Halide Perovskites: A New Era of Solution-Processed Electronics

Precursor Engineering Induced High-Efficiency Electroluminescence of Quasi-Two-Dimensional Perovskites: A Synergistic Defect Inhibition and Passivation Approach

Despite light-emitting diodes (LEDs) based on quasi-two-dimensional (Q-2D) perovskites being inexpensive and exhibiting high performance, defects still limit the improvement of electroluminescence efficiency and stability by causing nonradiative recombination. Here, an organic molecule, 1-(o-tolyl) biguanide, is used to simultaneously inhibit and passivate defects of Q-2D perovskites via in situ synchronous crystallization. This molecule not only prevents surface bromine vacancies from forming through hydrogen bonding with the bromine of intermediaries but also passivates surface defects through its interaction with uncoordinated Pb. Via combination of defect inhibition and passivation, the trap density of Q-2D perovskite films can be significantly reduced, and the emission efficiency of the film can be improved. Consequently, the corresponding LED shows an external quantum efficiency of 24.3%, and its operational stability has been increased nearly 15 times.

Multifunctional two-dimensional perovskite based solar cells for photodetectors and resistive switching

The escalating interest in low-dimensional perovskites stems from their tunable optoelectronic traits and robust stability. The pursuit of multifaceted optoelectronic devices holds substantial importance for energy-efficient and space-constrained systems. This investigation showcases the realization of multifunctional two-dimensional perovskite solar cells, incorporating transient light detection and resistive switching functions within a single device, achievable by facile external bias adjustments. Serving as a photodetector, the device exhibits commendable self-powered photodetection attributes, including an exceptionally low dark current density of 1 nA mm-2, a remarkable specific detectivity of 7.67 × 1012 Jones, a swift response time of 0.60 μs, and an expansive linear dynamic range of 72 dB. As a memristor, it showcases enduring performance across 4 × 102 cycles, a substantial on/off ratio of 106, and a rapid operation time of less than 1 μs. This endeavor unveils a pioneering avenue for advancing high-performance, air-stable multifunctional two-dimensional perovskite electronics.

Self-energy correction and numerical simulation for efficient lead-free double perovskite solar cells

Inorganic double perovskites have garnered significant attention due to their desirable characteristics, such as low-toxicity, stability and long charge-carrier lifetimes. However, most double perovskites, especially Cs2AgBiBr6, have wide bandgaps, which limits power conversion efficiencies. In this work, through the first principles method corrected by self-energy, we investigate the mechanical, electric and optical properties of Cs2B'B''Br6 (B' = Ag, Au, Cu; B'' = Bi, Al, Sb, In). Based on performance screening, three kinds of materials with good toughness, high carrier mobility and wide visible-light absorption (around 105 cm-1) are obtained, which are compared with Cs2AgBiBr6. Meanwhile, we use a SACPS-1D simulation to design lead-free double perovskites with excellent properties suitable for photovoltaic solar cell devices, which are made into a planar perovskite heterojunction. Ultimately, the optimal structure is determined to be FTO/WS2/Cs2CuBiBr6/spiro-OMeTAD/Ag, which achieves a power conversion efficiency of 14.08%, surpassing the conventional structure efficiency of 6.1%. It provides valuable guidance for the structure design of a lead-free double perovskite device and offers new insights into the development of optoelectronic devices for solar energy utilization.

Enhancing Visible-Light Absorption of 2D Carbon Nitride by Constructing 2D/2D van der Waals Heterojunctions of Carbon Nitride/Nitrogen-Superdoped Graphene

Carbon nitride sheets (CNs) down to the two-dimensional (2D) limit have been widely used in photoelectric conversion due to their inherent band gap and extremely short charge-carrier diffusion distance. However, the utilization of visible light remains low due to the rapid recombination of photogenerated electron-hole pairs and enlarged band gap. Here, atomically thin 2D/2D van der Waals heterojunctions (vdWHs) of N-superdoped graphene (NG) and CNs (CNs/NG) are fabricated via a facile electrostatic self-assembly method. Our results revealed that the vdWHs can increase the visible-light absorption of CNs by extending the absorption edge from 455 to up to 490 nm. The recombination of photogenerated electron-hole pairs is inhibited because superdoped N in CNs/NG facilitates the transmission of photogenerated carriers in the melon chain. This study opens a new avenue for narrowing the band gap and promoting photoexcited carrier separation in carbon-nitride-based materials.

Local modulation of Au/MoS2 Schottky barriers using a top ZnO nanowire gate for high-performance photodetection

Schottky junctions are commonly used for fabricating heterojunction-based 2D transition metal dichalcogenide (TMD) photodetectors, characteristically offering a wide detection range, high sensitivity and fast response. However, these devices often suffer from reduced detectivity due to the high dark current, making it challenging to discover a simple and efficient universal way to improve the photoelectric performances. Here, we demonstrate a novel approach for integrating ZnO nanowire gates into a MoS2-Au Schottky junction to improve the photoelectric performances of photodetectors by locally controlling the Schottky barrier. This strategy remarkably reduces the dark current level of the device without affecting its photocurrent and the Schottky detectivity can be modified to a maximum detectivity of 1.4 × 1013 Jones with -20 V NG bias. This work provides potential possibilities for tuning the band structure of other materials and optimizing the performance of heterojunction photodetectors.

