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There is a great demand for efficient electromagnetic interference (EMI) shielding materials due to exponential growth in wireless telecommunication devices. These devices emit electromagnetic radiation that can disrupt electronic devices, and cause health hazards. Therefore, it is crucial to develop materials that can shield devices and humans from exposure to electromagnetic radiation. In this context, nanocomposite materials offer huge advantages due to the dual possibility of tailoring the interfaces as well as using the complementary properties of magnetic and dielectric components in the nanocomposite to enhance the EMI shielding performance. This work shows that by a careful tuning of the synthesis parameters, we can grow biphasic lithium iron oxide (ferrimagnetic α-LiFe₅O₈ and paramagnetic α-LiFeO₂) nanocomposite with different relative fractions of the two phases. The variation of the phase fraction and the simultaneous growth of the two phases allow us to control the interfaces between the two phases as well as the physical properties of the nanocomposite, which have a direct effect on the EMI shielding performance. Detailed structural (X-ray diffraction), compositional (Raman spectroscopy), and morphological (high-resolution transmission electron microscopy) characterization is presented to understand the effect of the synthesis conditions on the EMI shielding parameters. Improved dielectric and magnetic properties together with an increased number of interfaces in the sample with nearly equal amounts of the two phases results in the best performance. This work demonstrates the significant potential of using biphasic magnetic oxide nanocomposites with controllable interfaces and physical properties for EMI shielding, which can form the base for more complex triphasic systems in the future.

Lead-free metal halide perovskites are emerging as less-toxic alternatives to their lead-based counterparts. However, their applicability in optoelectronic devices is limited, and the charge transport dynamics remain poorly understood. Understanding photo-induced charge and structural dynamics is critical for unlocking the potential of these novel systems. In this work, ultrafast optical and Raman spectroscopy combined with band structure calculations are employed to investigate the coupled electronic and vibrational dynamics in Caesium gold bromide, a promising lead-free perovskite. It is found that the band-edge charge transfer states are strongly coupled to Au & horbar;Br stretching phonon modes, leading to frequency modulation of absorption by coherent phonons. Early-stage relaxation is characterized by dynamics of delocalized charge transfer excitation and slowly decaying coherent phonons. The electronic and vibrational relaxation reveals a slow formation of a localized polaronic state in the 10-20 ps timescale. Using a displaced harmonic oscillator model, the polaronic binding energy is estimated to be approximate to 80 meV following lattice relaxation along the phonon modes. Strong exciton-phonon coupling and slow polaron formation via coupling to lattice modes make this material a promising testbed for the control of coherent phonons and localized polaronic states using light.

The adoption of perovskite solar cells (PSCs) requires improved resistance to high temperatures and temperature variations. Hole-selective self-assembled monolayers (SAMs) have enabled progress in the performance of inverted PSCs, yet they may compromise temperature stability owing to desorption and weak interfacial contact. Here we developed a self-assembled bilayer by covalently interconnecting a phosphonic acid SAM with a triphenylamine upper layer. This polymerized network, formed through Friedel-Crafts alkylation, resisted thermal degradation up to 100°C for 200 h. Meanwhile, the face-on-oriented upper layer exhibited adhesive contact with perovskites, leading to a 1.7-fold improvement in adhesion energy compared with the SAM-perovskite interface. We reported power conversion efficiencies exceeding 26% for inverted PSCs. The champion devices demonstrated less than 4% and 3% efficiency loss after 2,000 h damp heat exposure (85°C and 85% relative humidity) and over 1,200 thermal cycles between -40°C and 85°C, respectively, meeting the temperature stability criteria outlined in the International Electrotechnical Commission 61215:2021 standards.

