Two-Step Chemical Vapor Deposition-Synthesized Lead-Free All-Inorganic Cs3Sb2Br9 Perovskite Microplates for Optoelectronic Applications

Cs2AgSbI6 Nanocrystals: a New Air-Stable Iodide Double-Perovskite (Elpasolite) Semiconductor

Three-dimensional (3D) iodide double perovskites (elpasolites) are extremely rare due to inherent instability issues. Here, we report the discovery of an air-stable iodide elpasolite semiconductor in the form of nanocrystals with the composition Cs2AgSbI6, synthesized via halide exchange from Cs2AgSbBr6 nanocrystals. This composition, previously considered thermodynamically unstable based on computational predictions, shows a ∼1.8 eV optical gap with near-infrared photoluminescence. The nanocrystals are stable in air up to at least 140 °C. As one of only a few known examples of intermediate-bandgap 3D iodide double perovskites, Cs2AgSbI6 represents a promising platform for further development of this family of materials as well as for fundamental and optoelectronic investigations.

Variable Valence Ce-Based Cs2CeAgBr6 Perovskite Nanocrystals for Highly Selective Photoconversion of CO2 to CH4

Lead halide perovskites demonstrate outstanding luminescent characteristics. However, the inclusion of lead components restricts their extensive utilization. Halide perovskite materials, formulated as A2M(III)M(I)X6 or A2M(IV)X6, possess the potential to serve as stable and eco-friendly substitutes for optoelectronic applications. Nevertheless, their wide bandgap (>3 eV) hinders the practical implementation across various domains. Here, the variable valence Ce-based Cs₂CeAgBr₆ perovskite nanocrystals (NCs) are first synthesized with a bandgap of 2.65 eV. Intriguingly, the coexistence of trivalent and tetravalent Ce can cause localized spin of the f-layer electrons of Ce, leading to Ce3+/4+ (the Ce valence state ranges between III and IV) defects. By manipulating trivalent and tetravalent Ce source proportions, a dual Ce-based perovskite achieves a minimal Ce3+/4+ defect content of 1.4%. The as-prepared Cs₂CeAgBr₆ NCs exhibit exceptional efficiency in CO2 reduction driven by sunlight, with a CH4 selectivity greater than 70% and a super high charge transfer rate of 802.5 µmol·g-1 h-1, far surpassing previously reported findings. Additionally, theoretical calculations have elucidated the photocatalytic mechanism involved in CO₂ reduction. The outcomes of this investigation are expected to stimulate design and fabrication of novel lead-free perovskite nanocrystals.

Structurally and Electronically Anisotropic Nature of Bridgman-Grown Cs3Sb2Br9 Perovskite Single Crystal toward Efficient Photodetector

Cs3Sb2Br9, as a sort of novel lead-free perovskite single crystal, has the merits of high carrier mobility and a long diffusion length. However, the large-sized and high-crystallized Cs3Sb2Br9 single crystals are not easily obtained. Herein, we apply the vertical Bridgman method to grow centimeter-sized Cs3Sb2Br9 single crystal. The temperature-dependent crystal structure of Cs3Sb2Br9 is in situ characterized in the temperature range of 100-400 K. A novel crystallographic and electronic structure anisotropy of the as-grown Cs3Sb2Br9 single crystal along the transmission directions of [100] and [001] is experimentally and theoretically proved. Owing to the layered two-dimensional (2D) structure of Cs3Sb2Br9, quantum confinement effects prolong the lifetime of hot carriers, leading to their accumulation within the Sb-Br plane along the [100] direction, thereby resulting in a higher density of electronic states. Accordingly, the [100] device exhibits a carrier mobility higher than that of the [001] device, with the [100] device mobility being 4 orders of magnitude higher than that of the [001] device at 423 K, showing a remarkable anisotropy. The [100] device also shows responsivity ∼10 times higher than that of the [001] device.