Polymer-enhanced perovskite oxide-based photocatalysts: a review

Oxide perovskites (OPs) have emerged as promising photocatalysts for numerous applications, such as energy conversion, renewable fuels, and environmental remediation. Although OPs are gaining traction, their efficacies are still hindered by low charge carrier mobility and poor stability. This study investigated the function of polymers actively participating in OP structures to improve the overall characteristics. An overview of the polymer-enhanced perovskite oxide photocatalyst (PEPOP) field was effectively reviewed. These PEPOPs were demonstrated in photovoltaics, pollutant degradation, and gas conversion and reduction. Nonetheless, additional research is needed to explore the potential of PEPOPs to establish their efficacy in photocatalytic applications. The technological improvements of PEPOPs were hindered by significant challenges related to stability and sensitivity. The urgency of this review was apparent due to the fast-paced nature of research in the field of photocatalysis. Recent breakthroughs and emerging applications highlight the need for a comprehensive overview of PEPOPs and their enhanced catalytic capabilities. Consequently, a broad outlook was provided for the current state of PEPOP-related studies, highlighting the potential of these materials for future applications.

Controlled Synthesis of Lead-Free Double Perovskite Colloidal Nanocrystals for Nonvolatile Resistive Memory Devices

Although lead-free double perovskites such as Cs2AgBiBr6 have been widely explored, they still remain a daunting challenge for the controlled synthesis of lead-free double perovskite nanocrystals with highly tunable morphology and band structure. Here, we report the controlled synthesis of lead-free double perovskite colloidal nanocrystals including Cs2AgBiBr6 and Cs2AgInxBi1-xBr6 via a facile wet-chemical synthesis method for the fabrication of high-performance nonvolatile resistive memory devices. Cs2AgBiBr6 colloidal nanocrystals with well-defined cuboidal, hexagonal, and triangular morphologies are synthesized through a facile wet-chemical approach by tuning the reaction temperature from 150 to 190 °C. Further incorporating indium into Cs2AgBiBr6 to synthesize alloyed Cs2AgInxBi1-xBr6 nanocrystals not only can induce the indirect-to-direct bandgap transition with enhanced photoluminescence but also can improve its structural stability. After optimizing the active layers and device structure, the fabricated Ag/polymethylene acrylate@Cs2AgIn0.25Bi0.75Br6/ITO resistive memory device exhibits a low power consumption (the operating voltage is ∼0.17 V), excellent cycling stability (>10 000 cycles), and good synaptic property. Our study would enable the facile wet-chemical synthesis of lead-free double perovskite colloidal nanocrystals in a highly controllable manner for the development of high-performance resistive memory devices.

Lung Toxicity and Molecular Mechanisms of Lead-Based Perovskite Nanoparticles in the Respiratory System

Lead-based perovskite nanoparticles (Pb-PNPs) have found extensive applications across diverse fields. However, because of poor stability and relatively strong water solubility, the potential toxicity of Pb-PNPs released into the environment during their manufacture, usage, and disposal has attracted significant attention. Inhalation is a primary route through which human exposure to Pb-PNPs occurs. Herein, the toxic effects and underlying molecular mechanisms of Pb-PNPs in the respiratory system are investigated. The in vitro cytotoxicity of CsPbBr3 nanoparticles in BEAS-2B cells is studied using multiple bioassays and electron microscopy. CsPbBr3 nanoparticles of different concentrations induce excessive oxidative stress and cell apoptosis. Furthermore, CsPbBr3 nanoparticles specifically recruit the TGF-β1, which subsequently induces epithelial-mesenchymal transition. In addition, the biodistribution and lung toxicity of representative CsPbBr3 nanoparticles in ICR mice are investigated following intranasal administration. These findings indicate that CsPbBr3 nanoparticles significantly induce pulmonary inflammation and epithelial-mesenchymal transition and can even lead to pulmonary fibrosis in mouse models. Above findings expose the adverse effects and molecular mechanisms of Pb-PNPs in the lung, which broadens the safety data of Pb-PNPs.

Tailoring the Electron and Hole Landé Factors in Lead Halide Perovskite Nanocrystals by Quantum Confinement and Halide Exchange

The tunability of the optical properties of lead halide perovskite nanocrystals makes them highly appealing for applications. Halide anion exchange and quantum confinement enable tailoring of the band gap. For spintronics, the Landé g-factors of electrons and holes are essential. Using empirical tight-binding and k·p methods, we calculate them for nanocrystals of all-inorganic lead halide perovskites CsPbX3 (X = I, Br, Cl). The hole g-factor band gap dependence follows the universal law found for bulk perovskites, while for electrons, a considerable modification is predicted. Based on the k·p analysis, we conclude that this difference arises from the interaction of the bottom conduction band with the spin-orbit split electron states. These predictions are confirmed experimentally for electron and hole g-factors in CsPbI3 nanocrystals in a glass matrix, measured by time-resolved Faraday ellipticity in a magnetic field at cryogenic temperatures.

Regulating buried interface properties and alleviating micro-strain of crystals for efficient perovskite solar cells

Surface properties of SnO2 and their effects on the growth of perovskite films play a crucial role for perovskite solar cells (PSCs). Herein, a facile strategy to synchronously regulate the buried interface defects and energy level arrangement, as well as improve the crystallinity of perovskite films with alleviated micro-strain by pre-modifying the SnO2 surface with ammonium hexafluorophosphate (NH4PF6) is proposed. The device achieved the promising PCE of 22.50% and improved stability.

Solvent-antisolvent interactions in metal halide perovskites

The fabrication of metal halide perovskite films using the solvent-engineering method is increasingly common. In this method, the crystallisation of the perovskite layer is triggered by the application of an antisolvent during the spin-coating of a perovskite precursor solution. Herein, we introduce the current state of understanding of the processes involved in the crystallisation of perovskite layers formed by solvent engineering, focusing in particular on the role of antisolvent properties and solvent-antisolvent interactions. By considering the impact of the Hansen solubility parameters, we propose guidelines for selecting the appropriate antisolvent and outline open questions and future research directions for the fabrication of perovskite films by this method.

