All-inorganic CsPbBr3 Perovskite Research Articles

Free and self-trapped exciton emission in perovskite CsPbBr3 microcrystals.

The all-inorganic perovskite CsPbBr3 has been capturing extensive attention due to its high quantum yield in luminescence devices and relatively high stability. Its luminescence is dominated by free exciton (FE) recombination but additional emission peaks were also commonly observed. In this work, a CsPbBr3 microcrystal sample in the orthorhombic phase was prepared by the chemical vapor deposition method. In addition to the FE peak, a broad emission peak was found in this sample and it was attributed to self-trapped excitons (STEs) based on its photophysical properties. The STE emission can only be observed below 70 K. The derived Huang–Rhys factor is ∼12 and the corresponding phonon energy is 15.3 meV. Its lifetime is 123 ns at 10 K, much longer than that of FE emission. The STE emission is thought to be an intrinsic property of CsPbBr3.

Synthesis and characterization of all-inorganic (CsPbBr3) perovskite single crystals

This work investigates the synthesis of Cesium (Cs) based all-inorganic (CsPbBr3) perovskite single crystals (PSCs) at low temperatures (45 °C) for application in photosensitive devices.

One-pot synthesis of stable and functional hydrophilic CsPbBr3 perovskite quantum dots for "turn-on" fluorescence detection of Mycobacterium tuberculosis.

All-inorganic CsPbBr3 perovskite quantum dots (QDs) are widely studied owing to their excellent optoelectronic properties; however, they are usually hydrophobic and unstable in water and thus their biomedical applications are seriously limited. In this study, stable and hydrophilic CsPbBr3 QDs functionalized with carboxyl groups (CsPbBr3-COOH QDs) were prepared in one-pot with the aid of new ligands amino-poly(ethylene glycol)-carboxyl and perfluorooctyltriethoxylsilane. The aqueous solution of CsPbBr3-COOH QDs maintained the initial fluorescence intensity after 8 days of storage; the free carboxyl groups on the surface of CsPbBr3-COOH QDs were covalently conjugated with amino-terminal DNA to construct CsPbBr3 QDs-DNA probes for subsequent application. Then, a biosensing platform utilizing fluorescence resonance energy transfer between hydrophilic CsPbBr3 QDs-DNA and MoS2 nanosheets was developed for the sensitive and selective detection of the Mycobacterium tuberculosis DNA with a low limit of detection of 51.9 pM and the identification of drug-resistant clinical strains. This study advances the preparation of hydrophilic carboxyl-functionalized CsPbBr3 QDs with enhanced stability and extends their application in biomolecule detection.

Phase Control of Cs-Pb-Br Derivatives to Suppress 0D Cs4 PbBr6 for High-Efficiency and Stable All-Inorganic CsPbBr3 Perovskite Solar Cells.

The precise phase control of Cs-Pb-Br derivatives from 3D CsPbBr3 to 0D Cs4 PbBr6 highly determines the photovoltaic performance of all-inorganic CsPbBr3 perovskite solar cells (PSCs). Herein, the preferred phase conversion from precursor to Cs-Pb-Br derivatives is revealed by theoretically calculating the Gibbs free energies (∆G) of various phase conversion processes, allowing for a simplified multi-step solution-processable spin-coating method to hinder the formation of detrimental 0D Cs4 PbBr6 phase and enhance the photovoltaic performance of a PSC because of its large exciton binding energy, which is regarded as a recombination center. By further accelerating the interfacial charge extraction with a novel 2D transition metal dichalcogenide ReSe2 , the hole-free CsPbBr3 PSC achieves a champion efficiency of 10.67% with an impressive open-circuit voltage of 1.622V and an excellent long-term stability. This work provides an in-depth understanding on the precise Cs-Pb-Br perovskite phase control and the effect of derivatives on photovoltaic performance of advanced CsPbBr3 PSCs.

Single Crystal Halide Perovskite Film for Nonlinear Resistive Memory with Ultrahigh Switching Ratio.

Morre's law is coming to an end only if the memory industry can keep stuffing the devices with new functionality. Halide perovskite acts as a promising candidate for application in next-generation nonvolatile memory. As is well known, the switching ratio is the key device requirement of resistive memory to improve recognition accuracy. Here, the authors introduce an all-inorganic halide perovskite CsPbBr3 single crystal film (SCF) into resistive memory as an active layer. The Ag/CsPbBr3 /Ag memory cells exhibit reproducible resistive switching with an ultrahigh switching ratio (over 109 ) and a fast switching speed (1.8µs). It is studied that the Schottky barrier of metal/CsPbBr3 SCF contact follows the tendency of Schottky-Mott theory, and the Fermi level pinning effect is effectively reduced. The interface S parameter of metal/CsPbBr3 SCF contact is 0.50, suggesting a great interface contact is formed. The great interface contact contributes to the steady high resistance state (HRS), and then the steady HRS leads to an ultrahigh resistive switching ratio. This work demonstrates high performance from halide perovskite SCF-based memory. The introduction of halide perovskite SCF in resistive random access memory provides great potential as an alternative in future computing systems.

