An Introduction to 2D Metal Halide Perovskites

2D metal halide perovskites are neither fully two-dimensional nor fully perovskites. Instead of the usual perovskite structure, in 2D MHPs large organic cation molecules push apart connected metal-halide octahedra into layers containing one or more thicknesses of octahedra (denoted by the “n number”). The metal halide inorganic framework is semiconducting with bandgaps of ~ 2–4 eV; the organic molecules possess much larger bandgaps. As such, 2D MHPs are often classified as multiple quantum well structures, with quantum confinement effects being amplified as the width of the well layer decreases to the lower limit of n = 1. This chapter presents a review of the semiconductor physics of 2D MHPs, followed by articles about controlling the orientation of the perovskite layers relative to the substrate, controlling the n-number, and more. Together, the papers serve as an introduction to the synthesis, structure, and characterization of 2D MHPs.