Morphology-Dependent Charge Carrier Dynamics and Ion Migration Behavior of CsPbBr3 Halide Perovskite Quantum Dot Films

Exceptional electronic, optoelectronic, and sensing properties of inorganic Cs-based perovskites are significantly influenced by the defect chemistry of the material. Although organic halide perovskites that have a polycrystalline structure are heavily studied, understanding of the defect properties at the grain boundaries (GB) of inorganic Cs-based perovskite quantum dots (QDs) is still limited. Here, morphology-dependent charge carrier dynamics of CsPbBr₃ quantum dots at the nanoscale by performing scanning probe microscopy of thermally treated samples are investigated. The grain boundaries of defect-engineered samples show higher surface potential than the grain interiors under light illumination, suggesting an effective role of GBs as charge collection and transport channels. The lower density of crystallographic defects and lower trap density at GBs specifically of heat-treated samples cause insignificant dark current, lower local current hysteresis, and higher photocurrent, than the control samples. It is also shown that the decay rate of surface photovoltage of the heated sample is quicker than the control sample, which implies a considerable impact of ion migration on the relaxation dynamic of photogenerated charge carriers. These findings reveal that the annealing process is an effective strategy to control not only the morphology but also the optoelectrical properties of GB defects, and the dynamic of ion migration. Understanding the origin of photoelectric activity in this material allows for designing and engineering optoelectronic QD devices with enhanced functionality.

Porous and Water Stable 2D Hybrid Metal Halide with Broad Light Emission and Selective H2 O Vapor Sorption

In this work we report a strategy for generating porosity in hybrid metal halide materials using molecular cages that serve as both structure-directing agents and counter-cations. Reaction of the [2.2.2] cryptand (DHS) linker with Pb^II in acidic media gave rise to the first porous and water-stable 2D metal halide semiconductor (DHS)₂ Pb₅ Br₁₄ . The corresponding material is stable in water for a year, while gas and vapor-sorption studies revealed that it can selectively and reversibly adsorb H₂ O and D₂ O at room temperature (RT). Solid-state NMR measurements and DFT calculations verified the incorporation of H₂ O and D₂ O in the organic linker cavities and shed light on their molecular configuration. In addition to porosity, the material exhibits broad light emission centered at 617 nm with a full width at half-maximum (FWHM) of 284 nm (0.96 eV). The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens new pathways towards unexplored applications (e.g. solid-state batteries) for this class of hybrid semiconductors.

4,4'-(Anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) Lead Iodide C30H22N2Pb2I6: A Highly Luminescent, Chemically and Thermally Stable One-Dimensional Hybrid Iodoplumbate

A new one-dimensional hybrid iodoplumbate, namely, 4,4'-(anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) lead iodide C₃₀H₂₂N₂Pb₂I₆ (AEPyPbI), is reported here for the first time with its complete characterization. The material exhibits remarkable thermal stability (up to 300 °C), and it is unreactive under ambient conditions toward water and atmospheric oxygen, due to the quaternary nature of the nitrogen atoms present in the organic cation. The cation exhibits strong visible fluorescence under ultraviolet (UV) irradiation, and when its iodide is combined with PbI₂, it forms AEPyPb₂I₆, an efficient light-emitting material, with a photoluminescence emission intensity comparable to that of high-quality InP epilayers. The structure determination was obtained using three-dimensional electron diffraction, and the material was extensively studied by using a wide range of techniques, such as X-ray powder diffraction, diffuse reflectance UV-visible spectroscopy, thermogravimetry-differential thermal analysis, elemental analysis, Raman and infrared spectroscopies, and photoluminescence spectroscopy. The emissive properties of the material were correlated with its electronic structure by using state-of-the-art theoretical calculations. The complex, highly conjugated electronic structure of the cation interacts strongly with that of the Pb-I network, giving rise to the peculiar optoelectronic properties of AEPyPb₂I₆. The material, considering its relatively easy synthesis and stability, shows promise for light-emitting and photovoltaic devices. The use of highly conjugated quaternary ammonium cations may be useful for the development of new hybrid iodoplumbates and perovskites with optoelectronic properties tailored for specific applications.

Uncovering Aging Chemistry of Perovskite Precursor Solutions and Anti-aging Mechanism of Additives

The aging of precursor solutions is the major stumbling block for the commercialization of perovskite solar cells (PSCs). Herein, for the first time we used the state-of-the-art in situ liquid time-of-flight secondary ion mass spectrometry to molecularly explore the perovskite precursor solution chemistry. We identified that the methylammonium and formamidinium cations and the I^- anion are the motivators of the aging chemistry. Further, we introduced two kinds of Lewis bases, triethyl phosphate (TP) and ethyl ethanesulfonate (EE), as new additives in the solution and unraveled that both of them can protect the reactive cations from aging through weak interactions. Significantly, TP is superior to EE in enhancing long-term solution stability as it can well-maintain the internal interaction structures within the solution phase. The PSC derived from a fresh TP-doped solution delivered a high power conversion efficiency of 23.06 %, 92.23 % of which remained in that from a 21-day-old solution.

