Ferrovskites: Semiconductors with Adjustable Properties

• Applicants: Professorin Dr. Annika Bande; Professorin Dr. Carolin König; Professor Dr. Sebastian Polarz
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 575062610

Semiconductors composed of a lead halogenide structure with intercalated organic cations (= so called hybrid perovskites) are characterized by numerous, advantageous properties in optoelectronics. Other than in the case of almost any alternative semiconductor classes, one cannot only decorate the external surfaces with functional organic molecules, but one can install them as an integral part of the crystal lattice. Proposing those constituents exist in two states, respectively, they belong to the class of molecular switches; one can envision that the resulting hybrid materials represent adaptive semiconductors. Its properties shall depend on the degree of molecules in the switched state. The project focuses on 2-dimensional perovskites (Ruddlesden-Popper and Dion-Jacobson phases) comprising ammonium-terminated ferrocene derivatives in the interlayer regions. We will prepare tailor-made ferrocene compounds, synthesize the hybrid perovskites, and reveal their crystal structure by methods such as three-dimensional electron microdiffraction. Different types of quantum-well scenarios will be realized by adjusting the position of the ferrocene frontier orbitals with regard to the valence and conduction band of the perovskite phase. We expect that not only the energetic fit will influence the transport of charge carriers inside the material but also the distance of the ferrocenes to the perovskite sheet and their mutual alignment. Optoelectronic and the charge transport properties inside and between the layers will be investigated experimentally and clarified by advanced theoretical methods. The most exciting aspect of the described ferrovskite materials is that one can reversibly change the oxidation state of the present iron centers (FeII/III). The resulting ferrocenium units are expected to act as acceptor states for (adaptive) p-doping at low concentrations. However, at a higher density, charge transport inside the organometallic layer facilitates the formation of conducting paths and this, vice-versa, enables novel memristor properties.

• DFG Programme: Research Grants