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Wednesday, September 23, 2020
12:00 pm
Presenter: Jacky Even, PhD, Professor, INSA Rennes Engineering School, FOTON CNRS Laboratory
Abstract:
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.
Bio:
Jacky EVEN is full Professor at INSA Rennes engineering school since 1999 and senior member of the Academic Institute of France (IUF) since 2018. He received a PhD in Physics from the University of Paris VI in 1992. He was assistant professor at the Physics Department of Rennes University (1992−1999), in the field of molecular materials, combining theoretical and experimental approaches including neutron and X-ray scattering, Raman/FTIR spectroscopy, calorimetry, among others. In 1999, he moved to INSA and FOTON laboratory to create a simulation team, addressing fundamental questions on III-V semiconductor buried nanostructures as well as performing optoelectronic device simulations. FOTON laboratory conducts mainly research in the area of photonics for information technology, photovoltaic and light-emitting (LED, laser, ...) devices, silicon photonics, and InP-based optical telecommunications. The activity on halide perovskites was developed in parallel and initially focused on layered structures for light emission (2010-2014, French ANR project). The strong reactivity to the 2012 craze for 3D perovskites in photovoltaics of the joint FOTON/ISCR group in Rennes, is related to this pre-existing knowledge in the field.
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