Ultrathin Two‐Dimensional Organic–Inorganic Hybrid Perovskite Nanosheets with Bright,Tunable Photoluminescence and High Stability

Two‐dimensional (2D) organic–inorganic hybrid perovskite nanosheets (NSs) are attracting increasing research interest due to their unique properties and promising applications. Here, for the first time, we report the facile synthesis of single‐ and few‐layer free‐standing phenylethylammonium lead halide perovskite NSs, that is, (PEA)₂PbX₄ (PEA=C₈H₉NH₃, X=Cl, Br, I). Importantly, their lateral size can be tuned by changing solvents. Moreover, these ultrathin 2D perovskite NSs exhibit highly efficient and tunable photoluminescence, as well as superior stability. Our study provides a simple and general method for the controlled synthesis of 2D perovskite NSs, which may offer a new avenue for their fundamental studies and optoelectronic applications.     

A Layered Hybrid Perovskite Solar‐Cell Absorber with Enhanced Moisture Stability

Two‐dimensional hybrid perovskites are used as absorbers in solar cells. Our first‐generation devices containing (PEA)₂(MA)₂[Pb₃I₁₀] ( 1 ; PEA=C₆H₅(CH₂)₂NH₃⁺, MA=CH₃NH₃⁺) show an open‐circuit voltage of 1.18 V and a power conversion efficiency of 4.73 %. The layered structure allows for high‐quality films to be deposited through spin coating and high‐temperature annealing is not required for device fabrication. The 3D perovskite (MA)[PbI₃] ( 2 ) has recently been identified as a promising absorber for solar cells. However, its instability to moisture requires anhydrous processing and operating conditions. Films of 1 are more moisture resistant than films of 2 and devices containing 1 can be fabricated under ambient humidity levels. The larger bandgap of the 2D structure is also suitable as the higher bandgap absorber in a dual‐absorber tandem device. Compared to 2 , the layered perovskite structure may offer greater tunability at the molecular level for material optimization.     

Graded interface engineering of 3D/2D halide perovskite solar cells through ultrathin(PEA)_2PbI_4 nanosheets

2D halide perovskites have emerged as promising materials because of their stability and passivation effect in perovskite solar cells(PSCs).However,the introduction of bulky organic ammonium cations from 2D halide perovskites would decrease the device performance generally compared to the traditional 3D MAPbI_3.Incorporation of ultrathin 2D halide perovskite nanosheets(NSs) with 3D MAPbI_3 could address this issue.Herein,we re port a rationally designed PSCs with dimensional graded 3D/2D MAPbI_3/(PEA)2 PbI_4 heterojunction,in which 2D(PEA)2 PbI_4 NSs were synthesized and incorporated between 3D MAPbI_3 and hole-transporting layer.Besides the significantly improved stability,a notable increasement in power conversion efficiency(PCE) of 20% was obtained for the 3D/2D perovskite solar cells due to the favourable band alignment among(PEA)_2 PbI_4 NSs and the other components.The graded structure of MAPbI_3/(PEA)2 PbI_4 would upshift the energy level continuously,which enhances the hole extraction efficiency thus reduces the interface charge recombination,leading to the increasements of VOC from1.04 V to 1.07 V,Jsc from 21.81 mA/cm~2 to 23.15 mA/cm~2 and the fill factor from 67.89% to 74.78%,and therefore an overall PCE of 18.53%.     

Algae Extraction Controllable Delamination of Vanadium Carbide Nanosheets with Enhanced Near‐Infrared Photothermal Performance

The two‐dimensional (2D) vanadium carbide (V₂C) MXene has shown great potential as a photothermal agent (PTA) for photothermal therapy (PTT). However, the use of V₂C in PTT is limited by the harsh synthesis condition and low photothermal conversion efficiency (PTCE). Herein, we report a completely different green delamination method using algae extraction to intercalate and delaminate V₂AlC to produce mass V₂C nanosheets (NSs) with a high yield (90 %). The resulting V₂C NSs demonstrated good structural integrity and remarkably high absorption in near infrared (NIR) region with a PTCE as high as 48 %. Systemic in vitro and in vivo studies demonstrate that the V₂C NSs can serve as efficient PTA for photoacoustic (PA) and magnetic resonance imaging (MRI)‐guided PTT of cancer. This work provides a cost‐effective, environment‐friendly, and high‐yielding disassembly approach of MAX, opening a new avenue to develop MXenes with desirable properties for a myriad of applications.     

