Pb-Free Cs3Bi2I9 Perovskite as a Visible-Light-Active Photocatalyst for Organic Pollutant Degradation

Enhancing the Photocatalytic Activity of Halide Perovskite Cesium Bismuth Bromide/Hydrogen Titanate Heterostructures for Benzyl Alcohol Oxidation

Halide perovskite Cs3Bi2Br9 (CBB) has excellent potential in photocatalysis due to its promising light-harvesting properties. However, its photocatalytic performance might be limited due to the unfavorable charge carrier migration and water-induced properties, which limit the stability and photocatalytic performance. Therefore, we address this constraint in this work by synthesizing a stable halide perovskite heterojunction by introducing hydrogen titanate nanosheets (H2Ti3O7-NS, HTiO-NS). Optimizing the weight % (wt%) of CBB enables synthesizing the optimal CBB/HTiO-NS, CBHTNS heterostructure. The detailed morphology and structure characterization proved that the cubic shape of CBB is anchored on the HTiO-NS surface. The 30 wt% CBB/HTiO-NS-30 (CBHTNS-30) heterojunction showed the highest BnOH photooxidation performance with 98% conversion and 75% benzoic acid (BzA) selectivity at 2 h under blue light irradiation. Detailed optical and photoelectrochemical characterization showed that the incorporating CBB and HTiO-NS widened the range of the visible-light response and improved the ability to separate the photo-induced charge carriers. The presence of HTiO-NS has increased the oxidative properties, possibly by charge separation in the heterojunction, which facilitated the generation of superoxide and hydroxyl radicals. A possible reaction pathway for the photocatalytic oxidation of BnOH to BzH and BzA was also suggested. Furthermore, through scavenger experiments, we found that the photogenerated h+, e- and •O2- play an essential role in the BnOH photooxidation, while the •OH have a minor effect on the reaction. This work may provide a strategy for using HTiO-NS-based photocatalyst to enhance the charge carrier migration and photocatalytic performance of CBB.

Magnetron Sputtering Deposition of High Quality Cs3Bi2I9 Perovskite Thin Films

Nontoxic all-inorganic perovskites are among the most promising materials for the realization of optoelectronic devices. Here, we present an innovative way to deposit lead-free, totally inorganic Cs3Bi2I9 perovskite from vapor phase. Taking use of a magnetron sputtering system equipped with a radiofrequency working mode power supply and a single target containing the correct ratio of CsI and BiI3 salts, it was possible to deposit a Cs3Bi2I9 perovskitic film on silicon and soda-lime glass. The target composition was optimized to obtain a stoichiometric deposition, and the best compromise was found with a mix enriched with 20% w/w of CsI. Secondly, the effect of post-deposition thermal treatments (150 °C and 300 °C) and of the deposition on a preheat substrate (150 °C) were evaluated by analyzing the chemical composition, the morphology, the crystal structure, and the optical properties. The thermal treatment at 150 °C improved the uniformity of the perovskite film; the one at 300 °C damaged the perovskite deposited. Depositing on a preheated substrate at 150 °C, the obtained film showed a higher crystallinity. An additional thermal treatment at 150 °C on the film deposed on the preheated substrate showed that the crystallinity remains high, and the morphology becomes more uniform.

Synthesis and numerical simulation of formamidinium-based perovskite solar cells: a predictable device performance at NIS-Egypt

Formamidinium lead triiodide (δ-FAPbI₃)-based perovskite solar cells showed remarkable potential as light harvesters for thin-film photovoltaics. Herein, the mechanochemical synthesis of δ-FAPbI₃, MAPbI₃, and mixed-cation FA_1-xMA_xPbI₃ with (x = 0.3, 0.5, and 0.7) perovskite materials were prepared as a novel green chemistry method for scaling up production. Crystallinity, phase identification, thermal stability, optoelectronic properties, and nanoscale composition are discussed. The results demonstrated that the prepared mixed-cation samples are enhanced in the visible absorption region and are consistent with previous works. The crystal structure of δ-FAPbI₃ was altered to a cubic structure due to the change in FA-cation. Moreover, the performance of [Formula: see text]-FA-based perovskites was investigated using the Solar Cell Capacitance Simulator (SCAPS-1D) software. The validity of the device simulation was confirmed by comparing it to real-world devices. The photovoltaic characteristics and impact of absorber thickness on device performance were explained. The [Formula: see text]-FA-based solar cell with a 50% MA-doped molar ratio shows a better performance with an efficiency of 26.22% compared to 8.43% for δ-FAPbI₃. The outcome results of this work confirm the beneficial effect of mixed cations on device operation and advance our knowledge of the numerical optimization of perovskite-based solar cells.

