A photoelectric diode type X-ray detector based on CsCu2I3 wafer and a preparation method and application thereof

Abstract

The application relates to a photoelectric diode type X-ray detector based on a CsCu2I3 wafer and a preparation method and application thereof. The photoelectric diode type X-ray detector comprises a CsCu2I3 wafer and a device structure, the wafer comprises CsI and CuI powder raw materials, the CsCu2I3 wafer is prepared by grinding, mixing and hot pressing, and the molar ratio of CsI and CuI is 1:2. The device structure is cathode / hole transport layer / CsCu2I3 wafer / electron transport layer / anode. Therefore, the photoelectric diode type X-ray detection device based on the CsCu2I3 wafer is realized, so as to promote the application of the all-inorganic lead-free halide Cs-Cu-I system in X-ray direct detection. The functional layers in the application are environment-friendly, the preparation method is simple, the application has the potential of large-size and large-scale preparation, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of X-ray detection, and particularly relates to a photodiode type X-ray detector based on a CsCu2I3 wafer and a preparation method thereof and application thereof in medical imaging fields such as X-ray imaging systems. BACKGROUND

[0002] In recent years, how to design an X-ray imaging device with higher spatial resolution, lower X-ray usage dose and lower cost is the research goal of major X-ray imaging device companies and researchers in the field.

[0003] According to different photoelectric conversion processes, X-ray detectors can be divided into indirect and direct type detectors. The indirect type X-ray detector is cheaper, more stable and faster in response than the direct type X-ray detector, and has been widely used in ordinary flat panel X-ray detectors. However, to further improve the detection efficiency, the thickness of the absorption layer of the scintillator material needs to be greatly increased. Due to the scattering of the fluorescent signal, the fluorescent signal enhancement effect obtained by further increasing the thickness is very limited, and the spatial resolution of the imaging is sharply sacrificed. In addition, due to the afterglow characteristics of the scintillator, the response time is relatively slow, so a long exposure time is needed to obtain a clear X-ray image. Compared with the indirect type X-ray detector, the direct type X-ray detector has better spatial resolution, larger X-ray absorption coefficient and higher carrier mobility. Only millimeter level is needed to completely absorb kilovoltage X-rays, and there is no delay or ghosting.

[0004] The halide lead perovskite, which is currently more studied, is the development trend of optoelectronic devices in recent years. The halide lead perovskite can directly convert captured photons into carriers, has excellent carrier transport characteristics and a heavy atom (lead, bromine) composition structure, and provides a good opportunity for realizing direct X-ray detection. In 2015, Ramasamy et al. first prepared a photodetector based on all-inorganic perovskite nanocrystals, and the on-off photocurrent ratio reached 10 5 , and the rise and fall times were 24 ms and 29 ms, respectively. The disadvantage is that the uniformity and density of the nanocrystal thin film are not good, and the responsivity is only 0.2 A / W (Chemical Communications, 2016, 52(10): 2067-2070.). In 2017, Professor Li Xinjian's team of Zhengzhou University invented a one-step spin coating method for preparing an all-inorganic CsPbBr3 perovskite thin film photodetector, which achieved a responsivity as high as 55 A / W, and the minimum detection limit was 0.9 x 10 13 Jones, on-off current ratio 10 5, external quantum efficiency 16700%, rise and decay time is 430 / 318 seconds (Journal of Materials Chemistry C, 2017, 5 (33): 8355-8360.).

[0005] However, researchers have been exploring their alternatives to avoid the toxicity and instability of lead-based metal halide detection materials. By replacing heavy lead atoms and organic components, many new variants can be developed, such as all-inorganic ternary lead-free halides Cs-Cu-I system, Cs-Bi-I system, Cs-Ag-Bi-I system, etc. with good photophysical properties. All these materials show the potential of non-lead metal halides in optoelectronic detection devices. However, so far, there has been no report on X-ray direct detectors of CsCu2I3 system. Due to the characteristics of one-dimensional crystal structure, homogeneous melting characteristics and high spectral matching with some photoelectric sensors, CsCu2I3 has been proved to have excellent X-ray detection performance. In order to further study the application of CsCu2I3 material in the field of X-ray detectors, CsCu2I3 single crystal with low defect density can be used to prepare X-ray detectors, but the growth of large CsCu2I3 single crystal is difficult, the single crystal growth is time-consuming and the crystal size cannot be regulated as needed. The preparation of CsCu2I3 X-ray detector by spin coating method cannot meet the condition of micron-level thickness of the detector. In contrast, the polycrystalline perovskite wafer prepared by simple static pressure method has the advantages of easy scaling size and thickness, excellent detection performance, simple preparation method and environmental friendliness, so it has important application prospect and commercialization potential in direct X-ray detection and imaging panel. SUMMARY

[0006] The purpose of the present application is to solve the above-mentioned problems existing in the prior art in the field of X-ray detection, and to propose a photodiode type X-ray detector based on CsCu2I3 wafer and its preparation method and application.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0008] The technical scheme of the present application is implemented in the following manner: a photodiode type X-ray detector based on CsCu2I3 wafer, including preparation of CsCu2I3 microcrystal, preparation of ion-doped CsCu2I3 wafer and preparation of photodiode type X-ray detector, the thin film layer is formed by solution spin coating-high temperature annealing and evaporation;

[0009] The device structure of the light emitting diode is Cu / hole transport layer / CsCu2I3 wafer / electron transport layer / Ag.

