In the past years, solution-processed organometallic perovskite based solar cells have emerged as a promising thin-film photovoltaic technology. Presently, the intended optoelectronic applications of this class of materials are in the realm of conventional semiconductors, but the halide perovskite semiconductors and their nanostructures present specific symmetry and electronic properties, including giant spin-orbit coupling effects. The presentation will review some recent experimental results on monocrystals of halide perovskites, colloidal nanocrystals or thin-films. The presentation will address the ongoing debate about the nature of the exciton ground state in perovskite nanocrystals attractive for light emitting devices. The softness of the halide perovskite semiconductors will be also highlighted, while the role of the electron-phonon coupling is not yet fully understood for this unusual class of semiconductors. Related 2D multilayered phases, composed of perovskites multilayers sandwiched between two layers of large organic cations, have recently demonstrated interesting solar cells photostability under standard illumination as well as humidity resistance. These multilayered phases also offer extensive possibilities for chemical engineering that will be illustrated. From the physical viewpoint, intrinsic quantum and dielectric carrier confinements are afforded by the organic inner barriers, which lead to stable Wannier excitons at room temperature. However, solar cells or LED device efficiencies are most probably related to exciton dissociation through edge or bulk defect states, as shown from the investigation of both thin films and small exfoliated single crystals of 2D Ruddlesden-Popper perovskites.
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