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Lead halide perovskites have been explored ardently in the past decade owing to their excellent photophysical properties. High‐temperature cation exchange reactions have been employed to improve the stability and performance in perovskite lattice, but lacks control over size, shape, and stoichiometry. Herein, the solution phase interaction of cesium lead bromide (CsPbBr3) nanocrystals with monovalent and bivalent copper ions, under ambient conditions is systematically investigated. The introduction of Cu1+ explicitly initiates a one‐dimensional growth with a distinct phase transition, that is from cubic to orthorhombic, while Cu2+ induces a partial exchange with Pb2+ with no phase change. DFT calculations suggest that Cu1+ induces structural distortion via Cs1+ substitution, altering the Goldschmidt tolerance factor and perovskite octahedral tilting, leading to the phase transition. Additionally, the oleic acid/amine ligands used to stabilize the nanocrystals, are preferentially etched away to form complexes with Cu1+, initializing an oriented growth of the nanocubes to nanorods. A mechanistic investigation of the evolution of the nanorods gave insights on tuning the tolerance factor via room temperature modifications and cation exchanges in perovskites for anisotropy and morphology tuning. This effortlessly obtained perovskite nanorods with Cu1+ could find effective applications in optoelectronics, and as novel photocatalysts. [ABSTRACT FROM AUTHOR]

In recent years, the development of new efficient, fast, and intuitive materials and methods for photoluminescence (PL) sensing has become a research hotspot in analytical chemistry. Lead halide perovskite (LHP) materials have the characteristics of adjustable PL properties, high PL efficiency, and a variety of synthesis methods. Their PL is also sensitive to the change in specific factors in the environment. Based on these characteristics, LHP has shown good application prospects in the field of optical sensing. The study of the structural dimension, organic composition, or doped ions of LHP is helpful in exploring its sensing potential and proposing new sensing mechanisms, which have important research significance to promote sensing applications. In this review, the PL characteristics and sensing mechanisms, as well as their sensing applications of two- and three dimensional LHP, are discussed and summarized. [ABSTRACT FROM AUTHOR]

X-ray and γ-ray detection have been extensively studied and applied in medical imaging, security inspection, homeland security, non-destructive testing and other various fields. Perovskite materials have become excellent candidates for radiation detector devices due to their high radiation absorption coefficient, high carrier mobility-lifetime product and defect tolerance. The solution method offers significant advantages in the preparation of perovskite materials. It is a cost-effective approach that can be carried out at low temperatures or under ambient conditions. Additionally, it is also easier to implement for industrial production. This method plays a crucial role in optimizing the material system and achieving the preparation of high quality and large area crystal materials in the future. This paper analyzes the effects of crystal growth and material composition on radiation detection performance, focusing on the solution preparation of perovskite materials. The study aims to improve radiation detection performance by optimizing crystal growth quality and device structure design. Additionally, it also summarises the challenges faced by perovskite materials in the field of radiation detection and suggests future research directions. The results of this study are expected to serve as a reference for the industrialization of perovskite materials in the field of radiation detection. [ABSTRACT FROM AUTHOR]

The vapor–solid reaction technique holds potential for producing large‐scale organic–inorganic perovskite films, using a two‐step deposition process. The sucess of perovskite formation heavily relies on the crystallization of lead iodide (PbI2) precursor films. However, the high crystallinity of PbI2 can hinder organic vapors' diffusion and negatively affecting the solar cells by increasing charge recombination and accelerating degradation. To address this, pyridinium trifluoromethanesulfonate (PTFS) is introduced into the PbI2 precursor solution to control the nucleation and growth of PbI2 films. PTFS has been found to effectively suppresses PbI2 crystallization and enhance the integration of formamidinium ion (FA+) through hydrogen bonding, facilitating the full transformation of PbI2 into perovskite. It also minimizes defect formation by interacting with uncoordinated Pb2+ and FA+ ions. These modifications have significantly enhanced power conversion efficiency (PCE), reaching up to 21.19%, and the devices have maintained 93% of their initial performance after 1580 h of exposure to air. [ABSTRACT FROM AUTHOR]

Lead halide perovskites have emerged as the next‐generation materials for self‐powered photodetectors enabling operation without an external power source. In this study, a planar‐type photodetector based on metal‐doped p‐type MAPbBr3/n‐type MAPbBr3 single crystal showing excellent self‐powered photodetection properties is presented. The p‐n junction on the MAPbBr3 single crystal is formed by controlled epitaxial growth of Ag+‐doped MAPbBr3 SC (p‐type) on the facet of Sb3+‐doped MAPbBr3 SC (n‐type). The as‐integrated p‐n junction device with asymmetric electrodes shows a typical photovoltaic behavior with a high open circuit voltage of 0.95 V and great sensitivity to 530 nm illumination at zero bias with a responsivity of up to 0.41 A W−1 and a specific detectivity of 6.39 × 1011 Jones, which are among the highest values reported for MAPbBr3 single crystal‐based self‐powered photodetectors. In addition, the rise time and fall time of this device are as fast as 14 and 10 ms, respectively. These results pave the way for the fabrication of self‐powered perovskite‐based p‐n junction photodiode, which may find potential application in advanced photodiode and future optoelectronic devices. [ABSTRACT FROM AUTHOR]

