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Structure, Optical, and Photocatalytic Properties of Oxynitride Solid Solutions Ca <sub/> 1- <i>x</i> </sub> Sr <i> <sub/>x</sub></i> NbO <sub/>2</sub> N, CaNb <sub/> 1- <i>x</i> </sub> Ta <i> <sub/>x</sub></i> O <sub/>2</sub> N, and SrNb <sub/> 1- <i>x</i> </sub> Ta <i> <sub/>x</sub></i> O <sub/>2</sub> N Prepared from Soft-Chemistry Precursors
摘要： Three perovskite oxynitride solid solutions Ca1–xSrxNbO2N, CaNb1–xTaxO2N, and SrNb1–xTaxO2N were prepared by low temperature ammonolysis of soft-chemistry precursors. In particular, we present for the first time a way to synthesize the substitution series Ca1–xSrxNbO2N, which cannot be prepared by ammonolysis of classical solid state precursors. All samples were phase-pure and exhibit bandgaps in the visible light range that can be tailored by substitutions both of the A- and B-type cations. Rietveld analysis was applied to determine cell parameters and crystal structures. In the case of Ca1–xSrxNbO2N a structural change from orthorhombic to tetragonal was found. After loading with CoOx the photocatalytic activities in the solution-based methyl orange degradation were investigated and for SrNb1–xTaxO2N a considerable activity was found.
关键词： Perovskites,Photocatalysis,Oxynitrides,Hydrothermal synthesis,X-ray diffraction
更新于2025-09-04 15:30:14
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Unique ion diffusion properties in lead-free halide double perovskites: A first-principles study
摘要： Pb-free halide double perovskites (HDPs) are proposed as potential candidates for various optoelectronic applications to replace the mainstream hybrid organic-inorganic halide perovskites, e.g., CH3NH3PbI3. While it is known that ion di?usion is a critical problem to a?ect the structural and electronic stability of CH3NH3PbI3, the mechanism of ion di?usions in HDPs is still unclear and highly desired to be revealed. In this study, taking Cs2AgInX6 (X = Cl, Br) HDPs as prototypes, for the ?rst time we suggest that the fast ion di?usion of the dominant defects may play an important role in the performance stability of HDPs. Importantly, we ?nd that the Agi+ di?usion in a multi-ion concerted fashion has a much faster di?usion rate, compared to the VAg? and VX? di?usion in a single-ion fashion. It is revealed that HDPs exhibit quite di?erent di?usion properties from CH3NH3PbI3. Furthermore, we demonstrate that the di?usion rate of Agi+ in HDPs can be e?ectively suppressed by applying an epitaxial strain, which opens a promising way to enhance the performance stability of perovskite materials for various device applications.
关键词： Lead-free halide double perovskites,Ion di?usion,Performance stability,ab initio calculations,Solar cells
更新于2025-09-04 15:30:14
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Structural and thermodynamic limits of layer thickness in 2D halide perovskites
摘要： In the fast-evolving field of halide perovskite semiconductors, the 2D perovskites (A′)2(A)n?1MnX3n+1 [where A = Cs+, CH3NH3+, HC(NH2)2+; A′ = ammonium cation acting as spacer; M = Ge2+, Sn2+, Pb2+; and X = Cl?, Br?, I?] have recently made a critical entry. The n value defines the thickness of the 2D layers, which controls the optical and electronic properties. The 2D perovskites have demonstrated preliminary optoelectronic device lifetime superior to their 3D counterparts. They have also attracted fundamental interest as solution-processed quantum wells with structural and physical properties tunable via chemical composition, notably by the n value defining the perovskite layer thickness. The higher members (n > 5) have not been documented, and there are important scientific questions underlying fundamental limits for n. To develop and utilize these materials in technology, it is imperative to understand their thermodynamic stability, fundamental synthetic limitations, and the derived structure–function relationships. We report the effective synthesis of the highest iodide n-members yet, namely (CH3(CH2)2NH3)2(CH3NH3)5Pb6I19 (n = 6) and (CH3(CH2)2NH3)2(CH3NH3)6Pb7I22 (n = 7), and confirm the crystal structure with single-crystal X-ray diffraction, and provide indirect evidence for “(CH3(CH2)2NH3)2(CH3NH3)8Pb9I28” (“n = 9”). Direct HCl solution calorimetric measurements show the compounds with n > 7 have unfavorable enthalpies of formation (ΔHf), suggesting the formation of higher homologs to be challenging. Finally, we report preliminary n-dependent solar cell efficiency in the range of 9–12.6% in these higher n-members, highlighting the strong promise of these materials for high-performance devices.
