Centimeter-Sized Single Crystals of Two-Dimensional Hybrid Iodide Double Perovskite (4,4-Difluoropiperidinium)4AgBiI8 for High-Temperature Ferroelectricity and Efficient X-Ray Detection

Ferroelectricity and X-ray detection property have been recently implemented for the first time in hybrid bromide double perovskites. It sheds a light on achieving photosensitive and ferroelectric multifunctional materials based on 2D lead-free hybrid halide double perovskites. However, the low T_c, small P_s, and relatively low X-ray sensitivity in the reported bromide double perovskites hinder practical applications. Herein, the authors demonstrate a novel 2D lead-free iodide double perovskite (4,4-difluoropiperidinium)₄AgBiI₈ (1) for high-performance X-ray sensitive ferroelectric devices. Centimeter-sized single crystal of 1 is obtained and exhibits an excellent ferroelectricity including a high T_c up to 422 K and a large P_s of 10.5 μC cm⁻². Moreover, due to a large X-ray attenuation and efficient charge carrier mobility (μ)–charge carrier lifetime (τ) product, the crystal 1 also exhibits promising X-ray response with a high sensitivity up to 188 μC·Gy_air⁻¹ cm⁻² and a detection limit below 3.13 μGy_air·s⁻¹. Therefore, this finding is a step further toward practical applications of lead-free halide perovskite in high-performance photoelectronic devices. It will afford a promising platform for exploring novel photosensitive ferroelectric multifunctional materials based on lead-free double perovskites.     

Self-Healing Cs3Bi2Br3I6 Perovskite Wafers for X-Ray Detection

Self-healing of defects imposed by external stimuli such as high energy radiation is a possibility to sustain the operational lifetime of electronic devices such as radiation detectors. Cs₃Bi₂Br₃I₆ polycrystalline wafers are introduced here as novel X-ray detector material, which not only guarantees a high X-ray stopping power due to its composition with elements with high atomic numbers, but also outperforms other Bi-based semiconductors in respect to detector parameters such as detection limit, transient behavior, or dark current. The polycrystalline wafers represent a size scalable technology suitable for future integration in imager devices for medical applications. Most astonishingly, aging of these wafer-based devices results in an overall improvement of the detector performance—dark currents are reduced, photocurrents are increased, and one of the most problematic properties of X-ray detectors, the base line drift is reduced by orders of magnitude. These aging induced improvements indicate self-healing effects which are shown to result from recrystallization. Optimized synthetic conditions also improve the as prepared X-ray detectors; however, the aged device outperforms all others. Thus, self-healing acts in Cs₃Bi₂Br₃I₆ as an optimization tool, which is certainly not restricted to this single compound, it is expected to be beneficial also for many further polycrystalline ionic semiconductors.     

Discovering New Type of Lead-Free Cluster-Based Hybrid Double Perovskite Derivatives with Chiral Optical Activities and Low X-Ray Detection Limit

2D chiral hybrid perovskites have recently emerged as outstanding semiconductor materials. However, most of the reported 2D chiral perovskites have limited structural types and contain high levels of toxic lead, which severely hinders their further applications. Herein, by using a mixed-cation strategy, an unprecedented type of lead-free cluster-based 2D chiral hybrid double perovskite derivatives are successfully obtained, [(R/S-PPA)₄(IPA)₆Ag₂Bi₄I₂₄]·2H₂O ( 1-R and 1-S ), and [(R/S-PPA)₄(n-BA)₆Ag₂Bi₄I₂₄]·2H₂O ( 2-R and 2-S ) (R/S-PPA=R/S–1-phenylpropylamine; IPA=isopentylamine; n-BA=n-butylamine). Their inorganic skeletons are linked by binuclear {Bi₂I₁₀} and infinite chain {Ag₂Bi₂I₁₄}_∞, in which bismuth clusters and multiple coordination modes (e.g., tetrahedral AgI₄ and octahedral AgI₆) are introduced into the double perovskite system for the first time. This introduction induces distortion of the inorganic layer, which may facilitate the transfer of chirality from the chiral cations into achiral double perovskite skeletons. Further, circular dichroism measurements and circularly polarized light detection confirm their inherent chiral optical activities. In addition, 1-S exhibits an ultralow X-ray detection limit of 129.5 nGy s⁻¹, which is 42-fold lower than that of demands in regular medical diagnosis (5.5 µGy s⁻¹). This study provides a pathway to construct novel type of lead-free cluster-based double perovskite derivatives.     