Lead halide perovskite nanocrystals (NCs) with narrow, bright emission in the visible range are promising candidates for light‐emitting applications. Near‐unity quantum yields have been realized for green and red‐emitting perovskites, but efficient, stable blue‐emitting perovskite materials are scarce. Current methods to synthesize quantum‐confined CsPbBr3 NCs with blue emission are limited to specific wavelength ranges and still suffer from inhomogeneously broadened emission profiles. Herein, anisotropic blue‐green emitting CsPbBr3 NCs are synthesized in ambient atmosphere using a spontaneous crystallization method. Optical spectroscopy reveals a gradual, asymptotic photoluminescence (PL) redshift of pristine colloidal NCs after synthesis. During this process, the emission quality improves notably as the PL spectra become narrower and more symmetric, accompanied by a PL intensity increase. Electron microscopy indicates that the gradual redshift stems from an isotropic growth of the CsPbBr3 NCs in at least two dimensions, likely due to residual precursor ions in the dispersion. Most importantly, the growth process can be halted at any point by injecting an enhancement solution containing PbBr2 and organic capping ligands. Thus, excellent control over NC size is achieved, allowing for nanometer‐precise tunability of the respective emission wavelength in the range between 475 and 500 nm, enhancing the functionality of these already impressive NCs. [ABSTRACT FROM AUTHOR]

Perovskite/Silicon Tandem Solar Cells (PSTSCs) represent an emerging opportunity to compete with industry-standard single junction crystalline silicon (c-Si) solar cells. The maximum power conversion efficiency (PCE) of single junction cells is set by the Shockley–Queisser (SQ) limit (33.7%). However, tandem cells can expand this value to ~ 45% by utilising two stacked solar cells to harvest the solar spectrum more efficiently. 33.9% PCE has already been achieved with PSTSCs. This perspective analyses recent advances in PSTSC technology, with an emphasis on optimal perovskite composition, the problem and mitigation of light-induced halide phase segregation, self-assembled hole transporting monolayers and additives that can improve and stabilise the perovskite. Top-performing compositions show three cationic components (Cs+, FA+, Pb2+) and three anionic (I−, Br−, Cl−) with a bandgap between 1.55 and 1.77 eV and a theoretical maximum of 1.73 eV (717 nm). Anionic additives such as (Br3)− and SCN− reduce trap states and segregation. 2D-perovskite grain boundary interfaces are created with cationic alkylammonium additives such as methyl-phenethylammonium (MPEA) and result in improved performance. 2-, 3- or 4-terminal devices with a (partly) textured silicon heterojunction (SHJ) bottom cell are ideal. An ultra-thin interfacial recombination layer (~ 5 nm) of indium tin oxide (ITO) or indium zinc oxide (IZO) containing a carbazole-based hole transporting self-assembled monolayer (Me-4PACz) is used for optimal 2-terminal tandem devices. [ABSTRACT FROM AUTHOR]

Transient photocurrent is a widely applied characterization technique to probe the charge‐carrier photogeneration and extraction dynamics in perovskite optoelectronic devices. Despite the large number of studies on the properties of perovskite single‐crystals (SCs) photodetectors (PDs), the underlying mechanism that governs the spectral line shape of transient photocurrent is not fully understood. Here, methylammonium lead bromide (MAPbBr3)SC based PDs are used to study the effect of different electrode spacing and bias on the transient photocurrent response under blue and green light irradiation. The observed differences in the spectral line shape of the transient photocurrent are explained using three‐step carrier transport model, which reveals the occurrence of carrier trapping and a recombination process in MAPbBr3 SC. The findings are further corroborated by intensity‐dependent photocurrent and impedance spectroscopy analysis of the resulting PDs. This work provides a basic insight into the origin of the different behavior of transient photocurrent response under variable electrode distance, bias, and irradiance light, which is expected to help to further understand and optimize the performance of perovskite based PDs. [ABSTRACT FROM AUTHOR]

In this work, the thermostability of F- doped CsPbBr3 has been investigated through first principles calculations. Firstly, crystal structures of CsPbBr3-δFδ with different ratios of F- to Br- have been built. The influences substituting Br- by F- on the crystal structure, electronic band structure, absorption and the thermodynamic property has been investigated and presented. This substitution of Br- by F- could distinctly regulate and control the crystal structure, electronic band structure, thermal stability and the electron transfer process between the ligand ions and Pb2+. Electron transfer process and the thermostability were important for the performance of luminescence materials and CsPbBr3-δFδ with mixed Br- and F- as ligand ions of Pb2+ exhibited better thermal stability than that of CsPbBr3 and CsPbF3. The fluorinated perovskite materials could be a preferable choice for applying to luminescence materials. [ABSTRACT FROM AUTHOR]

A universal approach to calculating diffusion coefficients in lead halide perovskite single crystals, which have ionic and mixed ionic–electronic conductivity, is proposed. Using impedance spectroscopy, it is demonstrated how to model a non-ideal Warburg element and transmission line equivalent circuit to identify ionic diffusion in the material. The proposed method is applicable to samples of any thickness and electrical properties. Additionally, it is shown how to overcome the challenges of low-frequency impedance measurement and the non-ideal behavior of the elements through extrapolative modeling and approximation. [ABSTRACT FROM AUTHOR]

