Hybrid perovskite materials are one of the most promising candidates for optoelectronic applications, e.g., solar cells and LEDs, which can be produced at low cost compared to established materials. Although this field of research has seen a huge upsurge in the past decade, there is a major lack in understanding the underlying processes, such as shape-property relationships and the role of defects. Our aerosol-assisted synthesis pathway offers the possibility to obtain methylammonium lead bromide (MAPbBr3) microcrystals from a liquid single source precursor. The differently shaped particles are aligned on several substrates, without using a directing agent or other additives. The obtained particles show good stability under dry conditions. This allows us to characterize these materials and their pure surfaces at the single-crystal level using time- and spatially resolved methods, without any influences of size-dependent effects. By optimizing the precursor for the aerosol process, we were able to eliminate any purification steps and use the materials as processed. In addition, we performed theoretical simulations to deepen the understanding of the underlying processes in the formation of the different crystal facets and their specific properties. The model system presented provides insights into the shape-related properties of MAPbBr3 single crystals and their directed but ligand-free synthesis.

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.

The central promise of nanoparticle‐based materials is that cooperative properties may emerge, when individual quantum dots are positioned on a periodic lattice. Yet, there are only a few papers in the literature reporting such effects. Nevertheless, it is clear that the symmetry of the superlattice is decisive for the desired emergent phenomena. An interesting question is, how the symmetry of the initial monodisperse nanoparticles affects the structure of the colloidal crystal during self‐assembly processes. For instance, particles with a hexagonal cross‐section demonstrate self‐organization, which is very similar to spherical colloids. Likewise, one would also expect that trigonal nanoparticles behave similarly. Unfortunately, it is very hard to obtain monodisperse semiconductor colloids with a trigonal shape, because this requires a symmetry break during morphogenesis of the nanocrystal. While such a symmetry break is known in the literature for structures attached to a solid substrate, herein, colloidal synthesis of trigonal ZnO nanorods is successfully demonstrated, and the mechanism is elucidated via experimental and theoretical methods. 2D‐superlattices formed by such particles with trigonal cross‐section are compared to hexagonal analogues. It is found that there are distinct differences, which result in important differences in properties such as the formation of voids and also in optical properties.

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