Recent Advancements and Challenges for Low-Toxicity Perovskite Materials

Exposed (111) Plane Engineered of Lead-Free Perovskite Cs2SnCl6 Octahedra for DMC Sensing in LIB Electrolyte Leakage Detection

Dimethyl carbonate (DMC), as a major component of electrolytes, can be used as a marker for monitoring electrolyte leakage in lithium-ion batteries (LIBs). Herein, lead-free perovskite Cs2SnCl6 octahedra with (111) plane as the exposed surface are synthesized by a simple antisolvent method and the gas sensor based on these octahedra shows excellent adsorption performance for DMC molecules. The response value for 100 ppm DMC is 7.05 and response/recovery time is 82 s/83 s, as well as almost no degradation in performance during a one-month stability test. DFT calculations of the density of states and band structure reveal the adsorption of DMC molecules on perovskite surface. And it is first proposed that the adsorption conformations of DMC molecules have a significant influence on the adsorption energy. In situ infrared absorption spectrometry demonstrates the adsorption and decomposition process of DMC molecules. This mechanism provides crucial insights for the essence of lead-free perovskite gas sensing, while offering the guidance for designing high-performance lead-free perovskite gas sensing materials.

Perovskite CsCuClxBr3-x Microcrystals: Band Structure, Photochemical Stability, and Photocatalytic Properties

Although Pb-based metal halide perovskites (MHPs) have excellent photoelectric characteristics, its toxicity remains a limiting factor for its widespread application. In the paper, a series of CsCuClxBr3-x (x=1, 2, 3) MHPs microcrystals were developed and their hydrogen evolution performance in ethanol and HX (X=Cl, Br) were also studied. Among them, CsCuCl3 microcrystals exhibit high hydrogen evolution performance in both HX and ethanol, attributed to its longest average lifetime and suitable band structure. Additionally, the effect of different sacrificial agents on photocatalytic hydrogen production indicates that the photogenerated hole (h+) plays a critical role. MHPs can maintain a dynamic equilibrium of dissolution and precipitation in HX saturated aqueous solutions, thereby overcoming the stability issues associated with perovskite. The phase transition of CsCuClxBr3-x during photocatalysis is monitored by XRD technique. CsCuCl3 shows high stability in saturated HCl aqueous solution, and excellent photocatalytic performance with a hydrogen production rate of CsCuCl3 microcrystals reached 103.98 μmol g-1 at 210 min. Our study expands the development prospects of CsCuCl3 in the field of photocatalytic solar fuel generation.

Multiple Interactions in Polar Lead-Free Perovskites toward Highly Stable X-Ray Detection

Lead-free halide perovskites have emerged as a promising class of high-performance "green" X-ray detecting semiconductors due to their nontoxicity and strong X-ray absorption. However, ion migration caused by high operating electric field remains a bottleneck limiting the long-term stability of perovskite X-ray detectors. Herein, by introducing multiple halogen interactions in lead-free perovskites, stable X-ray detection is successfully realized. Specifically, 0D polar bismuth halide perovskites (R/S-BPEA)4Bi2I10 (1R/1S, R/S-BPEA = R/S-1-(4-bromophenyl)ethylammonium) are designed by introducing Br-substituted chiral organic cation BPEA, which exists with the molecular electrostatic forces between the Br atom and neighboring benzene ring and halogen interaction of Br···I. Notably, their introduction improves the activation energy of ion migration, which makes the dark current drift of the X-ray detector as low as 3.25 × 10-8 nA cm-1 s-1 V-1 at 2500 V cm-1. Furthermore, the excellent operational stability under prolonged X-ray irradiation and unchanged device sensitivity after 90 days of exposure to air, further demonstrates the improved stability of perovskites. Meanwhile, the chiral-polar characteristic of the 1R/1S gives them potential for self-powered detection, with a low detection limit of 183 nGy s-1 at zero bias for single-crystal devices. This study opens new avenues for the future development of "green", highly stable, self-powered radiation detectors.

