X-ray detection plays a key role in many fields such as medical imaging, safety inspection, non-destructive testing and scientific research. Compared with the conventional scintillator detector, the semiconductor direct detector has the advantages of high spatial resolution and simple system configuration. Halide perovskite is the preferred material for high sensitivity X-ray detection because of its high absorption coefficient, low trap density and large μτ product. The sensitivity of the three-dimensional (3D) lead halide X-ray detector has been increased to more than 20,000 µC Gyair-1 cm-2, which is several orders of magnitude higher than the commercially available alpha-SE detector (440 µC Gyair-1 cm-2). The detection limit of low-dimensional perovskite detectors has been reduced to below 5 nGyair s-1, which is more than three orders of magnitude lower than the alpha-SE X-ray detector. Although perovskite materials show potential, there are challenges in integrating all desirable properties into a single material. For example, 3D perovskites typically have high dark currents, high detection limits, and severe ion migration problems, while low-dimensional perovskites exhibit limited charge transport capabilities and therefore low X-ray sensitivity. From the perspective of semiconductor physics, high sensitivity requires a large μτ product, while low dark current and low detection limits require high resistivity (ρ = 1/neμ) - low carrier mobility (μ) and concentration (n). In this regard, there is a tradeoff limit between the μτ product and the resistivity of the material, with the upper limit defined by the ratio of carrier lifetime to concentration (τ/n). The aim of this study is to break the tradeoff between the μτ product and resistivity and achieve high sensitivity, low dark current and low detection limits by increasing the inherent carrier lifetime of the material.

By designing anti-perovskite materials with long carrier lifetimes, the performance tradeoff limitations of traditional X-ray detection materials are broken. The X-ray detector with high sensitivity, low dark current and ultra-low detection limit is realized. A new material design strategy is proposed to advance X-ray detection technology, contribute to the development of a wider range of anti-perovskite materials, and also provide new ideas for other optoelectronic applications:

(1) Studies have shown that carrier lifetime plays a key role in breaking the trade-off between the mu tau product and the resistivity. A novel organic-inorganic hybrid antiperovskite material was synthesized by constructing an indirect bandgap transition and a low symmetry hybrid orbital, which significantly increased the carrier lifetime to more than 3 ms.

(2) The synthetic material (2-HabCH)3Cl(PtI6) exhibits a large μτ product (10−3 cm2 V-1) and a high resistivity (1012 Ωcm).

(3) At -1V bias, the detector simultaneously achieves high sensitivity (1.0×104 μC Gyair-1 cm-2), low dark current (0.21 nA cm-2), and ultra-low detection limit (2.4 nGyair s-1), with excellent operational stability.

(4) Although the platinum (Pt) used is relatively expensive, this design strategy can be extended to include materials such as SnI62−, ZrI62-, HfI62-, ReI62-, OsI62- and IrI62-, providing new directions for customizing the electronic properties of perovskites.

A variety of test and characterization analysis techniques are used in this paper:

Time resolved photoluminescence (TRPL) test for measuring carrier lifetime and analyzing material carrier dynamics;

UV- visible (UV-VIS) absorption spectrum, used to analyze the light absorption characteristics of materials;

Density functional theory (DFT) calculations for understanding electronic structures and bandgaps;

□ Space charge Limited current (SCLC) method for measuring carrier mobility;

□ Time Flight (TOF) method for measuring carrier mobility;

□ Resistivity measurement for evaluating the dark current characteristics of materials;

□ Noise power spectrum density measurement, used to assess the noise level of the detector;

□ X-ray detector performance test, including sensitivity, dark current, detection limit and time response.

The carrier mobility of the synthetic material (2-Habch)3Cl(PtI6) is measured by the time-flight (TOF) method as 1.72 cm²V⁻¹s⁻¹, and the mobility lifetime product μτ is further obtained. The relationship between carrier mobility measured by TOF and other performance parameters of the detector, such as dark current, sensitivity and detection limit, is discussed. This information suggests that TOF technology plays an important role in evaluating and understanding the electronic properties of novel organic-inorganic hybrid antiperovskite materials and their applications in X-ray detectors.

FlyTOF is an important member of the HiTran transient integrated photoelectric characteristic measurement platform of Eastspectrum Technology. It is the source product of Eastspectrum Technology and the first automated and integrated time-of-flight mobility test commercial equipment in the industry.

The system uses Time-of-Flight (TOF) method to measure the mobility of semiconductor materials and related photoelectric properties, and is widely used in various semiconductor materials. Such as silicon-based semiconductor second generation semiconductor, third generation wide band gap semiconductor, organic semiconductor, perovskite semiconductor, quantum dot semiconductor, two-dimensional material semiconductor, metal-organic framework (MOF), covalent organic framework (COF) and so on. FlyTOF is based on the MagicBox mainframe of Dongpu Technology, equipped with convenient upper computer control and data measurement software, with highly integrated and automated features, which can help customers to make fast and accurate measurements.

□ Electron/hole mobility;

□ TOF transient photocurrent TPC;

□ Collected charge, charge collection efficiency, carrier mobility lifetime product;

□ Support variable temperature measurement, surface carrier mobility measurement, carrier 2D scanning imaging and other test parameters.

□ Organic semiconductor (NPB, MEH-PPV, PCBM)

□ Metal-Organic Frame (MOF)

□ Covalent Organic Frame (COF)

□ Perovskite materials (perovskite film, perovskite powder, perovskite single crystal)

□ Scintillator (cadmium zinc telluride, cadmium telluride)

□ Two-dimensional materials (graphene, two-dimensional perovskite film)

□ Elemental semiconductors (Si, Ge, etc.)

□ Compound Semiconductors (InGaAs)

□ Wide-band gap third generation semiconductor (SiC, GaN)

□ Quantum dot semiconductor (cadmium sulfide, cadmium telluride, perovskite)

□ Other semiconductor materials

▍Cited article

Anti-perovskites with long carrier lifetime for ultralow dose and stable X-ray detection

https://www.nature.com/articles/s41566-024-01482-3