High-Sensitivity Flexible X-Ray Detectors based on Printed Perovskite Inks

The demand for high-energy radiation detection systems combining high sensitivity, low-cost and large-area fabrication has pushed the research on hybrid perovskites as promising materials for X- and γ-photon detection, thanks to their high Z atoms, solution-processability, and high optoelectronic performance. Here, flexible direct X-ray detectors are demonstrated with outstanding real-time detection properties. They are based on printed micrometers-thick films of methylammonium lead triiodide nanocrystals inks, formulated in low boiling point and benign solvents. Record optoelectronic performances, such as high X-ray sensitivity (up to 2270 µC Gy⁻¹ cm⁻²), radiation tolerance over 2.2 Gy of total dose, and fast response time (48 ms) have been achieved by using a simple device architecture and materials processing The functionality under strong bending stress (strain > 10%) and under high X-ray energy (up to 150 keV) has been assessed, opening the way for flexible real-time direct radiation detectors and imagers, operating at low-voltages (bias < 4V) and apt to be fabricated by means of large-area scalable processes.     

Inch-Size Single Crystals of Lead-Free Chiral Perovskites with Bulk Photovoltaic Effect for Stable Self-Driven X-Ray Detection

Lead halide perovskites have made great advance in direct X-ray detection, however the presence of toxic lead and the requirement of high working voltages severely limit their applicability and operational stability. Thus, exploring “green” lead-free hybrid perovskites capable of detecting X-rays at zero bias is crucial but remains toughly challenging. Here, utilizing chiral R/S-1-phenylpropylamine (R/S-PPA) cations, a pair of 0D chiral-polar perovskites, (R/S-PPA)₂BiI₅ ( 1 R / 1 S ) are constructed. Their intrinsic spontaneous electric polarization induces a large bulk photovoltage of 0.63 V, which acts as a driving force to separate and transport photogenerated carriers, thus endowing them with the capability of self-driven detection. Consequently, self-driven X-ray detectors with a low detection limit of 270 nGy s⁻¹ are successfully constructed based on high-quality, inch-sized single crystals of 1 R . Notably, they show suppressed baseline drift under the self-driven mode, exhibiting superior operational stability. This study realizes self-driven X-ray detection in a single-phase lead-free hybrid perovskite by exploiting the intrinsic bulk photovoltaic effect, which sheds light on future explorations of lead-free hybrid perovskites toward “green” self-driven radiation detectors with high performance.     

Synergy of Organic and Inorganic Sites in 2D Perovskite for Fast Neutron and X-Ray Imaging

Fast neutron and X-ray imaging are considered complementary nondestructive detection technologies. However, due to their opposite cross-sections, development of a scintillator that is sensitive to both fast neutrons and X-rays within a single-material framework remains challenging. Herein, an organic–inorganic hybrid perovskite (C₄H₉NH₃)₂PbBr₄ (BPB) is demonstrated as a scintillator that fully meets the requirements for both fast neutron and X-ray detection. The hydrogen-rich organic component acts as a fast neutron converter and produces detectable recoil protons. The heavy atom-rich inorganic fraction efficiently deposits the energy of charged recoil protons and directly provides a large X-ray cross-section. Due to the synergy of these organic and inorganic components, the BPB scintillator exhibits high light yields (86% of the brightness of a commercial ZnS (Ag)/⁶LiF scintillator for fast neutrons; 22 000 photons per MeV for X-rays) and fast response times (τ_decay = 10.3 ns). More importantly, energy-selective fast neutron and X-ray imaging are also demonstrated, with high resolutions of ≈1 lp mm⁻¹ for fast neutrons and 17.3 lp mm⁻¹ for X-rays; these are among the highest resolution levels for 2D perovskite scintillators. This study highlights the potential of 2D perovskite materials for use in combined fast neutron and X-ray imaging applications.     

