1,721,004 research outputs found
Routes toward Long-Term Stability of Mixed-Halide Perovskites
Get PDFIn the recent anniversary issue of Trends in Chemistry, Brennan et al. review halide segregation in mixed-halide perovskites, discussing multiple perspectives on the underlying origins and reported routes to retard halide segregation. Here, we argue that only slowing down the segregation may be insufficient to achieve long-term stability
Accelerated Hot-Carrier Cooling in MAPbI3 Perovskite by Pressure-Induced Lattice Compression
Get PDFHot-carrier cooling (HCC) in metal halide perovskites above the Mott transition is significantly slower than in conventional semiconductors. This effect is commonly attributed to a hot-phonon bottleneck, but the influence of the lattice properties on the HCC behavior is poorly understood. Using pressure-dependent transient absorption spectroscopy, we find that at an excitation density below the Mott transition, pressure does not affect the HCC. On the contrary, above the Mott transition, HCC in methylammonium lead iodide is around 2-3 times faster at 0.3 GPa than at ambient pressure. Our electron-phonon coupling calculations reveal ∼2-fold stronger electron-phonon coupling for the inorganic cage mode at 0.3 GPa. However, our experiments reveal that pressure promotes faster HCC only above the Mott transition. Altogether, these findings suggest a change in the nature of excited carriers above the Mott transition threshold, providing insights into the electronic behavior of devices operating at such high charge-carrier densities
Thermodynamic stabilization of mixed-halide perovskites against phase segregation
Get PDFMixing iodide and bromide in halide perovskite semiconductors is an effective strategy to tune their band gap; therefore, mixed-halide perovskites hold great promise for color-tunable LEDs and tandem solar cells. However, the band gap of mixed-halide perovskites is unstable under (sun-)light, since the halides segregate into domains of different band gaps. Using pressure-dependent ultrafast transient absorption spectroscopy, we find that high external pressure increases the range of stable halide mixing ratios. Chemical compression, by inserting a smaller cation, has the same effect, which means that any iodide:bromide ratio can be stabilized by tuning the crystal volume and compressibility. We interpret these findings as an increased thermodynamic stabilization through alteration of the Gibbs free energy via the largely overlooked PΔV term
Charge Carrier Dynamics upon Sub-bandgap Excitation in Methylammonium Lead Iodide Thin Films: Effects of Urbach Tail, Deep Defects, and Two-Photon Absorption
Get PDFTo further understand the optoelectronic properties of metal halide perovskites, we investigate sub-bandgap absorption in methylammonium lead iodide (MAPbI3) films. Charge carrier dynamics are studied using time-resolved microwave conductivity measurements using sub-bandgap excitation. From changes in the decay dynamics as a function of excitation energy and intensity, we have identified three regimes: (i) Band-like charge transport at photon energies above 1.48 eV; (ii) a transitional regime between 1.48 and 1.40 eV; and (iii) below 1.40 eV localized optically active defects (8 × 1013 cm-3) dominate the absorption at low intensities, while two-photon absorption is observed at high intensities. We determined an Urbach energy of approximately 11.3 meV, indicative of a low structural and/or thermal disorder. Surprisingly, even excitation 120 meV below the bandgap leads to efficient charge transfer into electron (C60) or hole (spiro-OMeTAD) transport layers. Therefore, we conclude that for MAPbI3, the band tail states do not lead to nonradiative losses. ChemE/Opto-electronic Material
Perovskite escape room: Which photons leave the film, and which are trapped inside?