Modulation of the Excitation States in All-Inorganic Halide Perovskites via Sb3+ and Bi3+ Codoping

Sb³⁺-doped halide perovskites are promising candidates for solid-state lighting due to their diverse fluorescent colors and high efficiency. However, the mismatched high excitation energy with commercial UV chips is one of the critical issues to be addressed. Herein, a Bi³⁺ codoping strategy was established as a general and efficient approach to modulate the excitation spectrum from the Sb³⁺-doping center in all-inorganic perovskites of Cs₂InCl₅·H₂O, Cs₂NaInCl₆, and Rb₃InCl₆. The incorporated Bi³⁺ greatly enhanced the splitting of the A band (¹S₀-³P₁ transition) and boosts the enormous redshift of the low-energy branch in all these systems. The interactions persist strongly even at extremely low doping concentrations, suggesting a dipole-based long-range interaction. The results provide an in-depth insight into the contribution mechanism of Bi³⁺ to Sb³⁺ in all-inorganic perovskites, which throws light upon tuning the excitation spectrum of broadband emission from the extrinsic self-trapped exciton (STE).

Two-Terminal Nonvolatile Write-Once-Read-Many-Times Memory Based on All-Inorganic Halide Perovskite

Write-once-read-many-times (WORM) memory belonging to an important non-volatile memory type achieves the read-only state after the write operation and is used in the fields of data security storage widely. WORM memory has been developed based on a variety of materials. In recent years, halide perovskites have become the research hotspot material for this memory due to its excellent properties. Here, the all-inorganic CsPbBr₃ perovskite thin film was prepared on a FTO substrate by using a two-step method. The prepared CsPbBr₃ thin films have the characteristics of densely packed crystal grains and smooth surface. The device, having the FTO/CsPbBr₃/Al sandwich structure by evaporating the Al electrode onto the CsPbBr₃ thin film, represents the typical WORM behavior, with long data retention time (10⁴ s), a low operation voltage (2.1 V) and a low reading voltage (0.1 V). Additionally, the resistance transition mechanism of the resulting WORM devices was analyzed.

Inorganic Halide Perovskite Quantum Dots: A Versatile Nanomaterial Platform for Electronic Applications

Metal halide perovskites have generated significant attention in recent years because of their extraordinary physical properties and photovoltaic performance. Among these, inorganic perovskite quantum dots (QDs) stand out for their prominent merits, such as quantum confinement effects, high photoluminescence quantum yield, and defect-tolerant structures. Additionally, ligand engineering and an all-inorganic composition lead to a robust platform for ambient-stable QD devices. This review presents the state-of-the-art research progress on inorganic perovskite QDs, emphasizing their electronic applications. In detail, the physical properties of inorganic perovskite QDs will be introduced first, followed by a discussion of synthesis methods and growth control. Afterwards, the emerging applications of inorganic perovskite QDs in electronics, including transistors and memories, will be presented. Finally, this review will provide an outlook on potential strategies for advancing inorganic perovskite QD technologies.

Go beyond the limit: Rationally designed mixed-dimensional perovskite/semiconductor heterostructures and their applications

Halide perovskite heterojunctions rationally integrate the chemical and physical properties of multi-dimensional perovskites and judiciously chosen semiconductor materials, offering the promise of going beyond the limit of a single component. This emerging platform of materials innovation offers fresh opportunities to tune material properties, discover interesting phenomena, and enable novel applications. In this review, we first discuss the fundamentals of forming heterojunctions with perovskites and a wide range of semiconductors, and then we give an overview of the research progress of halide perovskite heterojunctions in terms of their optical, electrical, and mechanical properties, focusing on how the heterojunction tunes the energy band structure, electrical transport, and charge recombination behaviors. We further outline the progress of perovskite-based heterojunctions in optoelectronics. Finally, the challenges and future research directions for perovskite/semiconductor heterojunctions are discussed.

Synthesis, Structure, and Characterization of 4,4'-(Anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) Bismuth Iodide (C30H22N2)3Bi4I18, an Air, Water, and Thermally Stable 0D Hybrid Perovskite with High Photoluminescence Efficiency

4,4'-(Anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) bismuth iodide (C₃₀H₂₂N₂)₃Bi₄I₁₈ (AEPyBiI) was obtained as a black powder by a very simple route by mixing an acetone solution of BiI₃ and an aqueous solution of C₃₀H₂₂N₂I₂. This novel perovskite is air and water stable and displays a remarkable thermal stability up to nearly 300 °C. The highly conjugated cation C₃₀H₂₂N₂ ²⁺ is hydrolytically stable, being nitrogen atoms quaternarized, and this accounts for the insensitivity of the perovskite toward water and atmospheric oxygen under ambient conditions. The cation in aqueous solution is highly fluorescent under UV irradiation (emitting yellow-orange light). AEPyBiI as well is intensely luminescent, its photoluminescence emission being more than 1 order of magnitude greater than that of high-quality InP epilayers. The crystal structure of AEPyBiI was determined using synchrotron radiation single-crystal X-ray diffraction. AEPyBiI was extensively characterized using a wide range of techniques, such as X-ray powder diffraction, diffuse reflectance UV-vis spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopies, thermogravimetry-differential thermal analysis (TG-DTA), elemental analysis, electrospray ionization mass spectroscopy (ESI-MS), and photoluminescence spectroscopy. AEPyBiI displays a zero-dimensional (0D) perovskite structure in which the inorganic part is constituted by binuclear units consisting of two face-sharing BiI₆ octahedra (Bi₂I₉ ^3- units). The C₃₀H₂₂N₂ ²⁺ cations are stacked along the a-axis direction in a complex motif. Considering its noteworthy light-emitting properties coupled with an easy synthesis and environmental stability, and its composition that does not contain toxic lead or easily oxidable Sn(II), AEPyBiI is a promising candidate for environmentally friendly light-emitting devices.

