The presentation will focus on the interplay between structural, interfacial and optoelectronic properties of 2D multilayered halide perovskites, and their interfaces with 3D perovskites. At present, perovskite materials are mixed with each other in complex alloys and heterostructures, including 2D/3D compositions, combined with additives or protecting layers to improve their stability as well as assembled with carrier selective layers. After an introduction on 2D multilayered perovskites [1,2], this talk will present recent experimental results in collaboration with Rice University on a new versatile growth method to obtain 2D/3D perovskite bilayers, with tuning of 2D layer thickness and quantum confinement, and leading to excellent device stability [3]. Theoretical analysis nicely explains the difference of performances for ni- p or p-i-n devices [4]. [1] J.-C. Blancon et al, Semiconductor physics of organic-inorganic 2D halide perovskites, Nature Nano.15 969 (2020) [2] W. Li et al, Light-activated interlayer contraction in two-dimensional perovskites for high-efficiency solar cells, Nature Nano, 17, 45 (2022) [3] S. Sidhik et al, Deterministic fabrication of 3D/2D perovskite bilayer stacks for durable and efficient solar cells, Science 377, 1425 (2022) [4] B. Traore et al, A theoretical framework for microscopic surface and interface dipoles, work functions and valence band alignments in 2D and 3D halide perovskite heterostructures, ACS Energy Letters, 7, 349 (2022)