Controlling Quantum-Well Width Distribution and Crystal Orientation in Two-Dimensional Tin Halide Perovskites via a Strong Interlayer Electrostatic Interaction.

Two-dimensional (2D) tin halide perovskites have recently emerged as very promising materials for eco-friendly lead-free photovoltaic devices. However, the fine control of the bulky organic cations orderly embedding into the perovskite structure with a narrow quantum-well width distribution and favorable orientation is rather complicated. In this study, we proposed to introduce the F-substituted phenylethlammonium (PEA) cation (i.e., 4-fluorophenethylammonium FPEA) in 2D tin halide perovskite, which may mitigate phase polydispersity and crystal orientation, thus potentially increasing attainable charge-carrier mobility. A strong interlayer electrostatic attraction between electron-deficient F atoms and its adjacent phenyl rings aligns the crystal structure, working together with the validated dipole interaction. Therefore, the fluorination of organic cation leads to orderly self-assembly of solvated intermediates and promotes vertical crystal orientation. Furthermore, the interlayer electrostatic interaction serves as a supramolecular anchor to stabilize the 2D tin halide perovskite structure. Our work uncovers the effect of interlayer molecular interaction on efficiency and stability, which contributes to the development of stable and efficient low-toxicity perovskite solar cells.