In Situ Tetraalkylammonium Ligand Engineering of Organic-Inorganic Hybrid Perovskite Nanoparticles for Enhancing Long-Term Stability and Optical Tunability

Organic-inorganic hybrid perovskite nanoparticles (OIHP NPs) have attracted scientific attention owing to their efficient photoluminescence with optical tunability, which is highly advantageous for optoelectronic applications. However, the limited long-term stability of OIHP NPs has significantly hindered their practical application. Despite several synthetic strategies and encapsulation methods to stabilize OIHP NPs, complicated multi-step procedures are often required. In this study, we introduce an in situ ligand engineering method for stabilizing and controlling the optical properties of OIHP NPs using tetraalkylammonium (TAA) halides with various molecular structures at different concentrations. Our one-pot ligand engineering substantially enhanced the stability of the OIHP NPs without post-synthetic processes. Moreover, in certain cases, approximately 90% of the initial photoluminescence (PL) intensity was preserved even after a month under ambient conditions (room temperature, 20-50% relative humidity). To determine the role of ligand engineering in stabilizing the OIHP NPs, the surface binding properties of the TAA ligands were thoroughly analyzed using Raman spectroscopy. Specifically, the permanent positive charge of the TAA cations and consequent effective electrostatic interactions with the surfaces of the OIHP NPs are pivotal for preserving the initial PL intensity. Our investigation is beneficial for developing OIHP nanomaterials with improved stability and controlled photoluminescence for various optoelectronic applications, such as light-emitting devices, photosensitizers, photodetectors, photocatalysis, and solar cells.

Low-Dimensional Metal-Halide Perovskites as High-Performance Materials for Memory Applications

Metal-halide perovskites have drawn profuse attention during the past decade, owing to their excellent electrical and optical properties, facile synthesis, efficient energy conversion, and so on. Meanwhile, the development of information storage technologies and digital communications has fueled the demand for novel semiconductor materials. Low-dimensional perovskites have offered a new force to propel the developments of the memory field due to the excellent physical and electrical properties associated with the reduced dimensionality. In this review, the mechanisms, properties, as well as stability and performance of low-dimensional perovskite memories, involving both molecular-level perovskites and structure-level nanostructures, are comprehensively reviewed. The property-performance correlation is discussed in-depth, aiming to present effective strategies for designing memory devices based on this new class of high-performance materials. Finally, the existing challenges and future opportunities are presented.

A Review of Performance Prediction Based on Machine Learning in Materials Science

With increasing demand in many areas, materials are constantly evolving. However, they still have numerous practical constraints. The rational design and discovery of new materials can create a huge technological and social impact. However, such rational design and discovery require a holistic, multi-stage design process, including the design of the material composition, material structure, material properties as well as process design and engineering. Such a complex exploration using traditional scientific methods is not only blind but also a huge waste of time and resources. Machine learning (ML), which is used across data to find correlations in material properties and understand the chemical properties of materials, is being considered a new way to explore the materials field. This paper reviews some of the major recent advances and applications of ML in the field of properties prediction of materials and discusses the key challenges and opportunities in this cross-cutting area.

Reversible Phase Segregation and Amorphization of Mixed-Halide Perovskite Nanocrystals in Glass Matrices

Mixed-halide perovskites have attracted great attention in applications of lighting and photovoltaic devices due to their excellent properties. Understanding the phase segregation mechanism of mixed-halide perovskite has significance for suppressing the performance degradation of optoelectronic devices. Herein, we investigate the mixed-halide perovskite nanocrystals (NCs) in isolation from the external factors (oxygen, moisture, and pressure) using glass encapsulation, which shows excellent photostability against phase segregation. By monitoring the structural evolution of the NCs in glass matrices, the coexisting phase segregation and amorphization of mixed-halide perovskites are observed in real-time. The results show that thermal-induced local temperature increase plays a dominant role in the phase segregation of mixed-halide perovskite NCs. The recovery process is driven by the spontaneous crystallization of the amorphous mixed-halide phase. The clarified dynamic equilibrium process between the compositional segregation (mixing) and structural disorder (order) gives us a better insight into the reversible phase segregation mechanism of mixed-halide perovskite.

Unraveling the Effect of Halogen Ion Substitution on the Noise of Perovskite Single-Crystal Photodetectors

Halide mixing in perovskites has been an efficient way to engineer the bandgap, stability, and charge carrier mobility of lead halide perovskites, while its effect on the noise of lead halide perovskite photodetectors is still unknown. We present the preparation of mixed halide methylammonium lead perovskite single crystals by the solution temperature-decreasing method. Planar-structured photodetectors were constructed on the basis of these mixed halide perovskite single crystals. The effect of halogen ion substitution on the noise of devices was investigated by analyzing their dark current spectra. It is shown that the single-crystal photodetectors with higher levels of chloride suffer from larger noise thus have lower detectivity. Density functional theory calculations have also been proposed to reveal the effect of halogens on band structure. These results provide a comprehensive understanding of mixed halide perovskites and may help in the design and preparation of higher-performance devices.

Light-Controlled Reconfigurable Optical Synapse Based on Carbon Nanotubes/2D Perovskite Heterostructure for Image Recognition

Two-dimensional (2D) halide perovskite material is characterized by a mixed conducting behavior that possesses both electronic and ionic conductivity. The study on the influence of the light on ion migration in the 2D perovskite is helpful to improve the performance of perovskite-based optoelectronic devices. Here, we constructed an exfoliated 2D perovskite/carbon nanotubes (CNTs) heterostructure optical synapse, in which CNTs can be used as nanoprobes to qualitatively observe the ion aggregation or dissipation process in 2D perovskite, and found that light significantly changes the memory curve of the reconfigurable optical synapses. Through the molecular dynamic simulation, the dynamic process of ion migration in the heterostructure was simulated and the electrostatic interaction effect of nonequilibrium charge distribution of CNTs on iodide ion was demonstrated. Finally, an effective light-controlled process was realized through the synapses, which in situ regulated the performance of the weight-value discretized BP (WD-BP) neural network. This work lays a foundation for the future development of intelligent nano-optoelectronic devices.

