Formamidinium Lead Bromide Perovskite Research Articles

Fine‐Tuning Crystal Structures of Lead Bromide Perovskite Nanocrystals through Trace Cadmium(II) Doping for Efficient Color‐Saturated Green LEDs

AbstractDecreasing perovskite nanocrystal size increases radiative recombination due to the quantum confinement effect, but also increases the Auger recombination rate which leads to carrier imbalance in the emitting layers of electroluminescent devices. Here, we overcome this trade‐off by increasing the exciton effective mass without affecting the size, which is realized through the trace Cd2+ doping of formamidinium lead bromide perovskite nanocrystals. We observe an ~2.7 times increase in the exciton binding energy benefiting from a slight distortion of the [BX6]4− octahedra caused by doping in the case of that the Auger recombination rate is almost unchanged. As a result, bright color‐saturated green emitting perovskite nanocrystals with a photoluminescence quantum yield of 96 % are obtained. Cd2+ doping also shifts up the energy levels of the nanocrystals, relative to the Fermi level so that heavily n‐doped emitters convert into only slightly n‐doped ones; this boosts the charge injection efficiency of the corresponding light‐emitting diodes. The light‐emitting devices based on those nanocrystals reached a high external quantum efficiency of 29.4 % corresponding to a current efficiency of 123 cd A−1, and showed dramatically improved device lifetime, with a narrow bandwidth of 22 nm and Commission Internationale de I'Eclairage coordinates of (0.20, 0.76) for color‐saturated green emission for the electroluminescence peak centered at 534 nm, thus being fully compliant with the latest standard for wide color gamut displays.

Fine-Tuning Crystal Structures of Lead Bromide Perovskite Nanocrystals through Trace Cadmium(II) Doping for Efficient Color-Saturated Green LEDs.

Decreasing perovskite nanocrystal size increases radiative recombination due to the quantum confinement effect, but also increases the Auger recombination rate which leads to carrier imbalance in the emitting layers of electroluminescent devices. Here, we overcome this trade-off by increasing the exciton effective mass without affecting the size, which is realized through the trace Cd2+ doping of formamidinium lead bromide perovskite nanocrystals. We observe an ~2.7 times increase in the exciton binding energy benefiting from a slight distortion of the [BX6]4- octahedra caused by doping in the case of that the Auger recombination rate is almost unchanged. As a result, bright color-saturated green emitting perovskite nanocrystals with a photoluminescence quantum yield of 96 % are obtained. Cd2+ doping also shifts up the energy levels of the nanocrystals, relative to the Fermi level so that heavily n-doped emitters convert into only slightly n-doped ones; this boosts the charge injection efficiency of the corresponding light-emitting diodes. The light-emitting devices based on those nanocrystals reached a high external quantum efficiency of 29.4 % corresponding to a current efficiency of 123 cd A-1, and showed dramatically improved device lifetime, with a narrow bandwidth of 22 nm and Commission Internationale de I'Eclairage coordinates of (0.20, 0.76) for color-saturated green emission for the electroluminescence peak centered at 534 nm, thus being fully compliant with the latest standard for wide color gamut displays.

Composite of formamidinium lead bromide perovskite FAPbBr3 with reduced graphene oxide (rGO) for efficient H2 evolution from HBr splitting

Solar hydrobromic acid (HBr) splitting using perovskite photocatalysts provides an attractive avenue to store solar energy into hydrogen (H2) and bromine (Br2), while an efficient photocatalytic system is still demanded. As for the semiconductor photocatalyst, formamidinium perovskites show some superiorities in structural stability, light adsorption and charge dynamics compared to their methylammonium counterparts, which are fitter for the photocatalysis process. Herein, the composite of formamidinium lead bromide perovskite (FAPbBr3) with reduced graphene oxide (rGO) is prepared using a facile photoreduction method. Under simulated sunlight irradiation (AM1.5G, 100 mW cm−2), this FAPbBr3/rGO composite (100 mg) demonstrates a noteworthy enhancement in photocatalytic H2 evolution activity of 386.7 μmol h−1, and it exhibits a notable stability with no significant decrease after 50 h of repeated tests. The single particle PL (photoluminescence) microscope is employed to study the charge dynamics, revealing that rGO in the composite effectively promotes the carrier separation. This work provides a highly efficient and stable photocatalyst for HBr splitting, and offers an effective modification strategy on lead bromide perovskites.