Get PDFAlthough halide perovskite materials hold great promise for optoelectronics, defect-assisted recombination still limits their efficiency. In the April issue of Matter, Fassl et al. present an open-source model for analyzing the photoluminescence spectra of perovskite films, showing a much lower internal quantum efficiency than previously thought in the field
Lattice Compression Increases the Activation Barrier for Phase Segregation in Mixed-Halide Perovskites
Get PDFThe bandgap tunability of mixed-halide perovskites makes them promising candidates for light-emitting diodes and tandem solar cells. However, illuminating mixed-halide perovskites results in the formation of segregated phases enriched in a single halide. This segregation occurs through ion migration, which is also observed in single-halide compositions, and whose control is thus essential to enhance the lifetime and stability. Using pressure-dependent transient absorption spectroscopy, we find that the formation rates of both iodide- and bromide-rich phases in MAPb(BrxI1–x)3 reduce by 2 orders of magnitude on increasing the pressure to 0.3 GPa. We explain this reduction from a compression-induced increase of the activation energy for halide migration, which is supported by first-principle calculations. A similar mechanism occurs when the unit cell volume is reduced by incorporating a smaller cation. These findings reveal that stability with respect to halide segregation can be achieved either physically through compressive stress or chemically through compositional engineering
Author Correction: Chemical targets to deactivate biological and chemical toxins using surfaces and fabrics
Get PDFCorrection to: Nature Reviews Chemistry https://doi-org.proxy.library.uu.nl/10.1038/s41570-021-00275-4, published online 05 May 2021. The originally published article contained an incomplete acknowledgements section, which now reads as: This work is part of the Advanced Research Center for Chemical Building Blocks, ARC CBBC, which is co- founded and co- financed by the Netherlands Organisation for Scientific Research (NWO) and the Netherlands Ministry of Economic Affairs and Climate Policy. This work was supported by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation programme funded by the Ministry of Education, Culture and Science of the government of the Netherlands and the US Army Research Office (ARO), and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska- Curie grant agreement no. 801359. The authors thank T. Hartman (Utrecht University) for the graphical illustrations. This has been corrected in the HTML and PDF versions of the manuscript
Perovskite escape room: Which photons leave the film, and which are trapped inside?
No full textAlthough halide perovskite materials hold great promise for optoelectronics, defect-assisted recombination still limits their efficiency. In the April issue of Matter, Fassl et al. present an open-source model for analyzing the photoluminescence spectra of perovskite films, showing a much lower internal quantum efficiency than previously thought in the field
Combined In Situ Xray Powder Diffractometry/Raman Spectroscopy of Iron Carbide and Carbon Species Evolution in Fe(NaS)/-Al2O3 Catalysts during FischerTropsch Synthesis
Get PDFA Na-S promoted Fe-based Fischer-Tropsch synthesis (FTS) catalyst converts a H2/CO gas mixture into hydrocarbons with enriched C2-C4 olefin content. Above 300 °C, the carbon-depositing Boudouard reaction competes with the FTS reaction for CO as reactant. By making use of a combined in situ X-ray powder diffractometry (XRPD)/Raman spectroscopy setup, the simultaneous evolution of the FexOy/α-Fe/FexC phases and various formed carbon species has been monitored at 340 °C and 10 bar. CO carburized, Na-S promoted and unpromoted Fe(-Na-S)/α-Al2O3 catalysts were investigated. The various Fe phases present were quantified with Rietveld quantitative phase analysis (R-QPA) from the in situ collected XRPD patterns. The observed D- A nd G-bands in the in situ Raman spectra were analyzed for their relative intensities, band widths, and positions and compared to reference carbon materials. It was found that amorphous carbon with C sp3 and C sp2 in chain-like ordering evolved toward carbon nanofiber-like structures during FTS. Na-S promotion and initial CO carburization at temperatures ≥340 °C led to an increased amount of cyclic sixfold C sp2 species. Preliminary carbon deposits present in the catalysts decreased the initial fast increase of the Raman band intensities, while Na-S promotion increased Raman band intensity growth after the initial fast increase period. The carbon species evolution was unaffected by the presence of specific Fe carbides or by carbide-to-carbide transitions. Na-S promotion aided in the reduction of Fe3O4 by (H2:)CO to carbon-depositing Fe carbides. The results obtained add to our further understanding on the role of Fe and carbon species during a high-temperature FTS reaction
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