The perovskite-inspired bismuth halide semiconductor Cs3Bi2Br9 is widely investigated as a photoactive material for light-conversion applications. However, charge generation and separation are inherently limited by its modest sunlight absorption and strong exciton binding energy, respectively. Here, we demonstrate that both the light absorption and exciton dissociation are improved by controlled substitution of Br- with I- via mechanochemical synthesis of Cs3Bi2(Br1- xIx)9. X-ray diffraction and Raman analyses confirm atomic-level halide mixing and reveal a crystallographic phase transition near x = 0.8. From absorption measurements on thin films, we determine the absorption coefficient, Urbach tail, and exciton binding energy for several Cs3Bi2(Br1- xIx)9 compositions. From here, we find that the bandgap can be tuned from 2.59 to 1.93 eV (for x = 0.9), while exciton binding energies reach a minimum at x = 0.6. Finally, transient absorption spectroscopy measurements suggest a weak correlation between recombination lifetime and Urbach energy, where the longest lifetimes are observed for the materials with the lowest disorder. These results offer valuable insights for designing stable bismuth halide semiconductors with favorable light absorption properties and charge carrier dynamics.

ABSTRACT The perovskite‐inspired bismuth halide semiconductor Cs 3 Bi 2 Br 9 is widely investigated as a photoactive material for light‐conversion applications. However, charge generation and separation are inherently limited by its modest sunlight absorption and strong exciton binding energy, respectively. Here, we demonstrate that both the light absorption and exciton dissociation are improved by controlled substitution of Br − with I − via mechanochemical synthesis of Cs 3 Bi 2 (Br 1− x I x ) 9 . X‐ray diffraction and Raman analyses confirm atomic‐level halide mixing and reveal a crystallographic phase transition near x = 0.8. From absorption measurements on thin films, we determine the absorption coefficient, Urbach tail, and exciton binding energy for several Cs 3 Bi 2 (Br 1− x I x ) 9 compositions. From here, we find that the bandgap can be tuned from 2.59 to 1.93 eV (for x = 0.9), while exciton binding energies reach a minimum at x = 0.6. Finally, transient absorption spectroscopy measurements suggest a weak correlation between recombination lifetime and Urbach energy, where the longest lifetimes are observed for the materials with the lowest disorder. These results offer valuable insights for designing stable bismuth halide semiconductors with favorable light absorption properties and charge carrier dynamics.

Typical concentrations of volatile organic compounds (VOCs) in indoor environments range from hundreds of ppb to several ppm. Even at these low concentrations, prolonged indoor exposure to VOCs has been linked to sick building syndrome, a condition associated with adverse effects on human health. Therefore, an increasing amount of research has been focused on removing VOCs from indoor air. To research VOC degradation reactions at low concentrations, highly sensitive detection methods should be designed and employed. In this work, we report on the development of a photo-reaction setup, including VOC and CO2 detection at ppm-ppb level. We designed a temperature-controlled photocatalytic reactor that enables batch-mode photocatalytic reactions. The developed setup enables reliable testing of photocatalytic materials for VOC degradation at ppm-ppb levels, while allowing for precise yet flexible control of reaction conditions, including relative humidity (RH) control of the gas phase and adaptable light source selection. A gas chromatograph with a VOC and CO2 detection limit of 200-250 ppb analyzes the gas phase. The setup was benchmarked with acetone as model VOC and P25-TiO2 as widely used photocatalyst using simulated solar light and initial VOC concentrations between 5 and 1000 ppm. After photocatalytic degradation, acetone was detected down to 1 ppm.

Cs$_2$AgBiBr$_6$ shows promise for solution-processable optoelectronics, such as photovoltaics, photocatalysis and X-ray detection. However, various spectroscopic studies report rapid charge carrier mobility loss in the first picosecond after photoexcitation, limiting carrier collection efficiencies. The origin of this rapid mobility loss is still unclear. Here, we directly compare hot excitation with excitation over the indirect fundamental bandgap, using transient absorption and THz spectroscopy on the same Cs$_2$AgBiBr$_6$ thin film sample. From transient absorption spectroscopy, we find that hot carriers cool towards the band-edges with a cooling rate of 0.58 ps$^{-1}$, which coincides with the observed mobility loss rate from THz spectroscopy. Hence, our study establishes a direct link between the hot carrier cooling and ultrafast mobility loss on the picosecond timescale.