Theoretical Treatment of Nuclear Dynamics in Low-dimensional Systems

Tomas Edvinsson 

 Quantum confinement is a crucial phenomenon that affects the electronic and optical properties of semiconductors in low-dimensional systems. This effect, which is intrinsically tied to the spatial dimensions of the material, plays a significant role in modulating the properties of interest [1]. A material confined in 3-dimensions, so called quantum dots with 0-dimensional extension can achieve both enhanced and spectrally narrowed light emission. In two-dimensional (2D) structures such as quantum wells or nanoplatelets, quantum confinement arising from decreased thickness results in an enhanced oscillator strength, diminished dielectric screening, and increased exciton binding energy. We will here present experimental and theoretical results on quantum confined ZnO [2,3] and phonon-phonon and electron-phonon coupling effects. We will show how the excited state properties and the nuclear dynamics can explain the photoinduced ion migration in halide perovskites using stationary and time-dependent density functional theory [4,5]. Recent collaborative work have exploited this knowledge to mitigate ion migration and fabricate perovskite solar cells with certified efficiencies above 26% [6,7] with high tolerance to thermal stress [7]. We will also briefly discuss ongoing work that involves utilizing absorption-, emission-, and Raman spectroscopy to extract information on optical quantum confinement, exciton binding energies, and nuclear dynamics in 2D lead halide perovskites, along with their theoretical treatment using a model Bethe–Salpeter Equation and density functional perturbation theory to extract the nuclear dynamics.

References

[1]  Edvinsson, T. Optical Quantum Confinement and Photocatalytic Properties in Two-, One- and Zero-Dimensional Nanostructures. Royal. Soc. open sci. 2018, 5, 180387[

2]  Jacobsson, T. J.; Edvinsson, T., Quantum Confined Stark Effects in ZnO Quantum  Dots Investigated with Photoelectrochemical Methods, J. Phys. Chem. C 2014, 118, 12061.

[3] Raymand, D.,  Jacobsson, T.J., Hermansson, K., and  Edvinsson, T. Investigation of Vibrational Modes and Phonon Density of States in, ZnO Quantum Dots, J. Phys. Chem. C  2012, 116, 6893.

[4] Pazoki, M., Jacobsson, J. T., Kullgren, J., Johansson, E.M.J., Hagfeldt, A. Boschloo, G., Edvinsson, T.  Photoinduced Stark Effects and Mechanism of Ion Displacement in Perovskite Solar Cell Materials. ACS Nano, 2017, 11, 2823.

[5] Pazoki, M, Edvinsson, T. Nature of the excited state in lead iodide perovskite materials: Time-dependent charge density response and the role of the monovalent cation. Phys Rev B 2019, 100, 045203.

[6] Su, …, Edvinsson et al, Stereo-Hindrance Induced Conformal Self-Assembled Monolayer for High Efficiency Inverted Perovskite Solar Cells, Small 2024, 2407387.

[7] Dong, …, Edvinsson, et al, Self-assembled bilayer for perovskite solar cells with improved tolerance against thermal stresses, Nature Energy, 2025, 10, 342.

All-inorganic 2D halide perovskite nanoplatelets (PNPls) have recently garnered considerable interest in materials science. These materials exhibit outstanding optoelectronic properties, making them highly promising for applications in solar cells, LEDs, and photodetectors. The appeal of PNPls lies in their exceptional electronic and optical properties, which can be finely tuned across a wide range due to their unique structural characteristics. Initially, tuning the properties of PNPls focused on altering the elemental composition of the perovskite structure, specifically the halide component and/or the primary cation, shifting from organic to inorganic or between various organic molecules. In recent years, extensive research has indicated that another strategy for tuning PNPls' properties is based on the number of monolayers (MLs). A monolayer corresponds to a single microscopic layer of inorganic metal-halide octahedrons surrounded by large organic cations or ligands. While significant research has explored the optical properties of these systems, the role of phonons (lattice vibrations) in different dimensionalities remains underexplored. Additionally, a key scientific goal is a fundamental understanding of the collective carrier-phonon coupling in excited states, the thermalization process, initial charge separation, and final transport, including the mobility of electrons and holes and their relationship to charge carrier-lattice interactions. Since these phenomena are dimensionality- and phase-dependent, where the coupling between the excited state and phonons changes significantly with both dimensionality and phase, it is crucial to investigate the vibrational properties across different system dimensionalities and crystallographic phases to better understand the role of phonons in these materials.