A feasible lead upcycling route is designed to recover lead halide products from lead smelting residues and use as raw materials for synthesis of FAPbBr 3-x I x perovskite for piezocatalytic hydrogen production. Zinc impurities from lead smelting residues further enhance the catalytic performance of FAPbBr 3-x I x. Our study offers a new possibility for green application and sustainable development of lead halide perovskite. [Display omitted] • Recovering lead halide products from lead smelting residues and use to synthetize FAPbBr 3-x I x perovskite pieocatalysts. • The FAPbBr 3-x I x pieocatalyst synthetized by the recovered lead halides achieve piezocatalytic HER activity of 157.80 μmol·g-1·h-1 under ultrasonic power of 112 W. • Zinc(Zn2+) impurities from lead smelting residues dope in structure of FAPbBr 3-x I x and further enhance the piezocatalytic performance. • Confirmed the feasibility of upcycling Pb from lead smelting residues to lead halide perovskite materials. Organic lead halide perovskite is a promising piezocatalyst for piezocatalytic H 2 production, meanwhile, large amount of unutilized lead resources in lead smelting residues have caused ecological security and resource waste problems. Here, we report an efficient Pb upcycling approach to recover lead halides from lead smelting residues to create lead halide perovskites (r-FAPbBr 3-x I x), distinguished by the remarkable piezoelectric properties, for piezocatalytic H 2 evolution. Zinc impurities, concurrently from these residues, found their utilization in the partial substitution of Pb2+ within the halide octahedra of r-FAPbBr 3-x I x. The intervention of zinc enhancing desorption of hydrogen from r-FAPbBr 3-x I x and culminating in a pronounced H 2 yield as 157.80 μmol·g−1·h−1. Notably, the used r-FAPbBr 3-x I x that lost its functional prowess could be regenerated and exhibited a piezocatalytic capacity similar to its initial state, perpetuating a sustainable cycle of utility. This pioneering route to Pb upcycling furnishes an alternative avenue for the preparation and utilization of lead-based perovskites. [ABSTRACT FROM AUTHOR]

Due to the tunable bandgaps, high quantum efficiency, and long carrier diffusion length, perovskites have attracted significant attention as active materials for solar cells, nanoscale lasers, photodetectors, and light‐emitting diodes. Herein, laser‐induced dual‐wavelength emissions from the CsPbBr3xI3(1–x) perovskite alloy microcrystals are reported. Under a 375 nm laser illumination, the micro‐photoluminescence (PL) emission spectra of these microcrystals exhibit two emission bands at 570 and 690 nm with gradually increased and decreased PL intensity, respectively. Moreover, the time‐dependent emission wavelength of the two emission bands almost has no changes, while the PL intensity of both emission bands shows periodic fluctuations with the on–off switching of excitation light. This dual‐wavelength emission phenomenon suggests that phase segregation occurs in these perovskite microcrystals during laser illumination. These results would provide valuable design guidelines for perovskites‐based tunable nanophotonic devices and multi‐color displays. [ABSTRACT FROM AUTHOR]

One of the unique characteristics of semiconductors is the strong dependence of their properties on crystal defects and doping. However, due to the species diversity and low density, it is very difficult to control the type and concentration of the defects. In perovskite materials, crystal defects are randomly formed during the fast crystallization process, causing large heterogeneity of the samples. Here, in this work, we report a controllable method to introduce surface defects on CH3NH3PbI3 perovskite materials via the interaction with 1,4-benzoquinone (BQ) molecules on the gas and solid interface. After the adsorption of BQ molecules on the perovskite surface, surface defects can be generated by photoinduced chemical reactions. The concentration of the defects can thus be controlled by precisely regulating the laser irradiation time. The concentration of the defects can be characterized by a gradually decreased PL intensity and lifetime and was found to influence the atmospheric response and the subsequent acetone-induced degradation of the materials. These results demonstrate that crystal defects in perovskite materials can be controllably introduced, which provides a possible way to fully understand the correlation between the nature and chemical structure of these defects. [ABSTRACT FROM AUTHOR]

The lead halide perovskite material shows its unique photoelectric properties, the resulting conversion efficiency of perovskite solar cells. However, the efficiency comes to a bottleneck owing to that mechanism research fall behind the device research. Multiple excitons dynamics play an important role, especially in the lifetime and binding energy of multiple excitons. A long multiexciton lifetime is beneficial to the application for light-emitting devices and photovoltaic devices. Large multiexciton binding energy means a large Stokes shift in exciton absorption, thus avoiding the loss of linear absorption. To conclude, discussions are presented regarding views of current multiple excitons research in terms of the biexciton lifetime and biexciton binding energy that should be considered for further advances in materials and devices. [ABSTRACT FROM AUTHOR]

The high power conversion efficiency of perovskite solar cells reaching 25.5% today [1], raises the question on the relation between the photovoltaic performance and physical nature of these materials. To get a better understanding of the properties, good quality single crystals are highly demanded. In this paper we report on large single crystals of formamidinium lead halide grown by a combination of inverse temperature crystallization and seed growth. Structure, phase transitions, dielectric and optical properties of the single crystals are shown. [ABSTRACT FROM AUTHOR]

