Detection of X-ray photons by solution-processed organic-inorganic perovskites

Abstract

The evolution of real-time medical diagnostic tools such as angiography and computer tomography from radiography based on photographic plates was enabled by the development of integrated solid-state X-ray photon detectors, based on conventional solid-state semiconductors. Recently, for optoelectronic devices operating in the visible and near infrared spectral regions, solution-processed organic and inorganic semiconductors have also attracted immense attention. Here we demonstrate a possibility to use such inexpensive semiconductors for sensitive detection of X-ray photons by direct photon-to-current conversion. In particular, methylammonium lead iodide perovskite (CH₃NH₃PbI₃) offers a compelling combination of fast photoresponse and a high absorption cross-section for X-rays, owing to the heavy Pb and I atoms. Solution processed photodiodes as well as photoconductors are presented, exhibiting high values of X-ray sensitivity (up to 25 µC mGy_air^-1 cm^-3) and responsivity (1.9×10⁴ carriers/photon), which are commensurate with those obtained by the current solid-state technology.

Figure 1. MAPbI₃ perovskite basic properties.

Absorption coefficient/length as a function of photon energy, covering the infrared to X-ray spectral region. (b) Time of flight transients for two bias directions, providing approximate electron and hole mobility. (c) Crystal structure of the perovskite: blue spheres – MA, black spheres – I, centers of the octahedrons – Pb. The inset shows a cross sectional micrograph of a spray coated MAPbI₃ layer.

Figure 2. Photovoltaic device.

(a) Schematic of the layer stacking of the MAPbI₃ based p-i-n photodiode. (b) JV characteristics of the device in darkness and under AM1.5 illumination. (c) Time-resolved short-circuit photocurrent under X-ray exposure. The data shown in (b) and (c) are for a 260 ± 60 nm thick MAPbI₃ layer. (d) Averaged short-circuit X-ray photo-current as function of the dose-rate. In the inset, the sensitivity normalized to the active volume is given for 260 ± 60 nm, 360 ± 80 nm and 600 ±120 nm thick MAPbI₃ layers, respectively.

Figure 3. Visible and X-ray photoconductive devices.

(a) Responsivity- and absorbance- spectra of a 2 μm thick MAPbI₃ perovskite film in the visible spectral region. The inset shows the photoconducting device geometry with lateral interdigitate electrodes. (b) Photoresponse to a pulsed laser (10 ps, λ=532nm), providing a characteristic time at the full width at half maximum (FWHM) of 350 ps. (c) I-V characteristics of a 60 μm thick MAPbI₃ perovskite photoconductor in darkness and under X-ray illumination. (d) Photograph of a leaf (Begonia obliqua L.) and the corresponding X-ray image, (e), obtained with the photoconductor shown in (c). (f-i) X-ray images revealing the contents of a Kinder Surprise egg and the chip and RF-antenna integrated within an electronic key-card.