Rational chemical doping of metal halide perovskites

Discovering key factors determining perovskite bandgap under data scarcity inspired by knowledge distillation

Metal halide perovskites (MHPs) are promising candidates for next-generation optoelectronic applications due to their tunable compositions and exceptional optoelectronic properties. However, the compositional and structural diversity presents challenges for the optimization of their properties by traditional experimental and computational methods. Machine learning (ML) provides a data-driven approach for rapidly predicting material properties, yet in data-scarce MHP systems its predictive power and model explainability is limited. Herein, a small data ML framework tailored for MHP materials is developed, inspired by knowledge distillation to address this limitation. By generating a large set of inorganic MHP compositions via ionic substitution and utilizing the optimized unstructured learning model CrabNet_s, bandgap values are predicted with high precision. Additionally, physics-based chemical descriptors are designed, with CrabNet_s serving as a teacher model to train simpler student models, improving interpretability, while SHAP analysis identifies the contribution of each descriptor. B-site (the octahedrally-coordinated metal center in perovskite structures) electronegativity of inorganic MHPs is uncovered as the key compositional factor influencing bandgap values, enabling precise bandgap tuning by adjusting elemental ratios. This study enhances the application of ML in designing MHPs under small data conditions, offering a promising strategy for accelerating their development in optoelectronic applications.

Structural Phase Transition-Associated Ferroelectricity and Piezoelectric Energy Harvesting in 0D Halogenozincate Hybrid via Cation's Terminal Group Lengthening

Halogenometallate hybrids have garnered significant research interest for their unique structural properties, making them promising candidates for practical applications. However, due to preparation challenges and stability issues, molecular-based materials with ferroelectric properties are needed. Herein, zero-dimensional (0D) A2BX4-type halogenozincate hybrids, (C7H13NR)2ZnCl4 (R = H for 1; methyl for 2; ethyl for 3, n-propyl for 4, and n-butyl for 5), are synthesized. Despite the sole difference in the cation, only 5 displays a reversible ferroelectric phase transition (P41↔P43212). The ferroelectricity and its implementation in piezoelectric energy harvesting are demonstrated. Single-crystal structural analyses reveal the static-to-dynamic state change of the cation's terminal group drives the phase transition and associated properties. 5 achieves excellent ferroelectricity, including above room-temperature Curie temperature (330 K) and low coercive field (0.95 kV cm-1). Furthermore, flexible piezoelectric nanogenerators are fabricated using polyvinyl alcohol films incorporated with 5 at varying weight percentages (wt%). The 15 wt% composite device exhibits the highest open-circuit peak voltage of 74 V, a short-circuit peak current of 4 µA, and a power density of 0.40 mW cm-2. More importantly, it maintains stable performance over 5000 cycles. This finding provides a simple approach for designing low-dimensional hybrid ferroelectrics tailored for high-power output devices.

Modification Strategies of Bismuth-Based Halide Perovskites for Solar to Fuel Conversion by Photocatalytic CO2 Reduction

In light of the increasingly pressing energy and environmental challenges, the use of photocatalysis to convert solar energy into chemical energy has emerged as a promising solution. Halide perovskites have recently attracted considerable interest as photocatalysts due to their outstanding properties. Early developments focused on Lead-based perovskites, but their use has been severely restricted due to the toxicity of Lead. Consequently, researchers have introduced non-toxic elements to replace Lead, with common substitutes being transition metals such as Tin (Sn), Bismuth (Bi), and Antimony (Sb). Among them, Bi-based perovskites have demonstrated superior photocatalytic performance. Nevertheless, the inherent instability of perovskites and the severe recombination of charge carriers have necessitated the development of various modification strategies to enhance their performance. This Review discusses the modification strategies for Bi-based halide perovskites and illustrates the impact of these strategies on the photocatalytic performance. Finally, future research directions and challenges of Bi-based perovskites for photocatalysis are proposed.

Realization of Tunable Ferroelectricity in Perovskite Crystals for Multidirectional Self-Driven Photodetection

Halide perovskite ferroelectrics endowed with a distinctive spontaneous polarization effect have been regarded as prospective electroactive materials and are prevalently utilized in solar cells, photoelectric detection, and other domains. Among them, multipolar-axis ferroelectrics featuring multiple equivalent polarization directions are particularly desirable for diverse areas of applications. Nevertheless, the design and regulation of multipolar axis perovskite ferroelectrics remains a significant challenge. Here, guided by the strategy of layer regulation, we successfully designed and regulated a series of 2D homologous perovskites OA2Csn -1PbnBr3 n +1 (OA = n-octylammonium, n = 1-3). Notably, OA2Csn -1PbnBr3 n +1 exhibits layer-dependent ferroelectricity: OA2PbBr4 exhibits non-ferroelectricity, OA2CsPb2Br7 displays uniaxial ferroelectricity, while OA2Cs2Pb3Br10 has multiaxial ferroelectricity. Moreover, the devices fabricated based on OA2Cs2Pb3Br10 achieve high-performance self-driven photodetection in multiple directions. This precise layer-regulation strategy offers an efficient approach to obtaining and regulating multipolar-axis perovskite ferroelectrics, presenting the potential for next-generation optoelectronic devices.

In Situ Halide Vacancy Tuning of Low-Dimensional Lead Perovskites to Realize Multiple Adjustable Luminescence Performance

Surface defects play a crucial role in the photophysical properties and optoelectronic applications of perovskite materials. Although luminescent efficiency is improved through post-synthetic defect passivation, comprehensive optimization of photoluminescent performance via defect chemistry remains a significant challenge. Herein, a successful defect engineering strategy is demonstrated toward 0D perovskite of [DADPA]PbBr5 (DADPA = diaminodipropylamine) single crystal to achieve multiple adjustable luminescent properties. Through fine-tuning the crystallization environment to diminish Br vacancy (VBr), [DADPA]PbBr5 displays gradually evolutionary luminescence range from broadband blue-white to narrow green light emissions, with continuously adjustable dominant wavelengths (445-535 nm) and linewidths (134-27 nm). Meanwhile, the quantum yields increase significantly from 3.7% to 80.8%, and lifetime extends from 5.4 to 57.7 ns. This is the pioneering discovery in perovskite chemistry for simultaneous modification of multi-dimensional luminescent performances. Combined spectroscopic investigations and first-principles calculations indicate that the reducing VBr significantly narrows the bandgap and inhibits nonradiative recombination, which attenuates interband trap-state-associated broadband emission and facilitates the formation of bound exciton for enhanced emission efficiency. More remarkably, this universal strategy can be extended to other perovskite systems with similar luminescent adjustability, paving the way for applications of diverse perovskites with improved optoelectronic performance.

