Beatrice Fraboni1,2
Univ of Bologna1,INFN2
The demand for large area, low cost and flexible high-energy radiation detection systems for medical imaging and public security, has pushed the research to develop novel detectors combining high sensitivity and low-cost fabrication processes. Recently, lead-halide perovskites emerged as a very promising novel class of materials for X- and gamma-ray detection. Their success can be attributed to the excellent perovskite optoelectronic properties. The presence of heavy elements like Pb, Br or I inside the lead-halide perovskite structure ensures a high effective atomic number, resulting in a high absorption coefficient in the ionizing radiation energy range. For efficient detection, high absorption is not enough, the charge transport properties of the material also play a crucial role. Diffusion length of over 1μm and long lifetime of carriers have been attributed to perovskite even in polycrystalline form. Moreover, perovskites can be fabricated also in thin-film form at low temperature from solution opening the possibility to low-cost, large-area and flexible detectors. Flexible detectors are extremely appealing because they open completely new and unexplored functionalities and markets such as wearable electronics, smart walls, and nuclear waste pipe testing for industrial and citizens’ security, cultural heritage, and space applications.<br/><br/>We discuss how to improve the functionality as ionizing radiation detection of high-performing metal halide perovskites, targeting in both cases tens of microns perovskite active layer thickness and easily assembling onto flexible substrates: i) 3D perovskites, methylammonium lead triiodide (MAPbI3) and methylammonium lead tribromide (MAPbBr3), pure or in blends; ii) 2D/3D blends obtained by mixing 3D MAPbBr3 and 2D (based on larger organic ammonium cations) structure perovskites such as (PEA)2PbBr4; iii) 2D layered perovskites, (PEA)2PbBr4. Simple planar devices were fabricated on flexible substrates with the above detailed materials and their performances as ionizing radiation detectors have been tested under 40-150kVp X-ray beams and under MeV proton irradiation, also assessing their behaviour and stability for continuous operation at constant irradiation and bias.<br/>We report on a detailed study on the relation between composition and electronic transport at the nanoscale, a key factor in polycrystalline thin films, carried out by comparing simultaneously acquired XRF (X-Ray Fluorescence spectroscopy) and XBIC (X-Ray Beam Induced Current). Finally we will discuss preliminary results on deep electronic levels in 2D (PEA)2PbBr4 obtained by Photo-Induced Current Transient (PICTS) analyses, a powerful tool to understand the role of electrically active defects in optoelectronic grade materials