Large‐Scale Synthesis of Highly Luminescent Perovskite‐Related CsPb2Br5 Nanoplatelets and Their Fast Anion Exchange

All‐inorganic cesium lead‐halide perovskite nanocrystals have emerged as attractive optoelectronic nanomaterials owing to their stabilities and highly efficient photoluminescence. Herein we report a new type of highly luminescent perovskite‐related CsPb₂Br₅ nanoplatelets synthesized by a facile precipitation reaction. The layered crystal structure of CsPb₂Br₅ promoted an anisotropic two‐dimensional (2D) crystal growth during the precipitation process, thus enabling the large‐scale synthesis of CsPb₂Br₅ nanoplatelets. Fast anion exchange has also been demonstrated in as‐synthesized CsPb₂Br₅ nanoplatelets to extend their photoluminescence spectra to the entire visible spectral region. The large‐scale synthesis and optical tunability of CsPb₂Br₅ nanoplatelets will be advantageous in future applications of optoelectronic devices.     

Benign‐by‐Design Solventless Mechanochemical Synthesis of Three‐, Two‐, and One‐Dimensional Hybrid Perovskites

Organic–inorganic hybrid perovskites have attracted significant attention owing to their extraordinary optoelectronic properties with applications in the fields of solar energy, lighting, photodetectors, and lasers. The rational design of these hybrid materials is a key factor in the optimization of their performance in perovskite‐based devices. Herein, a mechanochemical approach is proposed as a highly efficient, simple, and reproducible method for the preparation of four types of hybrid perovskites, which were obtained in large amounts as polycrystalline powders with high purity and excellent optoelectronics properties. Two archetypal three‐dimensional (3D) perovskites (MAPbI₃ and FAPbI₃) were synthesized, together with a bidimensional (2D) perovskite (Gua₂PbI₄) and a “double‐chain” one‐dimensional (1D) perovskite (GuaPbI₃), whose structure was elucidated by X‐ray diffraction.     

Synthesis and Localized Photoluminescence Blinking of Lead‐Free 2D Nanostructures of Cs3Bi2I6Cl3 Perovskite

Two‐dimensional (2D) lead‐free halide perovskites have generated enormous perception in the field of optoelectronics due to their fascinating optical properties. However, an in‐depth understanding on their shape‐controlled charge‐carrier recombination dynamics is still lacking, which could be resolved by exploring the photoluminescence (PL) blinking behaviour at the single‐particle level. Herein, we demonstrate, for the first time, the synthesis of nanocrystals (NCs) and 2D nanosheets (NSs) of layered mixed halide, Cs₃Bi₂I₆Cl₃, by solution‐based method. We applied fluorescence microscopy and super‐resolution optical imaging at single‐particle level to investigate their morphology‐dependent PL properties. Narrow emission line widths and passivation of non‐radiative defects were evidenced for 2D layered nanostructures, whereas the activation of shallow trap states was recognized at 77 K. Interestingly, individual NCs were found to display temporal intermittency (blinking) in PL emission. On the other hand, NS showed temporal PL intensity fluctuations within localized domains of the crystal. In addition, super‐resolution optical image of the NS from localization‐based method showed spatial inhomogeneity of the PL intensity within perovskite crystal.     

A Photochemical Route towards Metal Sulfide Nanosheets from Layered Metal Thiolate Complexes

Synthesizing nanomaterials with anisotropic architectures, especially two‐dimensional (2D) nanosheets (NSs), is a key focus of materials science research. Metal sulfide nanosheets (MSNSs) are typically obtained involving exfoliation of bulk metal sulfides with layered structures. The synthesis of NSs of intrinsically non‐layered metal sulfides has received relatively less attention. Metal alkanethiolates with lamellar structures are now shown to serve as effective scaffolds for constructing NSs. A novel photochemical step was employed to transform 2D metal thiolates into MSNSs. By this strategy the 2D nature of metal thiolate precursors was preserved in the final products, resulting in the successful synthesis of NSs of binary PbS, CdS, and Cu₉S₅, as well as ternary wurtzite CuInS₂, Cu₂SnS₃. Results encourage the wider utilization of photochemical strategies in the synthesis of anisotropic MSNSs.     

