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Over the past decade, metal halide perovskite photovoltaics have been a major focus of research, with single-junction perovskite solar cells evolving from an initial power conversion efficiency of 3.8% to reach 25.5%. The broad bandgap tunability of perovskites makes them versatile candidates as the subcell in a tandem photovoltaics architecture. Stacking photovoltaic absorbers with cascaded bandgaps in a multi-junction device can potentially overcome the Shockley–Queisser efficiency limit of 33.7% for single-junction solar cells. There is now intense activity in developing tandem solar cells that pair perovskite with either itself or with a variety of mature photovoltaic technologies such as silicon and Cu(In,Ga)(S,Se)2 (CIGS). In this review, we survey recent advances in the field and discuss its outlook.A discussion of the evolution, present status and future outlook for tandem solar cells employing perovskite materials.

Perovskite solar cells have recently drawn significant attention for photovoltaic applications with a certified power conversion efficiency of more than 22%. Unfortunately, the toxicity of the dissolvable lead content in these materials presents a critical concern for future commercial development. This review outlines some criteria for the possible replacement of lead by less toxic elements, and highlights current research progress in the application of low-lead halide perovskites as optically active materials in solar cells. These criteria are discussed with the aim of developing a better understanding of the physio-chemical properties of perovskites and of realizing similar photovoltaic performance in perovskite materials either with or without lead. Some open questions and future development prospects are outlined for further advancing perovskite solar cells toward both low toxicity and high efficiency.

Perovskites are attracting an increasing interest in the wide community of photovoltaics, optoelectronic, and detection, traditionally relying on lead‐based systems. This Minireview provides an overview of the current status of experimental and computational results available on Ge‐containing 3D and low‐dimensional halide perovskites. While stability issues analogous to those of tin‐based materials are present, some strategies to afford this problem in Ge metal halide perovskites (MHPs) for photovoltaics have already been identified and successfully employed, reaching efficiencies of solar devices greater than 7 % at up to 500 h of illumination. Interestingly, some Ge‐containing MHPs showed promising nonlinear optical responses as well as quite broad emissions, which are worthy of further investigation starting from the basic materials chemistry perspective, where a large space for properties modulation through compositions/alloying/fnanostructuring is present. Germane to germanium: This Minireview provides an overview of current experimental and computational research in the field of Ge‐based 3D and low‐dimensional halide perovskites. Materials properties, including stability issues and structure‐property correlations are discussed, as well as present and future applications in various fields ranging from photovoltaics to nonlinear optics and optoelectronics.

Lithium metal solid‐state batteries (LMSBs) have attracted extensive attention over the past decades, due to their fascinating advantages of safety and potential for high energy density. Solid‐state electrolytes (SEs) with fast ionic transport and excellent stability are indispensable components in LMSBs. Heretofore, a series of inorganic SEs have been extensively explored, such as sulfide‐ and oxide‐based electrolytes. Unfortunately, they both have difficulty in achieving a satisfactory balance of conductivity and stability, and oxides suffer from a high impedance of grain boundaries, while sulfides encounter poor stability. Halide‐based solid electrolytes are gradually emerging as one of the most promising candidates for LMSBs due to their advantages of decent room temperature ionic conductivity (>10−3 S cm−1), good compatibility with oxide cathode materials, good chemical stability, and scalability. Herein, research and development of the widely studied metal halide SEs including fluorides, chlorides, bromides, and iodides are reviewed, mainly focusing on the structures and ionic conductivities as well as preparation methods and electrochemical/chemical stabilities. And then, based on typical metal halide solid electrolytes, we emphasize the interface issues (grain boundaries, cathode−electrolyte and electrolyte–anode interfaces) that exist in the corresponding LMSBs and summarize the related work on understanding and engineering these interfaces. Furthermore, the typical (or in situ) characterization tools widely used for solid‐state interfaces are reviewed. Finally, a perspective on the future direction for developing high‐performance LMSBs based on the halide electrolyte family is put out. The crystal structures and ionic conductivities for widely studied metal halide solid electrolytes, as well as their synthesis methods and electrochemical/chemical stabilities, are systematically summarized, with a special focus on the interface issues that exist in the corresponding lithium metal solid‐state batteries. Furthermore, the typical characterization tools widely used for solid‐state interfaces and some in situ experimental characterizations are reviewed.