In this study, we used Raman, photoluminescence, UV-Vis spectroscopy, both ex-situ and in-situ, to model the vibrational and optical properties of 2-6 MLs NPls as well as larger nanocrystals of oleic acid- and oleylamine-capped CsPbBr3. Our Raman measurements revealed that systematically varying the number of monolayers in the nanoplatelets leads to distinct changes in the relative intensities of the vibrational modes, which are sensitive to the number of monolayers. These changes in peak intensities provide valuable insights into the structural variations induced by the number of monolayers and suggest that Raman spectroscopy can be used for dimensionality analysis. These observations can be attributed to the quantum confinement effect, which becomes more pronounced as the thickness of the 2D nanoplatelets decreases. Additionally, strain generated in the materials upon forming lower thickness NPls can be identified through the shift of the Pb-Br vibrational mode. Furthermore, the measurements revealed that the tetragonal phase formation at room temperature is dominant in all prepared nanocrystal systems, with orthorhombic and cubic phases appearing at low and high temperatures, respectively. This is in addition to the phase-related and/or anharmonicity-related shift of phonon modes with temperature. Photoluminescence measurements revealed that, by changing the number of monolayers from 2-6, there is an enhancement of the photoluminescent intensity exponentially. This is attributed to the increase in the photoactive sites, where the number of the bright excitons increase with increasing the monolayers of the nanoplatelets, considering maintaining all the synthetic parameters the same, such as concentration.

When electrocatalysts are prepared, modification of the morphology is a common strategy to enhance their electrocatalytic performance. In this work, we have examined and characterized nanorods (3D) and nanosheets (2D) of nickel molybdate hydrates, which previously have been treated as the same material with just a variation in morphology. We thoroughly investigated the materials and report that they contain fundamentally different compounds with different crystal structures, chemical compositions, and chemical stabilities. The 3D nanorod structure exhibits the chemical formula NiMoO4·0.6H2O and crystallizes in a triclinic system, whereas the 2D nanosheet structures can be rationalized with Ni3MoO5–0.5x(OH)x·(2.3 – 0.5x)H2O, with a mixed valence of both Ni and Mo, which enables a layered crystal structure. The difference in structure and composition is supported by X-ray photoelectron spectroscopy, ion beam analysis, thermogravimetric analysis, X-ray diffraction, electron diffraction, infrared spectroscopy, Raman spectroscopy, and magnetic measurements. The previously proposed crystal structure for the nickel molybdate hydrate nanorods from the literature needs to be reconsidered and is here refined by ab initio molecular dynamics on a quantum mechanical level using density functional theory calculations to reproduce the experimental findings. Because the material is frequently studied as an electrocatalyst or catalyst precursor and both structures can appear in the same synthesis, a clear distinction between the two compounds is necessary to assess the underlying structure-to-function relationship and targeted electrocatalytic properties.

Solar cells and catalysis are two important applications in the field of renewable energy where the performances of the materials in these systems are influenced by the efficiency and stability of the electrodes. Here, we highlight the importance of understanding the dynamic processes in electrodes, such as ion migration, electrochemical reactions and surface restructuring, and how these phenomena can influence the overall performance of the systems. Lead halide perovskites have emerged as a promising class of materials with exciting optoelectronic properties, making them promising candidates for next-generation optoelectronics. The detailed electronic structure and photo excited charge density response in the excited state are here important to describe and optimize lead halide perovskites under operation [1,2]. Experiments from photoinduced Stark-effect experiment as well as corroborating theoretical investigations are presented and show that the excess energy after thermalization under blue-light illumination is large enough for overcoming the activation energy for iodide migration and can thus trigger ion movement and vacancy formation [2,3]. Here, a dipolar A-site cation would decrease the energy of defect formation, but instead impede defect migration [4] and also affect the excited state response and subsequently enhanced optoelectronic properties [5,6]. In an extension, the results give rationale for using dipolar A-site cations and mixed halide perovskites to decrease halide migration and the mechanistic origin of reported stability issues under blue and UV-light illumination. We present electrode materials reaching certified conversion above 26% solar-to-electricity power conversion. In the field of catalysis, we show that serial interconnected photo-absorbers are cost-effective solution to the spectral mismatch problem. Applying modified Cu-In-Ga-Se2 (CIGS) within the approach allows harvesting of photons up to 1200 nm in the solar spectrum and convert this energy into solar fuel beyond 13% STH module efficiency [7]. We will also outline how operando Raman spectroscopy can be utilized to unveil Fe-Ni based electrocatalyst reformulations into the active catalyst phase [8-10] and their structural integrity and how machine learning can guide us towards compositional choices in high entropy alloy catalysts [11,12].