TiO2 is widely studied as an efficient UV-light photocatalyst for organic compound degradation through reactive oxygen species (ROS) generation. TiO2 can be modified to show photocatalytic activity under visible light illumination by combining with visible-light absorbing metal oxides. Here, we investigated Co3O4/TiO2 composite materials as visible-light absorbing photocatalysts, with various weight loadings of Co3O4, for the decolorization of wastewater pollutant indigo carmine. Under green LED light, 1.4 wt% Co3O4/TiO2 showed the highest decolorization rate compared to other weight loadings and bare TiO2. While UV-Vis spectroscopy indicated that Co3O4/TiO2 composite materials and bare TiO2 cause similar dye decolorization behavior, NMR spectroscopy showed that after 24 h, reaction products were present in the reaction mixture for 1.4 wt% Co3O4/TiO2, while TiO2 showed no reaction products. The lack of photocatalytic activity of Co3O4/zeolite and other Co3O4/oxide composite materials suggests a synergistic effect between Co3O4 and TiO2, where a small amount of Co3O4 enables TiO2 to utilize visible light without compromising the surface area available for ROS creation. Lastly, we emphasize the need to be cautious when drawing conclusions regarding the dye degradation, since we showed that decolorization does not necessarily equate to full degradation, using a unique combination of UV-Vis and nuclear magnetic resonance spectroscopy.

Mechanochemical ball mill synthesis is an emerging method for producing complex materials, including alloyed halide elpasolite semiconductors. This solvent-free method offers precise control over chemical composition, enabling fine-tuning of the optical and mechanical properties. However, the formation mechanism of alloyed elpasolites remains unclear. In this work, we elucidate the crystallization kinetics of mechanochemical formation of Cs2AgBi0.5M0.5Br6 [M = Sb3+, In3+, or Fe3+] using in situ synchrotron X-ray diffraction experiments. We identify the reaction intermediates for the parent composition Cs2AgBiBr6, and we find that -Bi0.5Sb0.5- forms via a similar reaction pathway. Alloying with In3+ or Fe3+, on the other hand, occurs via an additional cation-exchange step. These insights into the mechanochemical formation mechanisms of alloyed AgBi-elpasolites provide guidelines toward rational compositional engineering of complex materials.

Cs2AgBiBr6 is an emerging double perovskite semiconductor with robust stability. However, its potential for photovoltaics is limited by its indirect band gap and localized electronic structure featuring a resonant exciton with a large binding energy. Cs2AgBi(IxBr1-x)(6) nanocrystals with iodide concentrations of up to 100% were recently demonstrated, but an atomistic understanding of how halide mixing affects the electronic and excited-state structure is missing. Here, we use first-principles GW and Bethe-Salpeter Equation calculations to show that halide mixing leads to a pronounced change in the band gap and character of optical excitations. Exciton binding energies are reduced by up to a factor of 5, with significantly more delocalized excitons in I-rich compounds. We further show that phase-pure bulk alloys with x <= 0.11 can be fabricated using mechanosynthesis and measure a red-shifted absorption in line with our calculations. Our study highlights that halide mixing in double perovskites can not only lead to significant band gap changes but may also be used for tuning excitonic properties.

