METHOD FOR PRODUCING A RADIATION DETECTOR AND RADIATION DETECTOR

Abstract

The invention relates to a method for producing a radiation detector used to detect ionizing radiation including a first inorganic-organic halide Perovskite material (24) as a direct converter material and/or as a scintillator material in a detector layer and to a radiation detector comprising a detector layer (24) produced by means of the steps of the method. In order to provide an approach for producing a thick layer (e.g. above 10 ?.Math.?) of Perovskite material suitable for a radiation detector, it is proposed to grow the material selectively on a seeding layer (23), yielding in a thick polycrystalline layer. One suitable seeding layer (23) to grow lead Perovskite material is made of a bromide Perovskite material.

Claims

1. A method for producing a radiation detector for ionizing radiation, comprising: including a first inorganic-organic halide Perovskite material as a direct converter material and/or as a scintillator material in a detector layer; providing a seeding layer including a second inorganic-organic halide Perovskite material different from the first inorganic-organic halide Perovskite material; and forming the detector layer by growing the first inorganic-organic halide Perovskite material from a solution on the seeding layer.

2. The method according to claim 1, wherein the first and second inorganic-organic halide Perovskite materials comprise methyl ammonium metal halide and/or formamidinium metal halide.

3. The method according to claim 2, wherein the metal halide is a lead halide or a tin halide.

4. The method according to claim 1, wherein the first inorganic-organic halide Perovskite material comprises an iodide, and the second inorganic-organic halide Perovskite material comprises a bromide.

5. The method according to claim 1, wherein the solution is a mixture of a metal acetate/hydrogen iodide solution and a methylamine/hydrogen iodide solution.

6. The method according to claim 1, further comprising including a light emission material in the detector layer.

7. The method according to claim 6, wherein the light emission material includes luminescent quantum dots and/or phosphor particles.

8. The method according to claim 1, wherein the detector layer has a thickness of 10 ?m or more.

9. The method according to claim 1, further comprising providing a planarizing charge blocking layer on the detector layer.

10. The method according to claim 1, further comprising providing a structure of the seeding layer by localized deposition of the second inorganic-organic halide Perovskite material by inkjet, slot-die and/or screen printing.

11. The method according to claim 10, further comprising roughening a surface of a substrate on which the seeding layer is to be deposited.

12. A radiation detector for detecting ionizing radiation, comprising a detector layer and a seeding layer including a second inorganic-organic halide Perovskite material different from a first inorganic-organic halide Perovskite material, and the detector layer is formed by growing the first inorganic-organic halide Perovskite material from a solution of the seeding layer.

13. The radiation detector according to claim 12, comprising: a substrate, a structured plurality of bottom electrodes, the detector layer and a top electrode, wherein on each of the bottom electrodes a portion of the seeding layer is provided, or a substrate, a structured plurality of electrodes and the detector layer, wherein on each of the electrodes a portion of the seeding layer is provided and the electrodes include anodes and cathodes.

14. The radiation detector according to claim 13, comprising a charge blocking layer between the bottom electrodes and the detector layer, between the anodes and cathodes and the detector layer and/or a charge blocking layer and/or a conducting layer between the detector layer and the top electrode.

15. The radiation detector according to claim 13, further comprising a plurality of photo detectors configured to sandwich the bottom electrodes or the anodes and cathodes with the detector material, wherein the photo detectors are configured to detect a light emission of the detector material caused by an incident radiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In the following drawings:

[0052] FIG. 1 shows a schematic partial diagram of a radiation detector in accordance with an embodiment of the invention,

[0053] FIG. 2 shows a schematic partial diagram of a radiation detector in accordance with another embodiment of the invention,

[0054] FIG. 3 shows a further schematic partial diagram illustrating a layer structure in accordance with a further embodiment of the invention, and

[0055] FIG. 4 shows a flow diagram illustrating step of the method according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0056] FIG. 1 shows a schematic diagram of a radiation detector in accordance with an embodiment of the invention.

[0057] The basic structure includes a substrate 1 with structured bottom electrodes 2 on it. On top of the bottom electrode 2 an electron blocking layer (not shown) might be present. On top of the arrangement of substrate 1 and bottom electrodes 2 a halide Perovskite layer 4 is placed, with a seeding layer 3 provided on the bottom electrodes 2. This layer 4 might be thin (100 nm-100 ?m) for mammography, thicker (100-2000 ?m) for general X-ray and CT and quite thick (1-20 mm) for SPECT or PET.