Tumor‐Microenvironment‐Induced Degradation of Ultrathin Gadolinium Oxide Nanoscrolls for Magnetic‐Resonance‐Imaging‐Monitored,Activatable Cancer Chemotherapy

The development of biodegradable inorganic nanoparticles with a tumor microenvironment‐activated therapeutic mode of action is urgently needed for precision cancer medicine. Herein, the synthesis of ultrathin lanthanide nanoscrolls (Gd₂O₃ NSs) is reported, which biodegrade upon encountering the tumor microenvironment. The Gd₂O₃ NSs showed highly controlled magnetic properties, which enabled their high‐resolution magnetic resonance imaging (MRI). Importantly, Gd₂O₃ NSs degrade in a pH‐responsive manner and selectively penetrate tumor tissue, enabling the targeted release of anti‐cancer drugs. Gd₂O₃ NSs can be efficiently loaded with an anti‐cancer drug (DOX, 80 %) and significantly inhibit tumor growth with negligible cellular and tissue toxicity both in vitro and in vivo. This study may provide a novel strategy to design tumor microenvironment‐responsive inorganic nanomaterials for biocompatible bioimaging and biodegradation‐enhanced cancer therapy.     

Tumor‐Microenvironment‐Induced Degradation of Ultrathin Gadolinium Oxide Nanoscrolls for Magnetic‐Resonance‐Imaging‐Monitored,Activatable Cancer Chemotherapy

The development of biodegradable inorganic nanoparticles with a tumor microenvironment‐activated therapeutic mode of action is urgently needed for precision cancer medicine. Herein, the synthesis of ultrathin lanthanide nanoscrolls (Gd₂O₃ NSs) is reported, which biodegrade upon encountering the tumor microenvironment. The Gd₂O₃ NSs showed highly controlled magnetic properties, which enabled their high‐resolution magnetic resonance imaging (MRI). Importantly, Gd₂O₃ NSs degrade in a pH‐responsive manner and selectively penetrate tumor tissue, enabling the targeted release of anti‐cancer drugs. Gd₂O₃ NSs can be efficiently loaded with an anti‐cancer drug (DOX, 80 %) and significantly inhibit tumor growth with negligible cellular and tissue toxicity both in vitro and in vivo. This study may provide a novel strategy to design tumor microenvironment‐responsive inorganic nanomaterials for biocompatible bioimaging and biodegradation‐enhanced cancer therapy.     

Synthesis of WOn‐WX2 (n=2.7, 2.9; X=S,Se) Heterostructures for Highly Efficient Green Quantum Dot Light‐Emitting Diodes

Preparation of two‐dimensional (2D) heterostructures is important not only fundamentally, but also technologically for applications in electronics and optoelectronics. Herein, we report a facile colloidal method for the synthesis of WO_n ‐WX₂ (n =2.7, 2.9; X=S, Se) heterostructures by sulfurization or selenization of WO_n nanomaterials. The WO_n ‐WX₂ heterostructures are composed of WO_2.9 nanoparticles (NPs) or WO_2.7 nanowires (NWs) grown together with single‐ or few‐layer WX₂ nanosheets (NSs). As a proof‐of‐concept application, the WO_n ‐WX₂ heterostructures are used as the anode interfacial buffer layer for green quantum dot light‐emitting diodes (QLEDs). The QLED prepared with WO_2.9 NP‐WSe₂ NS heterostructures achieves external quantum efficiency (EQE) of 8.53 %. To our knowledge, this is the highest efficiency in the reported green QLEDs using inorganic materials as the hole injection layer.     

Lead‐Free,Air‐Stable All‐Inorganic Cesium Bismuth Halide Perovskite Nanocrystals

Lead‐based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead‐based and the other is the poor stability. Lead‐free all‐inorganic perovskite Cs₃Bi₂X₉ (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand‐free Cs₃Bi₂Br₉ NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2–20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days.     