Insights into the adsorption of water and oxygen on the cubic CsPbBr3 surfaces: A first-principles study

The degradation mechanism of the all-inorganic perovskite solar cells in the ambient environment remains unclear. In this paper, water and oxygen molecule adsorptions on the all-inorganic perovskite (CsPbBr3) surface are studied by density-functional theory calculations. In terms of the adsorption energy, the water molecules are more susceptible than the oxygen molecules to be adsorbed on the CsPbBr3 surface. The water molecules can be adsorbed on both the CsBr- and PbBr-terminated surfaces, but the oxygen molecules tend to be selectively adsorbed on the CsBr-terminated surface instead of the PbBr-terminated one due to the significant adsorption energy difference. While the adsorbed water molecules only contribute deep states, the oxygen molecules introduce interfacial states inside the bandgap of the perovskite, which would significantly impact the chemical and transport properties of the perovskite. Therefore, special attention should be paid to reduce the oxygen concentration in the environment during the device fabrication process so as to improve the stability and performance of the CsPbBr3-based devices.

High performance hybrid MXene nanosheet/CsPbBr3 quantum dot photodetectors with an excellent stability

All-inorganic CsPbBr3 perovskite quantum dots (QDs) are considered as a new generation of photoelectric material for the implementations in photodetection owing to their remarkable optoelectronic properties and optimized stability. However, the combination of the abundant trap states and unfavorable carrier transportation poses a critical hurdle for the fabrication of high- performance photodetectors. In this study, a facile strategy to significantly enhance the performance of CsPbBr3 QD photodetectors via evenly blending 2D Ti3C2TX nanosheets is systematically demonstrated. The uniformly distributed Ti3C2TX nanosheets successfully confine incident fugacious photons throughout CsPbBr3 QD thin films as a result of the spontaneously intensified surface electromagnetic fields, and the transportation of photogenerated carriers from CsPbBr3 QDs are simultaneously accelerated due to the high conductivity and well-matched work function of the nanosheets. Meanwhile, the hot electrons excited from the nanosheets can also partially contribute to the increase in photocurrent, and thereby the performance of the device sensitively develops as a function of the concentration of the nanosheets. Correspondingly, a 300% enhancement is equally observed with external quantum efficiency and responsivity of the CsPbBr3 QD/MXene nanosheet photodetectors in comparison with the pristine one under 490 nm light illumination for a long period of 4 months in the atmospheric environment.

All-inorganic CsPbBr3 perovskite as potential electrode material for symmetric supercapacitor

Widening the possibilities of all-inorganic perovskite materials beyond well-investigated optoelectronic aspects, in this work it has been introduced as a potential electrode material for supercapacitors. Adopting an ambient condition, low-cost, solution processable facile approach we have prepared cesium lead bromide perovskite (CsPbBr3) rod shaped sample. As fabricated electrodes based on CsPbBr3 were subjected to cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) and electronic impedance spectroscopy (EIS) test. It offered good electrochemical features with specific capacitance of 121 F/g at the scan rate of 5 mV/s. Aqueous symmetric supercapacitor (SSC) with this electrode exhibited significant capacitive retention ∼73% of its initial capacitance even after 5000 charging and discharging cycles. Electrochemical behaviour registered form the CsPbBr3 is explained in details on the basis of diffusion-controlled process. Such results of the devised supercapacitors show its promises in other electrochemical applications and will pave a pathway to develop new perovskite materials for supercapacitors.

Electric Field Induced Electrorotation of 2D Perovskite Microplates.

High precision-controlled movement of microscale devices is crucial to obtain advanced miniaturized motors. In this work, we report a high-speed rotating micromotor based on two-dimensional (2D) all-inorganic perovskite CsPbBr3 microplates controlled via alternating-current (AC) external electric field. Firstly, the device configuration with optimized electric field distribution has been determined via systematic physical simulation. Using this optimized biasing configuration, when an AC electric field is applied at the four-electrode system, the microplates suspended in the tetradecane solution rotate at a speed inversely proportional to AC frequency, with a maximum speed of 16.4 × 2π rad/s. Furthermore, the electrical conductivity of CsPbBr3 microplates has been determined in a contactless manner, which is approximately 10−9–10−8 S/m. Our work has extended the investigations on AC electric field-controlled micromotors from 1D to 2D scale, shedding new light on developing micromotors with new configuration.