Exploring Temperature- and Pressure-Dependent Elastic Properties of Halide Perovskites and ElpasolitesLoreta Muscarella a, Huygen J. Jöbsis b, Bettina Baumgartner b, P. Tim Prins b, D. Nicolette Maaskant b, Andrei V. Petukhov b, Dmitry Chernyshov c, Charles J McMonagle c, Eline M. Hutter ba Department of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit Amsterdamb Utrecht University, Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Netherlandsc ESRF, The European Synchrotron, 71 Avenue des Martyrs, CS40220, 38043 Grenoble Cedex 9, FranceInternational Conference on Hybrid and Organic PhotovoltaicsProceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV24)València, Spain, 2024 May 12th - 15thOrganizer: Bruno EhrlerOral, Loreta Muscarella, presentation 173DOI: https://doi.org/10.29363/nanoge.hopv.2024.173Publication date: 6th February 2024Halide perovskites and elpasolites are key for optoelectronic applications due to their exceptional performance and adaptability. However, understanding their crucial elastic properties for synthesis and device operation remains limited. We performed temperature- and pressure-dependent synchrotron-based powder X-ray diffraction at low pressures (ambient to 0.06 GPa) to investigate their elastic properties in their ambient-pressure crystal structure. We found common trends in bulk modulus and thermal expansivity, with an increased halide ionic radius (Cl to Br to I) resulting in greater softness, higher compressibility and thermal expansivity in both class of materials. For non-cubic systems, in which the elastic properties are anisotropic, we obtained axis-dependent compressibility. The A cation has a minor effect, and mixed-halide compositions show intermediate properties. Notably, thermal phase transitions in MAPbI3 and CsPbCl3 induced lattice softening and negative expansivity for specific crystal axes, even at temperatures far from the transition point. These results emphasize the significance of considering temperature-dependent elastic properties, which can significantly impact device stability and performance during manufacturing or temperature sweeps. © FUNDACIO DE LA COMUNITAT VALENCIANA SCITOnanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. Our worldwide conferences cover cutting-edge materials topics like perovskite solar cells, photovoltaics, optoelectronics, solar fuel conversion, surface science, catalysis and two-dimensional materials, among many others.MATSUSPreviously nanoGe Spring Meeting (NSM) and nanoGe Fall Meeting (NFM), MATSUS is a multiple symposia conference focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.International Conference on Hybrid and Organic PhotovoltaicsInternational Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and OptoelectronicsThe main topics of the Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP) are discussed every year in Asia-Pacific for gathering the recent advances in the fields of material preparation, modeling and fabrication of perovskite and hybrid and organic materials. Photovoltaic devices are analyzed from fundamental physics and materials properties to a broad set of applications. The conference also covers the developments of perovskite optoelectronics, including light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and OptoelectronicsThe International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics (NIPHO) is the best place to hear the latest developments in perovskite solar cells as well as on recent advances in the fields of perovskite light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.

