbBr3) nanoparticle was modified successfully with a porphyrin (POR) bearing an -NH3+ head group. The nanoparticles are homogeneous with high crystallinity. The photoluminescence of CH3NH3PbBr3 is quenched completely by the chemically adsorbed POR molecules. The efficient energy transfer from CH3NH3PbBr3 to POR is responsible for the fluorescence quenching. The modified nanoparticles can be dispersed in organic solvents and the resulting dispersion remains stable for several days. This result provides a new way to tune the photophysical properties of organolead halide CH3NH3PbBr3 nanoparticles. Graphical abstract The organolead halide CH3NH3PbBr3 nanoparticle is prepared successfully by modifying a porphyrin (POR) bearing an -NH3+ head group as the capping ligand. The photoluminescence of perovskite is quenched completely by the chemically adsorbed POR molecules which have confirmed that the POR molecules are anchored on the surface of CH3NH3PbBr3 nanoparticle. The result shows that the quenching is caused by the process of energy transfer from CH3NH3PbBr3 nanoparticle to POR, which is beneficial to study surface engineering in organometallic halide perovskite materials. [ABSTRACT FROM AUTHOR]

In this study, a simply structured perovskite-based ultraviolet C (UVC) sensor was prepared using a one-step, low-temperature solution-processing coating method. The UVC sensor utilized CH3NH3PbBr3 perovskite as the light-absorbing layer. To improve the characteristics of CH3NH3PbBr3, an antisolvent process using toluene and the addition of CH3NH3Cl were introduced. The device with these modifications exhibited a response rise/fall time of 15.8/16.2 ms, mobility of 158.7 cm2/V·s, responsivity of 4.57 mA/W, detectivity of 1.02 × 1013 Jones, and external quantum efficiency of 22.32% under the 254-nm UV illumination. Therefore, this methodology could be a good approach in facilitating UVC detection.

Reprecipitation synthesis has been demonstrated to be a simple and convenient route to fabricate high quality perovskite quantum dots toward display applications, whereas the limited chemical yields (< 10%) and difficulty of purification limited its further application. In order to overcome this issue, we here report a modified emulsion synthesis by introducing phase transfer strategy, which achieving effective extraction of newly formed perovskite quantum dots into non-polar solvent and avoiding the degradation of perovskite quantum dots to a large extent. Based on this strategy, gram-scale CH3NH3PbBr3 quantum dots were fabricated in 10 mL (~0.02 mol/L) colloidal solution with chemical yields larger than 70%. The as fabricated CH3NH3PbBr3 quantum dots exhibit an emission peak of 453 nm and a full width at half maximum of only 14 nm. Moreover, electroluminescent devices based on blue emitting CH3NH3PbBr3 quantum dots were also explored with a maximum luminance of 32 cd/m2, showing potential applications in blue light emitting devices.

Abstract A room temperature solution processed ionic liquids (1-benzyl-3-methylimidazolium chloride)/C 60 bilayer were used as the electron transport layer in planar n-i-p structure CH 3 NH 3 PbBr 3 perovskite solar cells. The ionic liquids could effectively decrease the work function and improve the wettability of the perovskite precursor solution on the C 60 layer. Moreover, C 60 guarantees the excellent electron mobility. In comparison with devices with different ETLs, the IL/C 60 -based solar cells show greatly improved performance, achieving the PCE of 5.88% with a J sc of 6.14 mA/cm2, a V oc of 1.39 V, and a FF of 69.94%. Graphical abstract A room temperature solution processed ionic liquids (1-benzyl-3-methylimidazolium chloride)/C 60 bilayer were used as the electron transport layer in planar n-i-p structure CH 3 NH 3 PbBr 3 perovskite solar cells. The IL/C 60 -based solar cells exhibit the champion PCE of 5.88% with a J sc of 6.14 mA/cm2, a V oc of 1.39 V, and a FF of 69.94%. fx1 Highlights • The planar n-i-p structure Br-PSCs were obtained at room temperature. • Ionic-liquids/C 60 bilayer were used as the ETL in planar n-i-p structure Br-PSCs. • The IL/C 60 -based solar cells achieved the PCE of 5.88%. [ABSTRACT FROM AUTHOR]