Near-infrared luminescent materials: a review of their practical applications and prospective advancements

Near-infrared (NIR) spectroscopy has the characteristics of invisible human eyes, strong ability to penetrate biological tissues, fast response speed, non-destructive testing, and avoidance of autofluorescence interference. Therefore, NIR luminescent materials are widely used in various fields, including food monitoring, night vision supplementation, face recognition, in vivo imaging, biological analysis, safety monitoring, autonomous driving, and agricultural lighting. However, the lack of NIR luminescent materials with high quantum efficiency, wide bandwidth, and weak thermal quenching still hinders the development of NIR spectroscopy technology. Herein, we review the current research progress and luminescence mechanisms in NIR luminescent materials doped with rare earth (RE) ions, transition metal (TM) ions, and main-group ions, including Yb3+, Pr3+, Er3+, Eu2+, Nd3+, Ni2+, Mn2+, Mn4+, Fe3+, Cu2+, Cr3+, Bi2+, Sb3+ and other ion-doped NIR fluorescent materials. The optical properties, enhancement mechanisms of NIR luminescence, and modulation strategies to adjust the emission wavelength of active ion-doped NIR luminescent materials are highlighted, respectively. We further elaborate on the possible solutions to the design of broadband NIR luminescent materials. This study aims to help researchers in related fields understand the current research status, challenges, and future development trends of RE ion-, TM ion-, and main-group ion-doped NIR luminescent materials.

Decoding recombination dynamics in perovskite solar cells: an in-depth critical review

The remarkable optoelectronic properties of metal halide perovskites (MHPs) have established them as highly promising photovoltaic absorber materials, propelling the rapid advancement of perovskite solar cells (PSCs) that outperform many traditional alternatives in terms of power conversion efficiency (PCE). However, despite their advancements, PSC devices encounter significant non-radiative recombination losses, encompassing trap-assisted (Shockley-Read-Hall) recombination in bulk and interfaces of PSCs, which restricts their open-circuit voltage (VOC) and overall PCE, dragging it below the Shockley-Queisser (SQ) limit. The ongoing debate regarding the role of grain boundary (GB) recombination, whether it primarily manifests as bulk or surface recombination, has spurred extensive research aimed at elucidating these mechanisms. This review provides a critical comprehensive analysis of the thermodynamic correlations related to VOC losses, bridging the gap between the theoretical SQ limit and practical device performance. Subsequently, it delves into recent findings that aim to decipher the multifaced nature and origin of radiative and non-radiative recombination-induced losses within the device stack, assessing their impacts on overall performance. Furthermore, this review emphasizes the application of advanced machine learning techniques to discern dominant recombination mechanisms in PSCs. Finally, it summarizes the notable advanced strategies to mitigate undesirable non-radiative recombination losses, which pave the way to the thermodynamic efficiency limit.

Recent Developments of Advanced Broadband Photodetectors Based on 2D Materials

With the rapid development of high-speed imaging, aerospace, and telecommunications, high-performance photodetectors across a broadband spectrum are urgently demanded. Due to abundant surface configurations and exceptional electronic properties, two-dimensional (2D) materials are considered as ideal candidates for broadband photodetection applications. However, broadband photodetectors with both high responsivity and fast response time remain a challenging issue for all the researchers. This review paper is organized as follows. Introduction introduces the fundamental properties and broadband photodetection performances of transition metal dichalcogenides (TMDCs), perovskites, topological insulators, graphene, and black phosphorus (BP). This section provides an in-depth analysis of their unique optoelectronic properties and probes the intrinsic physical mechanism of broadband detection. In Two-Dimensional Material-Based Broadband Photodetectors, some innovative strategies are given to expand the detection wavelength range of 2D material-based photodetectors and enhance their overall performances. Among them, chemical doping, defect engineering, constructing heterostructures, and strain engineering methods are found to be more effective for improving their photodetection performances. The last section addresses the challenges and future prospects of 2D material-based broadband photodetectors. Furthermore, to meet the practical requirements for very large-scale integration (VLSI) applications, their work reliability, production cost and compatibility with planar technology should be paid much attention.

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.

Hydrogen-Bonding-Driven Design of Organic-Inorganic Hybrid Ferroelastics with Reversible Photoisomerization

The development of photoresponsive ferroelastics, which couple light-induced macroscopic mechanical and microscopic domain properties, represents a frontier in materials science with profound implications for advanced functional applications. In this study, we report the rational design and synthesis of two new organic-inorganic hybrid ferroelastic crystals, (MA)(Me4N)[Fe(CN)5(NO)] (MA = methylammonium) (1) and (MA)(Me3NOH)[Fe(CN)5(NO)] (2), using a dual-organic molecular design strategy that exploits hydrogen-bonding interactions for tailoring ferroelastic properties. Specifically, 1 exhibits a two-step phase transition at 138 and 242 K, while the introduction of a hydroxyl group in 2 stabilizes its ferroelastic phase to a significantly higher temperature, achieving a phase transition at 328 K, 86 K above that of 1. This enhancement is attributed to hydrogen bonding between the hydroxyl group of Me3NOH+ and the nitroprusside anion, which suppresses lattice dynamics and reinforces structural stability. Remarkably, 2 demonstrates a large spontaneous strain of 0.153, vastly exceeding the 0.021 of 1, and undergoes an 11% size change along the b-axis in response to thermal stimuli. Both compounds exhibit reversible, photoinduced nitrosyl-linkage isomerization, as confirmed by IR spectroscopy, transitioning between the ground state (N-bound nitrosyl) and the metastable state (O-bound nitrosyl). This integration of photoresponsive functionality with ferroelastic properties establishes a versatile platform for energy-efficient actuation, adaptive devices, and multifunctional sensing applications. These findings offer an innovative pathway for designing next-generation hybrid materials with enhanced tunable properties.

Near-Full-Spectrum Emission Realized in a Single Lead Halide Perovskite across the Visible-Light Region

The engineering of tunable photoluminescence (PL) in single materials with a full-spectrum emission represents a highly coveted objective but poses a formidable challenge. In this context, the realization of near-full-spectrum PL emission, spanning the visible light range from 424 to 620 nm, in a single-component two-dimensional (2D) hybrid lead halide perovskite, (ETA)2PbBr4 (ETA+=(HO)(CH2)2NH3 +), is reported, achieved through high-pressure treatment. A pressure-induced phase transition occurs upon compression, transforming the crystal structure from an orthorhombic phase under ambient conditions to a monoclinic structure at high pressure. This phase transition driven by the adaptive and dynamic configuration changes of organic amine cations enables an effective and continuous narrowing of the band gap in this halide crystal. The hydrogen bonding interactions between inorganic layers and organic amine cations (N-H⋅⋅⋅Br and O-H⋅⋅⋅Br hydrogen bonds) efficiently modulate the organic amine cations penetration and the octahedral distortion. Consequently, this phenomenon induces a phase transition and results in red-shifted PL emissions, leading to the near-full-spectrum emission. This work opens a possibility for achieving wide PL emissions with coverage across the visible light spectrum by employing high pressure in single halide perovskites.