Wide Bandgap Perovskites: A Comprehensive Review of Recent Developments and Innovations

Recent advances in wide-bandgap (WBG) perovskite solar cells (PSCs) demonstrate a burgeoning potential to significantly enhance photovoltaic efficiencies beyond the Shockley-Queisser limit for single-junction cells. This review explores the multifaceted improvements in WBG PSCs, focusing on novel compositions, halide substitution strategies, and innovative device architectures. The substitution of iodine with bromine and organic ions such as FA and MA with Cs in the perovskite lattice is emphasized for its effectiveness in achieving higher open-circuit voltages and reduced thermalization losses. Furthermore, the integration of advanced charge transport layers and interface engineering techniques is discussed as critical to minimizing open-circuit voltage (VOC) deficits and improving the photo-stability of these cells. The utilization of WBG PSCs in diverse applications such as semitransparent devices, indoor photovoltaics, and multijunction tandem devices is also explored, addressing both their current limitations and potential solutions. The review culminates in a comprehensive assessment of the current challenges impeding the industrial scale-up of WBG PSC technology and offers a perspective on future research directions aimed at realizing highly efficient and stable WBG PSCs for commercial photovoltaic applications.

Full-Color Gamut White Light Emission From Mn-doped Cs3Cu2X5 Nanocrystals via Lattice Engineering

Cs3Cu2X5-based lead-free material (X = Cl, Br, and I) nanocrystals (NCs) are promising eco-friendly materials for various optoelectronic applications. Although manganese (Mn2+) ion doping into Cs3Cu2X5 may widen the emission color gamut, incorporating them is challenging because of the robust tetrahedral [CuX4] and triangular [CuX3] structures. This paper addresses this challenge using a lattice engineering strategy, which induces appropriate lattice shrinkage by replacing I- with Cl- in the Cs3Cu2I5 NC structure. The promotion effect of Cl- substitution on the Mn2+ doping is confirmed by structural and chemical analysis, indicating the formation of highly crystalline NCs. The Mn-doping modifies the electronic structures of Cs3Cu2X5 by reducing the band gap energy and forming effective energy transition pathways. The emission range of the NCs is expanded from blue to orange and finally manifest full-color gamut white light emission. The continuous broad spectrum is attributed to the combined blue emission of self-trapped excitons and the yellow-orange emission of the Mn2+ d-d energy transition. A white light-emitting diode with Mn-doped Cs3Cu2X5 NCs as a color conversion layer exhibit stable white emission with CIE coordinates of (0.34, 0.32) and a correlated color temperature of 5010 K, closely matching daylight conditions and is applied as an intelligent artificial sunlight.

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.

Space-Confined Growth of Ultrathin P-Type GeTe Nanosheets for Broadband Photodetectors

As p-type phase-change degenerate semiconductors, crystalline and amorphous germanium telluride (GeTe) exhibit metallic and semiconducting properties, respectively. However, the massive structural defects and strong interface scattering in amorphous GeTe films significantly reduce their performance. In this work, two-dimensional (2D) p-type GeTe nanosheets are synthesized via a specially designed space-confined chemical vapor deposition (CVD) method, with the thickness of the GeTe nanosheets reduced to 1.9 nm. The space-confined CVD method improves the crystallinity of ultrathin GeTe by lowering the partial pressure of the reactant gas, resulting in GeTe nanosheets with excellent p-type semiconductor properties, such as a satisfactory on/off ratio of 105. Temperature-dependent electrical measurements demonstrate that variable-range hopping and optical-phonon-assisted hopping mechanisms dominate transport behavior at low and high temperatures, respectively. GeTe devices exhibit significantly high responsivity (6589 and 2.2 A W-1 at 633 and 980 nm, respectively) and detectivity (1.67 × 1011 and 1.3 × 108 Jones at 633 and 980 nm, respectively), making them feasible for broadband photodetectors in the visible to near-infrared range. Furthermore, the fabricated GeTe/WS2 diode exhibits a rectification ratio of 103 at zero gate voltage. These satisfactory p-type semiconductor properties demonstrate that ultrathin GeTe exhibits enormous potential for applications in optoelectronic interconnection circuits.