Low-Cost and Large-Area Hybrid X-Ray Detectors Combining Direct Perovskite Semiconductor and Indirect Scintillator

Both semiconductors and scintillators have their own advantages in direct and indirect X-ray detection, respectively. However, they are also limited by their intrinsic properties and detection mechanisms. Here, a low-cost and large-area flat X-ray detector is reported by combining a cesium silver bismuth bromide (Cs₂AgBiBr₆) perovskite semiconductor with a ethylenebis-triphenylphosphonium manganese (II) bromide ((C₃₈H₃₄P₂)MnBr₄) scintillator through fast tableting processes. Cs₂AgBiBr₆ and (C₃₈H₃₄P₂)MnBr₄ can attenuate the X-ray photons to induce charge carriers that are collected through the continuous Cs₂AgBiBr₆ grains. (C₃₈H₃₄P₂)MnBr₄ blocks the Cs₂AgBiBr₆ ions migration paths at the grain boundaries to reduce the device dark current/noise and improves the working stability. Most charges generated by (C₃₈H₃₄P₂)MnBr₄ are transferred to the adjacent Cs₂AgBiBr₆, and recombined charges radiate light through scintillation, which will be further absorbed by the surrounding Cs₂AgBiBr₆ perovskite, and further induce collectable charges for indirect X-ray detection, avoiding the unwanted light scattering, self-absorption, or afterglow effects of scintillators. The hybrid X-ray detector displays a high sensitivity of 114 µC Gy_air⁻¹ cm⁻² to 120 keV_p hard X-rays with a lowest detectable dose rate of 0.2 μGy_air s⁻¹, showing 75 times lower detection limit compared to (C₃₈H₃₄P₂)MnBr₄ scintillator, which provides a new path for X-ray flat-panel design.     

Eco-Friendly and Highly Efficient Light-Emission Ferroelectric Scintillators by Precise Molecular Design

Hybrid manganese halide has attracted much attention in the field of environment friendly ferroelectric and photo-responsive multifunctional materials. Here, the highly efficient photoluminescent inorganic framework MnBr₄²⁻ is utilized to conceive and synthesize a series of hybrid manganese bromide compounds [RQ]₂MnBr₄ by introducing precisely designed quasi-spherical cations [RQ]⁺ (R  =  H, Me, Et, FEt, Q  =  quinuclidine). The accurate and effective modification of cations not only achieves the satisfactory ferroelectricity, but also enhances the photoluminescence quantum yield from 38.7% to 83.65%. Moreover, [FEtQ]₂MnBr₄ shows a highly efficient X-ray scintillator performance, including a large range of linear response to X-ray dose rate from 0.3 to 414.2  μ Gy_air s⁻¹, a high light yield of 34 438 photons per MeV, and a low detection limit of 258 nGy_air s⁻¹. This work provides an efficient strategy for the preparation of hybrid manganese halide ferroelectrics with highly efficient light-emission and X-ray detection.     

An Environmentally Stable and Lead‐Free Chalcogenide Perovskite

Organic–inorganic halide perovskites are intrinsically unstable when exposed to moisture and/or light. Additionally, the presence of lead in many perovskites raises toxicity concerns. Herein, a thin film of barium zirconium sulfide (BaZrS₃), a lead‐free chalcogenide perovskite, is reported. Photoluminescence and X‐ray diffraction measurements show that BaZrS₃ is far more stable than methylammonium lead iodide (MAPbI₃) in moist environments. Moisture‐ and light‐induced degradations in BaZrS₃ and MAPbI₃ are compared by using simulations and calculations based on density functional theory. The simulations reveal drastically slower degradation in BaZrS₃ due to two factors—weak interaction with water and very low rates of ion migration. BaZrS₃ photodetecting devices with photoresponsivity of ≈46.5 mA W^?1 are also reported. The devices retain ≈60% of their initial photoresponse after 4 weeks under ambient conditions. Similar MAPbI₃ devices degrade rapidly and show a ≈95% decrease in photoresponsivity in just 4 days. The findings establish the superior stability of BaZrS₃ and strengthen the case for its use in optoelectronics. New possibilities for thermoelectric energy conversion using these materials are also demonstrated.     

