Making and Breaking Chiral Metal Halide Perovskites

Two-dimensional (2D) hybrid organic-inorganic metal halide perovskite (MHP) semiconductors exhibit strong light absorption, broad wavelength tunability, compositional as well as structural diversity, strong quantum confinement, and excitonic states. Recently, it was found that it is possible to add another property, that is asymmetry, via intercalation of chiral organic molecules into these 2D layered structures. Introducing chirality into MHP semiconductors enables the control of light, charge, and spin without magnetic components. Generally, chiral structures are compositionally identical but geometrically distinct. Through incorporation of chiral molecules, the material loses the mirror plane and inversion symmetry, and can differently absorb right-/ left-circularly polarized light.

In this talk I will first discuss the synthesis of chiral 2D R-/S-MBA₂PbI₄ thin films which are based on the chiral organic cations R- and S-α-methylbenzylamine. In situ grazing incident wide angle X-ray scattering (GIWAXS) was used to follow the transformation from reagents to products and shows highly oriented thin films. Different synthesis processes and parameters such as solvents and antisolvents will be discussed. In the second part I will focus on the effect of humidity during synthesis and humidity-induced degradation on the structure and chiroptical properties. Incidence angle dependent GIWAXS measurements reveal that degradation initiates at the film/substrate interface instead of at the air/film surface. While there is no significant change in the texture of the films, we find PbI2, 1D MBAPbI₃ and hydrate phase formation upon humidity exposure.