Abstract
Methylammonium lead tribromide (MAPbBr3) perovskite single crystals demonstrate to be excellent direct X-ray and gamma-ray detectors with outstanding sensitivity and low limit of detection. Despite this, thorough studies on the photophysical effects of exposure to high doses of ionizing radiation on this material are still lacking. In this work, we present our findings regarding the effects of controlled X-ray irradiation on the optoelectronic properties of MAPbBr3 single crystals. Irradiation is carried out in air with an imaging X-ray tube, simulating real-life application in a medical facility. By means of surface photovoltage spectroscopy, we find that X-ray exposure quenches free excitons in the material and introduces new bound excitonic species. Despite this drastic effect, the crystals recover after 1 week of storage in dark and low humidity conditions. By means of X-ray photoelectron spectroscopy, we find that the origin of the new bound excitonic species is the formation of bromine vacancies, leading to local changes in the dielectric response of the material. The recovery effect is attributed to vacancy filling by atmospheric oxygen and water.
Highlights
Since the publication of two seminal papers in 2012,1,2 the research on organometal halide perovskites (OHPs) for optoelectronic applications has been growing at a rapid pace
These materials show remarkable properties, such as tunable bandgap, long charge carrier diffusion length, defect tolerance, high absorption coefficient, and low-cost fabrication.[3,4]. These are the main reasons of interest for their exploitation in research domains ranging from solar cells and photovoltaic to radiation detection for security and medical applications.[5]
Gamma-ray detectors are instead exploited in fields such as radiological security and nuclear defense.[6−8] In particular, methylammonium lead tribromide perovskite (MAPbBr3) single crystals demonstrated very promising results for high-sensitivity X-ray and gamma-ray detectors, combining high stopping power, due to the presence of Pb, with low trap density, high charge collection efficiency, small dark current density, and high bulk resistivity.[9,10]
Summary
Since the publication of two seminal papers in 2012,1,2 the research on organometal halide perovskites (OHPs) for optoelectronic applications has been growing at a rapid pace These materials show remarkable properties, such as tunable bandgap, long charge carrier diffusion length, defect tolerance, high absorption coefficient, and low-cost fabrication.[3,4] These are the main reasons of interest for their exploitation in research domains ranging from solar cells and photovoltaic to radiation detection for security and medical applications.[5] Their chemical composition is generally identified as ABX3 where A is a monovalent organic cation (e.g., methylammonium, CH3NH3+, or formamidinium, HC(NH2)2+), B is a divalent metal cation (e.g., Pb2+ or Sn2+), and X is a halogen anion (e.g., I−, Br−, and Cl−). Gamma-ray detectors are instead exploited in fields such as radiological security and nuclear defense.[6−8] In particular, methylammonium lead tribromide perovskite (MAPbBr3) single crystals demonstrated very promising results for high-sensitivity X-ray and gamma-ray detectors, combining high stopping power, due to the presence of Pb, with low trap density, high charge collection efficiency, small dark current density, and high bulk resistivity.[9,10] MAPbBr3 single crystals, with their easy and low-cost fabrication process, could be a valid alternative to the current state-of-the art materials for room-temperature solidstate direct detection, such as silicon or cadmium zinc telluride, which are still affected by severe limitations such as high energy consumption and expensive growth facilities for their processing
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