Cs2 AgBiBr6 Research Articles

Application of multifunctional artificial synapse Cs2AgBiBr6 in pain simulation, Pavlov learning, letter learning and number recognition

Artificial synapses combined with artificial neural networks can develop next-generation computer framework. This computer framework has the characteristics of low energy consumption, high density, self-learning and self-storage. We designed and prepared artificial synapse based on all-inorganic perovskite Cs2AgBiBr6 (CABB). This work studies the synaptic excitatory behavior of CABB synapses in neurology. By applying electrical spikes, it can exhibit excitatory behaviors similar to biological synapses. On this basis, using its synaptic excitement, we simulated some conceived functions of human-like artificial intelligence, including pain simulation, Pavlov learning, letter learning and number recognition. After testing, it can be found that CABB synapse can complete these tasks. In order to realize number recognition, we designed a multi-layer neural network according to the weight update method of CABB synapse. It shows a recognition accuracy of 91.57 %.

Unveiling the potential of lead-free Cs2AgBiBr6 (CABB) perovskite for solar cell application

The remarkable structural stability and optoelectronic properties of Cs2AgBiBr6 (CABB) material have positioned it as a highly appealing candidate for the solar cell application. The research focused on modeling and examination of perovskite solar cells utilizing Cs2AgBiBr6 as the active material, incorporating various electron transport layers (ETL) and hole transport layers (HTL). The device structure comprised of ITO/ZnO:Al/ZnO/Cs2AgBiBr6/Cu2O/Au. This optimized device, shows Voc = 1.67 V, Jsc = 15.52 mA/cm2, fill factor (FF) = 71.32 %, and conversion efficiency = 18.5 %. Active layer defects and trap charges at the interface of the CABB layer can trap photo generated electrons and holes, permitting higher carrier recombination. That reduces both open circuit voltage and short circuit current density. The conversion efficiency deteriorates from 18.5 % to 2.65 % when the defect density increases from 1 × 1010/cm3 from 1 × 1016/cm3. Also trap charges and multiple trap charges play a vital role in the performance of the CABB solar cell.

Enhanced photocatalytic hydrogen evolution through suppressed electron–hole recombination in Cs2AgBiBr6-NC/g-C3N4 nanocomposites

One-pot in situ synthesis of 4–6 nm particles of Cs2AgBiBr6 on a g-C3N4 matrix gives a marginal enhancement in the HER from 44.9 μmol g−1 h−1 to 268 μmol g−1 h−1.

Facet-specific ligand dynamics: scaling the descriptors of Cs2AgBiBr6 nanocrystals.

Facet control by primary amines can bolster the optoelectronic parameters of A2BIB'IIIX6 perovskite nanocrystals (NCs) with large indirect bandgaps. The 18-C amine competitively attaches to the (222) facet of Cs2AgBiBr6 (CABB) NCs, 16-C and 14-C bind to (400) and (440), and 12-C binds to (400). The NCs with only the (400) facet decrease the bandgap and exciton binding energy by 0.26 eV and 15 meV, respectively.

Amine Gas-Induced Reversible Optical Bleaching of Bismuth-Based Lead-Free Perovskite Thin Films.

Reversible optical property changes in lead-free perovskites have recently received great interest due to their potential applications in smart windows, sensors, data encryption, and various on-demand devices. However, it is challenging to achieve remarkable color changes in their thin films. Here, methylamine gas (CH3 NH2 , MA0 ) induced switchable optical bleaching of bismuth (Bi)-based perovskite films is demonstrated for the first time. By exposure to an MA0 atmosphere, the color of Cs2 AgBiBr6 (CABB) films changes from yellow to transparent, and the color of Cs3 Bi2 I9 (CBI) films changes from dark red to transparent. More interestingly, the underlying reason is found to be the interactions between MA0 and Bi3+ with the formation of an amorphous liquefied transparent intermediate phase, which is different from that of lead-based perovskite systems. Moreover, the generality of this approach is demonstrated with other amine gases, including ethylamine (C2 H5 NH2 , EA0 ) and butylamine (CH3 (CH2 )3 NH2 , BA0 ), and another compound, Cs3 Sb2 I9 , by observing a similar reversible optical bleaching phenomenon. The potential for the application of CABB and CBI films in switchable smart windows is investigated. This study provides valuable insights into the interactions between amine gases and lead-free perovskites, opening up new possibilities for high-efficiency optoelectronic and stimuli-responsive applications of these emerging Bi-based materials.