Summary: Lead halide perovskites are considered as a material of choice for solar cell applications. However, there are challenges: organic cations in halide perovskites are unstable, and lead is toxic. To address these issues, we propose and investigate some potential alternatives to lead in the form of A2BX6 perovskites using the first‐principles calculations. Besides simple approximation potentials, we use a highly successful hybrid functional HSE06, to calculate the electronic, optical, and thermoelectric properties of A2PdI6 (A = K, Rb, and Cs). Our calculations show that K2PdI6, Rb2PdI6, and Cs2PdI6, are narrow bandgap semiconductors with bandgap of 0.8, 0.92, and 0.9 eV, respectively. The valence band maximum (VBM) of A2PdI6 is mainly composed of I‐5p orbitals while the conduction band minimum (CBM) is formed of Pd‐4d and I‐5p orbitals. Due to the ideal bandgap and excellent light absorption, Rb2PdI6 stands out as a potential candidate for usability in tandem solar cells. In addition, p‐type doping at a carrier concentration of 1 × 1018 cm−3 makes these perovskites a material of choice for thermoelectric energy applications. [ABSTRACT FROM AUTHOR]

The main drawback of the methylammonium lead halide perovskite solar cells is their degradation in ambient atmosphere. To investigate ambient-air-induced cell degradation, spectral dependencies of open-circuit voltage (VOC), fill factor (FF) and the power conversion efficiency (PCE) have been acquired (for the first time reported in literature). Our custom-made measurement system allowed us to perform measurements of the abovementioned entities in situ directly in vacuum during and after thermal deposition of the electrode. We also studied how these parameters in vacuum changed after cell exposure to ambient air for 85 min (50 nm top electrode) and for 180 min (100 nm top Ag electrode). For fresh CH3NH3PbI3–xClx cell (never been in open air) with very high shunt resistance of 3·107 Ω·cm2 (with practically no shorts and therefore FF could be determined mainly by charge carrier recombination processes) we found that FF in vacuum increased along with an increase of the incident photon energy from 0.55 at 760 nm up to 0.82 at 400 nm. Hypothesis considering hot polaron participation in charge carrier photogeneration and recombination processes as well as another competing hypothesis were offered as possible explanations for the observed FF increase. The kinetics of short-circuit photocurrent EQE with a change in pressure was also investigated. It was also shown that perovskite solar cell degradation could be noticeably reduced by increasing the top Ag electrode thickness to at least 100 nm, which could possibly facilitate the usual encapsulation process. [ABSTRACT FROM AUTHOR]

Development of hybrid organic-inorganic perovskite solar cells (PSC) has been one of the hottest research topics since 2013. Within brief literature review, we would like to achieve two objectives. Firstly, we would like to indicate that a whole set of physical properties, such as high change carrier mobility, very low recombination rates, large carrier life time and diffusion length, large absorption coefficients and very weak exciton binding energies, are defining high power conversion efficiency (PCE) of methyl ammonium lead trihalide SC. The second objective is to draw attention to some, in our opinion, important aspects that previously have not been satisfactory addressed in literature. Although degradation of PSC is widely discussed, processes at very first exposure to ambient conditions after deposition of top electrode are uncovered. [ABSTRACT FROM AUTHOR]

Reducing pinholes formation and enhancing surface coverage of hybrid organic-inorganic halide perovskite (MAPbI 3) film is critical in most application such as photovoltaics and memory device. These applications usually incorporate Titanium Dioxide (TiO 2) which is widely used to improve carrier injection as well as film morphology. Taking into account the fabrication and preparation cost, rather than forming a bilayer device, this work demonstrates the design of a facile two-step coating method in producing higher surface quality of single layer MAPbI 3 modified with the addition of TiO 2 nanoparticles. The study of this novel MAPbI 3 -TiO 2 compound reveals an enhanced movement of iodide vacancies towards the ITO interfaces while considering the effect of grain size and film uniformity. Hence, the Resistive Random Access Memory (ReRAM) devices employing the MAPbI 3 -TiO 2 compound shows to aid in improving V SET and V RESET voltage values in which molar ratio of Pb to Ti of 5% in MAPbI 3 -TiO 2 layer shows improved V SET and V RESET values of 3.6 V and −1.1 V. This study is believed to aid as a forefront in understanding the applicability of a single layer MAPbI 3 -TiO 2 in multiple applications. [ABSTRACT FROM AUTHOR]

This Review examines how the intermarriage of perovskite and metal‐organic framework crystals brings new paradigms for material design and functionality. The strategic combination of halide perovskites and metal–organic frameworks (MOFs) has generated a new family of porous composite materials that will enable new applications, including optoelectronic, catalysis, sensing, and data encryption. This Review surveys the current progress of this exciting new area. Fundamental aspects, including perovskite nucleation and growth, heterojunction electron–hole transfer, electronic structure, and luminescence within confined spaces, are highlighted, with suggestions of approaches by which guest confinement within MOFs can be synthetically designed. We further address the underlying principles and discuss the new insights and tools for the manipulation of these composite materials for the development of synthetic microporous semiconducting composites, as well as new strategies for host–guest interfacial engineering. [ABSTRACT FROM AUTHOR]

The utilization of mixed cations is beneficial for taking the advantages of cations and achieving highly efficient perovskite solar cells (PSCs). Herein, the precisely small incorporation of CH(NH2)2 (FA) cations in methyl ammonium lead iodide (MAPbI3) enables the formation of compact, smooth perovskite film with high crystallinity. Consequently, the short-circuit current and the fill factor of the PSCs based on FAxMA1-xPbI3 perovskite are greatly improved, leading to the enhanced device efficiency. The champion PSC based on FA0.1MA0.9PbI3 exhibits a remarkably high efficiency of 22.02%. Furthermore, the PSCs based on FA0.1MA0.9PbI3 perovskite also show improved device stability. This work provides a simple approach to fabricate high-quality perovskite films and high-performance PSCs with better stability. [ABSTRACT FROM AUTHOR]