Förster Resonance Energy Transfer Assisted Enhancement in Optoelectronic Properties of Metal Halide Perovskite Nanocrystals

Regulated excited state energy and charge transfer play a pivotal role in nanoscale semiconductor device performance for efficient energy harvesting and optoelectronic applications. Herein, we report the influence of Förster resonance energy transfer (FRET) on the excited-state dynamics and charge transport properties of metal halide perovskite nanocrystals (PNCs), CsPbBr₃, and its anion-exchanged counterpart CsPbCl₃ with CdSe/ZnS quantum dots (QDs). We report a drop in the FRET efficiency from ∼85% (CsPbBr₃) to ∼5% (CsPbCl₃) with QDs, inviting significant alteration in their charge transport properties. Using two-probe measurements we report substantial enhancement in the current for the blend structure of PNCs with QDs, originating from the reduced trap sites, compared to that of the pristine PNCs. The FRET-based upshot in the conduction mechanism with features of negative differential resistance and negligible hysteresis for CsPbBr₃ PNCs can add new directions to high performance-based photovoltaics and optoelectronics.

Ultrafast Antisolvent Growth of Single-Crystalline CsPbCl3 Microcavity for Low-Threshold Room Temperature Blue Lasing

All-inorganic perovskite CsPbCl₃ has recently attracted considerable attention due to its great potentials for the development of high-efficiency, deep-blue optoelectronic devices. Particularly, single-crystalline CsPbCl₃ planar microstructures provide good platforms for both fundamental studies and nanophotonics applications from lasers and detectors to amplifiers. In this study, we report an ultrafast antisolvent deposition route to fabricate single-crystalline CsPbCl₃ microplatelets (MPs). The as-grown MPs exhibit uniform morphology, strong emission, and outstanding gain property. Room temperature photoluminescence lasing is realized at 428 nm with a low threshold of 11.5 μJ cm^-2 and high net optical gain up to 720 cm^-1. These findings advance fundamental understanding on the fabrication and optoelectronic applications of low-dimensional CsPbCl₃ perovskite structures.

Electrode Engineering in Halide Perovskite Electronics: Plenty of Room at the Interfaces

Contact engineering is a prerequisite for achieving desirable functionality and performance of semiconductor electronics, which is particularly critical for organic-inorganic hybrid halide perovskites due to their ionic nature and highly reactive interfaces. Although the interfaces between perovskites and charge-transporting layers have attracted lots of attention due to the photovoltaic and light-emitting diode applications, achieving reliable perovskite/electrode contacts for electronic devices, such as transistors and memories, remains as a bottleneck. Herein, a critical review on the elusive nature of perovskite/electrode interfaces with a focus on the interfacial electrochemistry effects is presented. The basic guidelines of electrode selection are given for establishing non-polarized interfaces and optimal energy level alignment for perovskite materials. Furthermore, state-of-the-art strategies on interface-related electrode engineering are reviewed and discussed, which aim at achieving ohmic transport and eliminating hysteresis in perovskite devices. The role and multiple functionalities of self-assembled monolayers that offer a unique approach toward improving perovskite/electrode contacts are also discussed. The insights on electrode engineering pave the way to advancing stable and reliable perovskite devices in diverse electronic applications.

Anomalous Structural Evolution and Glassy Lattice in Mixed-Halide Hybrid Perovskites

Hybrid halide perovskites have emerged as highly promising photovoltaic materials because of their exceptional optoelectronic properties, which are often optimized via compositional engineering like mixing halides. It is well established that hybrid perovskites undergo a series of structural phase transitions as temperature varies. In this work, the authors find that phase transitions are substantially suppressed in mixed-halide hybrid perovskite single crystals of MAPbI_3-x Br_x (MA = CH₃ NH₃ ⁺ and x = 1 or 2) using a complementary suite of diffraction and spectroscopic techniques. Furthermore, as a general behavior, multiple crystallographic phases coexist in mixed-halide perovskites over a wide temperature range, and a slightly distorted monoclinic phase, hitherto unreported for hybrid perovskites, is dominant at temperatures above 100 K. The anomalous structural evolution is correlated with the glassy behavior of organic cations and optical phonons in mixed-halide perovskites. This work demonstrates the complex interplay between composition engineering and lattice dynamics in hybrid perovskites, shedding new light on their unique properties.

Chemical Potential Diagram Guided Rational Tuning of Electrical Properties: A Case Study of CsPbBr3 for X-ray Detection

Controlling the carrier polarity and concentration underlies most electronic and optoelectronic devices. However, for the intensively studied lead halide perovskites, the doping tunability is inefficient. In this work, taking CsPbBr₃ as an example, it is revealed that the coexistence of metallic Pb or CsBr₃ /Br₂ , rather than the precursor ratio, can provide Pb-rich/Br-poor or Br-rich/Pb-poor chemical conditions, enabling the tunability of electrical properties from weak n-type, intrinsic, to moderate p-type. Experimentally, under Br₂ -exposure treatment, a shift of the Fermi level as large as 1.00 eV is achieved, which is one of the highest value among all kinds of doping methods. The X-ray detector based on the intrinsic CsPbBr₃ exhibits excellent performance, with a negligible dark-current drift of 7.1 × 10^-4 nA cm^-1 s^-1 V^-1 , a low detection limit of 103.6 nGy_air s^-1 , and a high sensitivity of 9085 μC Gy_air ^-1 cm^-2 . This work provides a critical understanding and guidance for tuning the electrical properties of lead halide perovskites, which establishes good foundations for achieving intrinsic perovskite semiconductors and also constructing potential homojunction devices.