Highly stable lead-free perovskite Cs2AgBiBr6/UiO-66 Z-scheme heterostructures with enhanced photocatalytic activity for CO2 photoreduction and organic dyes degradation

Excessive combustion of traditional fossil fuels causes seriously global warming (Carbon dioxide, CO2) and energy crisis. Photocatalytic CO2 conversion to fuels has emerged as one of the most effective strategies. Herein, an environmentally friendly nanocomposite based on lead-free Cs2AgBiBr6 (CABB) perovskite nanocrystals and the UiO-66 metal–organic framework was fabricated by a facile ultrasonic process for efficient CO2 photoreduction. The obtained CABB/UiO-66 consisted of uniform CABB nanocrystals (10–12 nm) attached to the UiO-66 surface and exhibited a high surface area (1031 m2/g). The composite displayed enhanced light-harvesting capacity than the individual components and provided sufficient active sites for promoting photocatalytic activity. A typical Z-scheme heterostructure between the CABB and UiO-66 was realized by forming an inner electric field, leading to the occurrence of efficient excited state charge transfer. The efficient charge transfer of CABB/UiO-66 inspired its use as an active photocatalyst for the reduction of CO2 with significantly improved photocatalytic activity against its individual components. Specifically, CABB/UiO-66 exhibited 38 and 40-fold improvement in catalytic activity compared to respective CABB and UiO-66 in terms of the total yield of CO, CH4, and C2H6. Moreover, the nanocomposite displayed excellent activity towards the oxidative photocatalytic degradation of aqueous environmental contaminant rhodamine B. We believe that this work provides a guide for designing lead-free perovskite-based renewable catalysts and offers new opportunities for the photocatalytic conversion of CO2 photoreduction.

Spray‐Coated Inorganic Lead‐Free Double Perovskite Cs2AgBiBr6 Based Large‐Scale Triboelectric Nanogenerator for Enhanced Energy Harvesting

Low‐cost and efficient large‐scale triboelectric nanogenerator (TENG) is considered as the new scheme for distributed mechanical conversion or renewable energy utilization. An extremely popular all‐inorganic lead‐free double perovskite Cs2AgBiBr6 (CABB) has emerged as extraordinary potential material in triboelectric semiconductors’ substitution, overcoming high‐impedance limitations associated with organic‐polymer‐insulator based materials. In this study, assembled by the certified available positive frictional material CABB, TENG with sandwiched structure of ITO/compact‐TiO2/mesoporous‐TiO2/CABB – the poly‐tetra‐fluoroethylene/Al exhibits appropriate performance on environmental stability and output capacity for which structure can impede charges decay. Fabrication process comparison shows that as an inexpensive large‐scale functional films preparation method, sprayed CABB TENG with brilliant relative dielectric constant and work function difference possess more distinguished output characteristics. This is confirmed by higher open‐circuit voltage of 105 V, larger short‐current density of 2.45 mA m−2 at 0.25 Hz motion parameter, and more abundant output power density of 0.76 W m−2 under 10 Hz. Further study confirms that both higher frequency and larger contact‐area are conducive to total output power, while terminal charging speed is inversely or positively proportional with capacitance or mechanical frequency. Final physical display effect of sprayed CABB TENG lights up at least 53 commercial yellow‐LEDs, holding decent energy conversion ability.

Optical Switching of Hole Transfer in Double Perovskite/Graphene Heterostructure.

Synergically combining their respective ultrahigh charge mobility and strong light absorption, graphene (Gr)/semiconductor heterostructures are promising building blocks for efficient optoelectronics, particularly photodetectors. Charge transfer (CT) across the heterostructure interface crucially determines device efficiency and functionality. Here we report that hole transfer processes dominate the ultrafast CT across strongly coupled double perovskite Cs2 AgBiBr6 /graphene (DP/Gr) heterostructures following optical excitation. While holes are the primary charges flowing across interfaces, their transfer direction, as well as efficiency, show a remarkable dependence on the excitation wavelength. For excitation with photon energies below the bandgap of DPs, the photoexcited hot holes in graphene can compete with the thermalization process and inject into in-gap defect states in DPs. In contrast, above-bandgap excitation of DP reverse the hole transfer direction, leading to hole transfer from the valence band of DPs to Gr. We further provide experimental evidence that increasing the excitation photon energy enhances CT efficiency for both below- and above-bandgap photoexcitation regimes, unveiling the positive role of excess energy in enhancing interfacial CT. The possibility of switching the hole transfer direction and, thus, the interfacial photogating field by tuning the excitation wavelength, provides a novel way to control the interfacial charge flow across a DP/Gr heterojunction. This article is protected by copyright. All rights reserved.