Because of the interesting features of the organic/inorganic halide perovskite (e.g., CH3NH3PbX3, X = Cl, Br) materials, such as long electron–hole diffusion length, high absorption coefficient and adjustable band gap, they have attracted a great deal of attention. In this research, CH3NH3PbX3 (X = Br, Cl) are synthesized and perovskite-based single-layer and perovskite-based bilayer diodes are fabricated. Using electron beam deposition technique, thin films of CH3NH3PbX3 (X = Br, Cl) hybrids with excellent homogeneity are manufactured. Absorption spectrum, X-ray spectrum and photoluminescence spectrum of organic/inorganic halide perovskites along with electroluminescence spectra, SEM micrographs and current–voltage characteristic of perovskite-based light-emitting diodes are investigated. Perovskite-based bilayer diodes are evaluated for the first time. The difference between the emission wavelengths of single-layer and bilayer diodes is the main characteristic of bilayer diodes. [ABSTRACT FROM AUTHOR]

As a direct bandgap semiconductor, organic-inorganic lead halide perovskite (MAPbX 3 , MA = CH 3 NH 3 , X = Cl, Br, I) have been considered as promising materials for laser due to their excellent optoelectronic properties. The perovskite materials with 1D and 2D shapes were widely prepared and studied for Fabry-Pérot mode and whispering-gallery-mode (WGM) microcavities, but cuboid-shape is rarely reported. In this work, we successfully fabricated single crystal cuboid-shaped MAPbBr 3 perovskite with different morphologies, named microcuboid-MAPbBr 3 (M-MAPbBr 3) and multi-step-MAPbBr 3 (MS-MAPbBr 3), via solvothermal method. Furthermore, the as-prepared crystals' excitonic recombination lifetime under different pumping energy density was studied by time-resolved photoluminescence (TRPL). Based on controllable morphology and remarkable lasing properties, these cuboid shaped single crystal perovskite could be a promising candidate for small laser, and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

ABX3‐type halide perovskite nanocrystals (NCs) have been a hot topic recently due to their fascinating optoelectronic properties. It has been demonstrated that A‐site ions have an impact on their photophysical and chemical properties, such as the optical band gap and chemical stability. The pursuit of halide perovskite materials with diverse A‐site species would deepen the understanding of the structure–property relationship of the perovskite family. In this work we have attempted to synthesize rubidium‐based perovskite NCs. We have discovered that the partial substitution of Rb+ by Cs+ help to stabilize the orthorhombic RbPbBr3 NCs at low temperature, which otherwise can only be obtained at high temperature. The inclusion of Cs+ into the RbPbBr3 lattice results in highly photoluminescent Rb1−xCsxPbBr3 NCs. With increasing amounts of Cs+, the band gaps of the Rb1−xCsxPbBr3 NCs decrease, leading to a redshift of the photoluminescence peak. Also, the Rb1−xCsxPbBr3 NCs (x=0.4) show good stability under ambient conditions. This work demonstrates the high structural flexibility and tunability of halide perovskite materials through an A‐site cation substitution strategy and sheds light on the optimization of perovskite materials for application in high‐performance optoelectronic devices. Adding stability: Lead halide perovskite nanocrystals (NCs) attract tremendous attention due to their extraordinary optical properties. Herein, we show that the partial substitution of Rb+ by Cs+ helps to stabilize the orthorhombic RbPbBr3 NCs at low temperature, which otherwise could only be obtained at high temperature (above 300 °C, see figure). [ABSTRACT FROM AUTHOR]

Abstract Lead halide perovskites (LHP) are an emerging class of photovoltaic (PV) materials that have drawn intense interest due to their power conversion efficiencies above 23% and their potential for low-cost fabrication. However, the toxicity of lead causes concern about its use in LHP-PV at large scales. Here, we quantified lead intensity and toxicity potential of LHP-PV in potential commercial production. Lead intensity in LHP-PV life cycles can be 4 times lower and potential toxic emissions can be 20 times lower than those in representative U.S. electricity mixes, assuming that PV operational lifetimes reach 20 years. We introduce the metric "toxicity potential payback time", accounting for toxic emissions in the life cycle of energy cycles, and showed that it is < 2 years for perovskite PVs produced by and displacing the same grid mix. The toxicity potential associated with the energy of manufacturing a PV system dominates that associated with release of embodied lead. Therefore, the use of lead should not preclude commercialization of LHP-PVs. Instead, effort should focus on development of low-energy manufacturing processes and long service lifetimes. Additional detailed investigations are needed to quantify the full life cycle of commercial production of perovskites and to minimize potential emissions. Graphical abstract Image 1 Highlights • Quantified lead intensity, toxicity potential of lead halide perovskite PV. • Toxicity potential from embodied energy much greater than from release of lead. • Perovskite PV has lower lead intensity and toxicity potential than grid electricity. • Toxicity potential payback time <2 years for perovskite PV. [ABSTRACT FROM AUTHOR]

