Exploring Non-Toxic Lower Dimensional Perovskites for Next-Generation X-Ray Detectors.

Owing to their extraordinary photophysical properties, organometal halide perovskites are emerging as a new material class for X-ray detection. However, the existence of toxic lead makes their commercialization questionable and should readily be replaced. Accordingly, several lead alternatives have been introduced into the framework of conventional perovskites, resulting in various new perovskite dimensionalities. Among these, Pb-free lower dimensional perovskites (LPVKs) not only show promising X-ray detecting properties due to their higher ionic migration energy, wider and tunable energy bandgap, smaller dark currents, and structural versatility but also exhibit extended environmental stability. Herein, first, the structural organization of the PVKs (including LPVKs) is summarized. In the context of X-ray detectors (XDs), the outstanding properties of the LPVKs and active layer synthesis routes are elaborated afterward. Subsequently, their applications in direct XDs are extensively discussed and the device performance, in terms of the synthesis method, device architecture, active layer size, figure of merits, and device stability are tabulated. Finally, the review is concluded with an in-depth outlook, thoroughly exploring the present challenges to LPVKs XDs, proposing innovative solutions, and future directions. This review provides valuable insights into optimizing non-toxic Pb-free perovskite XDs, paving the way for future advancements in the field.

Solvothermal synthesis of 3D hierarchical Cu2FeSnS4 microspheres for photocatalytic degradation of organic pollutants.

In this work, we prepared Cu2FeSnS4 (CFTS) microspheres via solvothermal method and studied their photocatalytic performance towards the degradation of organic pollutants. With increasing solvothermal temperature from 160 °C to 180 °C, the morphology of CFTS changes from irregular 2D to hierarchical 3D shapes. Hierarchical 3D CFTS microspheres packed with 2D nanosheets were successfully prepared at 180 °C. During the solvothermal process, octadecyl amine (ODA) acts as a capping agent to prevent the aggregation of particles, while L-cystine functions as an environmentally friendly sulfur source and complexing reagent. The large surface area and mesoporous structure of the as-prepared 3D hierarchical CFTS microspheres provide more active sites, enhance visible light absorption and promote charge separation and transfer, leading to the improved photodegradation performance for RhB and MB compared to the samples prepared at the temperature lower than 180 °C. This work provides a simple and low-cost method for the synthesis of 3D hierarchical CFTS towards photocatalytic applications.

Design of highly sensitive and selective ethanol sensor based on α-Fe2O3/Nb2O5 heterostructure.

The introduction of heterostructures is a new approach in gas sensing due to their easy and quick transport of charges. Herein, facile hydrothermal and solid-state techniques are employed to synthesize an α-Fe2O3/Nb2O5 heterostructure. The morphology, microstructure, crystallinity and surface composition of the synthesized heterostructures are investigated by scanning electron microscope, transmission electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy and Brunauer-Emmett-Teller analyses. The successful fabrication of the heterostructures was achieved via the mutual incorporation of α-Fe2O3 nanorods with Nb2O5 interconnected nanoparticles (INPs). A sensor based on the α-Fe2O3(0.09)/Nb2O5 heterostructure with a high surface area exhibited enhanced gas-sensing features, maintaining high selectivity and sensitivity, and a considerable recovery percentage towards ethanol gas. The sensing response of the α-Fe2O3(0.09)/Nb2O5 heterostructure at lower operating temperature (160 °C) is around nine times higher than a pure Nb2O5 (INP) sensor at 180 °C with the flow of 100 ppm ethanol gas. The sensors also show excellent selectivity, good long-term stability and a rapid response/recovery time (8s/2s, respectively) to ethanol. The superior electronic conductivity and upgraded sensitivity performance of gas sensors based on the α-Fe2O3(0.09)/Nb2O5 heterostructure are attributed due to its unique structural features, high specific surface area and the synergic effect of the n-n heterojunction. The promising results demonstrate the potential application of the α-Fe2O3(0.09)/Nb2O5 heterostructure as a good sensing material for the fabrication of ethanol sensors.

Laurionite Competes with 2D Ruddlesden-Popper Perovskites During the Saturation Recrystallization Process.

The room-temperature saturation recrystallization (RTSR) method has been extensively used to prepare all-inorganic lead halide perovskite (e.g., CsPbBr3) nanocrystals. Here, we revealed that the composition of the products prepared by the seemingly simple RTSR method could be extremely complex under different experimental parameters. The pH value of the solution and the protonation tendency of the amines influenced by the amounts and types of introduced amines, oleic acid, and water from the environment determined the composition of the final products. PbBr2, 2D Ruddlesden-Popper perovskites (RPPs) formed by perovskite layers separated by intercalating cations, and laurionite Pb(OH)Br would form under acidic, mildly acidic, and alkaline conditions, respectively. Based on the understanding of the formation mechanism, Pb(OH)Br microparticles with well-defined morphologies were prepared, which could be transformed into highly luminescent CH3NH3PbBr3 with the morphology unchanged. The protonated amine behaves as an intercalating layer during the formation of 2D RPPs. Phenylethylamine (PEA) was proven to be an appropriate amine to prepare pure RPP microplates because of its weaker alkalinity compared to aliphatic amines. The prepared (PEA)2PbBr4 RPP microplates showed strong deep-blue light emission with a PL peak at 415 nm, which could be fine-tuned by changing amines. This study proved the complex reaction pathways of the seemingly simple RTSR method and extended the RTSR method into the fabrication of 2D RPPs and laurionite with promising applications in optoelectronic devices.