Supra-ceramics: a molecule-driven frontier of inorganic materials

Discoveries and technological innovations over the past decade are transforming our understanding of the properties of ceramics, such as 'hard', 'brittle', and 'homogeneous'. For example, inorganic crystals containing molecular anions exhibit excellent secondary battery characteristics, and the fusion of inorganic solids and molecules results in innovative catalytic functions and physical properties. Different from the conventional ceramics such as metal oxides that are formed by monatomic cations and anions, unique properties and functions can be expected in molecular-incorporated inorganic solids, due to the asymmetric and dynamic properties brought about by the constituent molecular units. We name the molecular-incorporated inorganic materials that produce innovative properties and functions as supra-ceramics. In this article, we describe various kinds of supra-ceramics from the viewpoint of synthesis, analysis and physical properties/functions for a wide range of applications.

In Situ Fabrication of Highly Efficient and Stable Cs2NaInCl6: Sb3+@PVDF Composite Films for Optoelectronic Devices

Lead-free double perovskites (DPs) have superior phase stability and optical properties, which make them competitive for future applications in illumination and displays. However, the preparation of DPs was mainly based on high-temperature heating and hydrochloric acid as a solvent to form powders, which increased the risk and cost of the preparation process and limited its further application. In this study, the growth of Cs2NaInCl6: Sb3+ DPs in polyvinylidene difluoride (PVDF) films was achieved using an in situ fabrication strategy with DMSO as the solvent. The prepared Cs2NaInCl6: Sb3+@PVDF composite films (CFs) can achieve a bright blue emission under 302 nm irradiation. To achieve the optimal luminescent performance of CFs, the photoluminescence (PL) intensity of Cs2NaInCl6: Sb3+@PVDF CFs under various in situ preparation conditions was compared. In addition, the photoluminescence quantum yield (PLQY) of CFs was increased from 0.72% to 83.77% by adjusting the doping amount of Sb3+, and the fluorescence lifetimes t1 and t2 were 131.08 and 1048.52 ns, respectively. Temperature-dependent PL spectroscopy and density functional theory (DFT) calculations indicate that these excellent optical properties are derived from the self-trapped excitons (STEs) at the [SbCl6]3- octahedron and [InCl6]3- octahedron connected via Cl-Na-Cl. The CFs also demonstrated excellent environmental stability, maintaining a relatively stable PL intensity even under conditions of water immersion, high temperatures, and ultraviolet (UV) radiation. Finally, we used the CFs to assemble a blue light-emitting device (LED), which showed good and stable blue emission performance at different currents. This work can provide a new idea for preparing DPs, which is conducive to promoting their commercial application in high-performance optoelectronic devices.

Recent Advances in Structure Design and Application of Metal Halide Perovskite-Based Gas Sensor

Metal halide perovskites (MHPs) are emerging gas-sensing materials and have attracted considerable attention in gas sensors due to their unique bandgap structure and tunable optoelectronic properties. The past decade has witnessed significant developments in the gas-sensing field; however, their intrinsic structural instability and ambiguous gas-sensing mechanisms hamper their practical applications. Herein, we summarize the recent advances in MHP-based gas sensors. The physicochemical properties of MHPs are discussed at first. The structure design, including dimension design and engineering design, is overviewed as well as their fabrication methods, and we put forward our insights into the gas-sensing mechanism of MHPs. It is believed that enhanced understanding of gas-sensing mechanisms of MHPs are helpful for their application as gas-sensing materials, and structure design can enhance their stability, sensing sensitivity, and selectivity to target gases as gas sensors. Subsequently, the latest developments in MHP-based gas sensors are summarized according to their different application scenarios. Finally, we conclude with the current status and challenges in this field and propose future perspectives.

An efficient chemiluminescent probe based on Ni-doped CsPbBr3 perovskite nanocrystals embedded in mesoporous SiO2 for sensitive assay of L-cysteine

This study presents an efficient chemiluminescence (CL) probe based on perovskite nanocrystals (NCs) for detection of L-cysteine (L-Cys). It consists of nickel-doped CsPbBr3 NCs embedded in the mesoporous SiO2 matrix as CL reagent and cerium (IV) as an oxidant in aqueous environment. The probe was designed for the highly selective determination of L-Cys based on its remarkable enhancing effect on the CL intensity. The colloidal nanocomposite of nickel-doped CsPbBr3 NCs@SiO2 with photoluminescence quantum yield of 58% was fabricated by ligand-assisted re-precipitation method and characterized by using UV-Vis absorption, FT-IR, X-ray diffraction, and transmission electron microscopy. The sensor was utilized to determine L-Cys in the linear concentration range of 20-300 nM with a detection limit of 12.8 nM. Direct chemical oxidation of Ni-doped CsPbBr3 NCs@SiO2 by Ce(IV) was the single cause of the formation of the excited-state NCs and subsequent production of CL. The developed probe provides outstanding selectivity towards L-Cys over structurally related compounds. Accurate determination of L-Cys in human serum samples was achieved without interference, and the results were confirmed by HPLC method.

Discerning the Structure-Photophysical Property Correlation in Zero-Dimensional Antimony(III)-Doped Indium(III) Halide Hybrids

Zero-dimensional (0D) metal halide hybrids incorporating optically emissive Sb3+ dopants have received huge research attention as a result of dopant-based visible emission for lighting and scintillation applications. Indeed, there have been a plethora of reports on Sb3+ doping of indium halide (In-X)-based 0D hybrids that show strong dopant emission with varied emission wavelengths (λem) and photoluminescence quantum yields (PLQYs). However, discerning the structure-luminescence relation in these 0D-doped hybrids remains challenging because it necessitates exquisite synthetic control on the local metal (dopant) halide geometry/site asymmetry. Demonstrated here is synthetic control that allows tuning of the local metal halide geometry of the Sb3+ dopants in 0D In-X hybrids utilizing five different organic cations. Experimental analysis of the series of Sb3+-doped In-X hybrids reveals a strong correlation between the extent of local metal halide geometry distortion and their photophysical properties (λem and PLQY). Density functional theory calculations of the doped compounds, characterizing ground- and excited-state structural distortions and energetics, reveal the origin of the extent of luminescence behavior. The experimental-computational results reported herein unravel the operative structure-luminescence relation in 0D Sb3+-doped In-X hybrids, provide insight into the emission mechanism, and open up avenues toward rational synthesis of strongly emissive materials with desired emission color for targeted applications.

