Layer-resolved optical absorption in single-inorganic layer π-conjugated 2D hybrid perovskites from first principles*

Layered 2D hybrid organic-inorganic perovskite materials have provided a more chemically stable and optically tunable alternative to the traditional 3D hybrid perovskites. More recently, attention has shifted towards optical engineering of the organic layer by introducing π-conjugated molecules and chromophores to achieve excited-carrier transfer from the perovskite to the organic groups. In the limit of alternating single inorganic and organic layers, joint optical response could be maximized. In this study, we employ density functional theory and the Bethe-Salpeter equation to predict the ion-resolved optical response in ammonium-propyl-imidazole (API)-PbX₄ (X=I, Br, Cl) materials. We determine in which layers electrons and holes are excited as a function of photon energy. This analysis reveals a strong preference for electron and hole confinement within the perovskite layer at visible photon energies and organic-perovskite layer sharing of electrons and holes under near-UV photon energies. These results provide new insight into the limitations of simple π-conjugated organic layer participation for visible light absorption in layered hybrid perovskite systems.