Abstract Organic-inorganic perovskites have arrived at the forefront of solar technology due to their impressive carrier lifetimes and superior optoelectronic properties. By having the cm-sized perovskite single crystal and employing device patterning techniques, and the transfer length method (TLM), we are able to get the insight into the metal contact and carrier transport behaviors, which is necessary for maximizing device performance and efficiency. In addition to the metal work function, we found that the image force and interface charge pinning effects also affect the metal contact, and the studied single crystal CH 3 NH 3 PbBr 3 features Schottky barriers of 0.17 eV, 0.38 eV, and 0.47 eV for Au, Pt, and Ti electrodes, respectively. Furthermore, the surface charges lead to the thermally activated transport from 207 K to 300 K near the perovskite surface. In contrast, from 120 K to 207 K, the material exhibited three-dimensional (3D) variable range hopping (VRH) carrier transport behavior. Understanding these fundamental contact and transport properties of perovskite will enable future electronic and optoelectronic applications. Graphical abstract fx1 Highlights • The Schottky barrier height study of CH 3 NH 3 PbBr 3 single crystals with Pt, Au, and Ti contacts. • Image force and pinning effect at metal/perovskite junction interface. • The carrier transport study in the temperature ranging from 100 K to 300 K near CH 3 NH 3 PbBr 3 perovskite surface. [ABSTRACT FROM AUTHOR]

Abstract: Researchers have recently revealed that hybrid lead halide perovskites exhibit ferroelectricity, which is often associated with other physical characteristics, such as a large nonlinear optical response. In this work, the nonlinear optical properties of single crystal inorganic–organic hybrid perovskite CH3NH3PbBr3 are studied. By exciting the material with a 1044 nm laser, strong two‐photon absorption‐induced photoluminescence in the green spectral region is observed. Using the transmission open‐aperture Z‐scan technique, the values of the two‐photon absorption coefficient are observed to be 8.5 cm GW−1, which is much higher than that of standard two‐photon absorbing materials that are industrially used in nonlinear optical applications, such as lithium niobate (LiNbO3), LiTaO3, KTiOPO4, and KH2PO4. Such a strong two‐photon absorption effect in CH3NH3PbBr3 can be used to modulate the spectral and spatial profiles of laser pulses, as well as to reduce noise, and can be used to strongly control the intensity of incident light. In this study, the superior optical limiting, pulse reshaping, and stabilization properties of CH3NH3PbBr3 are demonstrated, opening new applications for perovskites in nonlinear optics. [ABSTRACT FROM AUTHOR]

Abstract: Light‐emitting halide perovskites are currently emerging as promising solution‐processed materials for optoelectronic applications, and correlations between their physical properties and morphologies are important drivers to guide material and device optimization. There is still a lack of precise control of the morphology in colloidal perovskite materials, and in the related studies of their shape‐dependent optical properties. Capitalizing on our previous works on the ligand‐assisted reprecipitation synthesis of colloidal perovskite nanocrystals, we have addressed the role of key experimental parameters in determining the degree of supersaturation that drives the crystallization of CH3NH3PbBr3 precursors. By adjusting the amount of ligands, we fabricated single crystalline CH3NH3PbBr3 nanocubes (size: ≈500 nm) and nanowires (length: 2–4.5 μm, width: ≈100 nm), and conducted steady‐state, time‐resolved, excitation power and temperature‐dependent photoluminescence measurements to investigate their shape‐dependent photoluminescence properties. [ABSTRACT FROM AUTHOR]