Lead-Free Bismuth-Based Perovskite X-ray Detector with High Sensitivity and Low Detection Limit

Bismuth-based halide perovskites have shown great potential for direct X-ray detection, attributable to their nontoxicity and advantages in detection sensitivity and spatial resolution. However, the practical application of such materials still faces the critical challenge of combining both high sensitivity and low detection limits. Here, we report a new type of zero-dimensional (0D) perovskite (HIS)BiI5 (1, where HIS2+ = histamine) with high sensitivity and a low detection limit. Structurally, the strong N-H···I hydrogen bonds between HIS2+ cations and inorganic frameworks enhance the rigidity of the structure and diminish the intermolecular distance between adjacent inorganic [Bi2I10]4- dimers. By virtue of such structural merits, single crystal 1 exhibits excellent physical properties perpendicular to both the (001) and (010) faces. Perpendicular to the (010) face, 1 exhibited a high electrical resistivity (2.31 × 1011 Ω cm) and a large carrier mobility-lifetime product (μτ) (2.81 × 10-4 cm2 V-1) under X-ray illumination. Benefiting from these superior physical properties, it demonstrates an excellent X-ray detection capability with a sensitivity of approximately 103 μC Gyair-1 cm-2 and a detection limit of 36 nGyair s-1 in both directions perpendicular to the (001) and (010) crystal faces. These results provide a promising candidate material for the development of new, lead-free, high-performance X-ray detectors.

In Situ Growth Method for Large-Area Flexible Perovskite Nanocrystal Films

Metal halide perovskites have shown unique advantages compared with traditional optoelectronic materials. Currently, perovskite films are commonly produced by either multi-step spin coating or vapor deposition techniques. However, both methods face challenges regarding large-scale production. Herein, we propose a straightforward in situ growth method for the fabrication of CsPbBr3 nanocrystal films. The films cover an area over 5.5 cm × 5.5 cm, with precise thickness control of a few microns and decent uniformity. Moreover, we demonstrate that the incorporation of magnesium ions into the perovskite enhances crystallization and effectively passivates surface defects, thereby further enhancing luminous efficiency. By integrating this approach with a silicon photodiode detector, we observe an increase in responsivity from 1.68 × 10-2 A/W to 3.72 × 10-2 A/W at a 365 nm ultraviolet wavelength.

Embedding Te4+ into Sn4+-Based Metal Halide To Passivate Structure Defects for High-Performance Light-Emitting Application

Low-dimensional lead-halide hybrids are an emerging class of optical functional material but suffer the problems of toxicity and poor air stability. Among lead-free metal halides, tin(IV)-based metal halides are promising optoelectronic materials due to their robust structure and environmental friendliness. However, their photoluminescence (PL) properties are poor, and the underlying mechanisms are still elusive. Herein, a stable Sn4+-based halide hybrid, (C4H7N2)2SnCl6, was developed, which however exhibits poor PL properties at room temperature (RT) due to the lattice defects and the robust crystal structure. To enhance its PL efficiency, the Te4+ ion with a stereoactive 5s2 lone pair has been introduced into the lattice. As a result, Te4+-doped (C4H7N2)2SnCl6 displays broadband orange emission (∼640 nm) with a PL efficiency of ∼46% at RT. Interestingly, Te4+-doped (C4H7N2)2SnCl6 shows triple emission bands at 80 K, which could be due to the synergistic effect of the organic cations and the self-trapped state induced by Te4+. Additionally, high-performance white light-emitting diodes were prepared using Te4+-doped (C4H7N2)2SnCl6, revealing the potential of this material for lighting applications. This study provides new insight into the PL mechanism of Sn4+-based metal-halide hybrids and thus facilitates the design and development of eco-friendly light-emitting metal halides.

