Superspace Architecture-Driven Energy Funneling in Layered Halide Perovskite Nanoplatelets

Layered hybrid perovskites offer a versatile platform for tailoring light-matter interactions, where alternative stacking of inorganic and organic layers creates complex couplings that disrupt the conventional crystal symmetry. Standard crystallographic models fall short of capturing the temperature-dependent stacking disorder and multiplet excitonic features in these systems. Here, we introduce a four-dimensional superspace framework, employing a phenomenological atomic modulation function, to describe the symmetry-breaking interactions in Ruddlesden-Popper L₂FA_{n -1}[Sn_0.022Pb_0.978]_nI_{3 n +1} (L: oleylamine, n ≥ 2) nanoplatelet superlattices. Temperature-tunable optical spectra reveal microcavity-like excitonic confinement, while ultrafast transient absorption spectroscopy uncovers sub-picosecond energy funneling through modulated quantum wells, facilitating a measurable and stable self-powered photoresponse across a broad spectral range at room temperature. A rare coexistence of negative thermal expansion and quenching arises from anisotropic octahedral distortions and electron-phonon interactions. These findings establish a new structure-function paradigm for designing thermally reconfigurable optoelectronic materials via engineered lattice modulation in hybrid perovskite superstructures.