Organic-inorganic lead halide perovskites quantum dots (OIPeQDs) have shown excellent performance and great promise for commercial applications. However, their instability is a major challenge for their commercial viability. To address this issue, this study optimized the precursor PbBr 2 to DMAPbBr 3 (DMA+ = (CH 3) 2 NH 2 +) and synthesis the CH 3 NH 3 PbBr 3 quantum dots (QDs) by ligand-assisted reprecipitation (LARP) method at room temperature. This process aims to provide a halogen-rich environment to reduce halide vacancy defects, as well as incorporating symmetrical A-site ions, which enhances hydrogen bonding between the halogen and organic cations. The QDs-DMAPbBr 3 obtained through this optimized precursor showed preferable time, water and light stability compared to those synthesized through conventional PbBr 2. The result demonstrates that the QDs-DMAPbBr 3 maintained 85.60% of the initial photoluminescence (PL) value even after one month. To test the stability of the QDs further, the QDs were mixed with deionized (DI) water at a 20:1 ratio, and the QDs-DMAPbBr 3 retained 408.33% of the initial PL value after 3 h. In addition, after continuous irradiation under a 365 nm ultraviolet lamp for 20 h, the PL value of the QDs-DMAPbBr 3 remained stable, at 65.48% of the initial value. These findings indicate that QDs-DMAPbBr 3 possess remarkable stability, which suggests their suitability for a wide range of applications. • Synthesis of QDs-DMAPbBr 3 using DMAPbBr 3 instead of PbBr 2 in the synthesis of CH 3 NH 3 PbBr 3 perovskite quantum dots. • Optimized QDs-DMAPbBr 3 perovskite quantum dots with excellent luminescence and high stability. • DMAPbBr 3 provides a halogen-rich environment and enhances hydrogen bonding between the halogen and organic cations. [ABSTRACT FROM AUTHOR]

A new strategy has been developed using peptides with amino and carboxylic functional groups as passivating ligands to produce methyl ammonium lead bromide (CH3NH3PbBr3) perovskite nanocrystals (PNCs) with excellent optical properties. The well-passivated PNCs can only be obtained when both amino and carboxylic groups are involved, and this is attributed to the protonation reaction between NH2 and COOH that is essential for successful passivation of the PNCs. To better understand this synergistic effect, peptides with different lengths have been studied and compared. Due to the polar nature of peptides, peptide-passivated PNCs (denoted as PNCspeptide) aggregate and precipitate from nonpolar toluene solvent, resulting in a high product yield (≈44%). Furthermore, the size of PNCspeptide can be varied from ≈3.9 to 8.6 nm by adjusting the concentration of the peptide, resulting in tunable optical properties due to the quantum confinement effect. In addition, CsPbBr3 PNCs are also synthesized with peptides as capping ligands, further demonstrating the generality and versatility of this strategy, which is important for generating high quality PNCs for photonics applications including light-emitting diodes, optical sensing, and imaging. [ABSTRACT FROM AUTHOR]

In this work, large-sized CH3NH3PbBr3 single crystals were successful grown using solution evaporation method with hydrohalic acid and N, N-Dimethylformamide (DMF) as solvent respectively. The lattice parameters of cubic CH3NH3PbBr3 were estimated using XRD method. The solubility of CH3NH3PbBr3 in hydrobromic acid was determined at the temperature range between 20 °C-90 °C. A special micro-solution crystallizer was designed to in-situ study the morphology of CH3NH3PbBr3 crystal. The largest crystal face was indexed by the XRD patterns and it would be {110} for CH3NH3PbBr3 grown from HBr solution and {100} from DMF solution. The results show that solvent would affect the morphology and crystal habit greatly during crystal growth from solution. [ABSTRACT FROM AUTHOR]

The results of the direct experimental evaluation of all elastic constants of single crystal hybrid organic-inorganic perovskite (HOIP) methylammonium lead bromide, a material known due to its possible solar-energy, optoelectronics, X-ray detector and thermoelectricity applications, are reported. The measurements of anisotropic elasticity of CH3NH3PbBr3by the technique of laser ultrasonics demonstrate that properties of HOIPs can be even more remarkable than the theoretical expectations: the extracted shear modulus is more than twice smaller, the universal anisotropy is more than twice higher, while the Debye temperature is more than 50° lower. Thus HOIPs can exhibit extremely low shear rigidity and extremely high anisotropy, both strongly overrunning the parameters which have been expected based on earlier first principles theoretical predictions. A simple theoretical model of granular crystal indicates that these observations could be related to the contributions of rotations/tilts of PbBr6octahedra to elastic response of cubic CH3NH3PbBr3. Another experimental observation is strong stiffening of shear rigidity with temperature increase from its room value up to 120 °C. Discovered elastic properties of HOIPs characterize them as exceptionally ductile/flexible/adaptive materials which could be deposited on corrugated/structured surfaces. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