Lead halide perovskites are used in thin-film solar cells, which owe their high efficiency to the long lifetimes of photocarriers. Various calculations find that a dynamical Rashba effect could significantly contribute to these long lifetimes. This effect is predicted to cause a spin splitting of the electronic bands of inversionsymmetric crystalline materials at finite temperatures, resulting in a slightly indirect band gap. Direct experimental evidence of the existence or the strength of the spin splitting is lacking. Here, we resonantly excite photocurrents in single crystalline (CH3NH3)PbI3 with circularly polarized light to clarify the existence of spin splittings in the band structure. We observe a circular photogalvanic effect, i.e., the photocurrent depends on the light helicity, in both orthorhombic and tetragonal (CH3NH3)PbI3. At room temperature, the effect peaks for excitation photon energies ΔE = 110 meV below the direct optical band gap. Temperaturedependent measurements reveal a sign change of the effect at the orthorhombic-tetragonal phase transition, indicating different microscopic origins in the two phases. Within the tetragonal phase, both ΔE and the amplitude of the circular photogalvanic effect increase with temperature. Our findings support a dynamical Rashba effect in this phase, i.e., a spin splitting caused by thermally induced structural fluctuations which break inversion symmetry. [ABSTRACT FROM AUTHOR]

In a physical vapor deposition process for fabrication of perovskite absorber layers it is an important prerequisite for large scale application to understand the reaction steps and the impact of the deposition parameters on the structural and compositional characteristics of vacuum deposited lead halide perovskite layers. In the sequential deposition method, we found a narrow and low lying temperature window for the transformation of a vapor deposited PbCl 2 base layer to CH 3 NH 3 PbI 3 perovskite by reaction with evaporated CH 3 NH 3 I. To modify the deposition parameter window, we systematically varied background pressure and substrate temperature and analyzed the resulting composition using X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The resulting reaction products and byproducts CH 3 NH 3 PbI 3 , CH 3 NH 3 PbCl 3 , PbICl, PbCl 2 , and PbI 2 were identified and the variation of their concentration in dependence of background pressure and substrate temperature is explained by discussion of a set of reaction equations and reaction mechanisms on a thermodynamic basis. [ABSTRACT FROM AUTHOR]

Perovskite semiconductor nanocrystals with different compositions have shown promise for applications in light-emitting devices. Dark excitonic states may suppress light emission from such nanocrystals by providing an additional nonradiative recombination channel. Here, we study the composition dependence of dark exciton dynamics in nanocrystals of lead halides by time-resolved photoluminescence spectroscopy at cryogenic temperatures. The presence of a spin-related dark state is revealed by magneto-optical spectroscopy. The energy splitting between bright and dark states is found to be highly sensitive to both halide elements and organic cations, which is explained by considering the effects of size confinement and charge screening, respectively, on the exchange interaction. These findings suggest the possibility of manipulating dark exciton dynamics in perovskite semiconductor nanocrystals by composition engineering, which will be instrumental in the design of highly efficient light-emitting devices. [ABSTRACT FROM AUTHOR]

Lead halide perovskites (LHPs) have shown remarkable promise for use in photovoltaics, photodetectors, light-emitting diodes, and lasers. Although solution-processed polycrystalline films are the most widely studied morphology, LHP nanowires (NWs) grown by vapor-phase processes offer the potential for precise control over crystallinity, phase, composition, and morphology. Here, we report the first demonstration of self-catalyzed vapor-liquid-solid (VLS) growth of lead halide (PbX2; X = Cl, Br, or I) NWs and conversion to LHP. We present a kinetic model of the PbX2 NW growth process in which a liquid Pb catalyst is supersaturated with halogen X through vapor-phase incorporation of both Pb and X, inducing growth of a NW. For PbI2, we show that the NWs are single-crystalline, oriented in the 〈1̄21̄0〉 direction, and composed of a stoichiometric PbI2 shaft with a spherical Pb tip. Low-temperature vapor-phase intercalation of methylammonium iodide converts the NWs to methylammonium lead iodide (MAPbI3) perovskite while maintaining the NW morphology. Single-NW experiments comparing measured extinction spectra with optical simulations show that the NWs exhibit a strong optical antenna effect, leading to substantially enhanced scattering efficiencies and to absorption efficiencies that can be more than twice that of thin films of the same thickness. Further development of the self-catalyzed VLS mechanism for lead halide and perovskite NWs should enable the rational design of nanostructures for various optoelectronic technologies, including potentially unique applications such as hot-carrier solar cells. [ABSTRACT FROM AUTHOR]

Revealing the crystal structure of lead halide perovskite nanocrystals is essential for the optimization of stability of these emerging materials in applications such as solar cells, photodetectors, and light-emitting devices. We use magneto-photoluminescence spectroscopy of individual perovskite CsPbBr3 nanocrystals as a unique tool to determine their crystal structure, which imprints distinct signatures in the excitonic sublevels of charge complexes at low temperatures. At zero magnetic field, the identification of two classes of photoluminescence spectra, displaying either two or three sublevels in their exciton fine structure, shows evidence for the existence of two crystalline structures, namely tetragonal D4h and orthorhombic D2h phases. Magnetic field shifts, splitting, and coupling of the sublevels provide a determination of the diamagnetic coefficient and valuable information on the exciton g-factor and its anisotropic character. Moreover, this spectroscopic study reveals the optical properties of charged excitons and allows the extraction of the electron and hole g-factors for perovskite systems. [ABSTRACT FROM AUTHOR]

