The work performed within this project included (a) solid-state mechanosynthesis of metal halide perovskite materials of current relevance to optoelectronics, (b) X-ray diffraction characterization of their long-range (>100 nm) structure, (c) solid-state NMR characterization of their short-range (<10 nm) structure, (d) characterization using optical spectroscopies, (e) establishing structure-property relationship based on the resulting data.
Mechanosynthesis is a highly atom-efficient way of preparing metal halide perovskites with yields approaching 100%. This allowed us to study a wide library of materials including low-dimensional lead halide perovskites, lead-free mixed-halide perovskites based on silver and bismuth, lead-free tin halide perovskites, and lead halide perovskites modulated with small organic molecules. We have successfully determined the atomic-level structure in these classes of materials using solid-state NMR.
Within the scope of understating lead-free materials based on silver and bismuth, we have successfully recorded NMR spectra, photoluminescence and charge carrier lifetimes, and correlated the results to obtain structure-property relationships. We have established the phase diagram of halide miscibility in Cs2AgBiX6 (X=Cl, Br, I) double halide perovskites. We then correlated the halide composition with the resulting charge carrier lifetimes and demonstrated the pernicious effect of iodide and bromide doping in this class of materials. The results have been published (Chem. Mater. 2020, 19, 8129–8138, doi: 10.1021/acs.chemmater.0c01255). We have also successfully synthesized and investigated the atomic-level structure and degradation pathways of a large library tin halide materials. These results have been published (J. Am. Chem. Soc. 2020, 17, 7813–7826, doi:10.1021/jacs.0c00647) as well as presented at international conferences.
In another study, we synthesized MHPs doped with a library of small organic molecules residing on the surface of the perovskite and revealed their atomic-level structure. These results were complemented by charge carrier lifetime measurements which have shown that one of the organic molecules leads to a substantial increase in charge carrier lifetimes and as such is a promising passivation agent for halide perovskites in optoelectronic devices. The study has also demonstrated that solid-state NMR is capable of determining the structure of dilute surface species on perovskite surfaces, which establishes it as a unique complementary tool to diffraction techniques in the field of metal halide perovskite materials research.