Research progresses on the application of perovskite in adsorption and photocatalytic removal of water pollutants

The problem of global water pollution and scarcity of water resources is becoming increasingly serious. Multifunctional perovskites can well drive adsorption and photocatalytic reactions to remove water pollutants. There are many advantages of perovskites, such as abundant oxygen vacancies, easily tunable structural morphology, stable crystal state, highly active metal sites, and a wide photo response range. However, there are few reviews on the simultaneous application of perovskite to adsorption and photocatalytic removal of water pollutants. Thus, this paper discusses the preparation methods of perovskite, the factors affecting the adsorption of water environmental pollutants by perovskite, and the factors affecting perovskite photocatalytic water pollutants. The particle size, specific surface area, oxygen vacancies, electron-hole trapping agents, potentials of the valence band, and conduction band in perovskites are significant influencing factors for adsorption and photocatalysis. Strategies for improving the performance of perovskites in the fields of adsorption and photocatalysis are discussed. The adsorption behaviors and catalytic mechanisms are also investigated, including adsorption kinetics and thermodynamics, electrostatic interaction, ion exchange, chemical bonding, and photocatalytic mechanism. It summarizes the removal of water pollutants by using perovskites. It provides the design of perovskites as high-efficiency adsorbents and catalysts for developing new technologies.

Preparation of Heterojunctions Based on Cs3Bi2Br9 Nanocrystals and g-C3N4 Nanosheets for Photocatalytic Hydrogen Evolution

Heterojunctions based on metal halide perovskites (MHPs) are promising systems for the photocatalytic hydrogen evolution reaction (HER). In this work, we coupled Cs₃Bi₂Br₉ nanocrystals (NCs), obtained by wet ball milling synthesis, with g-C₃N₄ nanosheets (NSs), produced by thermal oxidation of bulk g-C₃N_4, in air. These methods are reproducible, inexpensive and easy to scale up. Heterojunctions with different loadings of Cs₃Bi₂Br₉ NCs were fully characterised and tested for the HER. A relevant improvement of H₂ production with respect to pristine carbon nitride was achieved at low NCs levels reaching values up to about 4600 µmol g^-1 h^-1. This work aims to provide insights into the synthesis of inexpensive and high-performing heterojunctions using MHP for photocatalytic applications.

A Critical Review of the Use of Bismuth Halide Perovskites for CO2 Photoreduction: Stability Challenges and Strategies Implemented

Inspired by natural photosynthesis, the photocatalytic CO2 reduction reaction (CO2RR) stands as a viable strategy for the production of solar fuels to mitigate the high dependence on highly polluting fossil fuels, as well as to decrease the CO2 concentration in the atmosphere. The design of photocatalytic materials is crucial to ensure high efficiency of the CO2RR process. So far, perovskite materials have shown high efficiency and selectivity in CO2RR to generate different solar fuels. Particularly, bismuth halide perovskites have gained much attention due to their higher absorption coefficients, their more efficient charge transfer (compared to oxide perovskites), and their required thermodynamic potential for CO2RR. Moreover, these materials represent a promising alternative to the highly polluting lead halide perovskites. However, despite all the remarkable advantages of bismuth halide perovskites, their use has been limited, owing to instability concerns. As a consequence, recent reports have offered solutions to obtain structures highly stable against oxygen, water, and light, promoting the formation of solar fuels with promising efficiency for CO2RR. Thus, this review analyzes the current state of the art in this field, particularly studies about stability strategies from intrinsic and extrinsic standpoints. Lastly, we discuss the challenges and opportunities in designing stable bismuth halide perovskites, which open new opportunities for scaling up the CO2RR.