Surfactant-Free Synthesis of the Full Inorganic Perovskite CsPbBr3: Evolution and Phase Stability of CsPbBr3 vs CsPb2Br5 and Their Photocatalytic Properties

In the present study, the successful fabrication, through a surfactant-free one-pot synthesis in ethanol solution, of the all-inorganic halide perovskite CsPbBr3 has been achieved. The phase formation has been obtained for the first time, using the β-diketonate complexes [Pb(hfa)2diglyme]2 and Cs(hfa) (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = 2-methoxyethyl ether) and Br2 as the precipitating agent. The growth of CsPb2Br5 microcrystals has been obtained and stabilized under specific synthetic conditions, by controlling the phase transition from CsPbBr3 to CsPb2Br5 as well. The entire process was operated under acid-catalyzed conditions without any need of humidity control and hazardous organic solvents. The control of the aging time and the phase stability during the heat treatment represent the key points in order to selectively and reproducibly obtain the CsPbBr3 or CsPb2Br5 phases. Structural, morphological, and compositional characterizations of the final product show the formation of square microcrystals, with a grain size of up to 3 μm, of the pure and stable perovskite CsPbBr3 phase. Finally, promising results in photocatalytic degradation tests using rhodamine B solution have been obtained under UV light (λ = 360 nm) and visible light, showing high degradation yields of up to 81.9% and 58.4% for CsPbBr3 and CsPb2Br5, respectively.

Inorganic Ruddlesden-Popper Faults in Cesium Lead Bromide Perovskite Nanocrystals for Enhanced Optoelectronic Performance.

While the layered hybrid Ruddlesden-Popper (RP) halide perovskites have already established themselves as the frontrunners among the candidates in optoelectronics, their all-inorganic counterparts remain least explored in the RP-type perovskite family. Herein, we study and compare the optoelectronic properties of all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) with and without RP planar faults. We find that the RP-CsPbBr3 PNCs possess both higher exciton binding energy and longer exciton lifetimes. The former is ascribed to a quantum confinement effect in the PNCs induced by the RP faults. The latter is attributed to a spatial electron-hole separation across the RP faults. A striking difference is found in the up-conversion photoluminescence response in the two types of CsPbBr3 PNCs. For the first time, all-inorganic RP-CsPbBr3 PNCs are tested in light-emitting devices and shown to significantly outperform the non-RP CsPbBr3 PNCs.

Solution Epitaxy of Halide Perovskite Thin Single Crystals for Stable Transistors.

Halide perovskites hold promise for energy and optoelectronic applications due to their fascinating photophysical properties and facile processing. Among various forms, epitaxial thin single crystals (TSCs) are highly desirable due to their high crystallinity, reduced defects, and easy epitaxial integration with other materials. However, a cost-effective method for obtaining TSCs with perfect epitaxial features remains elusive. Here, we demonstrate a direct epitaxial growth of high-quality all-inorganic perovskite CsPbBr3 TSCs on various substrates through a facile solution process under near-ambient conditions. Structural characterizations reveal a high-quality epitaxy between the obtained perovskite TSCs and substrates, thus leading to efficiently reduced defects. The resultant TSCs display a low trap density (∼1011 cm-3) and a long carrier lifetime (∼10.16 ns). Top-gate/top-contact transistors based on these TSCs exhibit high on/off ratios of over 105, an optimal hole mobility of 3.9 cm2 V-1 s-1, almost hysteresis-free operation, and high stability at room temperature. Such a facile approach for the high-yield production of perovskite epitaxial TSCs will enable a broad range of high-performance electronic applications.

All-inorganic perovskite quantum dot light-emitting memories

Field-induced ionic motions in all-inorganic CsPbBr3 perovskite quantum dots (QDs) strongly dictate not only their electro-optical characteristics but also the ultimate optoelectronic device performance. Here, we show that the functionality of a single Ag/CsPbBr3/ITO device can be actively switched on a sub-millisecond scale from a resistive random-access memory (RRAM) to a light-emitting electrochemical cell (LEC), or vice versa, by simply modulating its bias polarity. We then realize for the first time a fast, all-perovskite light-emitting memory (LEM) operating at 5 kHz by pairing such two identical devices in series, in which one functions as an RRAM to electrically read the encoded data while the other simultaneously as an LEC for a parallel, non-contact optical reading. We further show that the digital status of the LEM can be perceived in real time from its emission color. Our work opens up a completely new horizon for more advanced all-inorganic perovskite optoelectronic technologies.