DFT Investigation of Structural Stability, Optical Properties, and PCE for All-Inorganic Csx(Pb/Sn)yXz Halide Perovskites

Employing all-inorganic perovskites as light harvesters has recently drawn increasing attention owing to the strong-bonded inorganic components in the crystal. To achieve the systematic and comprehensive understanding for the structures and properties of Csx(Pb/Sn)yXz (X = F, Cl, Br, I) perovskites, this work provides the comparison details about crystal structures, optical properties, electronic structures and power conversion efficiency (PCE) of 18 perovskites. The suitable band gaps are detected in CsSnCl3-Pm3̅m (0.96 eV), γ-CsPbI3-Pnma (1.75 eV), and CsPbBr3-Pm3̅m (1.78 eV), facilitating the conversion from absorbing photon energy to generating hole-electron pairs. γ-CsPbI3-Pnma and CsSnI3-P4/mbm show superior visible-absorption performance depending on their higher absorption coefficient (α); meanwhile, strong peaks can be observed in the real part (Re) of photoconductivity of CsPbBr3-Pbnm, γ-CsPbI3-Pnma, and CsSnI3-P4/mbm in the visible-light range, implying their better photoelectric conversion abilities. The perovskite/tungsten disulfide (WS2) heterojunctions are constructed to calculate the PCE. Although just the PCE result (14.43%) of CsSnI3-Pnma/WS2 is reluctantly competitive, the predictions of PCEs indicate that the PCE of PSCs (perovskite solar cells) can be improved by not only regulating the perovskite to upgrade its own performance but also designing the PSC structure reasonably including the selection of appropriate ETL/HTL (electron/hole transport layer), etc.

The electronic and optical properties of Cs2BX6 (B = Zr, Hf) perovskites with first-principle method

The electronic structures and absorption properties of Cs2BX6 halide compounds are investigated with first principle calculation and exchange correlation functional of GGA-PBE. Pressure and halogen ion doping are employed to regulate band gap. All materials suffer transition from indirect to direct band gap semiconductors but with different phase transition pressure. Structural and band structure calculating results show that the value of phase transition pressure is mainly determined by the volume of octahedron. When the volume of vacancy octahedron is much less than B-ion octahedron, the lowest band point of B-d orbitals transforms to Γ point, then the indirect semiconductors transform into direct band gap semiconductors. Calculating results of optical absorption implied that the systems have obvious blue shift, which result in the optical properties reduced. Based on suitable band gap and higher absorption coefficient, Cs2ZrI4Br2 can be an ideal candidate for perovskites solar cells.

Uncovering the Role of Electronic Doping in Lead-free Perovskite (CH3 NH3 )2 CuCl4-x Brx and Solar Cells Fabrication

Lead halide perovskites are attractive pigments to fabricate solar cells in the laboratory, owing to their high power conversion efficiency. However, given the presence of Pb, such materials also have a high level of toxicity and are carcinogenic for humans and aquatic life. Arguably, this hampers their acceptability for immediate commercialization. This study entails the synthesis, optoelectronic properties, and photovoltaic parameters of two-dimensional copper-based perovskites as an environmentally benign alternative to lead-based perovskites. The perovskites - (CH3 NH3 )2 CuCl4-x Brx with x=0.3 and 0.66 - are derivatives of the stable (CH3 NH3 )2 CuCl4 . The single crystals and powders diffractograms suggest compositions with variations in Cl/Br ratio and dissimilar bromine localization in the inorganic framework. The copper mixed halide perovskite exhibits a narrow absorption with a bandgap of 2.54-2.63 eV related to the halide ratio disparity (crystal color variation). These findings demonstrate the impact of halides to optimize the stability of methylammonium copper perovskites and provide an effective pathway to design eco-friendly perovskites for optoelectronic applications.