Halides and oxyhalides-based photocatalysts for abatement of organic water contaminants - An overview

Recently, halides (silver halides, AgX; perosvkite halides, ABX₃) and oxyhalides (bismuth oxyhalides, BiOX) based nanomaterials are noticeable photocatalysts in the degradation of organic water pollutants. Therefore, we review the recent reports to explore improvement strategies adopted in AgX, ABX₃ and BiOX (X = Cl, Br and I)-based photocatalysts in water pollution remediation. Herein, the photocatalytic degradation performances of each type of these photocatalysts were discussed. Strategies such as tailoring the morphology, crystallographic facet exposure, surface area, band structure, and creation of surface defects to improve photocatalytic activities of pure halides and BiOCl photocatalysts are emphasized. Other strategies like metal ion and/or non-metal doping and construction of composites, adopted in these photocatalysts were also reviewed. Furthermore, the way of production of active radicals by these photocatalysts under ultraviolet/visible light source is highlighted. The deciding factors such as structure of pollutant, light sources and other parameters on the photocatalytic performances of these materials were also explored. Based on this literature survey, the need of further research on AgX, ABX₃ and BiOX-based photocatalysts were suggested. This review might be beneficial for researchers who are working in halides and oxyhalides-based photocatalysis for water treatment.

Halide Double-Perovskite Semiconductors beyond Photovoltaics

Halide double perovskites, A₂M^IM^IIIX₆, offer a vast chemical space for obtaining unexplored materials with exciting properties for a wide range of applications. The photovoltaic performance of halide double perovskites has been limited due to the large and/or indirect bandgap of the presently known materials. However, their applications extend beyond outdoor photovoltaics, as halide double perovskites exhibit properties suitable for memory devices, indoor photovoltaics, X-ray detectors, light-emitting diodes, temperature and humidity sensors, photocatalysts, and many more. This Perspective highlights challenges associated with the synthesis and characterization of halide double perovskites and offers an outlook on the potential use of some of the properties exhibited by this so far underexplored class of materials.

Phonon-Mediated Slow Hot Carrier Dynamics in Lead-Free Cs3Bi2I9 Perovskite Single Crystal

In this report, we study the hot carrier cooling mechanism of the Cs3Bi2I9 single crystal by using femtosecond transient reflectance (fs-TR) spectroscopy. We find an unusual slow hot carrier cooling associated with longitudinal optical (LO) and coherent longitudinal acoustic phonons (CLAPs) emission during the deexcitation of the hot carriers. We posit the interplay between the hot-carriers and the LO and CLA phonons in subpicosecond to subnanosecond time scales, respectively, by analyzing the TR kinetics upon perturbation with excess energy. Furthermore, we measured the CLAPs propagation velocity in Cs3Bi2I9, the crystal, ranging from 1820 to 2000 ms-1. The elastic constants and frequency of Brillouin oscillations were estimated as 20.08 GPa and 14.66 GHz, respectively. Our discovery delivers new physical insights into how the hot carriers in Cs3Bi2I9 single crystal are coupled with a crystal lattice that controls the hot carrier dynamics.

Boosted Inner Surface Charge Transfer in Perovskite Nanodots@Mesoporous Titania Frameworks for Efficient and Selective Photocatalytic CO2 Reduction to Methane

Exploring high-efficiency and stable halide perovskite-based photocatalysts for the selective reduction of CO₂ to methane is a challenge because of the intrinsic photo- and chemical instability of halide perovskites. In this study, halide perovskites (Cs₃ Bi₂ Br₉ and Cs₂ AgBiBr₆ ) were grown in situ in mesoporous TiO₂ frameworks for an efficient CO₂ reduction. Benchmarked CH₄ production rates of 32.9 and 24.2 μmol g^-1  h^-1 with selectivities of 88.7 % and 84.2 %, were achieved, respectively, which are better than most reported halide perovskite photocatalysts. Focused ion-beam sliced-imaging techniques were used to directly image the hyperdispersed perovskite nanodots confined in mesopores with tunable sizes ranging from 3.8 to 9.9 nm. In situ X-ray photoelectronic spectroscopy and Kelvin probe force microscopy showed that the built-in electric field between the perovskite nanodots and mesoporous titania channels efficiently promoted photo-induced charge transfer. Density functional theory calculations indicate that the high methane selectivity was attributed to the Bi-adsorption-mediated hydrogenation of *CO to *HCO that dominates CO desorption.