We investigate solution-grown single-crystal methylammonium lead iodide (MAPbI3) nanowires and nanoplates with spatially resolved photocurrent mapping. Sensitive perovskite photodetectors with Schottky contacts are fabricated by directly transferring the nanostructures on top of prepatterned gold electrodes. Scanning photocurrent microscopy (SPCM) measurements on these single-crystal nanostructures reveal a minority charge carrier diffusion length up to 21 μm, which is significantly longer than the values observed in polycrystalline MAPbI3 thin films. When the excitation energy is close to the bandgap, the photocurrent becomes substantially stronger at the edges of nanostructures, which can be understood by the enhancement of light coupling to the nanostructures. These perovskite nanostructures with long carrier diffusion lengths and strong photonic enhancement not only provide an excellent platform for studying their intrinsic properties but may also boost the performance of perovskite-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Organic-inorganic lead halide perovskite semiconductors have recently reignited the prospect of a tunable, solution-processed diode laser, which has the potential to impact a wide range of optoelectronic applications. Here, we demonstrate a metal-clad, second-order distributed feedback methylammonium lead iodide perovskite laser that marks a significant step toward this goal. Optically pumping this device with an InGaN diode laser at low temperature, we achieve lasing above a threshold pump intensity of 5 kW/cm² for durations up to ∼25 ns at repetition rates exceeding 2 MHz. We show that the lasing duration is not limited by thermal runaway and propose instead that lasing ceases under continuous pumping due to a photoinduced structural change in the perovskite that reduces the gain on a submicrosecond time scale. Our results indicate that the architecture demonstrated here could provide the foundation for electrically pumped lasing with a threshold current density Jth < 5 kA/cm² under sub-20 ns pulsed drive. [ABSTRACT FROM AUTHOR]

CH3NH3PbI3-xClx is a commonly used chemical formula to represent the methylammonium lead halide perovskite fabricated from mixed chlorine- and iodine-containing salt precursors. Despite the rapid progress in improving its photovoltaic efficiency, fundamental questions remain regarding the atomic ratio of Cl in the perovskite as well as the reaction mechanism that leads to its formation and crystallization. In this work we investigated these questions through a combination of chemical, morphological, structural and thermal characterizations. The elemental analyses reveal unambiguously the negligible amount of Cl atoms in the CH3NH3PbI3-xClx perovskite. By studying the thermal characteristics of methylammonium halides as well as the annealing process in a polymer/perovskite/FTO glass structure, we show that the formation of the CH3NH3PbI3-xClx perovskite is likely driven by release of gaseous CH3NH3Cl (or other organic chlorides) through an intermediate organometal mixed halide phase. Furthermore, the comparative study on CH3NH3I/PbCl2 and CH3NH3I/PbI2 precursor combinations with different molar ratios suggest that the initial introduction of a CH3NH3+ rich environment is critical to slow down the perovskite formation process and thus improve the growth of the crystal domains during annealing; accordingly, the function of Cl− is to facilitate the release of excess CH3NH3+ at a relatively low annealing temperatures. [ABSTRACT FROM AUTHOR]

• A series of CsPbX 3 /P-Y 2 O 3 (X=Cl, Br, I) composites were synthesized. • General stability improvement was observed after PQDs encapsulation in P-Y 2 O 3. • CsPbBrI 2 /P-Y 2 O 3 was selected to explicate the potential for WLED application. Recently, all-inorganic lead halide perovskite quantum dots (PQDs) have raised great attention for various outstanding properties. Although it is a promising candidate for white light emitting diodes (WLED) application, stability issue remains a challenge. In this work, by using a one-step strategy, we successfully achieved nano-sized Y 2 O 3 nanoparticle assisted stability enhancement of multiple all-inorganic lead halide perovskite. Photostability and environmental stability tests show that all dispersed composites retain most of the fluorescence properties. A WLED is fabricated based on as-prepared CsPbBrI 2 /P-Y 2 O 3 composite. The Commission Internationale de I'Eclairage (CIE) color coordinates of the fabricated WLED is (0.34, 0.35), which is close to the standard white emission coordinate (0.33, 0.33). The luminous efficiency of as-prepared WLED is 61 lm/W with a color render index (CRI) of 83, demonstrating that CsPbBrI 2 /P-Y 2 O 3 is potential for application in lighting and display technologies. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient and stable P3HT/CsPbBr 3 composite photocatalyst was fabricated. • There is strong interaction between P3HT and CsPbBr 3. • Boosted charge separation was achieved by coupling CsPbBr 3 with P3HT. • The P3HT/CsPbBr 3 composite exhibits high photocatalytic activity in CO 2 reduction. The suitable band structure and exceptional light harvesting abilities render lead halide perovskite (LHP) nanocrystals promising alternative for photocatalytic CO 2 reduction. However, pristine LHPs usually exhibit unsatisfactory photocatalytic activity in CO 2 reduction due to the high radiative recombination, low charge separation, and insufficient stability. To overcome these obstacles, herein, a poly(3-hexylthiophene-2,5-diyl) (P3HT)/CsPbBr 3 composite was fabricated by encapsulating the CsPbBr 3 quantum dots (QDs) into a P3HT conducting polymer, which could act as a protective layer as well as a hole transporter. Owing to the efficient charge transfer brought by the synergic effect between the two components, the P3HT/CsPbBr 3 composite exhibited outstanding photocatalytic performance in CO 2 reduction, with an electron consumption rate high up to 475.3 μmol g−1 h−1, which was approximately 10-times higher than that of pristine CsPbBr 3 QDs. Our study provides new insight into the design and fabrication of conducting polymers/LHP heterogeneous photocatalysts, which show great potentials in artificial photosynthesis. [ABSTRACT FROM AUTHOR]