A Potential Checkmate to Lead: Bismuth in Organometal Halide Perovskites, Structure, Properties, and Applications.

The remarkable optoelectronic properties and considerable performance of the organo lead-halide perovskites (PVKs) in various optoelectronic applications grasp tremendous scientific attention. However, the existence of the toxic lead in these compounds is threatening human health and remains a major concern in the way of their commercialization. To address this issue, numerous nontoxic alternatives have been reported. Among these alternatives, bismuth-based PVKs have emerged as a promising substitute because of similar optoelectronic properties and extended environmental stability. This work communicates briefly about the possible lead-alternatives and explores bismuth-based perovskites comprehensively, in terms of their structures, optoelectronic properties, and applications. A brief description of lead-toxification is provided and the possible Pb-alternatives from the periodic table are scrutinized. Then, the classification and crystal structures of various Bi-based perovskites are elaborated on. Detailed optoelectronic properties of Bi-based perovskites are also described and their optoelectronic applications are abridged. The overall photovoltaic applications along with device characteristics (i.e., V OC, J SC, fill factor, FF, and power conversion efficiency, PCE), fabrication method, device architecture, and operational stability are also summarized. Finally, a conclusion is drawn where a brief outlook highlights the challenges that hamper the future progress of Bi-based optoelectronic devices and suggestions for future directions are provided.

Application of a Triple-Conducting Heterostructure Electrolyte of Ba0.5Sr0.5Co0.1Fe0.7Zr0.1Y0.1O3-δ and Ca0.04Ce0.80Sm0.16O2-δ in a High-Performance Low-Temperature Solid Oxide Fuel Cell.

Dual-ion electrolytes with oxygen ion and proton-conducting properties are among the innovative solid oxide electrolytes, which exhibit a low Ohmic resistance at temperatures below 550 °C. BaCo0.4Fe0.4Zr0.1Y0.1O3-δ with a perovskite-phase cathode has demonstrated efficient triple-charge conduction (H+/O2-/e-) in a high-performance low-temperature solid oxide fuel cell (LT-SOFC). Here, we designed another type of triple-charge conducting perovskite oxide based on Ba0.5Sr0.5Co0.1Fe0.7Zr0.1Y0.1O3-δ (BSCFZY), which formed a heterostructure with ionic conductor Ca0.04Ce0.80Sm0.16O2-δ (SCDC), showing both a high ionic conductivity of 0.22 S cm-1 and an excellent power output of 900 mW cm-2 in a hybrid-ion LT-SOFC. In addition to demonstrating that a heterostructure BSCFZY-SCDC can be a good functional electrolyte, the existence of hybrid H+/O2- conducting species in BSCFZY-SCDC was confirmed. The heterointerface formation between BSCFZY and SCDC can be explained by energy band alignment, which was verified through UV-vis spectroscopy and UV photoelectron spectroscopy (UPS). The interface may help in providing a pathway to enhance the ionic conductivities and to avoid short-circuiting. Various characterization techniques are used to probe the electrochemical and physical properties of the material containing dual-ion characteristics. The results indicate that the triple-charge conducting electrolyte is a potential candidate to further reduce the operating temperature of SOFC while simultaneously maintaining high performance.

Ultrastable Laurionite Spontaneously Encapsulates Reduced-dimensional Lead Halide Perovskites.

Reduced dimensional lead halide perovskites (RDPs) have attracted great research interest in diverse optical and optoelectronic fields. However, their poor stability is one of the most challenging obstacles prohibiting them from practical applications. Here, we reveal that ultrastable laurionite-type Pb(OH)Br can spontaneously encapsulate the RDPs in their formation solution without introducing any additional chemicals, forming RDP@Pb(OH)Br core-shell microparticles. Interestingly, the number of the perovskite layers within the RDPs can be conveniently and precisely controlled by varying the amount of CsBr introduced into the reaction solution. A single RDP@Pb(OH)Br core-shell microparticle composed of RDP nanocrystals with different numbers of perovskite layers can be also prepared, showing different colors under different light excitations. More interestingly, barcoded RDP@Pb(OH)Br microparticles with different parts emitting different lights can also be prepared. The morphology of the emitting microstructures can be conveniently manipulated. The RDP@Pb(OH)Br microparticles demonstrate outstanding environmental, chemical, thermal, and optical stability, as well as strong resistance to anion exchange processes. This study not only deepens our understanding of the reaction processes in the extensively used saturation recrystallization method but also points out that it is highly possible to dramatically improve the performance of the optoelectronic devices through manipulating the spontaneous formation process of Pb(OH)Br.