Perovskite Photosensors Integrated with Silver Resonant‐Cavity Color Filters Display Color Perception Beyond That of the Human Eye

Organic hybrid perovskite‐based photosensors generally display high responsivities and ultrafast response speeds, but their high dark currents with low detectivities have impeded their commercial applications. In this study, these problems are overcome by modifying the device structure and performing defect passivation of the perovskite. An inverted ITO/NiO_x/perovskite/PCBM/BCP/Ag structure is applied to minimize the leakage current from the interlayers. In addition, a urea additive is embedded and the thickness of the perovskite layer is optimized, resulting in an ultralow dark current (<2 pA), a peak detectivity of greater than 1.42 × 10¹⁴ Jones, and a high linear dynamic range (LDR) of up to 162 dB (in the response range from 20.25 to 6.80 × 10^‐8 mW cm^‐2). Using high‐purity color filters, combined with a well‐defined white light illumination system derived from a 3A solar simulator, the photosensitivity is evaluated under light of various hues and intensities (down to 10^‐9 mW cm^‐2). The optimized color sensors under blue, green, orange, and red hues of light display LDRs of greater than 139 dB in the mesopic vision regime (wavelengths: 400–700 nm) between 10^‐6 and 10^‐3 mW cm^‐2—outperforming human visual color perception.     

Sequencing and Welding of Molecular Single‐Crystal Optical Waveguides

Molecular crystals are promising anisotropic optical transducing media for next‐generation optoelectronic microdevices that will be capable of secure transduction of information and impervious to external electromagnetic interference. However, their full potential has not been explored yet due to their poor processability, low mechanical compliance, pronounced brittleness and high proneness to cracking that often result in irrecoverable damage. These issues are detrimental to their ability to transduce light. Here, a novel strategy is presented based on 3D epitaxial crystal growth of organic/inorganic crystals based on charge‐assisted hydrogen bonds that can be used to efficiently weld broken molecular single‐crystalline optical waveguides and restore their light‐transducing capability. This approach can also be applied to prepare asymmetric multidomain crystalline heterostructures starting from isostructural molecular tectons, resulting in novel opto/electro/mechanical functionalities in the hybrid materials. It also removes an important obstacle toward wider application of molecular crystals in the next‐generation optoelectronics.     

Enhancing Organic Semiconductor Molecular Packing Using Perovskite Interfaces to Improve Singlet Fission

Singlet fission, a process by which one singlet exciton is converted into two lower energy triplet excitons, is sensitive to the degree of electronic coupling within a molecular packing structure. Variations in molecular packing can be detrimental to triplet formation and triplet–triplet separation, ultimately affecting the harvesting of triplets for electricity in organic photovoltaic devices. Here, six phase-pure molecular packing structures of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) with varying optoelectronic properties are isolated using 2D lead halide perovskites as tunable, crystalline surfaces for crystallization. Transient absorption spectroscopy reveals that while triplet formation is fast (<100 fs) regardless of template structure, the increased ordering in perovskite-templated samples speeds up triplet–triplet separation and recombination, providing evidence that the benefits of phase-purity offset minor variations in molecular packing. Molecular dynamics modeling of the interface reveals that perovskite-templating allows for closer packing of TIPS-pentacene molecules for all perovskite templates. With an extensive number of organic molecule-perovskite pairings, this work provides a methodology to use ordered, periodic surfaces to elucidate structure–property relationships of small organic molecules in order to adjust structural or optoelectronic responses, such as molecular packing and singlet fission.     