Large-area CsPbBr3 perovskite films grown with effective one-step RF-magnetron sputtering

In this work, we demonstrated the large-area film growth of all-inorganic perovskite CsPbBr3 with semiconductor industry compatible radio frequency magneton sputtering technology. This approach avoids the use of toxic organic solvents, which are required extensively for the solution growth process of these perovskite films. Even on ordinary glass substrates, the CsPbBr3 film of 100 cm2 with a single phase and ultra-smooth surface can be grown under optimized sputtering conditions, among which the substrate temperature is proved very important. Temperature-dependent photoluminescence spectra and femtosecond transient absorption spectra studies show that no subband defect levels are observed in such perovskite films. The temperature-dependent resistivity measurement exhibits a typical thermally activated electrical behavior, and a bandgap of 2.24 eV is obtained, which is consistent with the optical measurements. Therefore, both the optical and electrical studies indicate that the CsPbBr3 film with high optical quality can be grown with effective one-step sputtering technology.

Carbon Nanodots as a Potential Transport Layer for Boosting Performance of All-Inorganic Perovskite Nanocrystals-Based Photodetector

A low-cost and simple drop-casting method was used to fabricate a carbon nanodot (C-dot)/all-inorganic perovskite (CsPbBr3) nanosheet bilayer heterojunction photodetector on a SiO2/Si substrate. The C-dot/perovskite bilayer heterojunction photodetector shows a high performance with a responsivity (R) of 1.09 A/W, almost five times higher than that of a CsPbBr3-based photodetector (0.21 A/W). In addition, the hybrid photodetector exhibits a fast response speed of 1.318/1.342 µs and a highly stable photocurrent of 6.97 µA at 10 V bias voltage. These figures of merits are comparable with, or much better than, most reported perovskite heterojunction photodetectors. UV–Vis absorption and photoluminescent spectra measurements reveal that the C-dot/perovskite bilayer heterojunction has a band gap similar to the pure perovskite layer, confirming that the absorption and emission in the bilayer heterojunction is dominated by the top layer of the perovskite. Moreover, the emission intensity of the C-dot/perovskite bilayer heterojunction is less than that of the pure perovskite layer, indicating that a significant number of charges were extracted by the C-dot layer. The studied band alignment of the C-dots and perovskites in the dark and under emission reveals that the photodetector has a highly efficient charge separation mechanism at the C-dot/perovskite interface, where the recombination rate between photogenerated electrons and holes is significantly reduced. This highly efficient charge separation mechanism is the main reason behind the enhanced performance of the C-dot/perovskite bilayer heterojunction photodetector.

All-inorganic CsPbBr3 perovskite solar cells with enhanced efficiency by exploiting lone pair electrons via passivation of crystal boundary using carbon nitride (g-C3N4) nanosheets

Fast extraction of photo-generated charge plays a crucial function in improving the photovoltaic conversion efficiency (PCE) of the perovskite solar cells (PSCs). Here, an effective strategy to decrease the charge recombination losses by introducing versatile carbon nitride (g-C3N4) nanosheets to the CsPbBr3 films was demonstrated. The incorporation of the g-C3N4 additive can restrain the nucleation and crystalline growth rate of perovskite films by an interaction of lone pair electrons from the exposed N atoms to the PbBr2 precursor, resulting in high-quality CsPbBr3 films with an increase in crystalline size. Notably, a ‘coupling effect’ between the lone pair electrons from g-C3N4 nanosheets and unsaturated Pb dangling bonds (Br vacancies) around the grain boundaries significantly decreases trap states caused by defects, leading to the fewer recombination centers in CsPbBr3 films. The g-C3N4 nanosheets serving as an energy barrier can also successfully suppress the recombination loss of back electrons with holes from the g-C3N4 interface, yielding a superior PCE of 8.0% with a fill factor of 80.25%. The result opens an alternative path to enhance the performance of CsPbBr3 PSCs by passivating the trap states of perovskite films with the improvement of the crystallization quality and charge extraction efficiency.

All-inorganic CsPbBr3 thin-film solar cells prepared by single-source physical vapor deposition

Long-term stability and large-area are key to the commercialization of perovskite solar cells, and the all-inorganic perovskite CsPbBr3 has higher stability compared to organic-inorganic hybrid perovskites. In this work, a simple single-source physical vapor deposition (SSPVD) method is proposed for the evaporation of CsPbBr3 crystal powder to deposit high-quality all-inorganic CsPbBr3 perovskite thin films. The results show that the CsPbBr3 thin films prepared by SSPVD are dense and uniform, with high crystallinity and full surface coverage. After annealing optimization, high-quality CsPbBr3 thin films with good crystallinity and uniformity were obtained. The CsPbBr3 thin film has a high visible absorption coefficient and an optical forbidden bandwidth of 2.33 eV. The CsPbBr3 perovskite thin-film solar cells prepared based on the SSPVD method have a photoelectric conversion efficiency (PCE) of 1.37% with good reproducibility and high stability. These results tentatively suggest that SSPVD is a promising method for preparing high-quality all-inorganic perovskite CsPbBr3 thin films for solar cell applications.

