Design, Synthesis, and Photocatalytic Application of Moisture-Stable Hybrid Lead-Free Perovskite

0-D and 1-D Perovskite-like Hybrid Bismuth(III) Iodides

Low-dimensional hybrid bismuth halide perovskites have recently emerged as a class of non-toxic alternative to lead perovskites with promising optoelectronic properties. Here, we report three hybrid bismuth(III)-iodides: 0-D (H2DAC)2Bi2I10 ⋅ 6H2O (H2DAC_Bi_I), 0-D (H2DAF)4Bi2I10 ⋅ 2I3 ⋅ 2I ⋅ 6H2O (H2DAF_Bi_I), and 1-D (H2DAP)BiI5 (H2DAP_Bi_I) (where H2DAC=trans-1,4-diammoniumcyclohexane; H2DAF=2,7-diammoniumfluorene and H2DAP=1,5-diammoniumpentane). Their synthesis, single-crystal X-ray structures, and photophysical properties are reported. The first two compounds comprise edge-sharing [Bi2I10]4- dimers, while the last compound has cis-corner-sharing 1-D chains of [BiI6]3- octahedra. Intercalation of triiodide (I3 -) and iodide (I-) ions enhance electronic coupling between the [Bi2I10]4- of H2DAF_Bi_I, leading to enhanced optical absorption, compared to H2DAC_Bi_I which lacks such intercalants. Furthermore, calorimetric and variable temperature X-ray diffraction measurements suggest a centrosymmetric to non-centrosymmetric phase transition (monoclinic P212121↔orthorhombic Pnma) of H2DAP_Bi_I at 448 K (in heating step) and at 443 K (in cooling step).

Naphthalenediimide/Iodobismuthate Hybrid Heterostructures: Water Resistance and Long-Lived Charge-Separated States

Organic-inorganic hybrid iodobismuthate perovskites have become promising semiconductive materials for their environmentally friendly and light-harvesting characteristics. However, their low-dimensional bismuth-iodide skeletons result in poor charge-separation efficiency, limiting their application in optoelectronic devices. To address this issue, the donor-acceptor (D-A) heterostructures have been introduced to the iodobismuthate hybrid materials by incorporating an electron-deficient N,N'-bis(4-aminoethyl)-1,4,5,8-naphthalene diimide (NDIEA) as the electron acceptor and organic counterpart. Five naphthalenediimide/iodobismuthate hybrid heterostructures, named (H2NDIEA)1.5·Bi2I9·3DMF (1), H2NDIEA·[Bi2I8(DMF)2]·2DMF (2), (H2NDIEA)2·Bi4I16·2H2O·4MeOH (3), (H2NDIEA)2·Bi4I16·8H2O (4), and [(H2NDIEA)2·Bi6I22]n·4nH2O (5) (DMF = N,N-dimethylformamide), were synthesized. Their crystal structures, water stabilities, charge-separated behaviors, and electrical properties have been studied through experimental and computational investigations. The results revealed that hybrids 3-5 exhibited high water resistance attributed to their tightly packed structures and robust H-bonds between solvent molecules and organic-inorganic supramolecular frameworks. Density functional theory calculations confirmed characteristic type-IIa band alignments of all the five hybrids, facilitating to the photoinduced charge separation. Moreover, the closer contact caused by the strong anion-π interactions between electron donors and acceptors in hybrid 5 leads to the long-lived charge-separated states and improved electrical properties compared to the other hybrids.

Strategies for improving the stability of perovskite for photocatalysis: A review of recent progress

Photocatalysis is currently a hot research field, which provides promising processes to produce green energy sources and other useful products, thus eventually benefiting carbon emission reduction and leading to a low-carbon future. The development and application of stable and efficient photocatalytic materials is one of the main technical bottlenecks in the field of photocatalysis. Perovskite has excellent performance in the fields of photocatalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), carbon dioxide reduction reaction (CO2RR), organic synthesis and pollutant degradation due to its unique structure, flexibility and resulting excellent photoelectric and catalytic properties. The stability problems caused by perovskite's susceptibility to environmental influences hinder its further application in the field of photocatalysis. Therefore, this paper innovatively summarizes and analyzes the existing methods and strategies to improve the stability of perovskite in the field of photocatalysis. Specifically, (i) component engineering, (ii) morphological control, (iii) hybridization and encapsulation are thought to improve the stability of perovskites while improving photocatalytic efficiency. Finally, the challenges and prospects of perovskite photocatalysts are discussed, which provides constructive thinking for the potential application of perovskite photocatalysts.

