Functional interfacial additives as energy valves in particle-based gradient structures made of organic-inorganic perovskite phases

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Recently, so-called hybrid perovskites such as CH3NH3PbX3 (X = Hal) have moved into the focus of international research because of their extraordinary semiconductor properties. A special feature is, the band-gap can be adjusted precisely by substitution in the anion lattice. The band-gap also depends on the extension of perovskite layers. One then speaks of Ruddlesden-Popper phases (RPPs), in which an organic phase has become an integral part of the crystal, a phenomenon unlike to other semiconductors. This makes the design of the internal and external interfaces highly important for RPPs. RPPs are established and well-investigated for alkyl ammonium compounds as interfacial additives. However, because of the electrically insulating character one is interested to advance to functional interfacial additives (FIAs). This is, where we begin. The proposed research project comprises the organic synthesis of new FGAs and their utilization for the preparation of RPP microparticles. For the direct interaction with the perovskite surfaces the FGAs carry a cationic head-group, attached to a -conjugated side chain. In addition, we aim at implementing photo-switchable groups, and the corresponding FGAs should be established as energy valves. The systems should now be developed further in work package 1 based on our successful, preliminary work on single-source precursors for hybrid perovskites, as well as on thiophene- and azobenzene-based FGAs. In work package 2, the generation of the microparticles is done in combination with single-particle studies, which represent ideal models for understanding the ensemble situation. We will finally (work package 3) assemble microparticles possessing a different band-gap into multi-junction architectures with gradient character. This should lead to energy cascades in the resulting particle-based materials. The work packages are accompanied by extensive photophysical measurements for determining and quantification of the intra-particle and inter-particle energy transfer mechanisms.