1. Park B., SM Jain S.M., Zhang X., Hagfeldt A., Boschloo B., Edvinsson T. ACS Nano 9, 2088 (2015)2. Pazoki, M., Jacobsson, J. T., Kullgren, J., Johansson, E.M.J., Hagfeldt, A., Boschloo, G., Edvinsson, T. ACS Nano 11, 2823 (2017).3. Pazoki, M, Edvinsson, T. Phys Rev B, 100, 045203 (2019).4. Pazoki, M., Wolf, M.J., Edvinsson, T, Kullgren, J. Nano Energy 38, 537–543 (2017).5. Pazoki, M., Hagfeldt, A., Edvinsson, T. Characterization Techniques for Perovskite Solar Cell Materials and Devices, Elsevier (2020).6. Imani, R., Borca, C.H., Pazoki, M. Edvinsson, T., RSC Adv. 12, 25415 (2022).

7. Pehlivan, I. B. Sagui, N. A.,Oscarsson, J., Qiu, Z., Zwaygardt, W., Lee, M., Mueller, M., Haas, S., Stolt, L., Edofff, M., Edvinsson, T. J Mater Chem A. 10,12079 (2022)8. Qiu, Z., Tai, C-W., Niklasson, G.A., Edvinsson, T.  Energy Environ. Sci. 12, 572 (2019)

9. Dürr, R.N., Maltoni, P., Tian, H., Jousselme, B., Hammarström, L., Edvinsson, T. ACS Nano 15, 13504 (2021)10. Dürr, R.N., Maltoni, P., Feng, S., Ghorai, S., Ström, P., Tai, C-W., Araujo, R B., Edvinsson, T.Inorg. Chem. 63, 2388 (2024)

11. Araujo, R.B., Bayrak, P. I, Edvinsson, T. Nano Energy, 105, 108027 (2023)

12. Araujo. R.B., Edvinsson, T. ACS Catal. 14, 3742 (2024)

Zinc oxide, ZnO, is an intriguing material with applications spanning from simple to highly advanced and sophisticated technologies. Its wide direct band gap has made it useful as UV-absorbing additive in everything from sunscreens and rubber to advanced plastics.  Various nanoscale morphologies of ZnO have also emerged as promising candidates for a large set of new high-tech applications. Among these are UV-lasers, light-emitting diodes, field emitters, piezoelectric and spintronic devices, gas sensors, transparent conductors, photovoltaics, and photocatalysis.  Several of these nanoscale applications benefit from the control of the energy states where the position, nature, and relation between the states in the material affect the optical behavior. This is especially true for low-dimensional ZnO nanoparticles where the properties of the states will be a function of particle size if dimensions are made small enough.[1] Here we present experimental methods to extract the optical band edges and fluorescing trap states in ZnO quantum dots by combining electrochemistry and UV-spectroscopy.[2,3] We present the shift of band gap with particle size and how the absolute band edges shifts for up to 18 different sizes of low-dimensional  ZnO nanoparticles below the quantum confinement size regime. Time-resolved fluorescence data in the quantum confined regime and the possibility for surface stabilized excitons will be presented.[4]The development of collective vibrations and eventually phonons in the materials are also presented by combining experimental Raman spectroscopy and theoretical simulations where the vibrational quantum confinement regime as larger than the corresponding electronic quantum confinement. [5] We finally present a quantum confined Stark effect that disappears when dimensions of the particles approaches the bulk band gap regime at around 9 nm.[6] We will also briefly touch upon our more recent work on utilizing Raman spectroscopy to extract electron-phonon coupling in ZnO, and optical quantum confinement and exciton emission in 2D lead halide perovskites.

[1] Edvinsson, T. Optical Quantum Confinement and Photocatalytic Properties in Two-, One- and Zero-Dimensional Nanostructures. Royal. Soc. open sci. 2018, 5: 180387.