Utilizing the Undesirable Oxidation of Lead-Free Hybrid Halide Perovskite Nanosheets for Solar-Driven Photocatalytic C(sp3)─H Activation: Unraveling the Serendipity

Hybrid halide perovskites (HHPs), whose every branch generates intrusiveness, have been utilized in solar cells from a broader perspective. However, the inclusiveness of employing HHP as a photocatalyst is in its initial stage. This study mainly focuses on the unexpected utilization of, so far, undesirable material vacancy-ordered MA2SnBr6 quantum dots synthesized from MASnBr3 nanosheets. Here, the quantum confinement grounded a large blue shift in ultraviolet (UV) and photoluminescence (PL) spectra with a Stokes shift of 420 meV, where the band gap increase is observed as size decreases in MA2SnBr6. Remarkably, MA2SnBr6 exhibits air and moisture stability, better charge transfer, and high oxidation potential compared to MASnBr3. The first-principles-based atomistic computations reveal the strain relaxation in the Sn-Br framework that structurally stabilizes the MA2SnBr6 lattice. Furthermore, the direct band gap and strongly localized valence band edge give rise to a new potential photocatalyst MA2SnBr6 for efficient solar-driven C(sp3)─H activation of cyclohexane and toluene under ambient conditions.

One-Year Water-Stable and Porous Bi(III) Halide Semiconductor with Broad-Spectrum Antibacterial Performance

Hybrid metal halide semiconductors are a unique family of materials with immense potential for numerous applications. For this to materialize, environmental stability and toxicity deficiencies must be simultaneously addressed. We report here a porous, visible light semiconductor, namely, (DHS)Bi2I8 (DHS = [2.2.2] cryptand), which consists of nontoxic, earth-abundant elements, and is water-stable for more than a year. Gas- and vapor-sorption studies revealed that it can selectively and reversibly adsorb H2O and D2O at room temperature (RT) while remaining impervious to N2 and CO2. Solid-state NMR measurements and density functional theory (DFT) calculations verified the incorporation of H2O and D2O in the molecular cages, validating the porous nature. In addition to porosity, the material exhibits broad band-edge light emission centered at 600 nm with a full width at half-maximum (fwhm) of 99 nm, which is maintained after 6 months of immersion in H2O. Moreover, (DHS)Bi2I8 exhibits bacteriocidal action against three Gram-positive and three Gram-negative bacteria, including antibiotic-resistant strains. This performance, coupled with the recorded water stability and porous nature, renders it suitable for a plethora of applications, from solid-state batteries to water purification and disinfection.

Water-Stable Hybrid Lead-Free Perovskite for Negative Temperature Coefficient Thermistors

Negative temperature coefficient (NTC) thermistors feature higher sensitivities and faster response speeds and thereby have particular applications in many fields. However, current NTC thermistors are mostly based on inorganic ceramic materials, which show obvious drawbacks in material synthesis, property modulation, and flexible film fabrication. Herein, we report, for the first time, the promising application of an inorganic-organic hybrid NTC thermistor. A new lead-free hybrid iodo bismuthate [1,1',1″-(benzene-1,3,5-triyl)tris(3-methyl-1H-imidazol-3-ium)]Bi₂I₉ [denoted as (Me₃TMP)Bi₂I₉] was synthesized by a "double-free" strategy. (Me₃TMP)Bi₂I₉ features a lead-free binuclear bismuth iodine anion charge compensated by a "classic hydrogen-bond-free" cation. (Me₃TMP)Bi₂I₉ exhibits remarkable stability in water and UV light irradiation and shows the largest temperature sensitivity coefficient among all reported NTC materials. Theoretical calculation and detailed structural analysis disclose that the seriously distorted (BiI₆) octahedra are responsible for the intriguing NTC effect for (Me₃TMP)Bi₂I₉.

