Proton Transfer-Driven Modification of 3D Hybrid Perovskites to Form Oriented 2D Ruddlesden-Popper Phases

Herein, it is shown how a proton transfer process between the organic moiety in 3D methylammonium lead halide perovskite and the introduced aliphatic alkylamines provides the basis for a fabrication route toward hybrid 3D/2D perovskites and finally purely 2D Ruddlesden-Popper (RP) perovskite phases, predominantly the n = 1 phase. Five alkylamines with varying aliphatic chain lengths, such as butylamine, octylamine, dodecylamine, hexadecylamine, and octadecylamine as antisolvents in toluene, are used, which quickly protonate during the spin-coating deposition of thin perovskite films. Formation of hydrogen bonds between protonated alkylamines and lead halide slabs leads to mixed 3D/2D hybrid perovskites, where the ratio between the 3D and 2D phases can be adjusted by the concentration of the alkylamine containing antisolvents. Longer-chain aliphatic alkylamines (12 carbon atoms or greater) are most prone to slice 3D perovskite into layered perovskites with efficient green emission reaching up to 38% for their photoluminescence quantum yield in films. Above a certain concentration threshold, 3D perovskite can be completely modified into 2D RP perovskite phases with crystalline orientation parallel to the substrate. The introduced facile perovskite phase modification approach provides a convenient way toward different kinds of 2D RP metal halide perovskite films with attractive optical properties.