Introduction

Recently, metal halide perovskites have been hailed by many as the “wonder” semiconductor for photovoltaics, because of their outstanding optoelectronic properties and facile solution processability. Perovskite-based solar cells have reached a power conversion efficiency record above 25% in just more than a decade of research. Halide perovskite semiconductors constitute a wide family of materials with different structures, dimensionality, morphology, and corresponding optoelectronic properties. The goal of this chapter is to introduce the reader to the fascinating world of perovskite semiconductors, from their first adoption in optoelectronics to the latest discoveries. In particular, we focus on halide perovskites with low dimensionality and we connect the structural and electronic dimensionality to the material's stability and optoelectronic properties.