Investigation On The Dynamics Of Carriers In Two-Dimensional Perovskite Materials

Two-dimensional(2D)organic-inorganic hybrid perovskites are promising materials for next-generation optoelectronic devices owning to their structural and functional versatility and enhanced ambient stability.Recent studies have started to focus on investigating the process of energy transfer and charge transfer in 2D organic-inorganic hybrid perovskites.By changing the types of organic groups and using transient absorption spectroscopy techniques,we studied the energy transfer process between the triplet state of organic molecules and lead halide inorganic octahedrons,and the effects of the preparation process on the materials.The specific content of this paper is summarized as follows:(1).Here we fabricate 2D lead halide perovskites containing naphthalene methylamine(NMA)cations to study naphthalene triplet sensitization by inorganic excitons.We find that triplet sensitization proceeds via a two-step mechanism initiated by sub-picosecond hole transfer from the inorganic layer to naphthalene.We also provide spectroscopic evidence for triplet excimer formation,i.e.,the association between triplet and ground state molecules.The intensity ratio between the excimer and triplet emissions can be tuned via the percentage of the NMA cations in the organic layer,offering a route to tunable white-light emitters using 2D hybrid perovskites.In addition,we found that the triplet state of naphthylmethylamine can directly absorb photons to form excited states in the 2D perovskite single crystal samples.(2).We prepared 2D organic-inorganic hybrid perovskite material using cyclohexylmethylamine and cyclohexyl-p-dimethylamine as organic groups to form a Ruddlesden-Popper phase and a Dion-Jacobson phase 2D perovskite film.By changing the preparation process,the distribution and proportion of different n-value components in the film are changed.Through transient absorption spectroscopy,we discovered the unique phenomenon that 2D perovskite materials prepared with cyclohexylmethylamine have small n-value components distributed on the upper surface of the film,large n-value components and three-dimensional components distributed on the lower surface.2D perovskite materials prepared using cyclohexyl-p-dimethylamine have a chaotically distributed structure.In the experiment of changing the preparation process,it was found that adding DMSO to the solvent and using chlorobenzene as the anti-solvent will effectively increase the large n value and 3D-like composition.Moreover,we find that using ammonium thiocyanate as additive will lead components of the film rearranged and extend the lifetime of carriers.