37 research outputs found
Local Structure and Dynamics in Methylammonium, Formamidinium, and Cesium Tin(II) Mixed-Halide Perovskites from 119Sn Solid-State NMR.
Organic-inorganic tin(II) halide perovskites have emerged as promising alternatives to lead halide perovskites in optoelectronic applications. While they suffer from considerably poorer performance and stability in comparison to their lead analogues, their performance improvements have so far largely been driven by trial and error efforts due to a critical lack of methods to probe their atomic-level microstructure. Here, we identify the challenges and devise a 119Sn solid-state NMR protocol for the determination of the local structure of mixed-cation and mixed-halide tin(II) halide perovskites as well as their degradation products and related phases. We establish that the longitudinal relaxation of 119Sn can span 6 orders of magnitude in this class of compounds, which makes judicious choice of experimental NMR parameters essential for the reliable detection of various phases. We show that Cl/Br and I/Br mixed-halide perovskites form solid alloys in any ratio, while only limited mixing is possible for I/Cl compositions. We elucidate the degradation pathways of Cs-, MA-, and FA-based tin(II) halides and show that degradation leads to highly disordered, qualitatively similar products, regardless of the A-site cation and halide. We detect the presence of metallic tin among the degradation products, which we suggest could contribute to the previously reported high conductivities in tin(II) halide perovskites. 119Sn NMR chemical shifts are a sensitive probe of the halide coordination environment as well as of the A-site cation composition. Finally, we use variable-temperature multifield relaxation measurements to quantify ion dynamics in MASnBr3 and establish activation energies for motion and show that this motion leads to spontaneous halide homogenization at room temperature whenever two different pure-halide perovskites are put in physical contact
In situ NMR approach of the local structure of molten materials at high temperature
The developments of NMR spectroscopy at high temperature now allow us to study in situ a great number of molten materials. This technique is sensitive to local environment around the nucleus, and gives selective and quantitative information not limited by the disorder existing in liquids. NMR can thus provide a microscopic approach of the structure and dynamics of molten compounds by means of knowledge of different species existing in the melt, the average coordination, or nature of the first neighbors.We present high temperature NMR approach of molten fluoride systems of nuclear interest and description of the local structure around each nucleus, and its evolution with the composition
Combining solid state NMR, powder X-ray diffraction, and DFT calculations for CsSc3F10 structure determination
International audienc
New Electrochemical Approach for the Synthesis of Pd‐PdO/C Electrocatalyst and Application to Formic Acid Electrooxidation
International audienc
Synthesis of HfO2 from hafnium hydroxide hydrate
International audienc
Study of the NaF-ScF3 system as a molten bath for production of Sc alloys: A combination of NMR and molecular dynamics simulations
International audienc
Non-isothermal decomposition of platinum acetylacetonate as a cost-efficient and Size-Controlled Synthesis of Pt/C nanoparticles
International audienc