Fabrication for formanmidinium lead bromide perovskite for light emission

In recent decades, perovskite semiconductors have been developed rapidly with excellent performance in light-emitting diodes (LEDs) and solar cells (SCs). Recent reports indicated that both the highest external quantum efficiency (EQE) of perovskite materials (PEM) that can be used for light-emitting diodes and the power conversion efficiency (PCE) of perovskite solar cells have reached a very high value compared to the previous. In this study, electroluminescence from formamidinium lead bromide perovskite is presented. The spin-coating method was used to procedure simple devices with a fluorine-doped tin oxide/formamidinium lead bromide perovskite/fluorine-doped tin oxide structure. The structure showed a green luminescence with the center wavelength at 545 nm. In the future, we will study the fabrication of devices with the structural layers: fluorine-doped tin oxide / poly(3,4-ethylene dioxythiophene) : poly(styrene sulfonate) / perovskite / electron transport layer / Ag to create so-called PeLEDs.

Unveiling the Electronic Band Structure and Temporal Dynamics of Excited Carriers in Formamidinium Lead Bromide Perovskite

AbstractIn this study, the electronic band structure and the dynamics of the excited carriers in the formamidinium lead bromide (FAPbBr3) perovskite are investigated by combining the information obtained from steady‐state absorption, photoluminescence, femtosecond transient absorption spectroscopy, photoelectron spectroscopy, and density functional theory calculations. A detailed description of the electronic transitions in the UV–vis energy range has been provided, giving an estimation of the exciton binding energy (40 ± 5 meV), the transition energy from the first valence band (VB1) to the conduction band (CB1) (electronic bandgap at 2.37 ± 0.01 eV) and assigning the broad peak at ≈3.4 eV to the transition from the second innermost valence band (VB2) to CB1. The temporal dynamics of the excited carriers involved in these transitions are investigated using different excitation energies and carrier densities. Different trends are observed in the dynamics of the transient signals associated with the VB1→CB1 (PB1) and VB2→CB1 (PB2) transitions. As the carrier density increased, PB1 exhibited a slowing down of its rise time, while PB2 showed an acceleration attributed to the thermalization of the excited holes in VB2. These valuable findings have the potential to unlock new strategies aimed at maximizing the efficiencies and performance of perovskite‐based solar cell devices.

FAPbBr3@PbBr(OH) phosphor with high stability for anti-counterfeiting application via water induction

Organic–inorganic hybrid perovskite nanocrystals have become a very widely used as semiconductor light-emitting materials. However, perovskite nanocrystals face stability challenges, which is a key factor hindering their application. In this paper, by introducing water into the synthesis of formamidinium lead bromide (FAPbBr3) perovskite, ultra-stable FAPbBr3@PbBr(OH) fluorescent material was prepared. The photoluminescence intensity of the material after the addition of water increased 2.9 times compared with that before the addition of water. The excellent green fluorescence emission was still maintained after four cycles of wash–dry treatment. Meanwhile, it also exhibits good ultraviolet and thermal stability. The above enhanced performance of FAPbBr3 nanocrystals is attributed the protection of PbBr(OH). In addition, the prepared material can be used in anti-counterfeit patterns. The anti-counterfeit patterns have good color rendering and the luminous color has a high dependence on temperature. Both of these features make it very valuable for various fluorescent anti-counterfeiting labels.

Printable High-efficiency and Stable FAPbBr3 Perovskite Solar Cells for Multifunctional Building-integrated Photovoltaics.

