The 3.8kg methylammonium lead tribromide perovskite crystal grown for high-energy gamma-ray detection, next to a Rubik's cube for scale. Credit: László Forró (EPFL).Perovskites are materials made up of organic compounds bound to a metal. Propelled into the forefront of materials' research because of their structure and properties, perovskites are earmarked for use in a wide range of applications, including solar cells, LED lights, lasers and photodetectors.
This last application, photo – or light – detection, is of particular interest to scientists in the School of Basic Sciences at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland who have developed a perovskite crystal that can detect gamma rays. Led by professors Lászlo Forró and Andreas Pautz, the scientists report their work in a paper in Advanced Science.
"This photovoltaic perovskite crystal, grown in this kilogram size, is a game changer," says Forró. "You can slice it into wafers, like silicon, for optoelectronic applications, and, in this paper, we demonstrate its utility in gamma-ray detection."
Gamma-rays are a kind of penetrating electromagnetic radiation that is produced from the radioactive decay of atomic nuclei, as occurs in nuclear or even supernovae explosions. Gamma-rays are at the shortest end of the electromagnetic spectrum, which means they have the highest frequency and the highest energy. Because of this, they can penetrate almost any material, and are used widely in homeland security, astronomy, industry, nuclear power plants, and environmental monitoring and research, as well as in medicine for detecting and monitoring tumors and osteoporosis.
But exactly because gamma rays can affect biological tissue, they need to be monitored, which requires simple, reliable and cheap gamma-ray detectors. The perovskite that the EPFL scientists developed is based on crystals of methylammonium lead tribromide (MAPbBr3) and seems to be an ideal candidate, meeting all these requirements.
Perovskites are first 'grown' as crystals, and the quality and clarity of the crystals determines the efficiency of the material when it is turned into thin films that can be used in devices like solar panels.
The perovskite crystals made by the EPFL scientists show high clarity with very low impurities. When the scientists tested the crystals, they found that gamma-rays generated photo-carriers with a high 'mobility-lifetime product', which is a measure of the quality of radiation detectors. In short, the perovskite crystal can efficiently detect gamma rays at room temperatures, through changes in its resistivity.
MAPbBr3 is part of the 'metal halide' family of perovskites, meaning that its crystals can be grown from abundant and low-cost raw materials. This synthesis can take place in solutions close to room temperature without needing expensive equipment.
Of course, this is not the first perovskite material developed for detecting gamma-rays. But the volume of most lab-grown metal halide perovskites is limited to about 1.2mL, which is hardly scalable to commercial levels. However, the team at EPFL also developed a unique method called 'oriented crystal-crystal intergrowth' that allowed them to make a whole liter of perovskite crystals, weighing 3.8kg in total.
"Personally, I enjoyed very much to work at the common frontiers of condensed matter physics, chemistry and reactor physics, and to see that this collaboration could lead to important application to our society," says Pavao Andricevic, the lead-author of the paper.
This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.