[0010] Step one, preparation of CsCu2I3 microcrystalline powder

[0011] The CsI and CuI powder raw materials are weighed, and the molar ratio of the CsI and CuI powder raw materials is 1:2. They are placed in a ball mill tank, the ball-to-material mass ratio is 1:1-1:5, the ball milling speed is 200-1000 rpm, and a large amount of uniformly mixed microcrystalline powder is obtained through mechanical grinding for 1-6 h;

[0012] Step two, ion doping

[0013] One or more of C60, graphite and black phosphorus are weighed and uniformly mixed with the CsCu2I3 microcrystalline powder, and the additive content is 1%-20% of the CsCu2I3 powder raw material;

[0014] Step three, preparation of CsCu2I3 wafer

[0015] The additive and the microcrystalline powder mixed raw material are weighed and added to the tablet press mold for hot pressing, the pressure can be selected to be 5-20 MPa, the temperature can be 80-200℃, and the pressure holding time can be 2-10 h to prepare the CsCu2I3 wafer;

[0016] In step three, by changing the size of the mold and the mass of the powder, a wafer with controllable size and thickness can be obtained.

[0017] Step four, preparation of the hole transport layer of the X-ray detector

[0018] The prepared CsCu2I3 wafer is placed in a spin coater, then spin-coated at 2000-4000 rpm for 30-100 s to obtain a hole transport layer Poly-TPD film, and the spin-coated Poly-TPD film is annealed at 80-150℃ for 10-30 min to prepare the hole transport layer;

[0019] Step five, preparation of the Cu electrode of the X-ray detector

[0020] The CsCu2I3 wafer coated with Poly-TPD obtained in step four is placed on an electrode mask and placed in a vacuum evaporation machine to prepare a Cu electrode.

[0021] Step six, preparation of the electron transport layer and Ag electrode of the X-ray detector

[0022] The CsCu2I3 wafer with the prepared Cu electrode and Poly-TPD layer is taken out of the evaporation box, turned over, placed on a mask, and placed in a vacuum evaporation machine to evaporate and prepare an electron transport layer and an Ag electrode, completing the preparation of the X-ray detector;

[0023] As a preferred embodiment, the ball-to-material ratio is 1:3, the ball milling speed is 400 rpm, and the ball milling time is 2 h.

[0024] As preferred, the adding amount of the solid additive accounts for 6% of the content of the CsCu2I3 powder raw material;

[0025] As preferred, the CsCu2I3 wafer with a size of 10 mm is prepared into a round sheet with a thickness of 300 um;

[0026] As preferred, the Cu electrode has a thickness of 150 nm, an area of a circle with a diameter of 8 mm, and an evaporation rate of

[0027] As preferred, the C60 electron transport layer has a thickness of 80 nm, and an evaporation rate of

[0028] As preferred, the Ag electrode has a thickness of 150 nm, an area of a circle with a diameter of 3 mm, and an evaporation rate of

[0029] Compared with the prior art, the present application has the following technical effects:

[0030] (1) The scheme proves that the CsCu2I3 wafer prepared by hot pressing can be used for a photodiode type X-ray detector, the introduction of the additive can effectively modify the defects of the CsCu2I3 wafer, adjust the energy level in the CsCu2I3 wafer, strengthen the X-ray absorption of the wafer, improve the response rate and reduce the hysteresis, and at the same time, enhance the stability and carrier transport performance. The prepared X-ray detector has good sensitivity and good application prospect;

[0031] (2) The scheme proves that the CsCu2I3 wafer prepared by hot pressing can be used for a photodiode type X-ray detector, the photodiode type X-ray detector has a simple preparation method, each functional layer is environmentally friendly and does not contain toxic heavy metals such as lead, and a wafer with regular morphology and high crystalline quality can be obtained, which is suitable for mass production; the method for preparing the photodiode type X-ray detector using the CsCu2I3 wafer is also applicable to other all-inorganic lead-free halides, so as to promote the development of the future direct type X-ray detector field. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 FIG. 1 is a structural schematic diagram of a photodiode type X-ray detector of the present application embodiment 1;