We report the solution-based synthesis and material characterization of the Cd substituted hybrid organic-inorganic lead halide perovskite CH 3 NH 3 Pb 1-x Cd x I 3 (x = 0.0, 0.03, 0.05, 0.08). Structure and morphology of the samples were investigated using XRD, FESEM and HRTEM techniques. XRD results confirmed a tetragonal perovskite structure (I4/ mcm) through the doping range. Optical absorption, band gap and bonding character were studied by UV–visible, FTIR and photoluminescence spectroscopy. Oxidation states, binding energy and chemical composition were determined by XPS and EDAX. A low value of Urbach energy (~14 meV) indicated high sample quality with low defects and trap states. The undoped samples had a direct energy gap of 1.56 eV, which reduced to 1.50 eV upon Cd doping. Most significantly, the absorption coefficient of CH 3 NH 3 Pb 1-x Cd x I 3 remained high (~103) above 750 nm in the spectrally important infrared range as compared to CH 3 NH 3 PbI 3 , which approached zero. The enhanced structural and optical properties upon Cd doping make these materials promising photo absorber candidates compared to undoped CH 3 NH 3 PbI 3. • Cd-doped perovskite CH 3 NH 3 Pb 1-x Cd x I 3 synthesized via a single step solution process. • Nanocrystalline tetragonal structure with low defects was preserved on Cd doping. • Cd doped samples exhibited a slight reduction in the optical energy gap. • Cd doping led to greatly enhanced absorption in the infra-red region above 750 nm. [ABSTRACT FROM AUTHOR]

Solar hydrogen conversion represents a clean and economic approach to addressing global energy and environmental issues, for which efficient photocatalysts are heavily pursued. Lead halide perovskites are promising candidates for efficient phtocatalysts in solar hydrogen generation due to their attractive properties in light absorption, photogenerated charge transportation, and utilization. However, photocatalytic applications of lead halide perovskites are limited owing to their poor stability in the presence of water or other polar solvent environment. This work presents the rational control of surface ligands in achieving a good balance between stability and photocatalytic activity of CsPbBr3 quantum dots (QDs). Detailed studies reveal that the deliberate surface ligands engineering is crucial for maximizing the photocatalytic activity of CsPbBr3 QDs while maintaining good QD stability. A certain amount of surface ligands protect the CsPbBr3 QDs from decomposition in moisture during the photocatalytic reaction while still enabling efficient charge transfer for photocatalytic reactions on the surface of QDs. The well‐controlled CsPbBr3 photocatalyst shows efficient visible light‐driven H2 generation with outstanding stability (≥160 h). [ABSTRACT FROM AUTHOR]

This paper explores the gas sensing properties of graphene nanolayers decorated with lead halide perovskite (CH3NH3PbBr3) nanocrystals to detect toxic gases such as ammonia (NH3) and nitrogen dioxide (NO2). A chemical-sensitive semiconductor film based on graphene has been achieved, being decorated with CH3NH3PbBr3 perovskite (MAPbBr3) nanocrystals (NCs) synthesized, and characterized by several techniques, such as field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Reversible responses were obtained towards NO2 and NH3 at room temperature, demonstrating an enhanced sensitivity when the graphene is decorated by MAPbBr3 NCs. Furthermore, the effect of ambient moisture was extensively studied, showing that the use of perovskite NCs in gas sensors can become a promising alternative to other gas sensitive materials, due to the protective character of graphene, resulting from its high hydrophobicity. Besides, a gas sensing mechanism is proposed to understand the effects of MAPbBr3 sensing properties. [ABSTRACT FROM AUTHOR]

Flexible photodetectors (PDs) are attracting more attention due to their promising applications in wearable optoelectronic devices, bendable imaging sensors, and implantable optoelectronics. For the easy‐processable technology of massively fabricating PDs, instead of the expensive and complex high‐vacuum technique, the well‐matched work function of their active materials is essential. Herein, all‐sprayed‐processable and large‐area PDs are demonstrated on common paper based on two‐dimensional (2D) CsPbBr3 nanosheets and conductive Ti3C2Tx (MXene). Ascribed to the superior conductivity of MXene, high crystallinity of 2D CsPbBr3, and their well‐matched work function, the as‐prepared PDs exhibit an outstanding on/off current ratio up to 2.3 × 103 and a remarkable photoresponse as fast as 18 ms. Specifically, the detectivity (D*) of 6.4 × 108 Jones and responsivity (R) of 44.9 mA W−1 under a bias of 10 V are achieved. Besides, after bending 1500 cycles, the as‐prepared PDs can still maintain the excellent flexibility and stability. Based on this, a superior‐quality and large‐area 1665 pixel sensor in 72 cm2 (≈24 units cm−2) is developed, and it can clearly transmit the image of "0" to realize the photocommunication function. This work provides a low‐cost method of massively producing the flexible large‐area PDs for wearable optoelectronic devices and expanded photocommunication. The on‐paper flexible photodetectors based on 2D perovskite nanosheets and Ti3C2Tx (MXene) as the active materials and electrode materials by all‐spraying method are demonstrated. The low‐cost photodetectors have high stability, flexibility, photoelectric performance, and can effectively realize the optical communication function of image sensing by large‐area arrays. This technique can be potentially expanded to other optoelectronic devices. [ABSTRACT FROM AUTHOR]