Lead‐Free Cs2AgBiBr6 Nanocrystals Confined in MCM‐48 Mesoporous Molecular Sieve for Efficient Photocatalytic CO2 Reduction

Exploring highly efficient and stable halide perovskite‐based materials for photocatalytic CO2 reduction is a great challenge due to their poor intrinsic instability. Coincidentally, mesoporous molecular sieves have received tremendous attention as adsorbents, catalysts, and catalyst carriers. Herein, lead‐free double perovskite of Cs2AgBiBr6 (CABB) nanocrystals are grown in situ in MCM‐48 mesoporous molecular sieve for photocatalytic CO2 reduction. A remarkable performance is achieved by the CABB@MCM‐48 composite, which far exceeds that of pristine CABB. The mechanism of the photocatalytic CO2 reduction reaction is systematically investigated by the combination of in situ diffuse reflectance infrared Fourier transform spectra and density functional theory calculations. The result indicates that the molecular sieve can not only enhance the adsorption of CO2 molecules, but also promote the CO2 activation by reducing the energy barriers. This study provides some new insights into the design of excellent perovskite/molecular sieve‐based catalysts for solar fuel applications.

NiFe-Layered Double Hydroxides/Lead-free Cs2AgBiBr6 Perovskite 2D/2D Heterojunction for Photocatalytic CO2 Conversion

Designing of heterojunction photocatalysts with appropriate interfacial contact plays crucial roles in enhancing the interfacial charge transfer/separation. A two-dimensional (2D)/2D face-to-face heterojunction is an ideal option since this architecture with a large contact area can provide abundant reactive centers and promote the interfacial charge transfer/separation between layers. Herein, a novel 2D/2D heterojunction of NiFe-layered double hydroxides (NiFe-LDH)/Cs2AgBiBr6 (CABB) was fabricated by electrostatic self-assembly of NiFe-LDH and CABB nanosheets. This unique 2D/2D architecture endowed NiFe-LDH/CABB with a large contact area and a short charge transport distance, assuring remarkable interfacial charge transfer/separation rates. As a result, the 2D/2D NiFe-LDH/CABB heterojunction exhibited significant improvement in photocatalytic CO2 reduction under visible light than the pristine counterparts. Based on density functional theory calculations and various characterizations, a step scheme charge-transfer mechanism was proposed. This investigation sheds light on the designing and manufacturing of highly efficient 2D/2D heterostructure photocatalysts for artificial photosynthesis.

Efficient Charge Transfer and Effective Active Sites in Lead-Free Halide Double Perovskite S-Scheme Heterojunctions for Photocatalytic H2 Evolution.

The practical application of lead-free double perovskite Cs2 AgBiBr6 in photocatalytic H2 evolution is still restricted due to the low activity and poor stability. The rational design of lead-free halide double perovskites heterojunctions with efficient charge transfer and effective active sites is a potential route to achieve the ideal prospect. Herein, in this work an S-scheme heterojunction of Cs2 AgBiBr6 with enriched Br-vacancies and WO3 nanorods (VBr -Cs2 AgBiBr6 /WO3 ) obtaining excellent visible-light responsive photocatalytic H2 evolution performance and durable stability is reported. The S-scheme heterojunction driven by the unaligned Fermi levels of these two semiconductors ensures the efficient charge transfer at the interface, and density functional theory calculations reveal the enriched Br vacancies on Cs2 AgBiBr6 (022) surfaces introduced by atom thermal vibration provide effective active sites for hydrogen evolution. The optimized VBr -Cs2 AgBiBr6 /WO3 S-scheme photocatalyst exhibits the photocatalytic hydrogen evolution rate of 364.89µmol g-1 h-1 which is 4.9-fold of bare VBr -Cs2 AgBiBr6 (74.44µmol g-1 h-1 ) and presents long-term stability of 12h continuous photocatalytic reaction. This work provides deep insights into the photocatalytic mechanism of VBr -Cs2 AgBiBr6 /WO3 S-scheme heterojunctions, which emerges a new strategy in the applications of perovskite-based photocatalysts.

In situ growth of lead-free perovskite Cs2AgBiBr6 on a flexible ultrathin carbon nitride sheet for highly efficient photocatalytic benzylic C(sp3)−H bond activation