Synapse-Mimetic Hardware-Implemented Resistive Random-Access Memory for Artificial Neural Network

Memristors mimic synaptic functions in advanced electronics and image sensors, thereby enabling brain-inspired neuromorphic computing to overcome the limitations of the von Neumann architecture. As computing operations based on von Neumann hardware rely on continuous memory transport between processing units and memory, fundamental limitations arise in terms of power consumption and integration density. In biological synapses, chemical stimulation induces information transfer from the pre- to the post-neuron. The memristor operates as resistive random-access memory (RRAM) and is incorporated into the hardware for neuromorphic computing. Hardware composed of synaptic memristor arrays is expected to lead to further breakthroughs owing to their biomimetic in-memory processing capabilities, low power consumption, and amenability to integration; these aspects satisfy the upcoming demands of artificial intelligence for higher computational loads. Among the tremendous efforts toward achieving human-brain-like electronics, layered 2D materials have demonstrated significant potential owing to their outstanding electronic and physical properties, facile integration with other materials, and low-power computing. This review discusses the memristive characteristics of various 2D materials (heterostructures, defect-engineered materials, and alloy materials) used in neuromorphic computing for image segregation or pattern recognition. Neuromorphic computing, the most powerful artificial networks for complicated image processing and recognition, represent a breakthrough in artificial intelligence owing to their enhanced performance and lower power consumption compared with von Neumann architectures. A hardware-implemented CNN with weight control based on synaptic memristor arrays is expected to be a promising candidate for future electronics in society, offering a solution based on non-von Neumann hardware. This emerging paradigm changes the computing algorithm using entirely hardware-connected edge computing and deep neural networks.

A review of memristor: material and structure design, device performance, applications and prospects

With the booming growth of artificial intelligence (AI), the traditional von Neumann computing architecture based on complementary metal oxide semiconductor devices are facing memory wall and power wall. Memristor based in-memory computing can potentially overcome the current bottleneck of computer and achieve hardware breakthrough. In this review, the recent progress of memory devices in material and structure design, device performance and applications are summarized. Various resistive switching materials, including electrodes, binary oxides, perovskites, organics, and two-dimensional materials, are presented and their role in the memristor are discussed. Subsequently, the construction of shaped electrodes, the design of functional layer and other factors influencing the device performance are analyzed. We focus on the modulation of the resistances and the effective methods to enhance the performance. Furthermore, synaptic plasticity, optical-electrical properties, the fashionable applications in logic operation and analog calculation are introduced. Finally, some critical issues such as the resistive switching mechanism, multi-sensory fusion, system-level optimization are discussed.

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.

Competing Energy Transfer-Modulated Dual Emission in Mn2+-Doped Cs2NaTbCl6 Rare-Earth Double Perovskites

A₂B^IB^IIIX₆ double perovskites are promising materials due to their outstanding photoelectronic properties and excellent stability in the environment. Herein, we synthesized Mn²⁺:Cs₂NaTbCl₆ with dual emission through a solvothermal method for the first time. Mn²⁺:Cs₂NaTbCl₆ double perovskites exhibit excellent environmental stability and high photoluminescence quantum yields (PLQYs). The Cs₂NaTbCl₆ was successfully doped with Mn²⁺ in two modes: at Mn-feeding concentrations below 1%, Mn²⁺ first tend to insert into the interstitial void, but if the Mn-feeding concentration exceeds 1%, Mn²⁺ will further substitute Na⁺ site of the Cs₂NaTbCl₆ lattice and thus both two doping modes coexist. After Mn²⁺ doping, efficient energy transfer from the ⁵D₄ level of Tb³⁺ ions to the ⁴T₁ level of Mn²⁺ ions occurs, resulting in tunable dual emission from the Tb³⁺⁵D₄ → ⁷F_J=6,5,4,3 transition and Mn²⁺⁴T₁ → ⁶A₁ transition. Further, LED based on the Mn²⁺:Cs₂NaTbCl₆ double perovskites exhibits excellent performance and stability. This work demonstrates a strategy to achieve novel lanthanide-based double perovskites with potential applications in photonics.

