Lead-free perovskites for X-ray detection

• Applicants: Professor Dr. Christoph J. Brabec, since 5/2021; Professor Dr. Wolfgang Heiss
• Subject Area: Synthesis and Properties of Functional Materials ; Experimental Condensed Matter Physics
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 404984854

Metal halide perovskite materials have revolutionized the field of solution processed semiconductor materials, due their outstanding opto-electronic properties, their simple processing and low costs. Solar cells based on these materials exhibit nowadays efficiencies close to those of the commonly used silicon devices. Current research is directed towards use of these materials in a large variety of opto-electronic devices, including light emitting diodes, lasers, or color converters. The applicants have started a novel direction for these materials, which is X-ray detection. Based on the first demonstration of X-ray detection with perovskites by the applicants in 2015, now there are vivid activities on X-ray detector developments in the scientific literature. While X-ray detectors are daily life products, which find many applications in fields starting from medical diagnostics, over safety inspections, to fundamental spectroscopic investigations of materials, the metal halide perovskites have to surpass some obstacles to be commercially applicable in X-ray detectors. The main objections to apply them are related to their chemical and structural lability and the potential high toxicity of the so far favored lead based perovskite materials. In this project we tackle these two major problems of metal-halide perovskite materials in general, and especially in the form of X-ray detectors.The detectors are based on a recently demonstrated technology to produce wafers with ~ mm thicknesses, which are optimized for X-ray absorption, by a two-step process – first microcrystalline perovskite powders will be synthesized by a simple precipitation method, and in the second step the powders are pressed into the wafer form. This technology was successfully demonstrated by us by making use of the common lead-perovskites and it will be developed further in this project with lead-free perovskites. In particular we will concentrate on perovskites based either on tin, or based on bismuth. Furthermore, various strategies will be tested to improve the chemical, structural and electronic stability of these materials and devices. The improvement of the stability will be obtained by several approaches, related to those reported in literature for solar cells, exhibiting in special cases operational lifetimes up to years. Basic investigations will concern the defect physics in the lead-free perovskites which are limiting the electronic performances, and the physical processes resulting in the high X-ray response, including photoconductive gain and multi-carrier excitation. Understanding these effects in more detail will speed up the development of the materials and devices, which at the end could result in commercially available and cost effective products, which find application in our daily life.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Privatdozent Dr. Gebhard Josef Matt, until 4/2021