[0058] On top of layer 4 a hole blocking layer might (not shown) be present. Also might there be a conducting layer (not shown) to reduce/prevent shorts of a top electrode 5 towards the substrate 1.

[0059] On top of the above mentioned layers, the top electrode 5 is deposited. The top electrode 5 might contain an electron injection layer (not shown).

[0060] Preferably the total structure is a diode. This can be achieved by having different work functions between the bottom and the top electrodes 2, 5.

[0061] The voltage applied on the total stack of layers should preferably put the diode in blocking mode to reduce dark current and increase the sensitivity and timing performance.

[0062] An advantage of the inorganic-organic halide Perovskite materials is that the energy gap and the mobility can be easily adjusted by varying the metals, halogen atoms and/or the organic groups as well as layer morphologies and multilayer device structures.

[0063] The stack of layers shown in FIG. 1 may be part of an imaging detector which consists of multiple pixels. The formation of the pixels can be done only at one or multiple parts of the layer stack, wherein, for example, the X-ray absorption layer (Perovskite material) can be segmented with gaps or isolating layers in between the pixels, and/or on a continuous absorption layer one or both electrodes can be segmented.

[0064] The arrow at the top of the figure symbolized the incident radiation, while furthermore the electric field between the electrodes 2, 5 is indicated schematically, together with generated charges (electrons and holes).

[0065] FIG. 2 shows a schematic partial diagram of a radiation detector in accordance with another embodiment of the invention.

[0066] According to the present invention, the Perovskite material(s) may be used also as light emitter to detect with good time resolution the signal with an extra photodetector and to measure the X-ray signal with good spatial resolution using the Perovskite material(s) as a direct conversion photoconductor. For time resolution the photodetector is preferably a sufficiently fast photodetector. It is also possible to use a silicon photo-multiplier (SiPM).

[0067] The arrangement of substrate 11, bottom electrode 12, seeding layer 13, Perovskite layer 14 and top electrode 15 basically corresponds to the corresponding arrangement shown in FIG. 1.

[0068] Additionally, elements 16 for detection of the light emission (illustrated by the smaller arrows from the Perovskite layer 14 downwards) are placed below the electrodes 12 for the direct conversion detection (i.e. electrodes 12 are used for direct conversion, while elements 16 are for scintillation light detection). In this case a (semi-)transparent electrode material is used for electrodes 12. The photo-detectors 16 placed on a base 17 are optimized to operate for the wavelength emitted by the conversion material in this mode. For, for example, CH.sub.3NH.sub.3PbI.sub.3 this would be in the infra-red part of the electromagnetic (EM) spectrum. The light absorption of the conversion material should preferably be mainly at other parts of the EM spectrum in such case to avoid self-absorption of the light emitted.

[0069] In the present embodiment, the photo-detectors 16 are larger than the electrodes 12 in order to measure the emitted light with high geometrical fill factor.

[0070] Deviation from the illustration of FIG. 3, the photo-detectors may be large detection elements that are common for a number of bottom electrodes. This allows getting the time stamp of the scintillation light, while the corresponding charge would be detected with high spatial resolution on electrodes 12.

[0071] FIG. 3 shows a further schematic partial diagram illustrating a layer structure in accordance with a further embodiment of the invention, which is quite similar to the structure illustrated in FIG. 1 and FIG. 2.

[0072] By not providing a top electrode as shown in FIGS. 1 to 3 and appropriately providing sub-sets of the electrodes 2, 12, 22 as anodes and cathodes, respectively, a laterally built-up diode may be provided.

[0073] A thick CH.sub.3NH.sub.3PbI.sub.3 Perovskite layer 24 can be grown by first providing a relatively thin CH.sub.3NH.sub.3PbBr.sub.3 layer 23 in a structured manner (e.g. by inkjet) on a glass substrate 21 on which bottom electrodes 22 are provided (it is also possible to provide the seeding layer 23 is an unstructured manner, e.g. by spin-coating). Then the sample is put in a Pb(II)acetate/HI solution (15 g Pb(II)acetate/60 ml concentrated (57% by weight) aqueous HI) at 100? C. while adding a CH.sub.3NH.sub.2/HI solution (100? C.; 3.58 g CH.sub.3NH.sub.2 (40% in water)/12 ml HI). Large crystals are formed which selectively grow on the CH.sub.3NH.sub.3PbBr.sub.3 layer and not on the glass surface. In conventional situations, usually a slow crystal growth is applied standardly. In the context of the present invention, however, it was found that after a few minutes the thick crystals on the substrate are already formed.