Perovskite solar cells (PSCs) show great promise for next-generation building-integrated photovoltaic (BIPV) applications because of their abundance of raw materials, adjustable transparency, and cost-effective printable processing. Owing to the complex perovskite nucleation and growth control, the fabrication of large-area perovskite films for high-performance printed PSCs is still under active investigation. Herein, wepropose an intermediate-phase-transition-assisted one-step blade coating for an intrinsic transparent formamidinium lead bromide (FAPbBr3 ) perovskite film. The intermediate complex optimized the crystal growth path of FAPbBr3 , resulting in a large-area, homogeneous, and dense absorber film. A champion efficiency of 10.86% with high open-circuit voltage up to 1.57V wasobtained with a simplified device architecture of glass/FTO/SnO2 /FAPbBr3 /carbon. Moreover, the unencapsulated devices maintained 90% of their initial power conversion efficiency after aging at 75°C for 1000h in ambient air, and 96% after maximum power point tracking for 500h. The printed semitransparent PSCs, with average visible light transmittance over 45%, demonstrated high efficiencies for both small devices (8.6%) and 10 × 10 cm2 modules (5.55%). Finally, the ability to customize the color, transparency, and thermal insulation properties of FAPbBr3 PSCs makes them high prospects as multifunctional BIPVs. This article is protected by copyright. All rights reserved.

Optimization of precursor concentration in formamidinium lead bromide thin films for perovskite-based light-emitting diode applications

Formamidinium lead bromide perovskite (FAPbBr3) are known as promising materials for light emitting diode (LED) applications in green range of electromagnetic waves due to their excellent optical and electrical properties and photoluminescence maxima located in 520–540 nm range. LED device performance based on FAPbBr3 is hindered by crystallinity of the film and morphological issues. In this study, we fabricated green FAPbBr3 LEDs using a two-step preparation method. We used thermal evaporation method to deposit PbBr2 films and then perovskite films were formed after spin coating FA solution on evaporated samples. By controlling the solution concentration, we obtained thin films with optimized morphology and grain size which resulted in LED device with green electroluminescence (EL). Turn-on voltage (and threshold voltage) is of importance. Lower threshold voltage and/or turn-on voltage is desirable for electronic devices. The EL spectrum has a full width at half-maximum (FWHM) parameter as narrow as 36 nm, a turn-on voltage of 2 V, and a luminance of 100 Cd cm−2. Moreover, the issue of color is very important in Pe-LED, and therefore, our finding is important. The novelty of the work is that to our knowledge, no one has obtained this value with the present synthesize method (Solution process method).

Self-assembled halide perovskite quantum dots in polymer thin films showing temperature-controlled exciton recombination.

Rationally assembled supramolecular structures of organic chromophores or semiconductor nanomaterials show excitonic properties different from individual molecules or nanoparticles. We report polymer-assisted assembly formation and thermal modulation of excitonic recombination in self-assembled formamidinium lead bromide perovskite quantum dots.

Highly Stable Lasing from Solution‐Epitaxially Grown Formamidinium‐Lead‐Bromide Micro‐Resonators

AbstractHigh‐quality epitaxial growth of oriented microcrystallites on a semiconductor substrate is demonstrated here for formamidinium lead bromide perovskite, by drop casting of precursor solutions in air. The microcrystallites exhibit green photoluminescence at room temperature, as well as lasing with low thresholds. Lasing is observed even though the substrate is fully opaque at the lasing wavelengths, and even though it has a higher refractive index as the perovskite active material. Moreover, the lasing is stable for more than 109 excitation pulses, which is more than what is previously achieved for devices kept in the air. Such highly stable lasing under pulsed excitation represents an important step towards continuous mode operation or even electrical excitation in future perovskite‐based devices.

