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, 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. Theoretical analysis nicely explains the difference of performances for n-i-p or p-i-n devices. Additional recent theoretical methodology will be also presented that aim at answering questions such as: i) How do these engineering strategies impact the work function and absolute valence band energy of the MHP material? ii) Is it correlated with surface/interface dipoles? iii) Is it possible to extract semi-empirical formula for molecular passivation at surface or transitivity rules for interface dipoles?