Real-Time Structural\nDynamics at the 3D/2D Perovskite\nInterface in CsPbBr<sub>3</sub>/PEA<sub>2</sub>PbBr<sub>4</sub> Nano-heterostructures

Three-dimensional\n(3D) and two-dimensional (2D) perovskite hybrid\nsystems, known for their exceptional optoelectronic properties and\nstability, are revolutionizing optoelectronic materials research.\nHowever, fundamental physics of the 3D/2D interfaces and their dynamics\nremain poorly understood. We use fluorescence microspectroscopy to\nstudy the photoluminescence (PL) properties of 3D/2D nano-heterostructures\nof CsPbBr<sub>3</sub>/PEA<sub>2</sub>PbBr<sub>4</sub> formed by postgrowth\nself-assembly. The in situ PL spectra uncover the presence of new\nstructural phases, quasi-2D PEA<sub>2</sub>Cs<sub><i>n</i>–1</sub>Pb<sub>n</sub>Br<sub>3<i>n</i>+1</sub> layers\nof varying <i>n</i>, at the 3D/2D interface and demonstrate\ntheir reversible restructuring under light excitation at room temperature.\nThe restructuring is a result of layer-by-layer cation diffusion at\nthe epitaxial interfaces, manifested as reversible spectral shifts\noccurring on a time scale of seconds. Such dynamics ultimately leads\nto optimized distribution of the quasi-2D phases in the system for\nefficient energy transfer from the 2D to the 3D phases. Our findings\nprovide new insights into controlling energy flow in 3D/2D perovskites\nfor next-generation optoelectronic devices.