Hybrid organic-inorganic perovskites are currently in the spotlight due to their use as active materials in optoelectronic applications. The most commonly used hybrid perovskites, the 3D hybrid perovskites, have a relatively limited compositional space due to strict constraints on the size of the ions that can be used. As a result, the different organic cations that can be used to obtain these hybrids is limited to a handful of examples. On the other hand, the constraints on the size of the organic cations for 2D layered hybrid perovskites are much more limited. This allows for the incorporation of more complex organic molecules into these hybrids. In this way, the inorganic layer can act as a template for the ordering of the organic chromophores in the organic layer. Moreover, by changing the stoichiometry of precursor solutions, multi-layered hybrid perovskites can be obtained that have properties intermediate between those of the 2D and 3D hybrid perovskite end-members. In this way, for example, the band gap and emission peak position of the material can be tuned.

In this talk, an overview of some of the recent work by the HyMaD group of Hasselt University on low dimensional hybrid perovskites will be presented. A pyrene derivative was synthesized for incorporation into hybrid compounds [1]. By tuning the precursor stoichiometry and optimizing the thermal annealing conditions, 2D and lower dimensional hybrids with different optical properties could be obtained based on this derivative. Using in-situ analysis techniques, the conversion of different hybrids into each other as a function of temperature could be elucidated. Further extension of the complexity and functionality of the organic layer could be achieved by making use of weak interactions between organic molecules [2]. In this way, small molecules could be intercalated into the organic layer through the formation of donor-acceptor charge-transfer complexes, altering the properties of the hybrids. Organic donor-acceptor charge-transfer complexes are a class of materials that have been studied extensively over the past decades for their interesting properties including ambipolar charge transport, metallicity, photoconductivity, ferroelectricity and even (low temperature) superconductivity. The incorporation of charge-transfer complexes into hybrid compounds is therefore expected to provide us with a lot of potential towards the design of hybrids containing a functional organic layer.