Recent developments in lead-free bismuth-based halide perovskite nanomaterials for heterogeneous photocatalysis under visible light

Halide perovskite materials, especially lead-based perovskites, have been widely used for optoelectronic and catalytic applications. However, the high toxicity of the lead element is a major concern that directs the research work toward lead-free halide perovskites, which could utilize bismuth as a promising candidate. Until now, the replacement of lead by bismuth in perovskites has been well studied by designing bismuth-based halide perovskite (BHP) nanomaterials with versatile physical-chemical properties, which are emerging in various application fields, especially heterogeneous photocatalysis. In this mini-review, we present a brief overview of recent progress in BHP nanomaterials for photocatalysis under visible light. The synthesis and physical-chemical properties of BHP nanomaterials have been comprehensively summarized, including zero-dimensional, two-dimensional nanostructures and hetero-architectures. Later, we introduce the photocatalytic applications of these novel BHP nanomaterials with visible-light response, improved charge separation/transport and unique catalytic sites. Due to advanced nano-morphologies, a well-designed electronic structure and an engineered surface chemical micro-environment, BHP nanomaterials demonstrate enhanced photocatalytic performance for hydrogen generation, CO₂ reduction, organic synthesis and pollutant removal. Finally, the challenges and future research directions of BHP nanomaterials for photocatalysis are discussed.

A universal hydrochloric acid-assistant powder-to-powder strategy for quick and mass preparation of lead-free perovskite microcrystals

Lead-free halide perovskite materials possess low toxicity, broadband luminescence and robust stability compared with conventional lead-based perovskites, thus holding great promise for eyes-friendly white light LEDs. However, the traditionally used preparation methods with a long period and limited product yield have curtailed the commercialization of these materials. Here we introduce a universal hydrochloric acid-assistant powder-to-powder strategy which can accomplish the goals of thermal-, pressure-free, eco-friendliness, short time, low cost and high product yield, simultaneously. The obtained Cs2Na0.9Ag0.1In0.95Bi0.05Cl6 microcrystals exhibit bright self-trapped excitons emission with quantum yield of (98.3 ± 3.8)%, which could retain (90.5 ± 1.3)% and (96.8 ± 0.8)% after continuous heating or ultraviolet-irradiation for 1000 h, respectively. The phosphor converted-LED exhibited near-unity conversion efficiency from ultraviolet chip to self-trapped excitons emission at ~200 mA. Various ions doping (such as Cs2Na0.9Ag0.1InCl6:Ln3+) and other derived lead-free perovskite materials (such as Cs2ZrCl6 and Cs4MnBi2Cl12) with high luminous performance are all realized by our proposed strategy, which has shown excellent availability towards commercialization.

Bismuth-Based Halide Perovskites for Photocatalytic H2 Evolution Application

Metal halide perovskites (MHPs), in particular lead-based perovskites, have earned recognized fame in several fields for their outstanding optoelectronic properties, including direct generation of free charge carriers, optimal ambipolar charge carrier transport properties, high absorption coefficient, point-defect tolerance, and compositional versatility. Nowadays, this class of materials represents a real and promising alternative to silicon for photovoltaic technologies. This worthy success led to a growing interest in the exploration of MHPs in other hot research fields, such as solar-driven photocatalytic water splitting towards hydrogen production. Nevertheless, many of these perovskites show air and moisture instability problems that considerably hinder their practical application for photocatalytic water splitting. Moreover, if chemical instability is a problem that can be in part mitigated by the optimization of the chemical composition and crystal structure, the presence of lead represents a real problem for the practical application of MHPs in commercial devices due to environmental and healthcare issues. To successfully overcome these problems, lead-free metal halide perovskites (LFMHPs) have gained increasing interest thanks to their optoelectronic properties, comparable to lead-based materials, and their more eco-friendly nature. Among all the lead-free perovskite alternatives, this mini-review considers bismuth-based perovskites and perovskite derivatives with a specific focus on solar-driven photocatalysis application for H₂ evolution. Special attention is dedicated to the structure and composition of the different materials and to the advantage of heterojunction engineering and the relative impact on the photocatalytic process.