Organic Spacer Cation Assisted Modulation of the Structure and Properties of Bismuth Halide Perovskites

ConspectusLead halide perovskites are under the spotlight of current research due to their potential for efficient and cost-effective next-generation optoelectronic devices. The unique photonic and electronic properties of these solution-processable materials brought them to the forefront of materials science. However, the toxicity and instability of lead-based perovskites are the major hurdles for their commercialization. These issues initiated an effort towards the development of environmentally friendly, lead-free perovskites. In this context, bismuth halide perovskites (BHPs) were ideal rivals for lead-based congeners due to their excellent chemical stability, lower toxicity, and structural versatility. Understanding the crystal structure and optoelectronic properties of BHPs is crucial for designing them for specific, tailor-made applications. This Account aims to review our recent research progress on the role of functional organic spacer cations in modulating the electronic confinements, optical properties, and photoconductivity of BHPs. We have employed a comprehensive experimental and theoretical investigation to probe the intriguing optical and electronic properties of these materials. Our findings on the structure-optoelectronic property correlations will be valuable guidelines for the rational selection of organic spacer cations in designing BHPs featuring low exciton binding energy, narrow optical bandgap, enhanced visible light absorption, and high photoconductivity. One of our key findings is that by increasing the electron affinity of the organic spacer ligands, photoconductivity and visible light absorption of BHPs could be significantly enhanced. We hope that the fundamental level understanding of the photophysical properties discussed in this Account will lead to new design rules for developing high-performance BHP materials.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Optical and Structural Property Tuning in Physical Vapor Deposited Bismuth Halides Cs3Bi2(I1-xBrx)9 (0 ≤ x ≤ 1)

Crystalline films of lead-free all-inorganic Cs3Bi2X9 (X = Br, I) perovskites have been deposited by radio frequency (RF)-magnetron sputtering providing high-quality, single-phase films as confirmed by structural, morphological, and optical property characterization. Progressive tuning of crystal structure characteristics and optical absorbance has been achieved in mixed Br/I phases Cs3Bi2(I1-xBrx)9 (0 ≤ x ≤ 1), highlighting a shift of the band gap from about 2.0 eV for Cs3Bi2I9 to 2.64 eV for Cs3Bi2Br9. X-ray diffraction and Raman scattering allowed defining the range of alloyed compositions where single-phase compositions are found. Finally, preliminary photocatalytic activity tests on the degradation of methylene blue provided solid data indicating the future possible exploitation of Bi-based perovskite derivative materials as active photocatalysts.

Low-Toxicity Perovskite Applications in Carbon Electrode Perovskite Solar Cells—A Review

Perovskite solar cells (PSCs) with earth-abundant carbon as an effective replacer for unstable hole-transporting materials and expensive electrodes is a recently proposed structure promising better air and moisture stability. In this review paper, we report on the latest advances and state of the art of Pb-free and low-Pb-content perovskites, used as absorbers in carbon-based perovskite solar cells. The focus is on the implementation of these, environmentally friendly and non-toxic, structures in PSCs with a carbon electrode as a replacement of the noble metal electrode typically used (C-PSCs). The motivation for this study has been the great potential that C-PSCs have shown for the leap towards the commercialization of PSCs. Some of their outstanding properties include low cost, high-stability, ambient processability and compatibility with most up-scaling methods (e.g., printing). By surpassing the key obstacle of toxicity, caused by the Pb content of the highest-performing perovskites, and by combining the advantages of C-PSCs with the Pb-free perovskites low toxicity, this technology will move one step further; this review summarizes the most promising routes that have been reported so far towards that direction.

Development of Cuboidal KNbO3@α-Fe2O3 Hybrid Nanostructures for Improved Photocatalytic and Photoelectrocatalytic Applications

Monophasic and hybrid nanostructures of KNbO₃ and α-Fe₂O₃ have been prepared using a hydrothermal process for photoelectrocatalytic and photocatalytic applications. Powder X-ray diffraction studies showed the formation of KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ with average grain sizes of 18.3, 11.5, and 26.1 nm and Brunauer-Emmett-Teller (BET) specific surface areas of 4, 100, and 20 m²/gm, respectively. Under simulated solar irradiation, the as-prepared heterostructure shows enhanced photoelectrocatalytic oxygen evolution reaction (OER) activity compared to pristine KNbO₃ and α-Fe₂O₃. Significant photocatalytic activity of as-synthesized KNbO₃/α-Fe₂O₃ heterostructure photocatalyst was obtained for removal of methylene blue organic dye under visible light, and the percentage activity was found to be 11, 49, and 89% for KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ photocatalysts, respectively. The dielectric constant was found to be 250.2, 65.2, and 251.5 for KNbO₃, α-Fe₂O₃, and KNbO₃/α-Fe₂O₃ heterostructure, respectively, at 50 °C and 500 kHz frequency.

Recent Progresses on Metal Halide Perovskite-Based Material as Potential Photocatalyst

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.