Lead‐Free,Air‐Stable All‐Inorganic Cesium Bismuth Halide Perovskite Nanocrystals

Lead‐based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead‐based and the other is the poor stability. Lead‐free all‐inorganic perovskite Cs₃Bi₂X₉ (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand‐free Cs₃Bi₂Br₉ NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2–20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days.     

Synthesis of WOn‐WX2 (n=2.7, 2.9; X=S,Se) Heterostructures for Highly Efficient Green Quantum Dot Light‐Emitting Diodes

Preparation of two‐dimensional (2D) heterostructures is important not only fundamentally, but also technologically for applications in electronics and optoelectronics. Herein, we report a facile colloidal method for the synthesis of WO_n ‐WX₂ (n =2.7, 2.9; X=S, Se) heterostructures by sulfurization or selenization of WO_n nanomaterials. The WO_n ‐WX₂ heterostructures are composed of WO_2.9 nanoparticles (NPs) or WO_2.7 nanowires (NWs) grown together with single‐ or few‐layer WX₂ nanosheets (NSs). As a proof‐of‐concept application, the WO_n ‐WX₂ heterostructures are used as the anode interfacial buffer layer for green quantum dot light‐emitting diodes (QLEDs). The QLED prepared with WO_2.9 NP‐WSe₂ NS heterostructures achieves external quantum efficiency (EQE) of 8.53 %. To our knowledge, this is the highest efficiency in the reported green QLEDs using inorganic materials as the hole injection layer.     

Stabilization of Highly Efficient and Stable Phase‐Pure FAPbI3 Perovskite Solar Cells by Molecularly Tailored 2D‐Overlayers

As a result of their attractive optoelectronic properties, metal halide APbI₃ perovskites employing formamidinium (FA⁺) as the A cation are the focus of research. The superior chemical and thermal stability of FA⁺ cations makes α‐FAPbI₃ more suitable for solar‐cell applications than methylammonium lead iodide (MAPbI₃). However, its spontaneous conversion into the yellow non‐perovskite phase (δ‐FAPbI₃) under ambient conditions poses a serious challenge for practical applications. Herein, we report on the stabilization of the desired α‐FAPbI₃ perovskite phase by protecting it with a two‐dimensional (2D) IBA₂FAPb₂I₇ (IBA=iso‐butylammonium overlayer, formed via stepwise annealing. The α‐FAPbI₃/IBA₂FAPb₂I₇ based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. In addition, it showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress, that is, simultaneous exposure with maximum power tracking to full simulated sunlight at 80 °C over 500 h.     

Partially Pyrolyzed Binary Metal–Organic Framework Nanosheets for Efficient Electrochemical Hydrogen Peroxide Synthesis

Herein, we developed a partially controlled pyrolysis strategy to create evenly distributed NiO nanoparticles within NiFe‐MOF nanosheets (MOF NSs) for electrochemical synthesis of H₂O₂ by a two‐electron oxygen reduction reaction (ORR). The elemental Ni can be partially transformed to NiO and uniformly distributed on the surface of the MOF NSs, which is crucial for the formation of the particular structure. The optimized MOF NSs‐300 exhibits the highest activity for ORR with near‐zero overpotential and excellent H₂O₂ selectivity (ca. 99 %) in 0.1 m KOH solution. A high‐yield H₂O₂ production rate of 6.5 mol g_cat^?1 h^?1 has also been achieved by MOF NSs‐300 in 0.1 m KOH and at 0.6 V (vs. RHE). In contrast to completely pyrolyzed products, the enhanced catalytic activities of partially pyrolyzed MOF NSs‐300 originates mainly from the retained MOF structure and the newly generated NiO nanoparticles, forming the coordinatively unsaturated Ni atoms and tuning the performance towards electrochemical H₂O₂ synthesis.     