Potassium Iodide-Modified Lead-Free Cs3Bi2I9 Perovskites for Enhanced High-Efficiency Solar Cells

Lead-free, bismuth-based perovskite solar cells (PSCs) are promising, non-toxic, and stable alternatives to lead-based PSCs, which are environmentally harmful and highly unstable under deprived air conditions. However, bismuth-based PSCs still suffer from low-power-conversion efficiency (PCE) due to their large bandgap and poor film morphology. Their poor film-forming ability is the greatest obstacle to Cs₃Bi₂I₉ progress in thin-film solar cell technology. This study synthesizes novel, lead-free perovskites with a small bandgap, excellent stability, and highly improved photovoltaic performance by integrating different amounts of potassium iodide (KI) into a perovskite precursor solution. KI incorporation improves the crystallinity of the perovskite, increases the grain size, and decreases the potential contact distribution, which is demonstrated by X-ray diffraction, electronic scanning microscopy, atomic force microscopy, and ultraviolet-visible spectroscopy. The Cs₃Bi₂I₉ PSC device with 2 vol. % incorporation of KI shows the highest PCE of 2.81% and Voc of 1.01 V as far as all the Bi-based cells fabricated for this study are concerned. The study demonstrates that incorporating KI in the Cs₃Bi₂I₉ perovskite layer highly stabilizes the resultant PSC device against humidity to the extent that it maintains 98% of the initial PCE after 90 days, which is suitable for solar cell applications. The devices also demonstrate greater resistance to airborne contaminants and high temperatures without encapsulation, opening up new possibilities for lead-free Cs₃Bi₂I₉ PSCs in future commercialization.

Band Gap and Topology of 1D Perovskite-Derived Hybrid Lead Halide Structures

The unprecedented structural flexibility of hybrid halide perovskites is accompanied by a wide range of useful optoelectronic properties, causing a high interest in this family of materials. However, there are no systematic studies yet on the relationships between the topology of structures derived of chain 1D hybrid halide perovskites and their optoelectronic properties such as the band gap as already reported for 3D and 2D hybrid halide perovskites. In the present work, we introduce a rational classification of hybrid lead iodide 1D structures. We provide a theoretical assessment of the relationship between the topology of 1D hybrid halide perovskite-derived structures with vertex-connected octahedra and show that the distortions of geometry of the chains of PbI6 octahedra are the main parameters affecting the band gap value while the distance between the chains of vertex-connected octahedra has a minor effect on the band gap.

Photoelectrochemical Application and Charge Transport Dynamics of a Water-Stable Organic-Inorganic Halide (C6H4NH2CuCl2I) Film in Aqueous Solution

A water-stable thin film composed of C₆H₄NH₂CuCl₂I was fabricated using spin-coating precursor solutions that dissolved equimolar amounts of C₆H₄NH₂I and CuCl₂ in N,N-dimethylformamide. Photoelectrochemical characteristics show that the C₆H₄NH₂CuCl₂I film demonstrated a stable photocurrent (∼1 μA/cm²) in an aqueous solution under white light (11.5 mW/cm²) even after 3000 s, while exhibiting a photon-to-current efficiency of 0.093% under AM1.5 (100 mW/cm²) illumination. However, these values were significantly lower than those of the CH₃NH₃PbX₃ (X = I, Cl) film in solid devices. The electron diffusion length L(e^-) (373 nm) and hole diffusion length L(h⁺) (177 nm) in the C₆H₄NH₂CuCl₂I photoelectrode were significantly lower than those of CH₃NH₃PbX₃, limiting the photoelectrochemical and photocatalysis performances. Moreover, L(h⁺) was shorter than L(e^-) in the C₆H₄NH₂CuCl₂I photoelectrode, resulting in the hole-collecting efficiency [η_c(h⁺)] being lower than the electron-collecting efficiency [η_c(e^-)]. A CuO interlayer was introduced as a hole transport layer for the C₆H₄NH₂CuCl₂I photoelectrode, which improved L(h⁺) and η_c(h⁺).

Sustainable one-pot synthesis of strontium phosphate nanoparticles with effective charge carriers for the photocatalytic degradation of carcinogenic naphthylamine derivative

In this work, a sustainable one-pot precipitation method was applied for synthesizing strontium phosphate nanoparticles (SrPO NPs), which can be utilized as effective charge separation photocatalysts for the degradation of oncogenic naphthylamine derivatives (congo red).