Visible-Light Photodetection by Zero-Dimensional Hybrid Indium-Halide with Minimal Structural Distortion and Reduced Band Gap

Perovskite-inspired zero-dimensional (0D) hybrid halides exhibit impressive light emission properties; however, their potential in photovoltaics is hindered by the absence of interconnection between the inorganic polyhedra, leading to acute radiative recombination and insufficient charge separation. We demonstrate that incorporating closely-spaced dissimilar polyhedral units with minimal structural distortion leads to a remarkable enhancement in visible-light photodetection capability. We designed 0D C24H72N8In2Br14 (HIB) with a tetragonal crystal system, replacing the Cs+ of Cs2InBr5.H2O (CIB) with 1,6-hexanediammonium (HDA) cation. HIB comprises [InBr6]3- octahedra, and [InBr4]- tetrahedra units spaced 3.9 Å apart by the HDA linker. The [InBr4]- unit is additionally linked to HDA via intercalated bromine through hydrogen and halogen bonding interactions, respectively. This structural arrangement lowers the dielectric confinement, thereby enhancing carrier density and mobility, and increasing the diffusion coefficient compared to CIB. With 3.6 % bromine vacancy within the [InBr4]- block, mid-gap states are created, reducing the direct band gap to 2.19 eV. HIB demonstrates an unprecedently high responsivity of 9975.9±201.6 mA W-1 under 3 V potential bias at 485 nm wavelength, among low-dimensional hybrid halides. In the absence of potential bias, the self-powered photodetection parameters are 81.2±3.0 mA W-1 and (6.98±0.21)×109 Jones.

Advancements in Scaling Up Perovskite Solar Cells: From Small-Area Devices to Large-Scale Modules

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded those of conventional thin-film solar cell technologies, and the speed at which this increase has been achieved is unprecedented in the history of photovoltaics. Despite the significant progress achieved by PSCs at the laboratory level, their commercial prospects still face two significant challenges: scaling up in size and ensuring long-term stability. Small-area devices (~1 cm2) are typically fabricated using spin-coating. However, this approach may not be suitable for preparing the large-area (>100 cm2) substrates required for commercialization. Thus, new materials and methods must be developed to facilitate the coating of large-area PSCs. This review will discuss the development of scaling up organic-inorganic hybrid PSCs and the challenges of increasing the device area. Furthermore, it will provide an overview of the methodologies for achieving high-efficiency perovskite solar modules.

Composites of (NH2)-MIL-53(Al) and CBB as bifunctional electrocatalysts for overall electrochemical water splitting in all pH solutions

Electrochemical water splitting is one of the most active areas of energy research, yet the benchmark electrocatalysts used for this area are based on expensive noble metals and transition metals, thus mainly reactions in alkaline solution. MOFs and halide perovskite are novel electrochemical catalysts but unstable in water basically. Here we report a study on composites of (NH2)-MIL-53(Al) MOFs and CBB halide perovskite (Cs3Bi2Br9), which exhibit obvious activity for overall electrochemical water splitting for long-term stability with little deactivation after 10 h in all pH solutions.

New visible-light-driven Bi2MoO6/Cs3Sb2Br9 heterostructure for selective photocatalytic oxidation of toluene to benzaldehyde

Herein, new Bi2MoO6/Cs3Sb2Br9 heterostructure (BiMo/CSB) was investigated for the first time as a visible-light-driven photocatalyst for C(sp3)-H bond activation using molecular oxygen as a green oxidant and toluene as a model substrate. The optimized BiMo/CSB photocatalyst exhibited enhanced toluene oxidation activity (2,346 μmol g-1h-1), which was almost two- and five-fold that of pristine CSB (1,165 μmol g-1h-1) and BiMo (482 μmol g-1h-1), respectively. The improved photocatalytic performance was essentially attributed to the formation of staggered band energy lineup in the BiMo/CSB hybrid, which promoted S-scheme charge transfer across the BiMo/CSB heterointerface as supported by ultraviolet photoelectron spectroscopy (UPS), density functional theoretical (DFT), time-resolve photoluminescence (TRPL), and photoelectrochemical studies. Spin-trapping electron paramagnetic resonance (EPR) and radical scavenging studies revealed that photoinduced hole, molecular oxygen, and superoxide radical are key active species in this photocatalytic system. The developed BiMo/CSB catalyst provided good selectivity toward benzaldehyde product (94-98 %), presumably due to the inhibiting effect of benzyl alcohol on benzaldehyde oxidation. No significant change in structure and morphology was observed for the spent catalyst, however small negative shift of Sb 3d and Bi 4f binding energy was found suggesting partial reduction of Sb3+ and Bi3+. This work not only provides a new visible-light-driven photocatalyst for C(sp3)-H bond activation but also opens the doors for exploitation of the conversion and functionalization of this inert bond toward the production of high value-added organic chemicals.