High‐Performance Non‐Volatile Flash Photomemory via Highly Oriented Quasi‐2D Perovskite

AbstractSolution‐processable organic–inorganic hybrid perovskite materials have been applied to a variety of optoelectronic devices due to its long exciton lifetime and small binding energy. It has emerged as promising front‐runners for next‐generation non‐volatile flash photomemory devices. However, the effect of crystal orientation of perovskite on the performance of photomemory still has not fully developed. Herein, non‐volatile flash photomemory with quasi‐2D perovskite/polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) as photoactive floating‐gate and p‐type semiconductor poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) as the chare‐transporting layer is successfully demonstrated. By adding phenylethylammonium bromide (PEABr) in formamidinium lead bromide perovskite (FAPbBr3), the crystal orientation of quasi‐2D perovskite is highly improved, which results in raised charge transfer efficiency from 76% to 90% compared to the pure FAPbBr3. Furthermore, ON/OFF current ratio of 104, low photo‐programming time of 5 ms under light intensity of 0.85 mW cm−2, charge transfer rate of 0.063 ns−1, and data storage capacity of over 7 bits (128 levels) in one cell can be achieved. In addition, the correlation between photo‐responsive current and photoluminescence (PL) is first examined by in operando PL measurement, which provides a new platform to explore the charge transfer process in photomemory.

Influence of adding 5-ammonium valeric acid bomide on the linear and nonlinear optical properties of formamidinium lead bromide perovskite films

Formamidinium lead bromide films doped with 5-Ammonium Valeric Acid Bromide, (FA)1-x(AVABr)xPbBr3 (0 ≤ x ≤ 0.25), were prepared using the spin coating method. X-ray diffraction analysis revealed that the percentage of α-FAPbBr3 to δ-FAPbBr3 phases is dependent on the amount of AVABr. The effect of increasing the concentration of AVABr in the formed film on the absorption band edge, absorbance, reflection, transmittance, absorption coefficient, extinction coefficient, refractive index, (real and imaginary) parts of the dielectric constant, (surface and volume) energy loss functions, (optical and electric) conductivities, and non-linear optical parameters (NLO) behaviors was studied in detail. All films displayed a limited reflection in the visible range (under 18%). The transmittance of the films doped with 5 and 10% AVABr became 83 and 85% as compared with the FAPbBr3 film (72%) at 600 nm. The optical band gap changed slightly between 2.26 and 2.29 eV depending on the amount of AVABr in the film. The high values of σopt and σele for the films doped with 5 and 10% AVABr are good indicators for the possible application of both films in optoelectronic applications. Films containing 5 and 10% AVABr have the highest NLO values. All films exhibited a single asymmetry peak located in the green emission range (542–549 nm).

Low temperature synthesis of ultra-green luminescent colloidal FAPbBr3 perovskite nanocrystals

According to the updated recommendation for displays standard (Rec. 2020), ultrapure green emitters with a narrow emission (below 25 nm) in the 525–535 nm spectral range are desired. However, finding an emitter material that can meet such requirements, is still challenging. To this purpose, organic–inorganic halide perovskites nanocrystals have been considered as promising high-color purity light emitters at a lower cost, that overcome the issues associated with conventional emitters. Herein, to reach these standards simultaneously, we have synthesized Formamidinium lead bromide perovskite nanocrystals (NCs) at room temperature by ligand-assisted reprecipitation (LARP). The obtained FAPbBr3 NCs coated with oleic acid and oleylamine show an average size of about 20 nm. FAPbBr3 NCs dispersions in hexane exhibited bright photoluminescence with a high quantum yield (74%). The color coordinates on CIE 1931 are (0.2, 0.75), with a corresponding strong green emission at 533 nm. The emission is characterized by an ultranarrow full width at half-maximum (FWHM = 22 nm), and long radiative lifetimes (≈82 ns). The synthesized FAPbBr3 NCs present ideal features toward solution-processable ultrapure green emitters.