A two‐dimensional organic–inorganic hybrid perovskite‐type semiconductor: poly[(2‐azaniumylethyl)trimethylphosphanium [tetra‐μ‐bromido‐plumbate(II)]]

Recently, with the prevalence of `perovskite fever', organic–inorganic hybrid perovskites (OHPs) have attracted intense attention due to their remarkable structural variability and highly tunable properties. In particular, the optical and electrical properties of organic–inorganic hybrid lead halides are typical of the OHP family. Besides, although three‐dimensional hybrid perovskites, such as [CH₃NH₃]PbX₃ (X = Cl, Br or I), have been reported, the development of new organic–inorganic hybrid semiconductors is still an area in urgent need of exploration. Here, an organic–inorganic hybrid lead halide perovskite is reported, namely poly[(2‐azaniumylethyl)trimethylphosphanium [tetra‐μ‐bromido‐plumbate(II)]], {(C₅H₁₆NP)[PbBr₄]}_n, in which an organic cation is embedded in inorganic two‐dimensional (2D) mesh layers to produce a sandwich structure. This unique sandwich 2D hybrid perovskite material shows an indirect band gap of ～2.700 eV. The properties of this compound as a semiconductor are demonstrated by a series of optical characterizations and indicate potential applications for optical devices.     

A Chiral Reduced‐Dimension Perovskite for an Efficient Flexible Circularly Polarized Light Photodetector

Chiral quasi‐2D perovskite single crystals (SCs) were investigated for their circular polarized light (CPL) detecting capability. Quasi‐2D chiral perovskites, [(R)‐β‐MPA]₂MAPb₂I₇ ((R)‐β‐MPA=(R)‐(+)‐β‐methylphenethylamine, MA=methylammonium), have intrinsic chirality and the capability to distinguish different polarization states of CPL photons. Corresponding quasi‐2D SCs CPL photodetector exhibit excellent detection performance. In particular, our device responsivity is almost one order of magnitude higher than the reported 2D perovskite CPL detectors to date. The crystallization dynamics of the film were modulated to facilitate its carrier transport. Parallel oriented perovskite films with a homogeneous energy landscape is crucial to maximize the carrier collection efficiency. The photodetector also exhibits superior mechanical flexibility and durability, representing a promising candidate for sensitive and robust CPL photodetectors.     

Self‐Template‐Directed Synthesis of Porous Perovskite Nanowires at Room Temperature for High‐Performance Visible‐Light Photodetectors

The unique optoelectronic properties and promising photovoltaic applications of organolead halide perovskites have driven the exploration of facile strategies to synthesize organometal halide perovskites and corresponding hybrid materials and devices. Currently, the preparation of CH₃NH₃PbBr₃ perovskite nanowires, especially those with porous features, is still a great challenge. An efficient self‐template‐directed synthesis of high‐quality porous CH₃NH₃PbBr₃ perovskite nanowires in solution at room temperature using the Pb‐containing precursor nanowires as both the sacrificial template and the Pb²⁺ source in the presence of CH₃NH₃Br and HBr is now presented. The initial formation of CH₃NH₃PbBr₃ perovskite layers on the surface of the precursor nanowires and the following dissolution of the organic component of the latter led to the formation of mesopores and the preservation of the 1D morphology. Furthermore, the perovskite nanowires are potential materials for visible‐light photodetectors with high sensitivity and stability.     

Room‐Temperature Ferroelectric Material Composed of a Two‐Dimensional Metal Halide Double Perovskite for X‐ray Detection

Although two‐dimensional (2D) metal–halide double perovskites display versatile physical properties due to their huge structural compatibility, room‐temperature ferroelectric behavior has not yet been reported for this fascinating family. Here, we designed a room‐temperature ferroelectric material composed of 2D halide double perovskites, (chloropropylammonium)₄AgBiBr₈, using an organic asymmetric dipolar ligand. It exhibits concrete ferroelectricity, including a Curie temperature of 305 K and a notable spontaneous polarization of ≈3.2 μC cm^?2, triggered by dynamic ordering of the organic cation and the tilting motion of heterometallic AgBr₆/BiBr₆ octahedra. Besides, the alternating array of inorganic perovskite sheets and organic cations endows large mobility‐lifetime product (μτ=1.0×10^?3 cm² V^?1) for detecting X‐ray photons, which is almost tenfold higher than that of CH₃NH₃PbI₃ wafers. As far as we know, this is the first study on an X‐ray‐sensitive ferroelectric material composed of 2D halide double perovskites. Our findings afford a promising platform for exploring new ferroelectric materials toward further device applications.