In Vivo Plain X-Ray Imaging of Cancer Using Perovskite Quantum Dot Scintillators

Real-time in vivo detection of cancer via attenuation-based plain X-ray imaging is proposed to fundamentally overcome the penetration depth limits of current fluorescence-based imaging techniques. Using cesium lead bromide (CsPbBr₃, CPB) quantum dot (QD) scintillators, real-time X-ray detection of 5 mm-sized Panc-1 cell tumors grown in a mouse is successfully performed. The QDs are rapidly co-synthesized and double-encapsulated with silicon dioxide (SiO₂) to completely prevent them from being aggregated, decomposed, or released; they are then conjugated with antibodies to target pancreatic cancer. Due to the dramatic X-ray attenuation, the X-ray signal from the CPB QDs placed under the 2 cm-thick tissue is clearly observed, while their fluorescence signal is not detected at all. In in vivo mouse experiments, the injection of a tiny amount (2.8 μg on a QD basis) of the CPB–SiO₂@SiO₂–Ab nanoparticles gives rise to a bright spot at the location of the tumor. Cell viability assay and histological analysis confirm the biocompatibility and nontoxicity of the nanoparticles.     

Core/Shell Metal Halide Perovskite Nanocrystals for Optoelectronic Applications

Core/shell structured metal halide perovskite nanocrystals (NCs) are emerging as a type of material with remarkable optical and electronic properties. Research into this field has been developing and expanding rapidly in recent years, with significant advances in the studies of the shell growth mechanism and in understanding of properties of these materials. Significant enhancement of both the stability and the optical performance of core/shell perovskite NCs are of particular importance for their applications in optoelectronic technologies. In this review, the recent advances in core/shell structured perovskite NCs are summarized. The band structures and configurations of core/shell perovskite NCs are elaborated, the shell classification and shell engineering approaches, such as perovskites and their derivative shells, semiconductor shell, oxide shell, polymer shell, etc. are reviewed, and the shell growth mechanisms are discussed. The prospective of these NCs in lighting and displays, solar cells, photodetectors, and other devices is discussed in the light of current knowledge, remaining challenges, and future opportunities.     

激光等离子体X射线椭圆弯晶谱仪的设计

为了诊断0．2～2nm的激光等离子体X射线．研制了一种新型的基于时间分辨和空间分辨的聚焦型椭圆弯晶谱仪．采用两个完全相同且对称分布的通道可以同时获得谱线的空间和时间分辨率。给出了弯品谱仪的设计参数，采用了新颖的瞄准对中技术．并对光源偏离椭圆轴线造成的误差进行了分析。在“神光Ⅱ”靶室上进行打靶实验对该谱仪进行标定，利用X射线CCD相机成功地获取了谱线的图像．实验结果表明实测谱线波长与理论值吻合。     

Single Crystal Perovskite Solar Cells: Development and Perspectives

The efficiency of perovskite solar cells has increased to a certified value of 25.2% in the past 10 years, benefiting from the superior properties of metal halide perovskite materials. Compared with the widely investigated polycrystalline thin films, single crystal perovskites without grain boundaries have better optoelectronic properties, showing great potential for photovoltaics with higher efficiency and stability. Additionally, single crystal perovskite solar cells are a fantastic model system for further investigating the working principles related to the surface and grain boundaries of perovskite materials. Unfortunately, only a handful of groups have participated in the development of single crystal perovskite solar cells; thus, the development of this area lags far behind that of its polycrystalline counterpart. Therefore, a review paper that discusses the recent developments and challenges of single crystal perovskite solar cells is urgently required to provide guidelines for this emerging field. In this progress report, the optical and electrical properties of single crystal and polycrystalline perovskite thin films are compared, followed by the recent developments in the growth of single crystal perovskite thin films and the photovoltaic applications of this material. Finally, the challenges and perspectives of single crystal perovskite solar cells are discussed in detail.     