Wavelength-Tuneable Near-Infrared Luminescence in Mixed Tin-Lead Halide Perovskites

Near-infrared light-emitting diodes (NIR-LEDs) are widely used in various applications such as night-vision devices, optical communication, biological imaging and optical diagnosis. The current solution-processed high-efficiency perovskite NIR-LEDs are typically based on CsPbI₃ and FAPbI₃ with emission peaks being limited in the range of 700–800 nm. NIR-LEDs with longer emission wavelengths near to 900 nm can be prepared by replacing Pb with Sn. However, Sn-based perovskite LEDs usually exhibit a low efficiency owing to the high concentration of Sn-related defects and the rapid oxidation of Sn²⁺ to Sn⁴⁺, which further induces the device degradation. These problems can be solved by rationally adjusting the ratio between Pb content with Sn. Mixed Sn-Pb halide perovskites with a smaller bandgap and superior stability than pure Sn-based perovskites are promising candidates for manufacturing next-generation NIR emitters. In this study, we systematically investigated the optical properties of a family of hybrid Sn and Pb iodide compounds. The emission spectra of the mixed Sn-Pb halide perovskites were tuned by changing the Sn:Pb ratio. Consequently, the peak emission wavelength red-shifted from 710 nm to longer than 950 nm. The absorption and photoluminescence emission properties associated with different compositions were compared, and the results demonstrated the potential of MA- and FA-based mixed Sn-Pb halide perovskites for preparing low-cost and efficient NIR-LEDs. In addition, we clarified the influence of cations on the bandgap bowing effect and electronic properties of mixed Sn-Pb halide perovskites.

High-yield synthesis of CsPbBr3nanoparticles: diphenylphosphine as a reducing agent and its effect in Pb-seeding nucleation and growth

Based on the reported nucleation mechanisms for CsPbX₃and II-VI/IV-VI quantum dots, CsPbBr₃nanoparticles with a higher reaction-yield (up to 393% mass-increment) were synthetized by the hot-injection method. The introduction of diphenylphosphine (DPP) as a reducing agent improved nanoparticle nucleation and growth, giving out evidence for Pb-seeding in CsPbBr₃nanoparticles formation. Additionally, a clear influence of the DPP in a CsPbBr₃-Cs₄PbBr₆incomplete phase transformation was observed, marked by the appearance of several PbBr₂nanoparticles. This indicated the need for an improved ratio between the stabilizing agents and the precursors, due to the increased number of nucleation sites produced by DPP. The resulting CsPbBr₃nanoparticles showed high quality, as they displayed 70%-90% photoluminescence quantum yield; narrow size distribution with an average nanoparticle size of∼10 nm; and the characteristic cubic morphology reported in previous works. This increment in CsPbBr₃nanoparticles' reaction yield will contribute to making them a more attractive option for different optoelectronic applications.

A halogen bonding assembled hybrid copper halide framework as a promising hypotoxicity photodetector

The first halogen bonding assembled three-dimensional hybrid copper iodide was obtained by a facile and sustainable “All-in-One” synthesis strategy and shows great application potential as a hypotoxicity photodetector.

Two-/Three-Dimensional Perovskite Bilayer Thin Films Post-Treated with Solvent Vapor for High-Performance Perovskite Photovoltaics

Perovskite photovoltaics (PPVs) using three-dimensional (3D) perovskites incorporated with two-dimensional (2D) perovskites have drawn great concentration in both academic and industrial sectors. Here, we report high performance of PPVs based on the 2D/3D perovskite bilayer thin film post-annealed with solvent vapor. The 2D/3D perovskite bilayer thin film post-annealed with solvent vapor possesses enlarged crystal size and crystallinity and blue-shifted photoluminescence compared to a 3D MAPbI₃ thin film. Moreover, compared to the PPVs based on a 3D perovskite thin film, enlarged built-in potential, suppressed charge carrier recombination, boosted charge transport, and reduced charge carrier extraction time are observed from the PPVs based on the 2D/3D perovskite bilayer thin film post-annealed with solvent vapor. As a result, perovskite solar cells exhibit a power conversion efficiency of 22.13% and dramatically enhanced stability, and perovskite photodetectors show a photoresponsivity of 1.38 AW^-1, detectivity of 6.52 × 10¹⁴ cm Hz^1/2 W^-1, and linear dynamic range of over 167 dB at room temperature. These results demonstrate that we develop a simple method to approach high-performance PPVs by the 2D/3D perovskite bilayer thin film.