The mechanism of alkali doping in CsPbBr3: A first-principles perspective

All-inorganic CsPbBr3 perovskite doped with alkali metal atoms has been attracting increasing attention due to its superior optoelectronic properties. However, there still exists significant uncertainty regarding the doping mechanism. One view of the mechanism is that alkali metal atoms tend to substitute Cs in CsPbBr3 crystals. Another view is that Li and Na tend to intercalate into interstitial sites because their radii are much smaller than that of Cs. To elucidate the doping mechanism, it is necessary to investigate the point defects physics of alkali metal elements in CsPbBr3. In this work, by using first-principles calculations we find that alkali metal atoms energetically prefer to substitute for Cs or Pb atoms in CsPbBr3 crystals under different chemical potential conditions. To determine the alkali metal atoms doping site, one should consider the chemical potential of synthesis conditions, the dopant valence states, and atomic radii. Notably, alkali metal atoms doping mainly introduces shallow levels, which is helpful for improving the p-type conductivity of CsPbBr3.

An excellent impedance-type humidity sensor based on halide perovskite CsPbBr3 nanoparticles for human respiration monitoring

Abstract Humidity sensors with fast response, high accuracy and low-power consumption are critical importance in smart home and health monitoring applications. Herein, we demonstrate an excellent impedance relative humidity sensor based on all-inorganic halide perovskite CsPbBr3 nanoparticles (NPs) under low working-voltage (20 mV). The CsPbBr3 NPs humidity sensor exhibits fast response and recovery behavior at room temperature. Moreover, the sensor demonstrates excellent repeatability, low hysteresis and good stability. The humidity sensing mechanism of CsPbBr3 NPs is further studied and discussed by employing an electrochemical impedance spectroscopy measurement. Furthermore, the respiratory monitoring face mask based on CsPbBr3 humidity sensor shows accurate and stable performance, suggesting perovskite CsPbBr3 NPs based humidity sensor have great potential in future real-time health status monitoring applications.

Dimensionality Control of SnO2 Films for Hysteresis-Free, All-Inorganic CsPbBr3 Perovskite Solar Cells with Efficiency Exceeding 10.

The all-inorganic cesium lead bromide (CsPbBr3) perovskite solar cells (PSCs) have attracted considerable interest because of their outstanding environmental stability and low manufacturing cost. However, the state-of-the-art mesoscopic titanium dioxide (TiO2) electron-transporting layers (ETLs) always present low electron mobility, are destructive to perovskites under ultraviolet light illumination, as well as possess high sintering temperature. Nanostructured tin dioxide (SnO2) is a promising electron-transporting material for high-efficiency PSCs due to matching energy-level alignment with the perovskite layer, improved optical transparency, high electron mobility, excellent photostability, and low-temperature processing. Furthermore, rapid but poorly controlled perovskite crystallization makes it difficult to scale up planar PSCs for industrial applications. To address this issue, we adopt a dimensional SnO2 ETL to change the surface wettability for uniform perovskite coverage over large areas and the growth of large-sized CsPbBr3 grains, resulting in a maximum grain size of 1.65 μm. Moreover, the dimensional SnO2 ETL could increase the interfacial contact area between the CsPbBr3 layer and the ETL and enhance the electronic contact for efficient electron extraction to suppress or to eliminate the notorious hysteresis behavior. As expected, a power conversion efficiency (PCE) of 9.51% with an almost hysteresis-free phenomenon is achieved through dimensionality control of SnO2 films attributed to the remarkably enhanced light harvesting, accelerated electron extraction, diminished defect density, and reduced charge recombination. Upon further interfacial modification with graphene quantum dots (GQDs), the PSC based on the two-dimensional SnO2 ETL achieves a champion PCE of 10.34% due to the improved energy-level alignment at the device interface. Moreover, the best all-inorganic CsPbBr3 PSC free of encapsulation retains 93% of initial efficiency over 10 days at 80% relative humidity. This work provides an effective dimensionality control strategy for optimized charge transportation and enlarged perovskite grain size to make stable and efficient all-inorganic CsPbBr3 PSCs.