Recent progress of metal halide perovskite materials in heterogeneous photocatalytic organic reactions

Photocatalytic technology is widely regarded as an important way to utilize solar energy and achieve carbon neutrality, which has attracted considerable attentions in various fields over the past decades. Metal halide perovskites (MHPs) are recognized as "superstar" materials due to their exceptional photoelectric properties, readily accessible and tunable structure, which made them intensively studied in solar cells, light-emitting diodes, and solar energy conversion fields. Since 2018, increased attention has been focused on applying the MHPs as a heterogeneous visible light photocatalyst in catalyzing organic synthesis reactions. In this review, we present an overview of photocatalytic technology and principles of heterogeneous photocatalysis before delving into the structural characteristics, stability, and classifications of MHPs. We then focus on recent developments of MHPs in photocatalyzing various organic synthesis reactions, such as oxidation, cyclization, C-C coupling etc., based on their classifications and reported reaction types. Finally, we discuss the main limitations and prospects regarding the application of metal halide perovskites in organic synthesis.

The past 10 years of molecular ferroelectrics: structures, design, and properties

Ferroelectricity, which has diverse important applications such as memory elements, capacitors, and sensors, was first discovered in a molecular compound, Rochelle salt, in 1920 by Valasek. Owing to their superiorities of lightweight, biocompatibility, structural tunability, mechanical flexibility, etc., the past decade has witnessed the renaissance of molecular ferroelectrics as promising complementary materials to commercial inorganic ferroelectrics. Thus, on the 100th anniversary of ferroelectricity, it is an opportune time to look into the future, specifically into how to push the boundaries of material design in molecular ferroelectric systems and finally overcome the hurdles to their commercialization. Herein, we present a comprehensive and accessible review of the appealing development of molecular ferroelectrics over the past 10 years, with an emphasis on their structural diversity, chemical design, exceptional properties, and potential applications. We believe that it will inspire intense, combined research efforts to enrich the family of high-performance molecular ferroelectrics and attract widespread interest from physicists and chemists to better understand the structure-function relationships governing improved applied functional device engineering.

Chiral Materials for Optics and Electronics: Ready to Rise?

Chiral materials have gained burgeoning interest in optics and electronics, beyond their classical application field of drug synthesis. In this review, we summarize the diverse chiral materials developed to date and how they have been effectively applied to optics and electronics to get an understanding and vision for the further development of chiral materials for advanced optics and electronics.

Chiral-Achiral Cations Intercalation Induced Lead-Free Chiral-Polar Hybrid Perovskites Enable Self-Powered X-Ray and Ultraviolet-Visible-Near-Infrared Photo Detection

Lead halide hybrid perovskites have made great progress in direct X-ray detection and broadband photodetection, but the existence of toxic Pb and the demand for external operating voltage have severely limited their further applications and operational stability improvements. Therefore, exploring "green" lead-free hybrid perovskite that can both achieve X-ray detection and broadband photodetection without external voltage is of great importance, but remains severely challenging. Herein, using centrosymmetric (BZA)3BiI6 (1, BZA = benzylamine) as a template, a pair of chiral-polar lead-free perovskites, (BZA)2(R/S-PPA)BiI6 (2-R/S, R/S-PPA = (R/S)-1-Phenylpropylamine) are successfully obtained by introducing chiral aryl cations of (R/S)-1-Phenylpropylamine. Compared to 1, chiral-polar 2-R presents a significant irradiation-responsive bulk photovoltaic effect (BPVE) with an open circuit photovoltage of 0.4 V, which enables it with self-powered X-ray, UV-vis-NIR broadband photodetection. Specifically, 2-R device exhibits an ultralow detection limit of 18.5 nGy s-1 and excellent operational stability. Furthermore, 2-R as the first lead-free perovskite achieves significant broad-spectrum (377-940 nm) photodetection via light-induced pyroelectric effect. This work sheds light on the rational crystal reconstruction engineering and design of "green" hybrid perovskite toward high-demanded self-powered radiation detection and broadband photodetection.

Toward stabilization of formamidinium lead iodide perovskites by defect control and composition engineering

Phase instability poses a serious challenge to the commercialization of formamidinium lead iodide (FAPbI3)-based solar cells and optoelectronic devices. Here, we combine density functional theory and machine learning molecular dynamics simulations, to investigate the mechanism driving the undesired α-δ phase transition of FAPbI3. Prevalent iodine vacancies and interstitials can significantly expedite the structural transition kinetics by inducing robust covalency during transition states. Extrinsically, the detrimental roles of atmospheric moisture and oxygen in degrading the FAPbI3 perovskite phase are also rationalized. Significantly, we discover the compositional design principles by categorizing that A-site engineering primarily governs thermodynamics, whereas B-site doping can effectively manipulate the kinetics of the phase transition in FAPbI3, highlighting lanthanide ions as promising B-site substitutes. A-B mixed doping emerges as an efficient strategy to synergistically stabilize α-FAPbI3, as experimentally demonstrated by substantially higher initial optoelectronic characteristics and significantly enhanced phase stability in Cs-Eu doped FAPbI3 as compared to its Cs-doped counterpart. This study provides scientific guidance for the design and optimization of long-term stable FAPbI3-based solar cells and other optoelectronic devices through defect control and synergetic composition engineering.

Doping strategies for inorganic lead-free halide perovskite solar cells: progress and challenges

In recent years, remarkable advancements have been achieved in the field of halide perovskite solar cells (PSCs). However, the commercialization of PSCs has been impeded by challenges such as Pb leakage and the instability of hybrid organic-inorganic perovskites (HOIPs). Hence, the future lies in the development of environmentally friendly inorganic lead-free halide perovskites (LFHPs) based on elements like Sn, Ge, Bi, Sb, and Cu, which show great promise for photovoltaic applications. However, LFHP photovoltaic cells still face challenges such as low efficiency, poor film quality, and stability in comparison to HOIPs. These limitations significantly hinder their further development. To address these issues, element doping strategies, including cationic and anionic doping, as well as the use of additives, are frequently employed. These strategies aim to improve film quality, passivate defects, reduce the band gap, and enhance device performance and stability. In this paper, we aim to provide a comprehensive review of the recent research progress in doping strategies for LFHPs.