This study conducted an in-depth investigation on the anisotropic Rashba effect in the perovskite CH3NH3PbBr3 by combining density functional theory with relativistic pseudopotentials. It was discovered that the distortion of the Pb—Br octahedra resulted in the splitting of the triplet states at the conduction band minimum due to the spin-orbit coupling (SOC) effect and lattice deformation, leading to strong anisotropy in different directions. The maximum coefficient of Rashba band splitting reached 2.0 eVA, and the mechanism of the Rashba effect formation was explained through the analysis of energy levels and charge density distribution. These research findings contribute to a deeper understanding of the properties of CH3NH3PbBr3 and provide a theoretical basis for its potential applications in the field of spintronics. [ABSTRACT FROM AUTHOR]

Organic-inorganic perovskite materials are successfully employed for optoelectronics (UV–Visible photodetector and solar cell) and ionization radiation detector. The radiation hardness is a key issue for ionization applications based on perovskite materials. Here, the radiation effect on optical, structural and electrical properties of methylamine bromide (CH 3 NH 3 PbBr 3) single crystals under high dose gamma photons are systematically investigated. It is demonstrated from the X-ray diffraction pattern and surface morphologies that single crystals are evenly divided into several pieces after receiving an accumulative dose of 16.56 kGy. The transmittances significantly decrease with increasing the irradiation dose. It is shown from the photoluminescence spectroscopy that sub-bandgap emission is present after irradiation. The sensitivity of CH 3 NH 3 PbBr 3 -based photoconductor improves about tenfold after irradiation at 5.52 kGy, and the highest sensitivity is 1.12 mC Gy−1 cm−2 when the applied voltage is 4 V. This phenomenon of improving the electrical properties of the crystal after gamma-ray irradiation is correlated with decomposition and self-healing behavior. • High performance radiation sensor perovskite-based photoconductor has been achieved. • Gamma-ray irradiation induces ion migration inside the perovskite crystal. • Self-healing behavior was observed in the crystal after gamma-ray irradiation. • The X-ray detection sensitivity of the device is improved after low-dose radiation. [ABSTRACT FROM AUTHOR]

In this study, a simply structured perovskite-based ultraviolet C (UVC) sensor was prepared using a one-step, low-temperature solution-processing coating method. The UVC sensor utilized CH3NH3PbBr3 perovskite as the light-absorbing layer. To improve the characteristics of CH3NH3PbBr3, an antisolvent process using toluene and the addition of CH3NH3Cl were introduced. The device with these modifications exhibited a response rise/fall time of 15.8/16.2 ms, mobility of 158.7 cm2/V·s, responsivity of 4.57 mA/W, detectivity of 1.02 × 1013 Jones, and external quantum efficiency of 22.32% under the 254-nm UV illumination. Therefore, this methodology could be a good approach in facilitating UVC detection. [ABSTRACT FROM AUTHOR]

Perovskite-based semiconductors, such as methylammonium and cesium lead halides (MPbX 3 : M = CH 3 NH 3 + or Cs + ; X = I - , Br - , or Cl - ), have attracted immense attention for several applications, including radiation detection, due to their excellent electronic and optical properties. 1,2,3,4,5,6 In addition, the combination of perovskites with other materials enables unique device structures. For example, robust and reliable diodes result when combined with metal oxide semiconductors. This device can be used for detection of nonionizing and ionizing radiation. In this paper, we report a unique perovskite single-crystal-based neutron detector using a heterojunction diode based on single-crystal MAPbBr 3 and gallium oxide (Ga 2 O 3 ) thin film. The MAPbBr 3 /Ga 2 O 3 diodes demonstrate a leakage current of ∼7 × 10 -10 A/mm 2 , an on/off ratio of ∼10 2 , an ideality factor of 1.41, and minimal hysteresis that enables alpha particle, gamma-ray, and neutron detection at a bias as low as (-5 V). Gamma discrimination is further improved by 85% by optimizing the thickness of the perovskite single crystal. The MAPbBr 3 /Ga 2 O 3 diodes also demonstrate a neutron detection efficiency of ∼3.92% when combined with a 10 B neutron conversion layer.

