Low dimensional halide perovskites have been intensively explored in recent years due to their tunable band gaps and exciton binding energies and increased stability with respect to bulk halide perovskites. Using first-principles calculations, we show that dimensional reduction leads to modified excited state dynamics. In 2D hybrid organic–inorganic perovskites, we find that the formation of localized layer edge states is stabilized by internal electric fields created by polarized molecular alignment of organic cations in 2D perovskites. This occurs in 2D perovskites two layers or thicker, suggesting that control over these molecular components would facilitate exciton dissociation, leading to longer carrier lifetimes.

In superlattice assemblies of halide perovskite nanocrystals, we study how aging of the sample affects their spectroscopic properties. Gradual contraction of the superlattices and subsequent coalescence of the nanocrystals is shown to a lead to band gap renormalization and a shortening of the photoluminescence lifetime due to the energy transfer between nanocrystals. Overall, the aging of perovskite nanocrystal assemblies dramatically alters their emission properties and that should not be overlooked when studying collective optoelectronic phenomena.