Sb-Doped Cs3 TbCl6 Nanocrystals for Highly Efficient Narrow-Band Green Emission and X-Ray Imaging

Metal halide nanocrystals (NCs) with high photoluminescence quantum yield (PLQY) are desirable for lighting, display, and X-ray detection. Herein, the novel lanthanide-based halide NCs are committed to designing and optimizing the optical and scintillating properties, so as to unravel the PL origin, exciton dynamics, and optoelectronic applications. Sb-doped zero-dimensional (0D) Cs3 TbCl6 NCs exhibit a green emission with a narrow full width of half maximum of 8.6 nm, and the best PLQY of 48.1% is about three times higher than that of undoped NCs. Experiments and theoretical calculations indicate that 0D crystalline and electronic structures make the exciton highly localized on [TbCl6 ]3- octahedron, which boosts the Cl- -Tb3+ charge transfer process, thus resulting in bright Tb3+ emission. More importantly, the introduction of Sb3+ not only facilitates the photon absorption transition, but also builds an effective thermally boosting energy transfer channel assisted by [SbCl6 ]3- -induced self-trapped state, which is responsible for the PL enhancement. The high luminescence efficiency and negligible self-absorption of the Cs3 TbCl6 : Sb nanoscintillator enable a more sensitive X-ray detection response compared with undoped sample. The study opens a new perspective to deeply understand the excited state dynamics of metal halide NCs, which helps to design high-performance luminescent lanthanide-based nanomaterials.

Building Block-Inspired Hybrid Perovskite Derivatives for Ferroelectric Channel Layers with Gate-Tunable Memory Behavior

Ferroelectric photovoltaics driven by spontaneous polarization (Ps ) holds a promise for creating the next-generation optoelectronics, spintronics and non-volatile memories. However, photoactive ferroelectrics are quite scarce in single homogeneous phase, owing to the severe Ps fatigue caused by leakage current of photoexcited carriers. Here, through combining inorganic and organic components as building blocks, we constructed a series of ferroelectric semiconductors of 2D hybrid perovskites, (HA)2 (MA)n-1 Pbn Br3n+1 (n=1-5; HA=hexylamine and MA=methylamine). It is intriguing that their Curie temperatures are greatly enhanced by reducing the thickness of inorganic frameworks from MAPbBr3 (n=∞, Tc =239 K) to n=2 (Tc =310 K, ΔT=71 K). Especially, on account of the coupling of room-temperature ferroelectricity (Ps ≈1.5 μC/cm2 ) and photoconductivity, n=3 crystal wafer was integrated as channel field effect transistor that shows excellent a large short-circuit photocurrent ≈19.74 μA/cm2 . Such giant photocurrents can be modulated through manipulating gate voltage in a wide range (±60 V), exhibiting gate-tunable memory behaviors of three current states ("-1/0/1" states). We believe that this work sheds light on further exploration of ferroelectric materials toward new non-volatile memory devices.

Dion-Jacobson to Alternating-Cations-Interaction Reconstruction toward Narrow Bandgap 2D Aromatic Hybrid Perovskite

The 2D aromatic Dion-Jacobson (DJ) hybrid perovskites combining advantages of high stability, enhanced light absorption, and favorable charge transport, are regarded as a kind of very promising materials for high-performance optoelectronic applications. However, due to the rigidity and large size of the aromatic ring, how to further reduce the interlayer distance to achieve better carrier transport and wider light response window still remain extremely challenging. Here, an interesting DJ-to-ACI (alternating-cations-interaction) reconstruction in 2D aromatic perovskite is first realized by inserting MA+ cations into (4-AP)PbI4 (1, 4-AP = 4-amidinopyridinium), successfully constructing an unprecedented ACI perovskite of (4-AP)(MA)2 Pb2 I8 (2, MA = methylamine). Remarkably, such a DJ-to-ACI reconstruction not only effectively reduces the interlayer spacing from 3.89 to 3.15 Å but also alleviates the structural distortion, which jointly causes a significant bandgap narrowing from 2.22 to 1.95 eV (smaller than all current 2D monolayered DJ perovskites), hence achieving a broad photodetection window over 660 nm. This work reports a novel narrow bandgap 2D ACI perovskite derived from the aromatic DJ motif, which sheds light on future regulations on the structure and properties of hybrid perovskites.

Alternating chiral and achiral spacers for constructing two-dimensional chiral hybrid perovskites toward circular-polarization-sensitive photodetection

The intrinsic integration of structural flexibility, chiroptical activity, and photoelectric properties endows the two-dimensional (2D) chiral hybrid perovskites (CHPs) with significant application potential in chiroptoelectronics and spintronics. However, the scarcity of suitable chiral organic ligands severely hinders their extensive construction, necessitating the development of new strategies for designing 2D CHPs. Herein, by exploiting a half substitution method, we created a pair of 2D CHPs with alternating cations in the interlayer space (ACI), (R/S-PPA)(PA)PbBr4 (2R/2S, PPA = 1-phenylpropylamine, PA = n-pentylamine), from the achiral Ruddlesden-Popper (RP) (PA)2PbBr4 (1). The successful chirality transfer induces 2R/2S to crystallize in the chiral P212121 space group and thus acquire appealing chiroptical activity. Consequently, the single-crystal devices of 2R exhibit good distinguishability to the left- and right-handed circularly polarized 405 nm lights with a photocurrent dissymmetric factor of 0.10 at 10 V bias. This work demonstrates an intriguing achiral RP to chiral ACI motif reconstruction in 2D halide hybrid perovskites, opening a door for expanding the family of 2D CHPs.

Integrating Achiral and Chiral Organic Ligands in Zero-Dimensional Hybrid Metal Halides to Boost Circularly Polarized Luminescence

Chiral zero-dimensional hybrid metal halides (0D HMHs) could combine excellent optical properties and chirality, making them promising for circularly polarized luminescence (CPL). However, chiral 0D HMHs with efficient CPL have been rarely reported. Here, we propose an efficient strategy to achieve simultaneously high photoluminescence quantum yield (PLQY) and large dissymmetry factor (glum ), by integrating achiral and chiral ligands into 0D HMHs. Specifically, three pairs of chiral 0D hybrid indium-antimony chlorides are synthesized by combing achiral guanidine with three types of chiral methylbenzylammonium-based derivatives as the organic cations. These chiral 0D HMHs exhibit near-unity PLQY and large glum values up to around ±1×10-2 . The achiral guanidine ligand is not only essential to crystallize these hybrid indium-antimony chlorides to achieve near-unity PLQYs, but also greatly enhances the chirality induction from organic ligands to inorganic units in these 0D HMHs. Furthermore, the choice of different chiral ligands can modify the strength of hydrogen bonding interactions in these 0D HMHs, to maximize their glum values. Overall, this study provides a robust way to realize efficient CPL in chiral HMHs, expanding their applications in chiroptical fields.

