Fig. 1. (Color online) (a) Spectrum region of X-ray to wavelength and photon energy. (b) Thomson scattering from an atom. An X-ray with a wave vector k scatters from an atom to the direction specified by k’. The scattering is assumed to be elastic. Reproduced with permission from Ref. [6]. (c) Compton scattering. A photon with energy and momentum scatters from an electron at rest with energy mc². The electron recoils with a momentum . Reproduced with permission from Ref. [6]. (d) Schematic diagram of photoelectric absorption process. An X-ray photon is absorbed and an electron ejected from the atom. The hole created in the inner shell (k) can be filled by Fluorescent X-ray emission. Electrons in an outer shell fill the hole, creating a photon. In this diagram the outer electron comes either from the L or M shell. In the former case the fluorescent radiation is referred to as the K_α line, and in the latter as K_β line.

Fig. 2. (Color online) (a) Working Principle of ion chamber. Reproduced with permission from Ref. [22]. (b) Semiconductor X-ray detectors’ two types of work modes: current mode and voltage mode. Reproduced with permission from Ref. [23]. (c) The linear absorption coefficients of different kinds of perovskite and conventional X-ray detectors. (d) Images of a piece of MAPbI₃ single crystal. Reproduced with permission from Ref. [52]. (e) Images of perovskite single crystals of MAPbBr₃ (left top), c-MAPbI₃ (right top), Cs₂AgBiBr₆ (left bottom) and (NH₃)₄Bi₂I₉ (right bottom). Reproduced with permission from Ref. [16–18, 53]. (f) Schematic representation of the ITC apparatus in which the crystallization vial is immersed within a heating bath. The solution is heated from room temperature and kept at an elevated temperature (80 °C for MAPbBr₃ and 110 °C for MAPbI₃) to initiate the crystallization. Reproduced with permission from Ref. [54]. (g) Schematic of layer stacking of the MAPbI₃-based PIN photodiode. Reproduced with permission from Ref. [20]. (h) Illustration of an all-solution-processed digital X-ray detector. Reproduced with permission from Ref. [21]. (i) Device stack of the MAPbI₃-wafer-based X-ray detector. Inset: Free-standing MAPbI₃ wafer (thickness: 1 mm). Reproduced with permission from Ref. [55]. (j) Preparation scheme for a thick CsPbBr₃ film using the four-step hot-pressing method. Reproduced with permission from Ref. [56].

Fig. 3. (Color online) (a) X-ray image of resolution test chart. Reproduced with permission from Ref. [42]. (b) An edge X-ray image used for calculation of MTF. Reproduced with permission from Ref. [76]. (c) A simplified schematic diagram of the cross section of a single pixel with a TFT. The charges generated by the absorption of X-rays drift towards their respective electrodes. The TFT is normally off and is turned on when the gate G₁ is addressed. Reproduced with permission from Ref. [11]. (d) Idealized MTF and MTF due to trapping. Reproduced with permission from Ref. [25].

Fig. 4. (Color online) (a) Left: Anrad’s mammographic FPXI (AXS-2430) is used in mammography markets. The field of view is 24 × 30 cm² and the FPXI have a pixel pitch of 85 μm. Right: an X-ray image of a hand from AXS-2430. Reproduced with permission from Ref. [11]. (b) Photograph (left) and corresponding X-ray image (right) of a leaf, obtained with the photoconductor in Ref. [20]. Reproduced with permission from Ref. [20]. (c) Left: image of spin-cast PI-MAPbI₃ on an a-Si:H TFT backplane. The inset in the left shows a single-pixel structure of TFT (scale bar 30 μm). Right: A hand X-ray image obtained from this MAPbI₃ FPXI. Reproduced with permission from Ref. [21]. (d) Left: The fabricated multi-pixel wafer-based Cs₂AgBiBr₆ polycrystalline detector. Right top: schematic illustration of the imaging process. Right bottom: X-ray image and optical image of ‘HUST’ symbol. Reproduced with permission from Ref. [18]. (e) Photograph of Si-integrated MAPbBr₃ single crystal with a 10 g weight attached to the MAPbBr₃ crystal. Reproduced with permission from Ref. [19]. (f) Left: schematic illustration of X-ray imaging with Si-integrated MAPbBr₃ single crystal detectors. Right: photo (top) and X-ray image (bottom) of an ‘N’ copper logo. Reproduced with permission from Ref. [19]. (g) Top: photo of the PIN array. Bottom: object photo (left) and X-ray image (right) for 100 keV energy. Reproduced with permission from Ref. [59].

Table 1. Performances and parameters of part of conventional and perovskite X-ray direct detectors. In “status” column, A is amorphous, S is single-crystal and P is polycrystalline.