Tuning optical and mechanical properties of Cs2AgBiBr6 double perovskites by controlled alloyingEline Hutter a, Huygen Jöbsis a, Loreta Muscarella a, Kostas Fykouras b, Linn Leppert ba Utrecht University, Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Netherlandsb Universiteit Twente, Drienerlolaan 5, Enschede, NetherlandsInternational Conference on Hybrid and Organic PhotovoltaicsProceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV24)València, Spain, 2024 May 12th - 15thOrganizer: Bruno EhrlerOral, Eline Hutter, presentation 105DOI: https://doi.org/10.29363/nanoge.hopv.2024.105Publication date: 6th February 2024Halide double perovskite semiconductors such as Cs2AgBiBr6 are widely investigated as a more stable, less toxic alternative to lead–halide perovskites in photoconversion applications including photovoltaics and photoredox catalysis. However, the relatively large (~2.1 eV) and indirect bandgap of Cs2AgBiBr6 limits efficient sunlight absorption. Similar to lead–halide perovskites, the bandgap of double perovskites can be manipulated through (partial) substitution of metals or halides with similarly charged ions. However, commonly used solvent-based synthesis routes often lead to the formation of domains or side phases, rather than solid solutions with controlled properties. This results in an inhomogeneous electronic landscape which is detrimental for photoconversion applications. Here, we show that mechanochemical synthesis methods, such as ball milling, are a valid route to synthesize phase-pure double perovskites. With the use of synchrotron radiation we followed the formation mechanisms during mechanochemical synthesis of Cs2Ag[BiM]Br6 (with M = Sb, In, or Fe or X = Cl, Br, or I), and identified new intermediate phases, providing insights into the reaction kinetics. We find that mechanochemical synthesis is a successful approach to make compounds that have not been reported via solution-based synthesis routes, such as Cs2AgBi0.5In0.5Br6, and Cs2AgBi1-xFexBr6. Where substitution with In3+ increases the band gap energy, it is lowered when replacing Bi3+ with Fe3+ or Br− with I−. Hence, the optical bandgap of Cs2AgBiBr6 can be tuned over the entire visible spectrum when partly substituting Bi3+ or Br−. For instance, we find that controlled replacement of Bi3+ with Fe3+ via mechanochemical synthesis results in a remarkable tunability of the absorption onset between 2.1 to ~1 eV. In addition, with synchrotron-based high pressure X-ray diffraction (XRD), we find that the softness of these materials varies with its chemical composition. Our first-principles density functional theory (DFT) calculations demonstrate that this bandgap reduction originates from a lowering of the conduction band minimum upon introduction of Fe3+, while the valence band remains constant. Additionally, our DFT calculations suggest that the bandgap becomes direct when 50% of Bi3+ is replaced with Fe3+. Finally, we find that the tunability of the conduction band minimum is reflected in the photoredox activity of these semiconductors. The improved understanding of the reaction mechanism of alloyed-AgBi double perovskites might help to overcome the current challenges faced with solution processing methods. Hence, opening up new avenues for enhancing the visible light absorption of double perovskite semiconductors and for harnessing their full potential in sustainable energy applications. References:[1] Huygen J. Jöbsis, Kostas Fykouras, Joost W.C. Reinders, Jacco van Katwijk, Joren M. Dorresteijn, Tjom Arens, Ina Vollmer, Loreta A. Muscarella, Linn Leppert, Eline M. Hutter, Conduction Band Tuning by Controlled Alloying of Fe into Cs2AgBiBr6 Double Perovskite Powders, Advanced Functional Materials, 2023[2] Loreta A Muscarella, Huygen J Jöbsis, Bettina Baumgartner, P Tim Prins, D Nicolette Maaskant, Andrei V Petukhov, Dmitry Chernyshov, Charles J McMonagle, Eline M Hutter, Which Ion Dominates the Temperature and Pressure Response of Halide Perovskites and Elpasolites?, J. Phys. Chem. Lett. 2023, 14, 40, 9042–9051© FUNDACIO DE LA COMUNITAT VALENCIANA SCITOnanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. Our worldwide conferences cover cutting-edge materials topics like perovskite solar cells, photovoltaics, optoelectronics, solar fuel conversion, surface science, catalysis and two-dimensional materials, among many others.MATSUSPreviously nanoGe Spring Meeting (NSM) and nanoGe Fall Meeting (NFM), MATSUS is a multiple symposia conference focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.International Conference on Hybrid and Organic PhotovoltaicsInternational Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and OptoelectronicsThe main topics of the Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP) are discussed every year in Asia-Pacific for gathering the recent advances in the fields of material preparation, modeling and fabrication of perovskite and hybrid and organic materials. Photovoltaic devices are analyzed from fundamental physics and materials properties to a broad set of applications. The conference also covers the developments of perovskite optoelectronics, including light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and OptoelectronicsThe International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics (NIPHO) is the best place to hear the latest developments in perovskite solar cells as well as on recent advances in the fields of perovskite light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.

Grain size and orientation's impact on charge carriers is explored via a new solvent engineering method for MAPbI 3 solar cells. Drift-diffusion simulations connect s-shaped JV curves to slower ions.

Halide perovskites and elpasolites are key for optoelectronic applications due to their exceptional performance and adaptability. However, understanding their crucial elastic properties for synthesis and device operation remains limited. We performed temperature- and pressure-dependent synchrotron-based powder X-ray diffraction at low pressures (ambient to 0.06 GPa) to investigate their elastic properties in their ambient-pressure crystal structure. We found common trends in bulk modulus and thermal expansivity, with an increased halide ionic radius (Cl to Br to I) resulting in greater softness, higher compressibility, and thermal expansivity in both materials. The A cation has a minor effect, and mixed-halide compositions show intermediate properties. Notably, thermal phase transitions in MAPbI3 and CsPbCl3 induced lattice softening and negative expansivity for specific crystal axes, even at temperatures far from the transition point. These results emphasize the significance of considering temperature-dependent elastic properties, which can significantly impact device stability and performance during manufacturing or temperature sweeps.

