The French National Center for Scientific Research (Centre national de la recherche scientifique, CNRS) is the largest governmental research organization in France and the largest fundamental science agency in Europe, employing over 30,000 staff members and a budget of €3.3 billions. In 2017 CNRS was 1st in Nature article Count Ranking, is the 5th patent filler in France and is ranked the 8th most innovative public research institution worldwide by Thomson Reuters. Institut Néel (NEEL) is the CNRS flagship laboratory for fundamental research in condensed matter physics. It is enriched by interdisciplinary activities at the interfaces with chemistry, engineering and biology. Its 450 members explore a vast field of science: superconductivity, quantum fluids, new materials, crystallography, surface science, quantum nanoelectronics, nanomechanics, nonlinear and quantum optics, spintronics, magnetism… NEEL has exceptional expertise in advanced technology, closely integrated in its research projects (i.e. design of the last cooling stage of the HFI instrument in the Planck Space Telescope). In the last 10 years it filled 50 applications for invention patents (a number of which in co-deposition with industrial partners) and has 15 active “know-how” licences agreements with industrial partners. The research team “Optics and Materials” (OPTIMA) has over 25 years of expertise [1] in crystal growth in solution of inorganic, organic and hybrid organic-inorganic compounds. Just over a year ago, NEEL, in collaboration with CEA, has started studying the growth in solution of hybrid perovskites MAPbBr3 single crystals and more specifically, the correlation between growth conditions and formation of defects. Within the WP3 of PEROXIS, NEEL will use its expertise and the knowledge gained on the solution growth of hybrid perovskite single crystals. In Task 3.1 we will design and realize a reactor for the growth of thick (500-1500 µm) layers onto the active matrixes of test vehicles. In task 3.3, NEEL will identify the growth conditions (precursor concentrations, solvent nature temperature profile, hydrodynamic…) of thick layers of hybrid perovskite from the seeding surface leading to continuous front-plates of high crystallinity. These conditions will be implemented in task 3.4 with the optimized seeding layer from Task 3.2 provided by CEA.
October 26, 2020
Electronic operation of perovskite single crystal devices unraveled
Metal halide perovskite single crystals are being explored as functional materials for a variety of optoelectronic applications. Among others, solar cells, field‐effect transistors, and X‐ and γ‐ray detectors have shown improved performance and stability. However, a general uncertainty exists about the relevant mechanisms governing the electronic operation. This is caused by the presence of mobile ions and how these defect species alter the internal electrical field, interact with the contact materials, or modulate electronic properties. Here, a set of high‐quality thick methylammonium lead tribromide single crystals contacted with low‐reactivity chromium electrodes are analyzed by impedance spectroscopy. Through examination of the sample resistance evolution with bias and releasing time, it is revealed that an interplay exists between the perovskite electronic conductivity and the defect distribution within the crystal bulk. Ion diffusion after bias removing changes the local doping density then governing the electronic transport. These findings indicate that the coupling between ionic and electronic properties relies upon a dynamic doping effect caused by moving ions that act as mobile dopants. In addition to electronic features, the analysis extracts values for the ion diffusivity in the range of 10−8 cm2 s−1 in good agreement with other independent measurements.