A Dual-Functional Perovskite-Based Photodetector and Memristor for Visual Memory

The imitation of human visual memory demands the multifunctional integration of light sensors similar to the eyes, and image memory, similar to the brain. Although humans have already implemented electronic devices with visual memory functions, these devices require a combination of various components and logical circuits. However, the combination of visual perception and high-performance information storage capabilities into a single device to achieve visual memory remains challenging. In this study, inspired by the function of human visual memory, a dual-functional perovskite-based photodetector (PD) and memristor are designed to realize visual perception and memory capacities. As a PD, it realizes an ultrahigh self-powered responsivity of 276 mA W-1 , a high detectivity of 4.7 × 1011  Jones (530 nm; light intensities, 2.34 mW cm-2 ), and a high rectification ratio of ≈100 (±2 V). As a memristor, an ultrahigh on/off ratio (≈105 ), an ultralow power consumption of 3 × 10-11  W, a low setting voltage (0.15 V), and a long retention time (>7000 s) are realized. Moreover, the dual-functional device has the capacity to perceive and remember light paths and store data with good cyclic stability. This device exhibits perceptual and cyclic erasable memory functions, which provides new opportunities for mimicking human visual memory in future multifunctional applications.

Synthesis of Efficient and Stable Tetrabutylammonium Copper Halides with Dual Emissions for Warm White Light-Emitting Diodes

In order to achieve a high color-rendering index (CRI) and low correlated color temperature (CCT) indoor lighting, single-component phosphors with broad-band dual emission are in high demand for white-light-emitting diodes (WLEDs). However, phosphors with such fluorescent properties are rare at present. Herein, we report a facile solid-state chemical method for the synthesis of single-component phosphor with broad-band emission and a large Stokes shift that can meet the requirements of future white-light sources. These new tetrabutylammonium copper halides phosphors have excellent warm white emission characteristics, and their luminescence peaks are located at 494 and 654 nm. The optimized photoluminescence (PL) quantum yield can reach 93.7 %. The typical CIE coordinate of the as-fabricated WLED is at (0.3620, 0.3731) with a CRI of 89 and low CCT of 4516 K.

Unraveling the Defect-Dominated Broadband Emission Mechanisms in (001)-Preferred Two-Dimensional Layered Antimony-Halide Perovskite Film

By adding molar-controlled SbCl₃ in a Cs₃Sb₂Cl₉ precursor, we employed a low-temperature solution-processed approach to prepare high-quality (001)-preferred Cs₃Sb₂Cl₉ thin film, which demonstrates a stable defect-dominated broadband emission at room temperature. Density functional theory calculations reveal that the defect emission originates from the donor-acceptor pair (DAP) recombination between chlorine vacancy (V_Cl) and cesium vacancy (V_Cs). Furthermore, V_Cl + V_Cs DAP is more stable on the (001) surface. The improved film quality and the more stable V_Cl + V_Cs DAP increase the activation energy related to defect states, resulting in an enhancement of the defect emission for the high-quality (001)-preferred film. This work provides deep insight into the key role of the (001) surface in defect emission and a feasible strategy to enhance the defect emission in 2D halide perovskites A₃B₂X₉ (A = CH₃NH₃, Cs, Rb; B = Bi, Sb; X = Cl, Br, I) by control of the thin film preferred orientation.