Nanostructured perovskites for nonvolatile memory devices

Perovskite materials have driven tremendous advances in constructing electronic devices owing to their low cost, facile synthesis, outstanding electric and optoelectronic properties, flexible dimensionality engineering, and so on. Particularly, emerging nonvolatile memory devices (eNVMs) based on perovskites give birth to numerous traditional paradigm terminators in the fields of storage and computation. Despite significant exploration efforts being devoted to perovskite-based high-density storage and neuromorphic electronic devices, research studies on materials' dimensionality that has dominant effects on perovskite electronics' performances are paid little attention; therefore, a review from the point of view of structural morphologies of perovskites is essential for constructing perovskite-based devices. Here, recent advances of perovskite-based eNVMs (memristors and field-effect-transistors) are reviewed in terms of the dimensionality of perovskite materials and their potentialities in storage or neuromorphic computing. The corresponding material preparation methods, device structures, working mechanisms, and unique features are showcased and evaluated in detail. Furthermore, a broad spectrum of advanced technologies (e.g., hardware-based neural networks, in-sensor computing, logic operation, physical unclonable functions, and true random number generator), which are successfully achieved for perovskite-based electronics, are investigated. It is obvious that this review will provide benchmarks for designing high-quality perovskite-based electronics for application in storage, neuromorphic computing, artificial intelligence, information security, etc.

Perovskite-Type 2D Materials for High-Performance Photodetectors

Photodetectors are light sensors in widespread use in image sensing, optical communication, and consumer electronics. In current smart optoelectronic technology, conventional semiconductors have encountered a bottleneck caused by inflexibility and opacity. With the ever-increasing demands for versatile optoelectronic applications, perovskite-type 2D materials demonstrate great potential for advanced photodetectors inspired by molecularly thin 2D materials. Through the reduction of thickness to thin or molecularly thin levels, single-crystalline 2D perovskites can exhibit superior optoelectronic performance characteristics, such as tunable absorption property by chemical design, enhanced carrier separation by remarkable photosensing capability, and improved carrier extraction by versatile band engineering. More importantly, perovskite-type 2D materials exhibit great potential for large-scale monolithic integration to achieve all-in-one sensing-memory-computing optoelectronic devices. In this Perspective, recent progress in 2D perovskite-based photodetectors is presented in detail. The focus is on growth strategies for reducing thickness, thickness-dependent optical and electrical properties, device engineering, heterojunction fabrication, and device performance. Finally, the current challenges and future prospects in this field are presented.

Screen-Overprinted Perovskite RGB Microdisk Arrays Based on Wet-Solute-Chemical Dynamics for Full-Color Laser Displays

Owing to outstanding optoelectronic properties, halide perovskites are great candidates for novel laser display applications. However, the realization of their practical flat-panel display applications is challenging because of the incapacity to controllably assemble different halide perovskite microlaser arrays onto an identical substrate as pixelated full-color panels due to intrinsic fragile crystal lattices. Here, perovskite red-green-blue (RGB) microdisk arrays are reported, acting as flat-panels for full-color laser displays. A universal screen-overprinting technology is developed to integrate full-color perovskite microdisk arrays on a prepatterned template, which is on the basis of wet-solute-chemical dynamics involving a combination of surface tailoring and solvent selection. Via such an overprinting method, perovskite RGB microlaser matrices with precise localizations and well-defined dimensions were fabricated on an identical substrate, and each set of RGB microlaser served as a pixel for full-color display panels. On this basis, static and dynamic laser displays have been demonstrated with as-prepared full-color panels. These results will provide novel design concepts and device structures for future full-color laser display applications.

Crystal structure of formamidinium–lead–chloride–dimethyl sulfoxide and phase relationship of related crystalline systems

We presented a new hybrid lead chloride–DMSO solvate, FAPbCl3–DMSO, and explained the crystallization of this solvate in DMSO by the formation enthalpy calculation.

All in One: A Versatile n-Perovskite/p-Spiro-MeOTAD p-n Heterojunction Diode as a Photovoltaic Cell, Photodetector, and Memristive Photosynapse

With their excellent optoelectronic properties, halide perovskite (HP) semiconductors have witnessed successful applications in many fields, such as solar cells, LEDs, photodetectors, transistors, and memristors. Exploiting their fascinating physical nature for the development of single nanodevices with multifunctionalities is significant yet remains challenging. We report a multifunctional device based on the n-perovskite/p-spiro-MeOTAD p-n heterojunction diode that enables the integration of photovoltaic, photodetection, and photosynaptic functions in a single device. The device exhibits a high photoelectronic conversion efficiency (PCE) of 17.64% under AM 1.5G illumination and excellent photodetection characteristics including a low drive voltage of 0.01 V, a short response time of 0.17 s, high switching repeatability, and stability. Coupled with the superior photomemristive effect of the device that can be used for the emulation of short- and long-term memory formation of visual synapses, these results suggest that the HP-based p-n heterojunction devices hold great potential in multifunctional integrated device applications.