关键词： Ruddlesden–Popper halide perovskites,homologous series,photovoltaics,formation enthalpy,layered compounds
更新于2025-09-04 15:30:14
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Redox oxides-based solar thermochemistry and its materialization to reactor/heat exchanger concepts for efficient solar energy harvesting, transformation and storage
摘要： Ca-Mn-based perovskites doped in their A- and B-site were synthesized and comparatively tested vs. the Co3O4/CoO and (Mn,Fe)2O3/(Mn,Fe)3O4 redox pairs with respect to thermochemical storage and oxygen pumping capability, as a function of the kind and extent of dopant. The perovskites’ induced heat effects measured via Differential Scanning Calorimetry are substantially lower: the highest reaction enthalpy recorded by the CaMnO3-δ composition was only 14.84 KJ/kg compared to 461.1 KJ/kg for Co3O4/CoO and 161.0 KJ/kg for (Mn,Fe)2O3/(Mn,Fe)3O4. Doping of Ca with increasing content of Sr decreased these heat effects; more than 20 at.% Sr eventually eliminated them. Perovskites with Sr instead of Ca in the A-site exhibited also negligible heat effects, irrespective of the kind of B site cation. On the contrary, perovskite compositions characterized by high oxygen release/uptake can operate as thermochemical oxygen pumps enhancing the performance of water/carbon dioxide splitting materials. Oxygen pumping via Ca0.9Sr0.1MnO3-δ and SrFeO3-δ doubled and tripled respectively, the total oxygen absorbed by ceria during its re-oxidation vs. that absorbed without their presence. Such effective pumping compositions exhibited practically no shrinkage during one heat-up/cool-down cycle. However, they demonstrated an increase of the coefficient of linear expansion due to the superposition of “chemical expansion” to thermal-only one, the effect of which on the long-term dimensional stability has to be further quantified through extended cyclic operation.
关键词： thermochemical cycles,redox oxides,thermochemical oxygen pumping,perovskites,thermochemical storage
更新于2025-09-04 15:30:14
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Enhanced Temperature-Tunable Narrow-Band Photoluminescence from Resonant Perovskite Nanograting
摘要： Tunable light-emitting nanostructures are prospective for reconfigurable compact optoelectronic devices. In this regard, halide perovskites are one of the most efficient class of materials, because of their outstanding electronic and optical properties as well as low cost of fabrication and nanostructuring. Here, we study the temperature-tunable reconfiguration of photonic modes in periodically nanostructured perovskite (MAPbI3) film probed by enhanced photoluminescence. We achieved the quality factors of resonances around 500 at wavelengths 750–760 nm. The experimental results are in well agreement with theoretical simulations. Our study reveals the origin of the emission enhancement from such kind of perovskite nanostructures and paves the way to highly directional, efficient, and tunable narrowband emission from optoelectronic devices.
关键词： Optoelectronic devices,Photoluminescence,Tunable light-emitting nanostructures,Halide perovskites,Nanogratings
更新于2025-09-04 15:30:14
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Tellurium-based Double Perovskites A2TeX6 with Tunable Bandgap and Long Carrier Diffusion Length for Optoelectronic Applications
摘要： Lead-free hybrid perovskites have attracted immense interest as environmentally friendly light absorbers. Here, we report on tellurium (Te)-based double perovskites A2TeX6 (A= MA, FA or BA, X = Br- or I-, MA= CH3NH3, FA= CH(NH2)2, BA= benzylamine) as potentially active materials for optoelectronic devices. This perovskites exhibit a tunable bandgap (1.42 eV-2.02 eV), a low trap density (～1010 cm-3), and a high mobility (～ 65 cm2 V-1 s-1). Encouragingly, the MA2TeBr6 single crystal with a bandgap of 2.00 eV possesses a long carrier lifetime of ~6 μs and corresponding carrier diffusion lengths of ~38 μm, which are ideal characteristics for a material for photodetectors and tandem solar cells. Moreover, A2TeX6 perovskites are relatively robust in ambient conditions, being stable for at least two months without showing any signs of phase change. Our findings bring to the forefront a family of lead-free Te-based perovskites for non-toxic perovskite optoelectronics.
