Efficient Interlayer Exciton Transport in Two-Dimensional Metal-Halide Perovskites

Two-dimensional (2D) metal-halide perovskites have emerged as a more robust alternative to their three-dimensional counterparts. Due to quantum and dielectric confinement effects, excitons dominate the energy transport characteristics in the thinnest members of the 2D perovskites family. Recently we have reported on the in-plane exciton diffusion using transient photoluminescence microscopy, where high diffusivities were found (0.2 cm²/s for PEA₂PbI₄). Using the same technique, here, we will show that this material exhibits remarkably efficient out-of-plane exciton transport (0.06 cm²/s) as well. This out-of-plane diffusivity translates to a diffusion length that exceeds 100 nm, making it relevant to device design. Moreover, we show that the energy transfer steps that underly the out-of-plane transport occur on a sub-ps timescale. Such ultrafast timescales are over two orders of magnitude faster than predictions using Förster theory. We will discuss the shortcomings of Förster theory for the 2D perovskites. Our results show that the excitonic energy transport is considerably less anisotropic than charge-carrier transport for 2D perovskites.

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