Single-crystal (SC) perovskite is currently a promising material due to its high quantum efficiency and long diffusion length. However, the reported perovskite photodetection range (<800 nm) and response time (>10 μs) are still limited. Here, to promote the development of perovskite-integrated optoelectronic devices, this work demonstrates wider photodetection range and shorter response time perovskite photodetector by integrating the SC CH 3 NH 3 PbBr 3 (MAPbBr 3 ) perovskite on silicon (Si). The Si/MAPbBr 3 heterojunction photodetector with an improved interface exhibits high-speed, broad-spectrum, and long-term stability performances. To the best of our knowledge, the measured detectable spectrum (405-1064 nm) largely expands the widest response range reported in previous perovskite-based photodetectors. In addition, the rise time is as fast as 520 ns, which is comparable to that of commercial germanium photodetectors. Moreover, the Si/MAPbBr 3 device can maintain excellent photocurrent performance for up to 3 months. Furthermore, typical gray scale face imaging is realized by scanning the Si/MAPbBr 3 single-pixel photodetector. This work using an ultrafast photodetector by directly integrating perovskite on Si can promote advances in next-generation integrated optoelectronic technology.

Encapsulation of luminescent perovskite quantum dots (QDs) into a solid matrix has been approved to be an efficient way to improve their stability. In this work, we reported a green encapsulation method to produce ultrastable CH 3 NH 3 PbBr 3 QDs incorporated into the SiO 2 matrix. Specifically, fresh-prepared CH 3 NH 3 PbBr 3 QDs were covalently embedded into silica by an aqueous sol-gel method assisted with CH 3 NH 3 Br, which not only effectively inhibited the water-driven degradation of QDs through surface coordination, but also strongly stabilized the QDs in solid powder via concentration gradient. As far as we know, this silica encapsulation of perovskite QDs in aqueous environments is reported for the first time. Luminescent properties of perovskite QDs during the course of gelation as well as in resulting composite powder were investigated using steady-state and time-resolved spectroscopies, and a 2 wt % QD-doped sample treated with 11.5 mM of CH 3 NH 3 Br was demonstrated to be the optimal phosphor. The green-emissive phosphor had a PLQY of 60.3% and a full width at half maxima of ∼25 nm, exhibiting ultrahigh stability tested by cycle heating (120 °C), continuous heating (80 °C, 60 h), and light irradiation (450 nm light, 350 h). The phosphor was readily blended with polymers and applied as a color-converting layer on blue light-emitting diodes.

The increasing demands for optical anti-counterfeiting technology require the development of versatile luminescent materials with multiple models and tunable photoluminescence. Herein, the combination of luminescent perovskite nanocrystals and lanthanide-based metal-organic frameworks (Ln-MOFs) has been developed to offer such a high-tech anti-counterfeiting solution. The hybrid materials have been fabricated via the encapsulation of perovskite CH 3 NH 3 PbBr 3 nanocrystals in europium-based metal-organic frameworks (Eu-MOFs) and they display multistage anti-counterfeiting behavior. CH 3 NH 3 PbBr 3 @Eu-MOF hybrids were developed in a two-step process, where the PbBr 2 @Eu-MOF precursor was formed first and, then, the composites can be formed quickly by the addition of CH 3 NH 3 Br into the precursors. Accordingly, the hybrid composites exhibited both excitation wavelength and temperature-dependent luminescence properties in the form of powders or films. Furthermore, the photoluminescence of the CH 3 NH 3 PbBr 3 @Eu-MOF composites can be quenched and recovered through water immersion and CH 3 NH 3 Br conversion, and the anti-counterfeiting applications have also been discussed. Therefore, this finding will open the opportunity to fabricate the hybrid materials with controlled photoluminescence properties, and it also acts as the emerging anti-counterfeiting materials in versatile fields.