关键词： Optoelectronic applications,Long carrier diffusion length,Tunable bandgap,Tellurium-based double perovskites
更新于2025-09-04 15:30:14
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Bright Orange Electroluminescence from Lead-Free Two-Dimensional Perovskites
摘要： Lead halide perovskites are important materials for solar cells and light emitting diodes (LEDs), but the toxicity of lead is a matter of concern for these and other commercial applications. Here, we demonstrate a lead-free two-dimensional (2D) Ruddlesden-Popper-type (C18H35NH3)2SnBr4 perovskite with a strong emission from the self-trapped states, whose photoluminescence quantum yields in colloidal suspension and in film are 88% and 68%, respectively. The insulating character of the organic oleylamine cation prevents electronic band formation between the [SnBr6]4- octahedron layers, which results in the Stokes-shifted orange emission. Electroluminescence of these 2D lead-free perovskite materials was demonstrated in an inverted LED structure with a low turn-on voltage of 2.2 V and a luminance of 350 cd/m2.
关键词： orange emission,two-dimensional perovskites,self-trapped states,lead-free,electroluminescence
更新于2025-09-04 15:30:14
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Non-Stoichiometric Redox Active Perovskite Materials for Solar Thermochemical Fuel Production: A Review
摘要： Due to the requirement to develop carbon-free energy, solar energy conversion into chemical energy carriers is a promising solution. Thermochemical fuel production cycles are particularly interesting because they can convert carbon dioxide or water into CO or H2 with concentrated solar energy as a high-temperature process heat source. This process further valorizes and upgrades carbon dioxide into valuable and storable fuels. Development of redox active catalysts is the key challenge for the success of thermochemical cycles for solar-driven H2O and CO2 splitting. Ultimately, the achievement of economically viable solar fuel production relies on increasing the attainable solar-to-fuel energy conversion ef?ciency. This necessitates the discovery of novel redox-active and thermally-stable materials able to split H2O and CO2 with both high-fuel productivities and chemical conversion rates. Perovskites have recently emerged as promising reactive materials for this application as they feature high non-stoichiometric oxygen exchange capacities and diffusion rates while maintaining their crystallographic structure during cycling over a wide range of operating conditions and reduction extents. This paper provides an overview of the best performing perovskite formulations considered in recent studies, with special focus on their non-stoichiometry extent, their ability to produce solar fuel with high yield and performance stability, and the different methods developed to study the reaction kinetics.
关键词： solar fuel,concentrating solar technologies,non-stoichiometric materials,perovskites,CO2/H2O splitting,hydrogen,thermochemical cycles,oxygen vacancies
更新于2025-09-04 15:30:14
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Er doped layered perovskites with Dual mode luminescent behavior and tunable multicolor upconversion emission
摘要： Er3+ doped BST nanoparticles with Aurivillius layered structure are synthesized through common solid state method. Photoluminescence spectroscopy has shown that these oxides are capable of emitting light under UV (366nm) and IR (980nm) source. The effect of Er3+ to Yb3+ concentration ratio on upconversion emission are investigated and possible upconversion and energy transfer mechanisms are suggested based on the number of photons participating in UC process. Shift in the upconversion emission from green to red region is visualized by CIE chromaticity diagram. The superiority of coexistence of stoke and anti-stoke emission in a single host lattice with a single activator ion, besides to tunability of UC luminescence only by controlling sensitizer/activator ratio are very interesting features which can be used to produce dual mode multicolor luminescent ink with high security level against forgery.
关键词： Aurivillius perovskites,Dual mode luminescent,Security ink,Upconversion
更新于2025-09-04 15:30:14
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The First 2D Hybrid Perovskite Ferroelectric Showing Broadband White-Light Emission with High Color Rendering Index
摘要： Luminescent ferroelectrics have attracted considerable attention in terms of integrated photoelectronic devices, most of which are focused on the multicomponent systems of rare-earth doping ferroelectric ceramics. However, bulk ferroelectricity with coexistence of strong white-light emission, especially in the single-component system, remains quite rare. Here, a new organic–inorganic hybrid ferroelectric of (C4H9NH3)2PbCl4 (1) is reported, adopting a 2D layered perovskite architecture, which exhibits an unprecedented coexistence of notable ferroelectricity and intrinsic white-light emission. Decent above-room-temperature spontaneous polarization of ≈2.1 μC cm?2 is confirmed for 1. Particularly, it also exhibits brilliant broadband white-light emission with a high color-rendering-index up to 86 under UV excitation. Structural analyses indicate that ferroelectricity of 1 originates from molecular reorientation of dynamic organic cations, as well as significant structural distortion of PbCl6 octahedra that also contribute to its white-light emission. This work paves an avenue to design new hybrid ferroelectrics for multifunctional application in the photoelectronic field.
关键词： organic–inorganic hybrids,ferroelectrics,white-light emissions,perovskites,2D materials
更新于2025-09-04 15:30:14