Halide double perovskite semiconductors such as Cs2AgBiBr6 are widely investigated as a more stable, less toxic alternative to lead-halide perovskites in light conversion applications including photovoltaics and photoredox catalysis. However, the relatively large and indirect bandgap of Cs2AgBiBr6 limits efficient sunlight absorption. Here, it is shown that controlled replacement of Bi3+ with Fe3+ via mechanochemical synthesis results in a remarkable tunable absorption onset between 2.1 and approximate to 1 eV. First-principles density functional theory (DFT) calculations suggest that this bandgap reduction originates primarily from a lowering of the conduction band upon the introduction of Fe3+, and predict a direct bandgap when >50% of Bi3+ is replaced with Fe3+. The tunability of the conduction band energy is found and reflected in the photoredox activity of these semiconductors. These findings open new avenues for enhancing the sunlight absorption of double perovskite semiconductors and for harnessing their full potential in sustainable energy applications.

Often the reactor or the reaction medium temperature is reported in the field of heterogeneous catalysis, even though it could vary significantly from the reactive catalyst temperature. The influence of the catalyst temperature on the catalytic performance and vice versa is therefore not always accurately known. We here apply EuOCl as both solid catalyst and thermometer, allowing for operando temperature determination. The interplay between reaction conditions and the catalyst temperature dynamics is studied. A maximum temperature difference between the catalyst and oven of +16 °C was observed due to the exothermicity of the methane oxychlorination reaction. Heat dissipation by radiation appears dominating compared to convection in this set-up, explaining the observed uniform catalyst bed temperature. Application of operando catalyst thermometry could provide a deeper mechanistic understanding of catalyst performances and allow for safer process operation in chemical industries.

The direct conversion of CH4 into fuels and chemicals produces less waste, requires smaller capital investments, and has improved energy efficiency compared to multistep processes. While the methane oxychlorination (MOC) reaction has been given little attention, it offers the potential to achieve high CH4 conversion levels at high selectivities. In a continuing effort to design commercially interesting MOC catalysts, we have improved the catalyst design of EuOCl by the partial replacement of Eu3+ by La3+. A set of catalytic solid solutions of La3+ and Eu3+ (i.e., La x Eu1-x OCl, where x = 0, 0.25, 0.50, 0.75, and 1) were synthesized and tested in the MOC reaction. The La3+-Eu3+ catalysts exhibit an increased CH3Cl selectivity (i.e., 54-66 vs 41-52%), a lower CH2Cl2 selectivity (i.e., 8-24 vs 18-34%), and a comparable CO selectivity (i.e., 11-28 vs 14-28%) compared to EuOCl under the same reaction conditions and varying HCl concentrations in the feed. The La3+-Eu3+ catalysts possessed a higher CH4 conversion rate than when the individual activities of LaOCl and EuOCl are summed with a similar La3+/Eu3+ ratio (i.e., the linear combination). In the solid solution, La3+ is readily chlorinated and acts as a chlorine buffer that can transfer chlorine to the active Eu3+ phase, thereby enhancing the activity. The improved catalyst design enhances the CH3Cl yield and selectivity and reduces the catalyst cost and the separation cost of the unreacted HCl. These results showcase that, by matching intrinsic material properties, catalyst design can be altered to overcome reaction bottlenecks.

AbstractDue to their excellent optoelectronic performance, and relatively easy processibility, halide perovskite semiconductors are used in highly efficient solar cells, LEDs, X‐ray detectors, and more recently in photo(electro)chemistry. Eline M. Hutter aims to obtain stable, non‐toxic perovskites for photoconversion applications.