The unstability of organolead halide perovskite under continuous illumination, moisture, and high temperature has seriously impeded its commercial development for long-period applications. Here, a facile method was developed to grow ultrastable CH 3 NH 3 PbBr 3 milliwires through the reaction of self-assembled PbBr 2 milliwire with CH 3 NH 3 Br at room temperature. The initial self-assembled PbBr 2 milliwire is that PbBr 2 complexed with dimethylformamide (DMF) molecular self-assemble into perovskite-type PbBr 2 . Crystal conversion from PbBr 2 to CH 3 NH 3 PbBr 3 milliwire occurred in the molecular exchange between CH 3 NH 3 Br and DMF. The synthesized CH 3 NH 3 PbBr 3 milliwires present high stability under high humidity ∼75%, continuous illumination, heating, and sustain ultrastability in air for more than 255 days. In addition, the CH 3 NH 3 PbBr 3 milliwire can be dynamically degraded and reconstructed in the presence of water molecules. The milliwires have strong band-edge photoluminescence (PL) with PL lifetime of ∼110 ns. On the basis of the mono-milliwire-constructed photodetector, it exhibits high photoresponse and fast response time of 0.407 s.

Metal halide perovskites have demonstrated breakthrough performances as absorber and emitter materials for photovoltaic and display applications respectively. However, despite the low manufacturing cost associated with solution-based processing, the propensity for defect formation with this technique has led to an increasing need for defect passivation. Here, we present an inexpensive and facile method to remedy surface defects through a postdeposition treatment process using branched alkylammonium cation species. The simultaneous realignment of interfacial energy levels upon incorporation of tetraethylammonium bromide onto the surface of CH 3 NH 3 PbBr 3 films contributes favorably toward the enhancement in overall light-emitting diode characteristics, achieving maximum luminance, current efficiency, and external quantum efficiency values of 11 000 cd m -2 , 0.68 cd A -1 , and 0.16 %, respectively., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The vapor-assisted solution method was developed to prepare high-quality organic-inorganic halide perovskite CH 3 NH 3 PbBr 3 (MAPbBr 3 ) thin films. We detailedly investigated the effect of evaporation time and temperature of MABr powder on the microstructure, crystallinity, and optical characterizations of MAPbBr 3 thin films, and a controllable morphology evolution with varying surface coverage was observed. Temperature-dependent and time-resolved photoluminescence measurements were carried out to investigate the optical transition mechanisms and carrier recombination dynamics of MAPbBr 3 thin films. Our results revealed that no structural phase transition occurred within the heating process (10-300 K). In addition to the exciton-related emission, a trapped charge-carrier emission appeared at a critical temperature of 140 K. The corresponding temperature sensitivity coefficient of band gap, exciton binding energy, and optical phonon energy of the MAPbBr 3 thin films were extracted from the experimental data. Furthermore, planar perovskite light-emitting diodes (PeLEDs) based on a Al/LiF/TPBi/MAPbBr 3 /NiO/ITO structure were fabricated, and a high-purity green emission at ∼532 nm with a low line width (25 nm) was achieved. The devices demonstrated remarkable performances with high luminance (6530 cd/m 2 ), current efficiency (8.16 cd/A), external quantum efficiency (4.36%), and power efficiency (4.49 lm/W). This research will provide valuable information for the preparation of high-quality perovskite thin films, facilitating their future applications in novel high-performance PeLEDs.