Deciphering the Carrier Transport Properties in Two-Dimensional Perovskites via Surface-Enhanced Raman Scattering

2D layered organic-inorganic perovskites have attracted substantial attention due to their high stability and promising optoelectronic properties. However, in-depth insights on the anisotropic carrier transport properties of these 2D perovskites are remaining challenging, while they are significant for further designing the high-performance device applications. Here, the carrier transport properties within 2D perovskite single crystals are investigated and a layered-carrier-transport model is developed through the non-invasive and non-destructive surface-enhanced Raman scattering techniques. The carrier transport features of 2D perovskites show clearly the thickness-, applied voltage- and anisotropy-dependent behaviors, which are demonstrated to origin from the quantum confinement effect. The findings elucidate the carrier transport mechanisms within 2D perovskites from their molecular level through Raman spectroscopy, thus providing a promising way for exploring the photo-physical properties in wide-ranged halide perovskites and designing highly efficient perovskite optoelectronic devices.

Enhancing the stability of CsPbX3 (X = Br, I) through combination with Y-zeolites for WLED application

The stability of perovskite quantum dots (PQDs) plays a vital role in practical devices. Besides silica coating, embedding PQDs in zeolites is another strategy to improve their stability significantly. Although the zeolite rigid framework has been reported to protect PQDs, there are few reports on the in situ synthesis of PQDs in zeolites. In this work, cubic phase CsPbX₃ (X = Br, I) nanocrystals were successfully prepared by the ion exchange method combined with a non-polar organic trigger. Dropping a certain amount of ZnM₂ (M = Br, I) solution into the intermediate product Cs₄PbCl₆ nanocrystals resulted in the formation of the final CsPbX₃ nanocrystals. The ZnM₂ solutions were prepared in non-polar solvents (hexane, octane, or chloroform). The highest photoluminescence quantum yield (PLQY) of the synthesized CsPbX₃@zeolite composites can reach 83%, with a lifetime of 1.37 μs. The stability of the CsPbX₃@zeolite composites thin film against damage from air and light is significantly improved. We fabricated white light-emitting diodes (WLEDs) using CsPbBr₃@zeolite as the green light source and CsPbI₃@zeolite as the red light source to further emphasize the practical application effect of the CsPbX₃@zeolite composites. This work not only provides a new method for the synthesis of CsPbX₃ nanocrystals but also involves the in situ synthesis of high stability CsPbX₃@zeolite composites within the zeolite.

High-efficiency planar heterojunction perovskite solar cell produced by using 4-morpholine ethane sulfonic acid sodium salt doped SnO2

Perovskite solar cells (PSCs) have become a promising photovoltaic (PV) technology. Meanwhile, developing an electron transport layer (ETL) has been an effective way to promote the power conversion efficiency (PCE) of PSCs. Here, a 4-morpholine ethane sulfonic acid sodium salt (MES Na⁺) doped SnO₂ ETL is utilized in planar heterojunction PSCs. The results show that the MES Na⁺ doped ETL can improve the crystallinity, and absorbance of perovskite films, and passivate interface defects between the perovskite film and SnO₂ ETL. The doping effect accounts for the enhancement of conductivity and the decreasing work function of SnO₂. When 10 mg mL^-1 MES Na⁺ was added to the SnO₂ precursor solution, the device showed the best performance Jsc, Voc, and FF of the PSCs values, which were 23.88 mA cm^-2, 1.12 V and 78.69%, respectively, and the PCE was increased from 17.43% to 21.05%. This doping ETL strategy provides an avenue for defect passivation to further increase the efficiency of perovskite solar cells.

Grain Boundary Engineering with Self-Assembled Porphyrin Supramolecules for Highly Efficient Large-Area Perovskite Photovoltaics

Grain boundary management is critical to the performance and stability of polycrystalline perovskite solar cells (PSCs), especially large-area devices. However, typical passivators are insulating in nature and limit carrier transport. Here, we design a supramolecular binder for grain boundaries to simultaneously passivate defects and promote hole transport across perovskite grain boundaries. By doping the monoamine porphyrins (MPs, M = Co, Ni, Cu, Zn, or H) into perovskite films, MPs self-assemble into supramolecules at grain boundaries. Organic cations in perovskites protonate MPs in supramolecules to form ammonium porphyrins bound on the perovskite grain surface, to passivate defects and extract holes from the perovskite lattice. Periodic polarons in supramolecules (especially NiP-supramolecule) promote the transport of extracted holes across boundaries, reducing nonradiative carrier recombination. The NiP-doped PSCs reveal a certified efficiency of 22.1% for an active area of 1.0 cm² with the remarkably improved open-circuit voltage and fill factor. The unencapsulated device retained over 80% initial performance under AM 1.5G solar light continuous illumination or heating at 85 °C over 3000 h.

Constructing van der Waals Heterogeneous Photocatalysts Based on Atomically Thin Carbon Nitride Sheets and Graphdiyne for Highly Efficient Photocatalytic Conversion of CO2 into CO

Atomically thin two-dimensional (2D) carbon nitride sheets (CNs) are attracting attention in the field of photocatalytic CO₂ reduction. Because of the rapid recombination of photogenerated electron-hole pairs and limited more active sites, the photocatalytic efficiency of CNs cannot meet the actual requirements. Here, atomically thin 2D/2D van der Waals heterostructures of metal-free graphdiyne (GDY)/CNs are fabricated through a simple electrostatic self-assembly method. Experimental characterizations along with first-principles calculations show that the introduction of GDY in CNs promoted the transport of photogenerated carriers in the melon chain, thus suppressing the recombination of photogenerated electron-hole pairs. Both in situ FTIR measurements and DFT calculation confirm that the introduced GDY served as the CO₂ adsorption site and enhanced the CO₂ adsorption capacity of the CNs/GDY heterostructure. Thanks to the 2D/2D van der Waals heterojunction, the optimized CNs/GDY enhances significantly the CO generation rate up to 95.8 μmol g^-1 that is 19.2-fold higher than that of CNs. This work provides a viable approach for the design of metal-free van der Waals heterostructure-based photocatalysts with high catalytic activity.