Investigation of Threshold Carrier Densities in the Optically Pumped Amplified Spontaneous Emission of Formamidinium Lead Bromide Perovskite Using Different Excitation Wavelengths

The high crystal quality of formamidium lead bromide perovskite (CH(NH2)2PbBr3 = FAPbBr3) was infiltrated in a mesoporous TiO2 network. Then, high-quality FAPbBr3 films were evaluated as active lasing media, and were irradiated with a picosecond pulsed laser to demonstrate amplified spontaneous emission (ASE), which is a better benchmark of its intrinsic suitability for gain applications. The behavior was investigated using two excitation wavelengths of 440 nm and 500 nm. Due to the wavelength-dependent absorbance spectrum and the presence of a surface adsorption layer that could be reduced using the shorter 440 nm wavelength, the ASE power dependence was strongly reliant on the excitation wavelength. The ASE state was achieved with a threshold energy density of ~200 µJ/cm2 under 440 nm excitation. Excitation at 500 nm, on the other hand, needed a higher threshold energy density of ~255 µJ/cm2. The ASE threshold carrier density, on the other hand, was expected to be ~4.5 × 1018 cm−3 for both excitations. A redshift of the ASE peak was detected as bandgap renormalization (BGR), and a BGR constant of ~5–7 × 10−9 eV cm was obtained.

In-situ growth behavior of FAPbBr3 on two-dimensional materials for photocatalytic reaction to controllable products

Constructing mixed dimensional materials have been regarded as an outstanding approach to maximum the advantages from materials of different dimensions. In this work, we prepared a mixed dimensional photocatalyst based on Formamidinium lead bromide (FAPbBr3) perovskite and 2D materials (2DMs). The aim of this work is to utilize distributions of the active sites in 2DMs, through growing FAPbBr3 on the different position of 2DMs, the concentration of photogenerated charges is manipulated, thus conducting different reactions. A pre-treatment using HBr to increase the unsaturated bonds in MoS2 presents significant influence on the FAPbBr3 growth and its photocatalytic product. The scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) confirm that the perovskite nanoparticles were well loaded on the 2D materials. The photocatalytic process and the heterojunction arrangement are demonstrated by X-ray photoelectron spectroscopy (XPS), time-resolved photoluminescence (TRPL), electron paramagnetic resonance (EPR) and surface photovoltage microscopy (SPVM). By adjusting the weight ratios and growth of FAPbBr3 on the top of 2DMs, the optimized composite photocatalyst (with 30 wt% of FAPbBr3) exhibits remarkable photoactivity for oxidation of benzyl alcohol into benzaldehyde (30 wt% FAPbBr3@WS2 performed 75.9% conversion in 4 h, approximately 9-fold than the pure 2DMs). Meanwhile, by growing FAPbBr3 on the edge of 2DMs, benzoic acid is obtained as the product. Although longer reaction time is needed, the photocatalyst performs outstanding activity (30 wt% FAPbBr3@MoS2 reached 84.5% conversion in 5 h).

Radiative lifetime-encoded unicolour security tags using perovskite nanocrystals

Traditional fluorescence-based tags, used for anticounterfeiting, rely on primitive pattern matching and visual identification; additional covert security features such as fluorescent lifetime or pattern masking are advantageous if fraud is to be deterred. Herein, we present an electrohydrodynamically printed unicolour multi-fluorescent-lifetime security tag system composed of lifetime-tunable lead-halide perovskite nanocrystals that can be deciphered with both existing time-correlated single-photon counting fluorescence-lifetime imaging microscopy and a novel time-of-flight prototype. We find that unicolour or matching emission wavelength materials can be prepared through cation-engineering with the partial substitution of formamidinium for ethylenediammonium to generate “hollow” formamidinium lead bromide perovskite nanocrystals; these materials can be successfully printed into fluorescence-lifetime-encoded-quick-read tags that are protected from conventional readers. Furthermore, we also demonstrate that a portable, cost-effective time-of-flight fluorescence-lifetime imaging prototype can also decipher these codes. A single comprehensive approach combining these innovations may be eventually deployed to protect both producers and consumers.