Performance Improvement of Lead-Based Halide Perovskites through B-Site Ion-Doping Strategies

Owing to their excellent properties, lead halide perovskites have attracted extensive attention in the photoelectric field. Presently, the certified power conversion efficiency of perovskite solar cells has reached 25.7%, the specific detectivity of perovskite photodetectors has exceeded 1014 Jones, and the external quantum efficiency of perovskite-based light-emitting diode has exceeded 26%. However, their practical applications are limited by the inherent instability induced by the perovskite structure due to moisture, heat, and light. Therefore, one of the widely used strategies to address the issue is to replace partial ions of the perovskites with ions of smaller radii to shorten the bond length between halides and metal cations, improving the bond energy and enhancing the perovskite stability. Particularly, the B-site cation in the perovskite structure can affect the size of eight cubic octahedrons and their gap. However, the X-site can only affect four such voids. This review comprehensively summarizes the recent progress in B-site ion-doping strategies for lead halide perovskites and provides some perspectives for further performance improvements.

Greatly Enhanced Resonant Exciton-Trion Conversion in Electrically Modulated Atomically Thin WS2 at Room Temperature

Excitonic resonance in atomically thin semiconductors offers a favorite platform to study 2D nanophotonics in both classical and quantum regimes and promises potentials for highly tunable and ultra-compact optical devices. The understanding of charge density dependent exciton-trion conversion is the key for revealing the underlaying physics of optical tunability. Nevertheless, the insufficient and inefficient light-matter interactions hinder the observation of trionic phenomenon and the development of excitonic devices for dynamic power-efficient electro-optical applications. Here, by engaging an optical cavity with atomically thin transition metal dichalcogenides (TMDCs), greatly enhanced exciton-trion conversion is demonstrated at room temperature (RT) and achieve electrical modulation of reflectivity of ≈40% at exciton and 7% at trion state, which correspondingly enables a broadband large phase tuning in monolayer tungsten disulfide. Besides the absorptive conversion, ≈100% photoluminescence conversion from excitons to trions is observed at RT, illustrating a clear physical mechanism of an efficient exciton-trion conversion for extraordinary optical performance. The results indicate that both excitons and trions can play significant roles in electrical modulation of the optical parameters of TMDCs at RT. The work shows the real possibility for realizing electrical tunable and multi-functional ultra-thin optical devices using 2D materials.

Precise Design of Molecular Ferroelectrics with High TC and Tunable Band Gap by Molecular Modification

Molecular ferroelectric materials are widely applied in piezoelectric converters, non-volatile memorizers, and photovoltaic devices due to their advantages of adjustable structure, lightweight, easy processing, and environmental friendliness. However, designing multifunctional molecular ferroelectrics with excellent properties has always been a great challenge. Herein, a multiaxial molecular ferroelectric is successfully designed by modifying the quasi-spherical cation dabco with CuBr₂ to obtain halogenated [Bretdabco]CuBr₄ (Bretdabco = N-bromoethyl-N'-diazabicyclo [2.2.2]octane), which crystallizes in polar point groups (C₆). Typical ferroelectric behaviors featured by the P-E hysteresis loop and switched ferroelectric domain are exhibited. Notably, the molecular ferroelectric shows a high T_C of 460 K, which is rare in the field and could greatly expand the application range of this material. In addition, the band gap is adjustable through the regulation of halogen. Both the UV absorption spectra and theoretical calculations indicate that the molecular ferroelectrics belong to a direct band gap (2.14 eV) semiconductor. This tunable and narrow band gap semiconductor molecular ferroelectric material with high T_C can be utilized more effectively in the study of optoelectronics and sensors, including piezoelectric energy harvesters. This research may provide a promising approach for the development of multiaxial molecular ferroelectrics with a tiny band gap and high T_C.

Phase transition and ionic conduction enhancement induced by co-doping of LiI and MnI2 in a one-dimensional lead iodide perovskite

Herein, we demonstrated the unique advantage of a mechanochemical reaction to prepare a salt with hard and soft acid and base ions concurrently by solution synthesis owing to the soft acid preferring to combine with the soft base and vice versa. We prepared Bu₄N_1-xLi_xMn_xPb_1-xI₃ (x = 0.011-0.14) by mechanochemical synthesis. The doping induced a structural phase transition at ∼342 K and much enhancement of ionic conduction above 342 K for all co-doped hybrids regarding Bu₄NPbI₃ because of the voids around the Mn²⁺/Li⁺ ions by doping.

Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution

Solution-processed semiconductors are in demand for present and next-generation optoelectronic technologies ranging from displays to quantum light sources because of their scalability and ease of integration into devices with diverse form factors. One of the central requirements for semiconductors used in these applications is a narrow photoluminescence (PL) line width. Narrow emission line widths are needed to ensure both color and single-photon purity, raising the question of what design rules are needed to obtain narrow emission from semiconductors made in solution. In this review, we first examine the requirements for colloidal emitters for a variety of applications including light-emitting diodes, photodetectors, lasers, and quantum information science. Next, we will delve into the sources of spectral broadening, including "homogeneous" broadening from dynamical broadening mechanisms in single-particle spectra, heterogeneous broadening from static structural differences in ensemble spectra, and spectral diffusion. Then, we compare the current state of the art in terms of emission line width for a variety of colloidal materials including II-VI quantum dots (QDs) and nanoplatelets, III-V QDs, alloyed QDs, metal-halide perovskites including nanocrystals and 2D structures, doped nanocrystals, and, finally, as a point of comparison, organic molecules. We end with some conclusions and connections, including an outline of promising paths forward.

Pressure-Tuned Multicolor Emission of 2D Lead Halide Perovskites with Ultrahigh Color Purity

The chemical diversity and structural flexibility of lead halide perovskites (LHPs) offer tremendous opportunities to tune their optical properties through internal molecular engineering and external stimuli. Herein, we report the wide-range and ultrapure photoluminescence emissions in a family of homologous 2D LHPs, [MeOPEA]₂ PbBr_4-4x I_4x (MeOPEA=4-methoxyphenethylammonium; x=0, 0.2, 0.425, 0.575, 1) enabled through internal chemical pressure and external hydrostatic pressure. The chemical pressure, induced by the C-H⋅⋅⋅π interactions and halogen doping/substitution strengthens the structural rigidity to give sustained narrow emissions, and regulates the emission energy, respectively. Further manipulation of physical pressure leads to wide-range emission tuning from 412 to 647 nm in a continuous and reversible manner. This work could open up new pathways for developing 2D LHP emitters with ultra-wide color gamut and high color purity which are highly useful for pressure sensing.