The selective conversion of organic pollutant toluene to high-value-added benzaldehyde and benzyl alcohol using green chemistry is of high research interest. However, the process remains challenging owing to the low adsorption of toluene molecules on the catalyst surface and the high dissociation energy of the C(sp3)−H bond. In this study, we developed an in situ assembly strategy to grow lead-free perovskite Cs2AgBiBr6 (CABB) on a flexible ultrathin carbon nitride sheet (UCNT) using an anti-solvent method, whereby a series of type II heterojunction structures of CABB-x@UCNT were constructed. This in situ preparation strategy enables UCNT to act as a nucleation site, thereby limiting the size of the CABB nanocrystals grown on it. In addition, the interfacial interaction between CABB and UCNT in the composite accelerates the separation of photogenerated carriers, which further facilitates electron-driven O2 reduction and hole-driven C(sp3)−H bond oxidation. Under simulated sunlight irradiation, the CABB-80@UCNT composite could effectively oxidize toluene to benzaldehyde and benzyl alcohol with a total conversion rate of 2630 μmol g−1 h−1, which is 10.7 and 6 times higher that of UCNT and CABB, respectively, and the reaction selectivity exceeds 85%. Herein, we report that CABB-x@UCNT composites achieve efficient benzylic C(sp3)−H bond activation, expand the photocatalytic application of CABB, and provide new ideas for developing various types of in situ heterojunction systems.

High Open-Circuit Voltage Cs2 AgBiBr6 Carbon-Based Perovskite Solar Cells via Green Processing of Ultrasonic Spray-Coated Carbon Electrodes from Waste Tire Sources.

Costs and toxicity concerns are at the center of a heated debate regarding the implementation of perovskite solar cells (PSCs) into commercial products. The first bottleneck could be overcome by eliminating the top metal electrode (generally gold) and the underlying hole transporting material and substituting both with one single thick layer of conductive carbon, as in the so-called carbon-based PSCs (C-PSCs). The second issue, related to the presence of lead, can be tackled by resorting to other perovskite structures based on less toxic metallic components. An interesting case is that of the double perovskite Cs2 AgBiBr6 , which at present still lacks the outstanding optoelectronic performances of the lead-based counterparts but is very stable to environmental factors. In this work, the processing of carbon electrodes onto Cs2 AgBiBr6 -based C-PSCs was reported, starting from an additive-free isopropanol ink of a carbon material obtained from the hydrothermal recycling of waste tires and employing a high-throughput ultrasonic spray coating method in normal environmental conditions. Through this highly sustainable approach that ensures a valuable step from an end-of-life to an end-of-waste status for used tires, devices were obtained delivering a record open circuit voltage of 1.293 V, which might in the future represent ultra-cheap solutions to power the indoor Internet of Things ecosystem.

Efficient and Selective Electroreduction of CO2 to HCOOH over Bismuth-Based Bromide Perovskites in Acidic Electrolytes.

Metal halide perovskites, primarily used as optoelectronic devices, have not been applied for electrochemical conversion due to their insufficient stability in moisture. Herein, two bismuth-based perovskites are introduced as novel electrocatalysts to convert CO2 into HCOOH in aqueous acidic media (pH 2.5), exhibiting a high Faradaic efficiency for HCOOH of >80 % in a wide potential range from -0.75 to -1.25 V. Their structural evolution against water was dynamically monitored by in situ spectra. Theoretical calculations further reveal that the formation of intermediate OCHO* on bismuth sites of Cs3 Bi2 Br9 (111) play a pivotal role toward HCOOH production, which has a lower energy barrier than that on Cs2 AgBiBr6 (001) surfaces. Significantly, CO2 reacts with protons instead of water which can enhance CO2 reduction rate and suppress hydrogen evolution by avoiding carbonate formation in acidic electrolytes. This work paves the way for the extensive investigation of halide perovskites in aqueous systems.

Self-Assembly of 2D Hybrid Double Perovskites on 3D Cs2 AgBiBr6 Crystals towards Ultrasensitive Detection of Weak Polarized Light.

We report the self-assembly of 2D double perovskite (BLA)2 CsAgBiBr7 (BLA=benzylammonium) on 3D Cs2 AgBiBr6 crystals, providing the first demonstration of polarization-sensitive photodetection using lead-free double perovskite heterocrystals (HCs). The (BLA)2 CsAgBiBr7 /Cs2 AgBiBr6 HC successfully combines the anisotropy of 2D double perovskites with the well-defined interface provided by heterogeneous integration. Driven by the built-in electric field in junction, photodetectors of HCs exhibit unique polarization dependence of zero-bias photocurrent with a large anisotropy ratio up to 9, which is 6 times amplified as compared to the pristine 2D (BLA)2 CsAgBiBr7 . More importantly, the present devices can remain polarization-sensitive with incident light intensity down to the nW cm-2 level. Our study on lead-free hybrid perovskite HCs marks a step toward establishing robust material foundations for fundamental scientific investigations and the development of optoelectronic devices.

Thermochromic Cs2 AgBiBr6 Single Crystal with Decreased Band Gap through Order-Disorder Transition.