Bulk assembly of a 0D organic tin(ii)chloride hybrid with high anti-water stability

A lead-free compound, (TBAC)SnCl₃ (TBAC = tetrabutylammonium chloride), with high anti-water stability was reported, which can be stable in water for 24 hours. Upon photoexcitation, this compound exhibits a green photoluminescence (PL) centered at 523 nm with a larger Stokes shift of 260 nm at room temperature (RT), stemming from self-trapped exciton (STE) emission.

Germanium-lead perovskite light-emitting diodes

Reducing environmental impact is a key challenge for perovskite optoelectronics, as most high-performance devices are based on potentially toxic lead-halide perovskites. For photovoltaic solar cells, tin-lead (Sn-Pb) perovskite materials provide a promising solution for reducing toxicity. However, Sn-Pb perovskites typically exhibit low luminescence efficiencies, and are not ideal for light-emitting applications. Here we demonstrate highly luminescent germanium-lead (Ge-Pb) perovskite films with photoluminescence quantum efficiencies (PLQEs) of up to ~71%, showing a considerable relative improvement of ~34% over similarly prepared Ge-free, Pb-based perovskite films. In our initial demonstration of Ge-Pb perovskite LEDs, we achieve external quantum efficiencies (EQEs) of up to ~13.1% at high brightness (~1900 cd m-2), a step forward for reduced-toxicity perovskite LEDs. Our findings offer a new solution for developing eco-friendly light-emitting technologies based on perovskite semiconductors.

Recent Progress of Chiral Perovskites: Materials, Synthesis, and Properties

Chiral materials with intrinsic inversion-symmetric structures possess many unique physicochemical features, including circular dichroism, circularly polarized photoluminescence, nonlinear optics, ferroelectricity, and spintronics. Halide perovskites have attracted considerable attention owing to their excellent optical and electrical properties, which are particularly suitable for realizing high power-conversion efficiency in solar cells. Recent studies have shown that chirality can be transferred from chiral organic ligands into halide perovskites and the resultant chiral perovskites combine the advantages of both chiral materials and halide perovskites; this provides an ideal platform to design next-generation optoelectronic and spintronic devices. In this progress report, the most recent advances are summarized in various chemical structures of chiral perovskites, their synthesis strategies, chirality generation mechanisms, and physical properties. Furthermore, the potential chiral-halide-perovskite-based applications are presented and the challenges and prospects of chiral perovskites are discussed. This report outlines the diverse construction strategies of and proposes research directions for chiral halide perovskites; thus, it provides insights into the design of novel chiral perovskites and facilitates investigation of the optoelectronic applications that employ chirality.

Tetrathiafulvalene-based double metal lead iodides: structures and electrical properties

Introducing electronically active organic components into lower dimensional metal halide compounds is an effective strategy to improve the electronic properties of hybrid metal halide materials. We have previously used this strategy to explore hybrid halides with tetrathiafulvalenes (TTFs) and a series of lead iodides and bismuth halides were isolated. The electronic properties were improved notably using this modification. In this work, we expand the study of TTF based main-group metal halides to double metal halides with mixed lead and copper transition metals. Two hybrid TTF-lead-cuprous iodides, formulated as [TTF]5[Pb2Cu2I10]·H2O (1) and [TTF]2[PbCu2I6] (2), and two monometal analogues of [TTF]2[Cu4I6]·H2O (3) and [TTF]2[Ag4I6] (4) were crystallographically characterized. The anion of 1 is a 0D cluster, while that of the others is a 1D chain structure. The anion structures of 1-4 are novel and are reported for the first time. The TTF moieties are stacked to form a 2D framework in 1 and 1D columns in 2-4. We found that the semiconductor properties of the hybrids are related to electron donation from an anion to a cation. The electronic state of the TTF cations is another significant factor that affects the electronic properties of the materials. More notably, this work proved that the conductivity and photoconductivity of the mixed metal iodides are superior to those of the monometal iodides.