The relationship between the structural asymmetry and optoelectronic properties of functional materials is an active area of research. The movement of charges through an oriented chiral medium depends on the spin configuration of the charges, and such systems can be used to control spin populations without magnetic components — termed the chiral-induced spin selectivity (CISS) effect. CISS has mainly been studied in chiral organic molecules and their assemblies. Semiconductors are non-magnetic extended systems that allow for the control of charge transport, as well as the absorption and emission of light. Therefore, introducing chirality into semiconductors would enable control over charge, spin and light without magnetic components. Chiral metal halide semiconductors (MHSs) are hybrid organic–inorganic materials that combine the properties of small chiral organic molecules with those of extended inorganic semiconductors. Reports of CISS in chiral MHSs have resulted in breakthroughs in our understanding of CISS and in the realization of spin-dependent optoelectronic properties. This Review examines the fundamentals and applications of CISS in chiral MHSs. The structural diversity and key structure–property relationships, such as chiral transfer from the organic to the inorganic components, are summarized. With a focus on the underlying chemistry and physics, the control of spin, light and charge in these semiconductors is explored. Chiral metal halide semiconductors are a new class of hybrid organic–inorganic materials that combine the properties of small chiral organic molecules with those of extended inorganic semiconductors. This Review highlights the design, properties and emerging applications of these chiral semiconductors, with an emphasis on structure–property relationships.

HighlightsSelf-powered direct X-ray detectors, based on FAPbBr3 255-nm-thick films deposited onto mesoporous TiO2 scaffolds, can withstand a 26-day uninterrupted X-ray exposure with negligible signal loss, demonstrating ultra-high operational stability.Bulk specific sensitivity is evaluated to be 7.28 C Gy−1 cm−3 at 0 V, an unprecedented value in the field of thin-film-based photoconductors and photodiodes for “hard” X-rays. Sensitivity of submicrometer-thick perovskite films to the X-rays produced by a medical linear accelerator used for cancer treatment is here demonstrated for the first time. Metal-halide perovskites are revolutionizing the world of X-ray detectors, due to the development of sensitive, fast, and cost-effective devices. Self-powered operation, ensuring portability and low power consumption, has also been recently demonstrated in both bulk materials and thin films. However, the signal stability and repeatability under continuous X-ray exposure has only been tested up to a few hours, often reporting degradation of the detection performance. Here it is shown that self-powered direct X-ray detectors, fabricated starting from a FAPbBr3 submicrometer-thick film deposition onto a mesoporous TiO2 scaffold, can withstand a 26-day uninterrupted X-ray exposure with negligible signal loss, demonstrating ultra-high operational stability and excellent repeatability. No structural modification is observed after irradiation with a total ionizing dose of almost 200 Gy, revealing an unexpectedly high radiation hardness for a metal-halide perovskite thin film. In addition, trap-assisted photoconductive gain enabled the device to achieve a record bulk sensitivity of 7.28 C Gy−1 cm−3 at 0 V, an unprecedented value in the field of thin-film-based photoconductors and photodiodes for “hard” X-rays. Finally, prototypal validation under the X-ray beam produced by a medical linear accelerator for cancer treatment is also introduced.

Lead (Pb) halide perovskites have witnessed highly promising achievements for high-efficiency solar cells, light-emitting diodes (LEDs), and photo/radiation detectors due to their exceptional optoelectronic properties. However, compound stability and Pb toxicity are still two main obstacles towards the commercialization of halide perovskite-based devices. Therefore, it is of substantial interest to search for non-toxic candidates with comparable photophysical characteristics. Metal-halide double perovskites (MHDPs), A BBʹX , are recently booming as promising alternatives for Pb-based halide-perovskites for their non-toxicity and significantly enhanced chemical and thermodynamic stability. Moreover, this family exhibits rich combinatorial chemistry with tuneable optoelectronic properties and thus a great potential for a broad range of optoelectronic/electronic applications. Herein, we present a comprehensive review of the MHDPs synthesized so far, and classified by their optical and electronic properties. We systematically generalize their electronic structure by both theoretical and experimental efforts to prospect the relevant optoelectronic properties required by different applications. The progress of the materials in various applications is explicated in view of the material structure-function relationship. Finally, a perspective outlook to improve the physical and optoelectronic properties of the materials is proposed aiming at fostering their future development and applications.