Hydrobromic acid-assisted size control of formamidinium lead bromide perovskite quantum dots at room temperature

Formamidinium lead bromide perovskite (FAPbBr3) nanostructures have aroused increasing attention considering their excellent optoelectronic performance and higher stability than their MA- and Cs-based counterparts. Herein, we synthesized size-tunable FAPbBr3 quantum dots (QDs) at room temperature. The size of the perovskite QDs could be ajusted from 5.4 to 2.3 nm by just varying the amount of Hydrobromic Acid (HBr) added into the precursor. As a result, the photoluminescence (PL) emissions exhibited large blueshift from 531 to 446 nm due to quantum confinement effect. Quantum mechanical calculations of the optical gap fitted well with the experimental results. We found that the addition of HBr not only increased the concentration of the Br− but also protonated the oleylamine ligands. The two events synergically governed the size-decreasing effect of the QDs with increasing amount of HBr. The size-tunable FAPbBr3 QDs showed great application prospect in the field of photoelectric devices.

Synthesis of brightly luminescent colloidal formamidinium lead bromide perovskite FAPbBr3 nanoplatelets with tunable emission

Hybrid halide perovskites are semicondoctor materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology. They have size-tunable emissions due to quantum size effects. In this work, the Formamidinium Lead Bromide perovskite CH(NH2)2PbBr3 nanoplatelets (NPLs) were successfully synthesized by ligand-assisted reprecipitation method under room condition, in which the emission color-tunability was realized via quantum size effect without anion–halide mixing, by varying the oleylamine to oleic acid volume ratio as surfactants, while the total amount of oleic acid remained unchanged. We are able to adjust the optical proprieties of FAPbBr3 NPLs and, consequently, their structural properties. The obtained colloidal solutions of FAPbBr3 nanoplatelets with uniform size exhibited different photoluminescence wavelengths covering the spectral region from 440 to 525 nm. The maximum absolute PL quantum yield (PLQY) of the green emission was measured to be as high as 80% at room temperature. The size of FAPbBr3 NPLs could be effectively tuned from 15.5 to 38.1 nm with an increase in the oleylamine and oleic acid ligands ratio.

The synthesis and characterisation of the highly stable perovskite nano crystals and their application to ink-jet printed colour conversion layers

We synthesised cesium lead bromide and formamidinium lead bromide perovskite colloidal nanocrystals by ligand-assisted reprecipitation method for the wide-colour gamut low-cost displays. The prepared perovskite colloidal nanocrystal solutions were formulated into the ink-jet printable homogeneous inks and uniformly coated as the colour conversion layers of the quantum dot organic light-emitting diode displays. The silica capped CsPbBr3 nanocrystals were very stable in high temperature observation while the FAPbBr3 showed the excellent long-term stability at room temperature even without the silica passivation. The ink-jet printed colour conversion films had very narrow full-width-at-half-maximums of around 20nm and high photoluminescence quantum yields of 73.0% and 76.9%, respectively. Particularly, the FAPbBr3 thin film had an excellent cut-off ratio of blue emission and exhibited external quantum efficiency of 5.39% when fabricated as the hybrid display devices.

Light-Induced Defect Healing and Strong Many-Body Interactions in Formamidinium Lead Bromide Perovskite Nanocrystals.

Organic lead halide perovskite (OLHP) nanocrystals (NCs) have paved the way to advanced optoelectronic devices through their extraordinary electrical and optical properties. However, understanding of the light-induced complex dynamic phenomena in OLHP NCs remains a subject of debate. Here we used wide field microscopy and time-resolved spectroscopy to correlate the local changes in photophysics and the dynamical behavior of photocarriers. We demonstrate that light-induced brightening of the photoluminescence from the formamidinium lead bromide NC films is related to the film preparation condition and reduction of trap density. The density of trap states is reduced via halide ion migration from interstitial position. Our femtosecond transient absorption study identifies transient Stark effect due to the generation of hot carriers. Because of slow carrier trapping, Auger recombination through many-body carrier-carrier interactions dominates over trion recombination. This work presents unprecedented insights into the light-driven processes enabling better device design in the future.