[2] Jacobsson, T. J.,  Edvinsson, T. Photoelectrochemical Determination of the Absolute Band Edge Positions as a Function of Particle Size for ZnO Quantum Dots, J. Phys. Chem. C, 2012, 116, 15692.

[3] Jacobsson, T. J.; Edvinsson, T. A Spectroelectrochemical Method for Locating Fluorescence Trap States in Nanoparticles and Quantum Dots, J. Phys. Chem. C 2013, 117, 5497.

[4] Jacobsson, T. J.; Viarbitskaya, S.; Mukhtar, E.; Edvinsson, T.,  A Size Dependent Discontinuous Decay Rate for the Exciton Emission in ZnO Quantum Dots,  Phys. Chem. Chem. Phys.  2014, 16, 13849.

[5] Raymand, D.,  Jacobsson, T.J., Hermansson, K., and  Edvinsson, T. Investigation of Vibrational Modes and Phonon Density of States in, ZnO Quantum Dots, J. Phys. Chem. C  2012, 116, 6893.

[6] Jacobsson, T. J.; Edvinsson, T., Quantum Confined Stark Effects in ZnO Quantum  Dots Investigated with Photoelectrochemical Methods, J. Phys. Chem. C 2014, 118, 12061

Constructing a Z-scheme heterojunction with enhanced photocatalytic hydrogen evolution for graphitic carbon nitride-based (g-C3N4) composites is challenging because integrating g-C3N4 with other semiconductors, without specific band structure design, typically results in type I or type II heterojunctions. These heterojunctions have lower redox ability and limited enhancement in photocatalysis. Herein, we select highly crystalline carbon nitride (HCCN) as a proof-of-concept substrate. For the first time, we develop a AgBr nanosphere/HCCN composite photocatalyst that features an all -solid -state direct Z-scheme heterojunction for visible-light photocatalytic hydrogen evolution. The electron transfer mechanism is initially studied from the band structures and Fermi levels of HCCN and AgBr. It is subsequently confirmed by X-ray photoelectron spectroscopy (XPS), and electron microscopy. The close heterojunction contact and the built-in electron field of the Z-scheme heterojunction promote the migration and separation of photogenerated electrons and holes in the composite photocatalyst. Due to the redistribution of charge carriers, the photocatalyst shows superior redox capability and a markedly enhanced hydrogen evolution performance compared to its individual components. Combining all the advantages, AgBr nanosphere/HCCN reached an apparent quantum efficiency (AQE) of 6 % under the illumination of 410 nm, which is 4 times higher than that of the single HCCN component.

Quantum confinement is one of the effects dictating semiconductors’ electronic and optical properties. This effect, regulated by the spatial extension of the semiconductor, has the potential to significantly modulate optical and electronic properties of interest. For instance, quantum confinement effects imposed by the small thickness of 2D nanoplatelets (NPLs) result in enhanced oscillator strength, reduced dielectric screening, and increased exciton binding energy. The relative effects are material-dependent and are modulated by the number of electrons and their orbital occupation in the specific material. Here, we investigate the effects of thickness on the vibrational and electronic structure properties of 2D halide perovskite (Csn−1PbnBr3n+1) nanoplatelets (NPLs) with n = 3, 4, and 5. We report the change in electronic structure as a function of platelet thickness as well as changes in vibrations. Our hypothesis is that the Raman intensities ratio between two dimensionally dependent modes would vary with the layer thickness of the NPLs due to the different vibrational-induced polarizability over n = 3, 4, and 5. To quantify and understand such an effect, Phonon dispersion, electronic structure and Raman intensities of the vibrational modes at the GAMMA point are computed for each thickness case using density functional perturbation theory (DFPT) and density functional theory (DFT). For this task, we have built slab models from the tetragonal CsPbBr3 phase with a vacuum in the z direction to avoid (as much as possible) the interaction between periodic images. The change in relative intensities between the modes are in agreement with our experimental data from Raman spectroscopy, revealing the same trend in intensity change between the Raman active modes upon confinement. The effect is attributed to the reported change in electronic structure and subsequent polarizability change upon quantum confinement of the material into fewer layers.