[0074] Between the CH.sub.3NH.sub.3PbI.sub.3 layer 24 and the top electrode 25, a planarizing electron injection layer 26 (an example of a charge blocking layer) is provided.

[0075] Also the structures of FIG. 1 and FIG. 2 include the seeding layers 3 and 13, respectively, in correspondence to the CH.sub.3NH.sub.3PbBr.sub.3 layer 23.

[0076] FIG. 4 shows a flow diagram illustrating step of the method according to an embodiment of the invention.

[0077] After providing a substrate with bottom electrodes, desired portions thereof are roughened in roughening step 100 in order to enhance the contact stability between the deposited CH.sub.3NH.sub.3PbBr.sub.3 layer.

[0078] The in following seeding step 101, a CH.sub.3NH.sub.3PbBr.sub.3 layer is provided as a seeding layer.

[0079] After the seeding step 101, a layer growth step 102 is provided, in which the detector layer including CH.sub.3NH.sub.3PbI.sub.3 as inorganic-organic halide Perovskite material is provided, as discussed above. The layer growth step includes in this case an inclusion sub-step 103 of including a light emission material in the detector layer.

[0080] The provision of the detector layer in the layer growth step 102 is followed by a planarizing step 104, in which a planarizing layer in form of a charge blocking layer is provided.

[0081] This is followed by a completion step 105 in which further steps for completing the radiation detector are included. Additional discussion thereof is not needed, as the skilled person is sufficiently familiar with such further steps.

[0082] In addition to the steps shown in FIG. 4, the radiation detector may be provided with photo detectors (see FIG. 2), in order to provide a combined direct and indirect detection.

[0083] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0084] Additional (light) emitter materials may be incorporated and distributed in the active Perovskite layer(s). The Perovskite material may absorb X-ray and may transfer part of the absorbed energy to the additional emitter material. This emitter material might then emit the light preferably having a wavelength outside of the absorption band of the Perovskite material(s). This light can then be detected by a photo-detector.

[0085] It is possible and contemplated to stack two or more different Perovskite materials on top of each other with (an) electrode(s) between the materials. Then two or more different X-ray energies might be detected by the difference in response/sensitivity of the materials. This is of particular interest for applications in spectral CT.

[0086] The present invention includes the use of methyl ammonium lead halide Perovskites (CH.sub.3NH.sub.3Pb(I/Br/Cl).sub.3) as a semiconductor photo-detector material.

[0087] Lead-free detectors may be provided by replacing the Pb components by Sn in the Perovskites materials (CH.sub.3NH.sub.3Sn(I/Br/Cl).sub.3). The resulting detector has less environmental issues than one including Pb.

[0088] It is possible to structure the growth of the Perovskite material(s) by locally depositing by e.g. inkjet of the thin layer of, for example, CH.sub.3NH.sub.3PbBr.sub.3 on an oxidic/metallic conductor on which, for example, CH.sub.3NH.sub.3PbI.sub.3 would not grow by itself to a satisfactory amount. To enhance the sticking of the CH.sub.3NH.sub.3PbBr.sub.3 layer, a surface roughening might be provided. In addition or in alternative to this, another approach may include selectively depositing a non-sticking layer like SiO.sub.2 to achieve or enhance selective growth of, for example, the CH.sub.3NH.sub.3PbI.sub.3.

[0089] The present invention may be implemented also by using organic substrates. If the organic layers are not conductive, this crystal growth is then more suited for scintillators.

[0090] The present invention may particularly be employed to benefit in the areas of mammography, CT, PET scanners (including multimodal), nuclear medicine (planar cameras, SPECT), safety (e.g. nuclear plants and environment), security, particle and high energy physics, non-destructive inspection, astrophysics and hunting for (mineral) resources, even though this list in not exhaustive.

[0091] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0092] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality.

[0093] A single processor, device or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0094] Any reference signs in the claims should not be construed as limiting the scope.