Fig. 1: Structural analysis before and after unlocking the surface octahedral tilt.

a, b Schematic illustration of exfoliation step liberating the steric constrain imposed by bilayer of BA cations in bulk and unlocking surface octahedral tilt in exfoliated RPP by taking n = 4 as an example. Two layers of BA chains are interlocked in the bulk (a) and leaving only one layer of BA on top upon splicing (b). c Simulation models of exfoliated monolayer surface and bulk interface. The tilt degree of BA molecule with respect to c axis is defined as Ω angle. d Schematic representation of the out-of-plane tilts and in-plane tilt of octahedral halide frame. θ and γ are used to measure the degree of octahedral tilt in out-of-plane and in-plane, respectively.