Organic-inorganic hybrid perovskite materials exhibit a variety of physical properties. Pronounced coupling between phonon, organic cations, and the inorganic framework suggest that these materials exhibit strong light-matter interactions. The photoinduced strain of CH 3 NH 3 PbBr 3 is investigated using high-resolution and contactless in situ Raman spectroscopy. Under illumination, the material exhibits large blue shifts in its Raman spectra that indicate significant structural deformations (i.e., photostriction). From these shifts, the photostrictive coefficient of CH 3 NH 3 PbBr 3 is calculated as 2.08 × 10 -8 m 2 W -1 at room temperature under visible light illumination. The significant photostriction of CH 3 NH 3 PbBr 3 is attributed to a combination of the photovoltaic effect and translational symmetry loss of the molecular configuration via strong translation-rotation coupling. Unlike CH 3 NH 3 PbI 3 , it is noted that the photostriction of CH 3 NH 3 PbBr 3 is extremely stable, demonstrating no signs of optical decay for at least 30 d. These results suggest the potential of CH 3 NH 3 PbBr 3 for applications in next-generation optical micro-electromechanical devices., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The inherent instability of CH 3 NH 3 PbX 3 remains a major technical barrier for the industrial applications of perovskite materials. Recently, the most stable surface structures of CH 3 NH 3 PbX 3 have been successfully characterized by using density functional theory (DFT) calculations together with the high-resolution scanning tunneling microscopy (STM) results. The two coexisting phases of the perovskite surfaces have been ascribed to the alternate orientation of the methylammonium (MA) cations. Notably, similar surface defect images (a dark depression at the sites of X atoms) have been observed on surfaces produced with various experimental methods. As such, these defects are expected to be intrinsic to the perovskite crystals and may play an important role in the structural decomposition of perovskite materials. Understanding the nature of such defects should provide some useful information toward understanding the instability of perovskite materials. Thus, we investigate the chemical identity of the surface defects systematically with first-principles density functional theory calculations and STM simulations. The calculated STM images of the Br and Br-MA vacancies are both in good agreement with the experimental measurements. In vacuum conditions, the formation energy of Br-MA is 0.43 eV less than the Br vacancy. In the presence of solvation effects, however, the formation energy of a Br vacancy becomes 0.42 eV lower than the Br-MA vacancy. In addition, at the vacancy sites, the adsorption energies of water, oxygen, and acetonitrile molecules are significantly higher than those on the pristine surfaces. This clearly demonstrated that the structural decomposition of perovskites are much easier to start from these vacancy sites than the pristine surfaces. Combining DFT calculations and STM simulations, this work reveals the chemical identities of the intrinsic defects in the CH 3 NH 3 PbX 3 perovskite crystals and their effects on the stability of perovskite materials.

The performance of hybrid perovskite-based light-emitting diodes (LEDs) is markedly enhanced by the application of a NiO x electrode interlayer and moderate methylamine treatment. A hybrid perovskite-based LED exhibits a peak luminous efficiency of 15.9 cd A -1 biased at 8.5 V, 407.65 mA cm -2 , and 65 300 cd m -2 , showing a distinctive impact for future applications., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Two-photon-pumped amplified spontaneous emission (ASE) of CH3NH3PbBr3 microdisks (MDs) were investigated by using femtosecond laser system. Low threshold at 2.2 mJ cm(-2) was obtained. Also, emission spectral tunability from 500 to 570 nm was demonstrated by synthesis the mixed halide perovskite MDs. The spatial effect of photoluminescence (PL) properties under one-photon and two-photon excitation were also studied by means of two-photon laser scanning microscope (TPLSM) and time-resolved PL spectroscopy. It was found that the band to band emission of near-surface regions and photocarriers' diffusion from near-surface regions to interior regions is significant for one-photon excitation. By contrast, reabsorption of emission under two-photon excitation plays a major role in the emission properties of the MDs. These results will give a more comprehensive understanding of the nonlinear effect of CH3NH3PbBr3 single crystals.

High-quality perovskite monocrystalline films are successfully grown through cavitation-triggered asymmetric crystallization. These films enable a simple cell structure, ITO/CH3 NH3 PbBr3 /Au, with near 100% internal quantum efficiency, promising power conversion efficiencies (PCEs) >5%, and superior stability for prototype cells. Furthermore, the monocrystalline devices using a hole-transporter-free structure yield PCEs ≈6.5%, the highest among other similar-structured CH3 NH3 PbBr3 solar cells to date., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)