Transition metal-doped germanium oxide nanozyme with enhanced enzyme-like activity for rapid detection of pesticide residues in water samples

Designing highly active nanozymes for bioanalysis and environmental sensing remains a challenge. In this study, transition metal, palladium (Pd) and iron (Fe), doped germanium oxide (GeO₂) nanozyme was designed and optimized. Compared with the pristine GeO₂ nanozyme, the transition metal doped GeO₂ nanozyme have lower Michaelis-Menten constants and higher catalytic activity, indicating that the Pd and Fe doped GeO₂ nanozyme not only enhance their affinity for the substrate but also improve its catalytic activity. In addition, a colorimetric sensor based on the GeO₂@Pd-H₂O₂-TMB system was constructed for the visual detection of simazine in water samples due to the good affinity between TMB and simazine. This sensor has good selectivity and sensitivity with a detection limit of 6.21 μM because of the highest catalytic performance of GeO₂@Pd nanozyme. This study broadens the application of nanozymes in environmental field and other nanozymes can also be enhanced in activity by simple transition metal doping.

Circular polarized light-dependent anomalous photovoltaic effect from achiral hybrid perovskites

Circular polarized light-dependent anomalous bulk photovoltaic effect - a steady anomalous photovoltaic current can be manipulated by changing the light helicity, is an increasingly interesting topic in contexts ranging from physics to chemistry. Herein, circular polarized light-dependent anomalous bulk photovoltaic effect is presented in achiral hybrid perovskites, (4-AMP)BiI5 (ABI, 4-AMP is 4-(aminomethyl)piperidinium), breaking conventional realization that it can only happen in chiral species. Achiral hybrid perovskite ABI crystallizes in chiroptical-active asymmetric point group m (Cs), showing an anomalous bulk photovoltaic effect with giant photovoltage of 25 V, as well as strong circular polarized light - sensitive properties. Significantly, conspicuous circular polarized light-dependent anomalous bulk photovoltaic effect is reflected in the large degree of dependence of anomalous bulk photovoltaic effect on left-and right-CPL helicity, which is associated with left and right-handed screw optical axes of ABI. Such degree of dependence is demonstrated by a large asymmetry factor of 0.24, which almost falls around the highest value of hybrid perovskites. These unprecedented results may provide a perspective to develop opto-spintronic functionalities in hybrid perovskites.

Recent Developments of Microscopic Study for Lanthanide and Manganese Doped Luminescent Materials

Luminescent materials are indispensable for applications in lighting, displays and photovoltaics, which can transfer, absorb, store and utilize light energy. Their performance is closely related with their size and morphologies, exact atomic arrangement, and local configuration about photofunctional centers. Advanced electron microscopy-based techniques have enabled the possibility to study nanostructures with atomic resolution. Especially, with the advanced micro-electro-mechanical systems, it is able to characterize the luminescent materials at the atomic scale under various environments, providing a deep understanding of the luminescent mechanism. Accordingly, this review summarizes the recent achievements of microscopic study to directly image the microstructure and local environment of activators in lanthanide and manganese (Ln/Mn²⁺ )-doped luminescent materials, including: 1) bulk materials, the typical systems are nitride/oxynitride phosphors; and 2) nanomaterials, such as nanocrystals (hexagonal-phase NaLnF₄ and perovskite) and 2D nanosheets (Ca₂ Ta₃ O₁₀ and MoS₂ ). Finally, the challenges and limitations are highlighted, and some possible solutions to facilitate the developments of advanced luminescent materials are provided.

Spray-coated perovskite hemispherical photodetector featuring narrow-band and wide-angle imaging

Sphere imagers featuring specific wavelength recognition and wide-angle imaging are required to meet the fast development of modern technology. However, it is still challenging to deposit high-quality photosensitive layers on sphere substrates from low-cost solution processes. Here we report spray-coated quasi-two-dimensional phenylethylammonium/formamidinium lead halide (PEA₂FA_n-1Pb_nX_3n+1) perovskite hemispherical photodetectors. The crystallization speed is manipulated by perovskite compositions, and the film thickness can be controlled by spray-coating cycles and solution concentration from tens of nanometers to hundreds of micrometers with a fast velocity of 1.28 × 10^-4 cm³ s^-1. The lens-free hemispherical photodetectors allow light response at a wide incident angle of 180°. Simultaneously, the wavelength selective response from visible to the near-infrared range is achieved with full width at half maximums (FWHMs) of ~20 nm, comparable to single-crystal devices. Wide-angle and wavelength-selective imaging are also demonstrated, which can find potential applications in intelligent recognition and intraoperative navigated surgery.

Boosting the Self-Trapped Exciton Emission in Cs2NaYCl6 Double Perovskite Single Crystals and Nanocrystals

Halide double perovskites have aroused substantial research interest because of their unique optical properties and intriguing flexibility for various compositional adjustments. Herein, we report the synthesis and photophysics of rare-earth element yttrium (Y)-based double perovskite single crystals (SCs) and nanocrystals (NCs). The pristine Cs₂NaYCl₆ bulk SCs exhibit a weak sky-blue emission with a low photoluminescence quantum yield (PLQY) of 7.68% based on the self-trapped exciton (STE), while no PL emission was observed for NCs. Excitingly, the STE emission of SCs and NCs is greatly enhanced via Sb³⁺ doping. The optimized Cs₂NaYCl₆:Sb³⁺ SCs and NCs exhibit high PLQYs up to 82.5% and 51.8%, respectively. Theoretical calculations and charge-carrier dynamic studies demonstrate that the giant emission enhancement after Sb³⁺ doping is related with the enhancement of the sensitization of the emissive STE states, the passivating of the nonradiative carrier trapping processes, and the regulation of carrier-phonon coupling.

Two-photon absorption in halide perovskites and their applications

Active research on halide perovskites has given us a deep understanding of this family of materials and their potential for applications in advanced optoelectronic devices. One of the prominent outcomes is the use of perovskite materials for nonlinear optical applications. Two-photon absorption in perovskites, in particular their nanostructures, has been extensively studied and shows huge promise for many applications. However, we are still far from a thorough understanding of two-photon absorption in halide perovskites from a micro to macro perspective. Here we summarize different techniques for studying the two-photon absorption in nonlinear optical materials. We discuss the in-depth photophysics in two-photon absorption in halide perovskites. A comprehensive summary about the factors which influence two-photon absorption provides the direction to improve the two-photon absorption properties of halide perovskites. A summary of the recent applications of two-photon absorption in halide perovskites provides inspirations for engineers to utilize halide perovskites in two-photon absorption device development. This review will help readers to have a comprehensive and in-depth understanding of the research field of two-photon absorption of halide perovskites from microscopic mechanisms to applications. The article can serve as a manual and give inspiration for future researchers.