The Impact of X-Ray Radiation on Chemical and Optical Properties of Triple-Cation Lead Halide Perovskite: from the Surface to the Bulk

Understanding the effects of X-rays on halide perovskite thin films is critical for accurate and reliable characterization of this class of materials, as well as their use in detection systems. In this study, advanced optical imaging techniques are employed, both spectrally and temporally resolved, coupled with chemical characterizations to obtain a comprehensive picture of the degradation mechanism occurring in the material during photoemission spectroscopy measurements. Two main degradation pathways are identified through the use of local correlative physico-chemical analysis. The first one, at low X-Ray fluence, shows minor changes of the surface chemistry and composition associated with the formation of electronic defects. Moreover, a second degradation route occurring at higher fluence leads to the evaporation of the organic cations and the formation of an iodine-poor perovskite. Based on the local variation of the optoelectronic properties, a kinetic model describing the different mechanisms is proposed. These findings provide valuable insight on the impact of X-rays on the perovskite layers during investigations using X-ray based techniques. More generally, a deep understanding of the interaction mechanism of X-rays with perovskite thin films is essential for the development of perovskite-based X-ray detectors and solar for space applications.     

Strategies Toward Efficient Blue Perovskite Light-Emitting Diodes

Substantial progress has been made in blue perovskite light-emitting diodes (PeLEDs). In this review, the strategies for high-performance blue PeLEDs are described, and the main focus is on the optimization of the optical and electrical properties of perovskites. In detail, the fundamental device working principles are first elucidated, followed by a systematical discussion of the key issues for achieving high-quality perovskite nanocrystals (NCs) and quasi-2D perovskites. These involve ligand optimization and metal doping in enhancing the carrier transport and reducing the traps of perovskite NCs, as well as the perovskite phase modulation and defect passivation in improving energy transfer and emission efficiency of quasi-2D perovskites. The strategies for efficient 3D mixed-halide perovskite and lead-free perovskite blue LEDs are then briefly introduced. After that, other strategies, including effective charge transport layer, efficient perovskite emission system, and effective device architecture for high light outcoupling efficiency, are further discussed to boost the blue PeLED performances. Meanwhile, the testing standard of blue PeLED lifetime is suggested to enable the direct comparisons of the device operational stability. Finally, challenges and future directions for blue PeLEDs are addressed.     

Ultrafast Thermodynamic Control for Stable and Efficient Mixed Halide Perovskite Nanocrystals

Low photoluminescence quantum yield (PLQY) and spectra instability, the two most difficult challenges in blue‐emitting CsPbBr_xCl_3?x NCs, have not yet been solved. Quickly controlling the reaction thermodynamics is crucial to enhance crystallinity, thus PLQY and spectra stability, but it has been ignored until now. An ultrafast thermodynamic control (UTC) strategy is designed by utilizing liquid nitrogen to instantaneously freeze the superior crystal lattices of CsPbBr_xCl_3?x NCs formed at high temperature. The average cooling rate exhibits a 33‐fold increase compared to conventional ice‐water cooling (from 1.5 to 50 K s^?1). This UTC can make the reaction thermodynamic energy of the system lower than the threshold very quickly. Therefore, abrupt termination of further crystal growth can be achieved, which also avoids additional nucleation at low temperature. With the assist of defect passivation, the final blue‐emitting CsPbBr_xCl_3?x NCs exhibit an absolute PLQY of 98%, representing the highest value in Pb‐based blue perovskites to date. More importantly, they exhibit superior spectra instability. This UTC strategy not only represents a new avenue to synthesize perovskite NCs with excellent crystal quality and ultrahigh PLQY, but also provides a good reference to deal with the recognized bottleneck of spectra instability.     

Self‐Crystallized Multifunctional 2D Perovskite for Efficient and Stable Perovskite Solar Cells

Recently, perovskite solar cells (PSC) with high power‐conversion efficiency (PCE) and long‐term stability have been achieved by employing 2D perovskite layers on 3D perovskite light absorbers. However, in‐depth studies on the material and the interface between the two perovskite layers are still required to understand the role of the 2D perovskite in PSCs. Self‐crystallization of 2D perovskite is successfully induced by deposition of benzyl ammonium iodide (BnAI) on top of a 3D perovskite light absorber. The self‐crystallized 2D perovskite can perform a multifunctional role in facilitating hole transfer, owing to its random crystalline orientation and passivating traps in the 3D perovskite. The use of the multifunctional 2D perovskite (M2P) leads to improvement in PCE and long‐term stability of PSCs both with and without organic hole transporting material (HTM), 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) compared to the devices without the M2P.