Lead-free Cs2 AgBiBr6 double perovskite is considered to be a promising alternative to the traditional lead-based analogues due to its long carrier lifetime, high structural stability, and non-toxicity. However, the large band gap limits its absorption of visible light, which is not conducive to further optoelectronic applications. Herein, a thermochromic strategy is reported to decrease the band gap of Cs2 AgBiBr6 by approximately 0.36eV, obtaining the smallest reported band gap of 1.69eV under ambient conditions. The experimental data indicate that after annealing the Cs2 AgBiBr6 single crystals at 400°C, the silver (Ag) and bismuth (Bi) atoms occupy the B-site in a random way and form a partially disordered configuration. The formation of the antisite defects broadens the band edges and decreases the band gap. This work offers new insights into the preparation of narrow band gap lead-free double perovskites, and a deep understanding of their structural and electronic properties for further development in photoelectric devices.

Ultralow-Power Machine Vision with Self-Powered Sensor Reservoir.

A neuromorphic visual system integrating optoelectronic synapses to perform the in‐sensor computing is triggering a revolution due to the reduction of latency and energy consumption. Here it is demonstrated that the dwell time of photon‐generated carriers in the space‐charge region can be effectively extended by embedding a potential well on the shoulder of Schottky energy barrier. It permits the nonlinear interaction of photocurrents stimulated by spatiotemporal optical signals, which is necessary for in‐sensor reservoir computing (RC). The machine vision with the sensor reservoir constituted by designed self‐powered Au/P(VDF‐TrFE)/Cs2AgBiBr6/ITO devices is competent for both static and dynamic vision tasks. It shows an accuracy of 99.97% for face classification and 100% for dynamic vehicle flow recognition. The in‐sensor RC system takes advantage of near‐zero energy consumption in the reservoir, resulting in decades‐time lower training costs than a conventional neural network. This work paves the way for ultralow‐power machine vision using photonic devices.

Diverging Expressions of Anharmonicity in Halide Perovskites.

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2 AgBiBr6 , has been recently studied as a lead-free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead-based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead-based halide perovskites, the structural dynamics of Cs2 AgBiBr6 are investigated and are compared to its lead-based analog, CsPbBr3 . Using temperature-dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs2 AgBiBr6 has well-defined normal modes throughout the measured temperature range, while CsPbBr3 exhibits a complete breakdown of the normal-mode picture above 200K. It is suggested that the breakdown of the normal-mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to ourmain findings, an unreported phase of Cs2 AgBiBr6 is also discovered below≈37K.

Recombination and localization: Unfolding the pathways behind conductivity losses in Cs2AgBiBr6 thin films

Cs2AgBiBr6 (CABB) has been proposed as a promising nontoxic alternative to lead halide perovskites. However, low charge carrier collection efficiencies remain an obstacle for the incorporation of this material in optoelectronic applications. In this work, we study the optoelectronic properties of CABB thin films using steady state and transient absorption and reflectance spectroscopy. We find that optical measurements on such thin films are distorted as a consequence of multiple reflections within the film. Moreover, we discuss the pathways behind conductivity loss in these thin films, using a combination of microsecond transient absorption spectroscopy and time-resolved microwave conductivity measurements. We demonstrate that a combined effect of carrier loss and localization results in the conductivity loss in CABB thin films. Moreover, we find that the charge carrier diffusion length and grain size are of the same order of magnitude. This suggests that the material's surface is an important contributor to charge-carrier loss.

Tuning the Structural and Optoelectronic Properties of Cs2 AgBiBr6 Double-Perovskite Single Crystals through Alkali-Metal Substitution.

Lead-free double perovskites have great potential as stable and nontoxic optoelectronic materials. Recently, Cs2 AgBiBr6 has emerged as a promising material, with suboptimal photon-to-charge carrier conversion efficiency, yet well suited for high-energy photon-detection applications. Here, the optoelectronic and structural properties of pure Cs2 AgBiBr6 and alkali-metal-substituted (Cs1- x Yx )2 AgBiBr6 (Y: Rb+ , K+ , Na+ ; x= 0.02) single crystals are investigated. Strikingly, alkali-substitution entails a tunability to the material system in its response to X-rays and structural properties that is most strongly revealed in Rb-substituted compounds whose X-ray sensitivity outperforms other double-perovskite-based devices reported. While the fundamental nature and magnitude of the bandgap remains unchanged, the alkali-substituted materials exhibit a threefold boost in their fundamental carrier recombination lifetime at room temperature. Moreover, an enhanced electron-acoustic phonon scattering is found compared to Cs2 AgBiBr6 . The study thus paves the way for employing cation substitution to tune the properties of double perovskites toward a new material platform for optoelectronics.