High sensitivity organic inorganic hybrid X-ray detectors with direct transduction and broadband response

Abstract

X-ray detectors are critical to healthcare diagnostics, cancer therapy and homeland security, with many potential uses limited by system cost and/or detector dimensions. Current X-ray detector sensitivities are limited by the bulk X-ray attenuation of the materials and consequently necessitate thick crystals (~1 mm-1 cm), resulting in rigid structures, high operational voltages and high cost. Here we present a disruptive, flexible, low cost, broadband, and high sensitivity direct X-ray transduction technology produced by embedding high atomic number bismuth oxide nanoparticles in an organic bulk heterojunction. These hybrid detectors demonstrate sensitivities of 1712 µC mGy^-1 cm^-3 for "soft" X-rays and ~30 and 58 µC mGy^-1 cm^-3 under 6 and 15 MV "hard" X-rays generated from a medical linear accelerator; strongly competing with the current solid state detectors, all achieved at low bias voltages (-10 V) and low power, enabling detector operation powered by coin cell batteries.

Fig. 1

X-ray detector overview. a Device schematic structure. b Performance comparison of current solid state X-ray detectors—(1), (2), (3), (4), (5), (7), (9), (11), (14), (15), (16), (17), (18), (19), (20), and (24) are direct detectors, (6), (8), (21)^, and (22) are inorganic detectors, and (10), (12), (13) and (23) are indirect detectors—with the technology developed in this work—(25) Bi₂O₃-40, (26) Bi₂O₃-80, (27) Bi₂O₃-40 and (28) Bi₂O₃-40. The operating voltage is given adjacent to each data point. The total attenuation coefficient values of carbon, selenium, methylammonium lead iodide (MAPbI₃) and Bi₂O₃ are given as shaded areas showing the previous limits to detector technology based only on bulk attenuation processes. c An X-ray imager based on the hybrid X-ray detector and 70 kV X-ray image of a bolt taken using the X-ray imager

Fig. 2

Detector performance under X-ray irradiation. a X-ray photocurrent densities for devices with different Bi₂O₃ loadings from Bi₂O₃-0 to Bi₂O₃-40 and b from Bi₂O₃-0 to Bi₂O₃-80. c Averaged sensitivity values for six devices and the error bars represent the range of the sensitivity values. d Comparison between number of X-ray photons absorbed by each device and the number of charges extracted. e The voltage dependence of the Bi₂O₃-40 device, f X-ray photocurrent response of the Bi₂O₃-40 detector under 0, −0.1 and −1 V biases. g Rise and decay time constants (the error bars represent the standard error shown with respect to the fitted curves) for detectors with increasing Bi₂O₃ loadings under −10 V bias. h X-ray photocurrent response before and after bending for a flexible Bi₂O₃-40 device. i A prototype X-ray detector integrated into a plaster and detector bend radius (0.3 cm)

Fig. 3

Hard X-ray irradiation. Response of a Bi₂O₃-40 device under linear accelerator (LINAC) generated 6 and 15 MV X-rays, the consecutive peaks represent the response to dose rates of 114, 227, 340 and 454 µGy s⁻¹

Fig. 4

X-ray detector structural characterisation. a Grazing incidence wide angle X-ray scattering images of Bi₂O₃-0, Bi₂O₃-20, Bi₂O₃-40, Bi₂O₃-60 and Bi₂O₃-80. Here, the position of the poly(3-hexylthiophene-2,5-diyl) (P3HT), [6,6]-Phenyl C₇₁ butyric acid methyl ester (PCBM) and bismuth oxide (Bi₂O₃) resultant peaks are indicated. b Scanning electron microscopy cross sections of Bi₂O₃-10, Bi₂O₃-20 and Bi₂O₃-40 overlaid with energy dispersive X-ray spectroscopy imaging of the Bi₂O₃ nanoparticles (false coloured for clarity)

Fig. 5

Charge transport analysis. a Time-of-flight transients of electrons for the Bi₂O₃-20 device for the applied reverse-bias voltages from 8 to 20 V. b The double logarithmic plot of the time of flight transient presented in a. Electric field dependency of c electron mobility (data have been fitted to show the mobility dependency under the electric field) and d hole mobility of devices from Bi₂O₃-0 to Bi₂O₃-80. Here, the error bars represent the range of three measurements carried out under each condition. e The collected electron charge for different devices based on a fit to the Hecht equation

Fig. 6

X ray scattering by nanoparticles. a Simulated differential cross sections for X-ray scattering from Bi₂O₃ NPs with a diameter (d) of 40 nm. b The schematic of the inelastic Mie-scattering mechanism and c the mass attenuation coefficient curve of Bi₂O₃. Here, E_i, E_a and E_s are the energy of the incident X-ray photon, energy absorbed and the energy of the scattered photon, respectively. d The comparison of simulated differential cross section and extracted 1D data of experimental grazing incidence small angle X-ray scattering (GI-SAXS) at 8 keV energy for films with d = 20, 40 and 100 nm NPs. (The dotted line in a represents the extracted data at 8 keV.) e X-ray photocurrent response of the polymer diodes containing Bi₂O₃ NP sizes of 20, 40 and 100 nm and f the current density value with the spread for six detectors