Recent years have witnessed an incredibly high interest in perovskite-based materials. Among this class, metal halide perovskites (MHPs) have attracted a lot of attention due to their easy preparation and excellent opto-electronic properties, showing a remarkably fast development in a few decades, particularly in solar light-driven applications. The high extinction coefficients, the optimal band gaps, the high photoluminescence quantum yields and the long electron–hole diffusion lengths make MHPs promising candidates in several technologies. Currently, the researchers have been focusing their attention on MHPs-based solar cells, light-emitting diodes, photodetectors, lasers, X-ray detectors and luminescent solar concentrators. In our review, we firstly present a brief introduction on the recent discoveries and on the remarkable properties of metal halide perovskites, followed by a summary of some of their more traditional and representative applications. In particular, the core of this work was to examine the recent progresses of MHPs-based materials in photocatalytic applications. We summarize some recent developments of hybrid organic–inorganic and all-inorganic MHPs, recently used as photocatalysts for hydrogen evolution, carbon dioxide reduction, organic contaminant degradation and organic synthesis. Finally, the main limitations and the future potential of this new generation of materials have been discussed.

Metal halide perovskite nanocrystals have attracted great attention of researchers due to their unique optoelectronic properties such as high photoluminescence quantum yield (PLQY), narrow full width at half-maximum (FWHM), long exciton diffusion length and high carrier mobility, which have been widely used in diverse fields including solar cells, photodetectors, light-emitting diodes, and lasers. Very recently, metal halide perovskites have emerged as a new class of materials in photocatalysis due to their promising photocatalytic performance. In this review, we summarize the recent advances on synthesis, modification and functionalization, with a specific focus on the photocatalytic application of metal halide perovskite nanocrystals. Finally, a brief outlook is proposed to point out the challenges in this emerging area. The goal of this view is to introduce the photocatalytic application of the metal halide perovskites and motivate researchers from different fields to explore more potentials in catalysis.

Recently, many lead‐free metal halides with diverse structures and highly efficient emission have been reported. However, their poor stability and single‐mode emission color severely limit their applications. Herein, three homologous Sb3+‐doped zero‐dimensional (0D) air‐stable Sn(IV)‐based metal halides with different crystal structures were developed by inserting a single organic ligand into SnCl4 lattice, which brings different optical properties. Under photoexcitation, (C25H22P)SnCl5@Sb·CH4O (Sb3+−1) does not emit light, (C25H22P)2SnCl6@Sb‐α (Sb3+−2α) shines bright yellow emission with a photoluminescence quantum yield (PLQY) of 92%, and (C25H22P)2SnCl6@Sb‐β (Sb3+−2β) exhibits intense red emission with a PLQY of 78%. The above three compounds show quite different optical properties should be due to their different crystal structures and the lattice distortions. Particularly, Sb3+−1 can be successfully converted into Sb3+−2α under the treatment of C25H22PCl solution, accompanied by a transition from nonemission to efficient yellow emission, serving as a “turn‐on” photoluminescence (PL) switching. Parallelly, a reversible structure conversion between Sb3+−2α and Sb3+−2β was witnessed after dichloromethane or volatilization treatment, accompanied by yellow and red emission switching. Thereby, a triple‐mode tunable PL switching of off–onI–onII can be constructed in Sb3+‐doped Sn(IV)‐based compounds. Finally, we demonstrated the as‐synthesized compounds in fluorescent anticounterfeiting, information encryption, and optical logic gates. Three homologous compounds of Sb3+‐doped zero‐dimensional Sn(IV)‐based metal halides with different crystal structures were synthesized, and they show different optical properties. Particularly, the nonemitting Sb3+−1 can be converted into yellow‐emitting Sb3+−2α, and further turn into red‐emitting Sb3+−2β under the treatment of C25H22PCl and CH2Cl2 solution, respectively. Thus, a triple‐mode PL switching of off–onI–onII was constructed in Sb3+‐doped Sn(IV)‐based metal halides.