Towards ferroelectricity-inducing chains of halogenoantimonates(iii) and halogenobismuthates(iii)

In halogenoantimonate(iii) and halogenobismuthate(iii) organic–inorganic hybrids, chains of trans-connected octahedra, trans-[MX₅]_∞, are considered attractive anionic structures for inducing ferroelectricity. The latter is realized by displacing the bridging halogen atoms along the chain direction – the process that changes the polarity of the whole unit. Advances in the identification of such materials have been hindered, however, by substantial difficulty in obtaining such structures. Here we investigate structural and dielectric properties of three families of compounds based on 2-mercaptopyrimidinium, 2-aminopyrimidinium, and 2-amino-4-methylpyrimidinium cations in which 8 out of 12 compounds show trans-[MX₅]_∞ chains in their crystal structures. Two of the compounds adopt a polar P2₁ space group and are potentially ferroelectric. We perform a detailed structural analysis of all compounds with trans-[MX₅]_∞ chains discovered by far to understand the factors that lead to the chains' formation. We reveal that the size of a cation predominantly defines the accessibility of structures with this anionic form and we provide rules for designing hybrids with trans-[MX₅]_∞ chains to help guide future efforts to engineer materials with interesting non-linear electrical properties.

A discovered abundance of structures with rare and highly-desired anionic chains is examined to identify structural factors leading to the chains' formation.

Recent advances toward environment-friendly photodetectors based on lead-free metal halide perovskites and perovskite derivatives

Recently, metal-halide perovskites have emerged as promising materials for photodetector (PD) applications owing to their superior optoelectronic properties, such as ambipolar charge transport characteristics, high carrier mobility, and so on. In the past few years, rapid progress in lead-based perovskite PDs has been witnessed. However, the critical environmental instability and lead-toxicity seriously hinder their further applications and commercialization. Therefore, searching for environmentally stable and lead-free halide perovskites (LFHPs) to address the above hurdles is certainly a worthwhile subject. In this review, we present a comprehensive overview of currently explored LFHPs with an emphasis on their crystal structures, optoelectronic properties, synthesis and modification methods, as well as the PD applications. LFHPs are classified into four categories according to the replacement strategies of Pb²⁺, including AB(ii)X₃, A₃B(iii)₂X₉, A₂B(i)B(iii)'X₆, and newly-emerging perovskite derivatives. Then, we give a demonstration of the preliminary achievements and limitations in environment-friendly PDs based on such LFHPs and perovskite derivatives, and also discuss their applications in biological synapses, imaging, and X-ray detection. With the perspective of their properties and current challenges, we provide an outlook for future directions in this rapidly evolving field to achieve high-quality LFHPs and perovskite derivatives for a broader range of fundamental research and practical applications.

97.3% Pb-Reduced CsPb1-xGexBr3 Perovskite with Enhanced Phase Stability and Photovoltaic Performance through Surface Cu Doping

Ge doping has been regarded as an effective way to explore the low-toxicity inorganic halide perovskite. However, Ge²⁺ ions are easy to oxidize because the Ge dopant raises the valence band maximum (VBM) over the water oxidization (H₂O/O₂) potential. Here we find that surface Cu doping can bend down the band levels and decline the VBM of the CsPb_1-xGe_xBr₃ surface below the H₂O/O₂ potential, then prevent the Ge²⁺ from being oxidized into Ge⁴⁺ by water because the Cu dopant reduces the perovskite surface electron accumulation. Note that the Cu dopant prefers to locate at the perovskite surface rather than the interior, and it reduces the surface energy and enhances the stability. Consequently, the largest Pb reduction increases to 97.3% for the Cu-doped CsPb_1-xGe_xBr₃ surface. Moreover, the exciton binding energy and optical absorption of CsPb_1-xGe_xBr₃ could be further improved by the surface Cu dopant. This work provides guidance for finding low-toxicity stable inorganic perovskites.