Lattice Anchoring Stabilizes α-FAPbI3 Perovskite for High-Performance X-Ray Detectors

Abstract

Formamidinium lead iodide (FAPbI₃) perovskite exhibits an impressive X-ray absorption coefficient and a large carrier mobility-lifetime product (µτ), making it as a highly promising candidate for X-ray detection application. However, the presence of larger FA⁺ cation induces to an expansion of the Pb-I octahedral framework, which unfortunately affects both the stability and charge carrier mobility of the corresponding devices. To address this challenge, we develop a novel low-dimensional (HtrzT)PbI₃ perovskite featuring a conjugated organic cation (1H-1,2,4-Triazole-3-thiol, HtrzT⁺) which matches well with the α-FAPbI₃ lattices in two-dimensional plane. Benefiting from the matched lattice between (HtrzT)PbI₃ and α-FAPbI₃, the anchored lattice enhances the Pb-I bond strength and effectively mitigates the inherent tensile strain of the α-FAPbI₃ crystal lattice. The X-ray detector based on (HtrzT)PbI₃(1.0)/FAPbI₃ device achieves a remarkable sensitivity up to 1.83 × 10⁵ μC Gy_air^-1 cm^-2, along with a low detection limit of 27.6 nGy_air s^-1, attributed to the release of residual stress, and the enhancement in carrier mobility-lifetime product. Furthermore, the detector exhibits outstanding stability under X-ray irradiation with tolerating doses equivalent to nearly 1.17 × 10⁶ chest imaging doses.

Keywords: Conjugated organic cation; Lattice anchoring; Phase stability; X-ray detectors; α-FAPbI3 perovskite.

Fig. 1

Crystal structure and lattice stress of (HtrzT)PbI₃/FAPbI₃ perovskite. a Diagram of a blading-coating and hot-pressing method for preparing perovskite thick films. b High-resolution transmission electron microscopy (TEM) image of (HtrzT)PbI₃/FAPbI₃. c Expansion of the pink dashed square in b corresponding to the lattice of FAPbI₃ and (HtrzT)PbI₃ perovskites, and d the corresponding interplanar spacing. e, f Illustration of lattice match between (HtrzT)PbI₃ and FAPbI₃. g Williamson–Hall plots of FAPbI₃ and (HtrzT)PbI₃/FAPbI₃ films. h Residual strain calculated in corresponding films. i Schematic diagram of lattice structure with/without strain state

Fig. 2

Coordination with HtrzT and phase transition in FA-based perovskite. a Electrostatic surface potential (ESP) image of HtrzT⁺. b Fourier transform infrared (FTIR) spectra and c Raman spectra of HtrzT and HtrzT-PbI₂ complex. d Diagrams of calculated binding free energy of FAPbI₃ and HtrzT⁺. XPS spectra of FAPbI₃ and (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite: e Pb and f I. g Differential scanning calorimetry (DSC) of FAPbI₃ and (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite. h DFT calculations of the formation energy for perovskite

Fig. 3

Absorption spectra, photoluminescence properties and transient absorption spectroscopic measurements. a Electronic absorption spectra, b PL spectra and c TRPL spectra of α-FAPbI₃ and (HtrzT)PbI₃(1.0)/FAPbI₃. d Schematic of the perovskite film for TA measurement. e, f TA spectra pseudocolor images and g, h TA spectra recorded at different delay time of FAPbI₃ and (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite films. i TA kinetic traces of corresponding perovskite films

Fig. 4

Carrier transport properties and Kelvin probe force microscopy. Dark current–voltage characteristics of the a FAPbI₃ and b (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite devices measured using the SCLC method. Time-of-flight measurement for the c FAPbI₃ and d (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite films under 405-nm laser. Photo-electronic measurement for the e α-FAPbI₃ and f (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite films of photoconductivity curves. The corresponding CPD images of g α-FAPbI₃ and h (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite films, at light off and light on regions. i CPD variety at light on/off, in the g, h regions

Fig. 5

Sensitivity, detection limit, stability and X-ray images for X-ray detectors. a Sensitivity of α-FAPbI₃ and (HtrzT)PbI₃/FAPbI₃ perovskite X-ray detectors. b Summary of the reported sensitivity to electric field intensity for X-ray detectors based on perovskite thick films by slurry blading. c Signal-to-noise ratio (SNR) of the detectors under low dose rates. The black dashed line represents a SNR of 3. d X-ray response stability test of the detectors based on the (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite film under − 2 V bias. e Large-area (HtrzT)PbI₃(1.0)/FAPbI₃ perovskite films of 10 cm × 10 cm. f Optical images and g, h X-ray images of characters performing “kung fu” under a X-ray tube voltage of 40kV. i Optical images of the “pig” with a copper coin behind it. X-ray images for “pig” and the copper coin under the X-ray tube voltage of j 25 kV and k 40 kV