Design of Active Defects in Semiconductors: 3D Electron Diffraction Revealed Novel Organometallic Lead Bromide Phases Containing Ferrocene as Redox Switches

Abstract

Once the optical, electronic, or photocatalytic properties of a semiconductor are set by adjusting composition, crystal phase, and morphology, one cannot change them anymore, respectively, on demand. Materials enabling postsynthetic and reversible switching of features such as absorption coefficient, bandgap, or charge carrier dynamics are highly desired. Hybrid perovskites facilitate exceptional possibilities for progress in the field of smart semiconductors because active organic molecules become an integral constituent of the crystalline structure. This paper reports the integration of ferrocene ligands into semiconducting 2D phases based on lead bromide. The complex crystal structures of the resulting, novel ferrovskite (≃ ferrocene perovskite) phases are determined by 3D electron diffraction. The ferrocene ligands exhibit strong structure‐directing effects on the 2D hybrid phases, which is why the formation of exotic types of face‐ and edge‐sharing lead bromide octahedra is observed. The bandgap of the materials ranges from 3.06 up to 3.51 eV, depending on the connectivity of the octahedra. By deploying the redox features of ferrocene, one can create defect states or even a defect band leading to control over the direction of exciton migration and energy transport in the semiconductor, enabling fluorescence via indirect to direct gap transition.

4,4′-(Anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) Lead Iodide C30H22N2Pb2I6: A Highly Luminescent, Chemically and Thermally Stable One-Dimensional Hybrid Iodoplumbate

“…28 Furthermore, for hybrid organic−inorganic compounds, the presence of heavy atoms may lead to powder diffraction patterns with a large contribution of the inorganic fraction, which in some cases can totally masks the organic fraction scattering contribution. 29 On the other hand, if the phase of interest appears as submicrometric grains, 3D electron diffraction (3D ED) has proved to be a reliable method for structure determination 30 and has found wide application in the case of hybrid structures. 31 To fully exploit the potentialities of both XRPD and 3D ED, the following protocol has been adopted: (i) any new synthesis is characterized by XRPD; (ii) if the XRPD pattern cannot be fully indexed with known structures, 3D ED data are collected from few single nanocrystals to identify the new phase present in the sample and to measure the related unit cell; and (iii) if an unknown phase is detected, its crystal structure is solved by 3D ED and refined by Rietveld refinement against XRPD.…”

“…However, structure solution from XRPD may fail in case of large unit cells, low symmetry space groups, strong peak broadening, and also for the presence of possible contaminants . Furthermore, for hybrid organic–inorganic compounds, the presence of heavy atoms may lead to powder diffraction patterns with a large contribution of the inorganic fraction, which in some cases can totally masks the organic fraction scattering contribution …”

“…To fully exploit the potentialities of both XRPD and 3D ED, the following protocol has been adopted: (i) any new synthesis is characterized by XRPD; (ii) if the XRPD pattern cannot be fully indexed with known structures, 3D ED data are collected from few single nanocrystals to identify the new phase present in the sample and to measure the related unit cell; and (iii) if an unknown phase is detected, its crystal structure is solved by 3D ED and refined by Rietveld refinement against XRPD. Such a combination of methods was already successfully used in several pure organic compounds − and hybrid organic–inorganic materials. ,− …”

“… 28 Furthermore, for hybrid organic–inorganic compounds, the presence of heavy atoms may lead to powder diffraction patterns with a large contribution of the inorganic fraction, which in some cases can totally masks the organic fraction scattering contribution. 29 …”

“…Such a combination of methods was already successfully used in several pure organic compounds 32 − 35 and hybrid organic–inorganic materials. 29 , 36 − 38 …”