Optoelectronic properties of layered and 3D hybrid perovskites: recent results

In the past five years, solution-processed organometallic perovskite based solar cells have emerged as a promising thin-film photovoltaic technology with record conversion efficiencies as high as 23.3%. The presentation will review recent optical spectroscopy and diffraction results on 3D halide perovskites, as well as colloidal nanocrystals that also exhibit attractive light emission properties. Presently, the intended optoelectronic applications of this class of 3D materials are in the realm of semiconductors. But they can be described as unconventional semiconductors, because the spin-orbit coupling is giant and shows up in the conduction band. More, the band gap is direct with a critical wavevector located at one of the edges of the reference Brillouin zone, and among others, excitonic and Rashba-Dresselhaus effects, as well as electron-phonon coupling and lattice anharmonicity may play a crucial role. Related 2D multilayered phases, composed of perovskites multilayers sandwiched between two layers of large organic cations, have recently demonstrated improved solar cells photostability under standard illumination as well as humidity resistance, leading to conversion efficiencies in the 10-15% range.In this case, intrinsic quantum and dielectric carrier confinements are afforded by the organic inner barriers and a tunable perovskite layer thickness, which lead to stable Wannier excitons at room temperature.These excitations share some similarities with the ones observed in Van der Waals heterostructures. Solar cell and LED device operations are related to internal exciton dissociation through low energy states in multilayered perovskites, as shown from the investigations of both thin films and small exfoliated single crystals. Multilayered halide perovskites shall lead to extensive chemical engineering in the future.