Direct Detection of Near-Infrared Circularly Polarized Light via Precisely Designed Chiral Perovskite Heterostructures

Chiral metal halide perovskites (CMHPs) have recently shown great potential for direct circularly polarized light (CPL) detection. However, owing to the limited cutoff wavelength edge of these CMHPs, most of the detectors presented thus far are characterized only in the ultraviolet and visible range; CMHPs that target at the near-infrared (NIR) region are still greatly desired. Here, we design a novel CMHP heterostructure, synthesized via solution-processed epitaxial growth of crystalline 3D MAPbI₃ on a 2D chiral (R-BPEA)₂PbI₄ (R-BPEA = (R)-1-(4-bromophenyl)ethylammonium) crystal, and provide the first demonstration of self-powered direct NIR-CPL detection. Compared with individual chiral (R-BPEA)₂PbI₄, the heterostructure not only retains the spin selectivity but also allows much broader absorbance, especially beyond 780 nm, where the (R-BPEA)₂PbI₄ cannot absorb. Furthermore, the built-in electric potential in the heterojunction forces spontaneous separation/transport of photogenerated carriers, enabling the fabrication of devices operating without external energy supply. By making use of the abovementioned advantages, the self-powered CPL detectors of the (R-BPEA)₂PbI₄/MAPbI₃ heterostructures hence show competitive circular polarization sensitivity at 785 nm with a high anisotropy factor of up to 0.25. In addition, a large on/off switching ratio of ∼10⁵ and an impressive detectivity of ∼10¹⁰ Jones are also achieved. As a pioneer study, our results may broaden the material scope for future chiroptical devices based on CMHPs.

Microwave-Assisted Synthesis of Sulfur Quantum Dots for Detection of Alkaline Phosphatase Activity

Sulfur quantum dots (SQDs) are a kind of pure elemental quantum dots, which are considered as potential green nanomaterials because they do not contain heavy metal elements and are friendly to biology and environment. In this paper, SQDs with size around 2 nm were synthesized by a microwave-assisted method using sulfur powder as precursor. The SQDs had the highest emission under the excitation of 380 nm and emit blue fluorescence at 470 nm. In addition, the SQDs had good water solubility and stability. Based on the synthesized SQDs, a fluorescence assay for detection of alkaline phosphatase (ALP) was reported. The fluorescence of the SQDs was initially quenched by Cr (VI). In the presence of ALP, ALP-catalyzed hydrolysis of 2-phospho-L-ascorbic acid to generate ascorbic acid. The generated ascorbic acid can reduce Cr (VI) to Cr (III), thus the fluorescence intensity of SQDs was restored. The assay has good sensitivity and selectivity and was applied to the detection of ALP in serum samples. The interesting properties of SQDs can find a wide range of applications in different sensing and imaging areas.

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

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

Robust Spin-Dependent Anisotropy of Circularly Polarized Light Detection from Achiral Layered Hybrid Perovskite Ferroelectric Crystals

Circularly polarized light (CPL) detection has sparked overwhelming research interest for its widespread chiroptoelectronic and spintronic applications. Ferroelectric materials, especially emerging layered hybrid perovskite ferroelectrics, exhibiting striking bulk photovoltaic effect (BPVE) present significant possibilities for CPL detection by a distinctive working concept. Herein, for the first time, we demonstrate the realization of robust angular anisotropy of CPL detection in a new layered hybrid perovskite ferroelectric crystal (CPA)₂FAPb₂Br₇ (1, CPA is chloropropylammonium, FA is formamidinium), which crystallized in an optically active achiral polar point group. Benefiting from the notable spontaneous polarization (5.1 μC/cm²) and excellent semiconducting characteristics, single crystals of 1 exhibit remarkable BPVE under light illumination, with a high current on/off switching ratio (ca. 10³). More intriguingly, driven by the angular carrier drift originating from spin-dependent BPVE in optically active ferroelectrics, 1 displays highly sensitive self-powered CPL detection performance, showing a robust angular anisotropy factor up to 0.98, which is far more than those achieved by material intrinsic chirality. This work provides an unprecedented approach for realizing highly sensitive CPL detection, which sheds light on the further design of optically active ferroelectrics for chiral photonic applications.

Alcohol-Stable Perovskite Nanocrystals and Their In Situ Capsulation with Polystyrene

In recent years, lead halide perovskite nanocrystals (PNCs) have presented potential scalable applications in all fields due to their outstanding properties. However, most commonly used PNCs capped with oleic acid (OA) and oleylamine (OAm) suffer from bad stability in polar solutions and thus require various surface protections with organic or inorganic materials. Encapsulation with highly hydrophobic polystyrene (PS) is one of the most efficient ways to protect PNCs; however, the presently used swelling-shrinking strategy faces several challenges, such as weak interaction between PS chains and the surface ligands in nonpolar media causing a low encapsulation efficiency, and serious aggregation of PS particles during the shrinkage process leading to very different particle sizes. Herein, alcohol-stable polyacrylic acid-capped CsPbBr3 PNCs (i.e., PAA-PNCs) are first synthesized and then in situ encapsulated with PS shells by polymerizing styrene monomer on the PNC surfaces in a polar organic solvent (e.g., ethanol). The in situ PS-encapsulated PAA-PNCs (i.e., PAA-PNCs@iPS) exhibit outstanding monodispersity, remarkable water, heat, and UV stability, high fluorescence activity, and color purity. The unique synthesis strategy and good performances of PAA-PNCs@iPS will boost the applications of PNCs in LEDs, biological imaging, and chemosensing.

Ferroelasticity in Organic-Inorganic Hybrid Perovskites

Molecular ferroelastics have received particular attention for potential applications in mechanical switches, shape memory, energy conversion, information processing, and solar cells, by taking advantages of their low-cost, light-weight, easy preparation, and mechanical flexibility. The unique structures of organic-inorganic hybrid perovskites have been considered to be a design platform for symmetry-breaking-associated order-disorder in lattice, thereby possessing great potential for ferroelastic phase transition. Herein, we review the research progress of organic-inorganic hybrid perovskite ferroelastics in recent years, focusing on the crystal structures, dimensions, phase transitions and ferroelastic properties. In view of the few reports on molecular-based hybrid ferroelastics, we look forward to the structural design strategies of molecular ferroelastic materials, as well as the opportunities and challenges faced by molecular-based hybrid ferroelastic materials in the future. This review will have positive guiding significance for the synthesis and future exploration of organic-inorganic hybrid molecular ferroelastics.

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.