[0033] Figure 2 FIG. 2 is a flow chart of a method for preparing a CsCu2I3 wafer doped by hot pressing in the present application embodiment 1;

[0034] Figure 3 FIG. 3 is an I-V diagram of a comparison of light and dark current of an X-ray detection device prepared by the CsCu2I3 wafer prepared in the present application embodiment 1;

[0035] Figure 4 is the light response graph of the X-ray detection device prepared by the CsCu2I3 wafer prepared in Embodiment 1 of the present application under a 25V bias and a radiation dose of 3.82mGy / S;

[0036] Figure 5 is the light response graph of the X-ray detection device prepared by the CsCu2I3 wafer prepared in Embodiment 1 of the present application under a 25V bias and different doses of X-rays.

[0037] Figure 6 is the I-V graph of the light and dark current contrast of the X-ray detection device prepared by the CsCu2I3 wafer prepared in Embodiment 6 of the present application. DETAILED DESCRIPTION

[0038] The present application will be further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not used to limit the scope of the present application. In addition, it should be understood that after reading the content taught by the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope of the appended claims of the present application.

[0039] Embodiment 1 CsCu2I3 wafer-based photodiode type X-ray detector

[0040] comprising the following steps:

[0041] Step one, weigh 3.8971g of CsI and 5.7135g of CuI powder raw materials, place them in a ball mill jar, add 30g of agate balls, and ball mill at a speed of 400rpm for 2h to obtain a total amount of 9.61g of microcrystalline powder;

[0042] Step two, uniformly mix the powder in step one with 0.3g of C60 additive, and the microcrystalline powder changes from milky white to brown;

[0043] Step three, weigh 0.5g of the powder in step three, select a mold with a circular hole diameter size of 10mm, and use a press to press the wafer under the conditions of 170℃ and 10MPa for 4h;

[0044] Step four, prepare a hole transport layer for the wafer obtained in step three, weigh 12mg of Poly-TPD and dissolve it in 2mL of chlorobenzene solution, place the CsCu2I3 wafer in the spin coater in the glove box, then spin coat at 2000rpm for 45s to obtain a hole transport layer Poly-TPD film, and anneal the spin-coated Poly-TPD film at 120℃ for 20min to obtain a CsCu2I3 wafer covered with a Poly-TPD film.

[0045] Step five, the CsCu2I3 wafer coated with Poly-TPD obtained in step four is placed on the electrode mask plate and put into the vacuum evaporation machine to prepare a 150 nm Cu electrode.

[0046] Step six, the CsCu2I3 wafer with the prepared Cu electrode and Poly-TPD layer obtained in step five is taken out of the evaporation box, placed on the mask plate after turning over and put into the vacuum evaporation machine to evaporate and prepare a 50 nm C60 and a 150 nm Ag electrode, thus completing the preparation of the X-ray detector.

[0047] The device structure of the embodiment is shown in Figure 1 The step flow of the embodiment is shown in Figure 2 The thickness of the pressed wafer is about 350 μm. The I-V graph of the light and dark current contrast of the detector prepared in the example is shown in Figure 3 The current response graph of the detector prepared in the example under a 25 V bias and a radiation dose of 3.82 mGy / S is shown in Figure 4 The current response graph of the detector prepared in the example under different doses of X-ray irradiation under a 25 V bias is shown in Figure 5

[0048] Example 2: X-ray detector of a photodiode type based on a CsCu2I3 wafer

[0049] The following steps are included:

[0050] Step one, 3.8971 g of CsI and 5.7135 g of CuI powder raw materials are weighed and placed in a ball mill jar, 30 g of agate balls are added, and ball milling is performed at a speed of 400 rpm for 2 h to obtain a total amount of 9.61 g of microcrystalline powder;

[0051] Step two, the powder in step one is uniformly mixed with 0.3 g of C60 additive, and the microcrystalline powder changes from milky white to brown;

[0052] Step three, 0.5 g of the powder in step three is weighed, a mold with a circular hole diameter of 10 mm is selected, and the wafer is pressed by a press at a temperature of 180 °C and a pressure of 10 MPa for 4 h;

[0053] Step four, the CsCu2I3 wafer obtained in step three is placed on the electrode mask plate and put into the vacuum evaporation machine to prepare a 150 nm Cu electrode.

[0054] Step five, the CsCu2I3 wafer with the prepared Cu electrode obtained in step four is taken out of the evaporation box, placed on the mask plate after turning over and put into the vacuum evaporation machine to evaporate and prepare a 150 nm Ag electrode, thus completing the preparation of the X-ray detector.

[0055] ​The detector prepared in the present example has a good response to X-rays. Its dark current, current response under 25 V bias, and current response under different doses of X-ray irradiation under 25 V bias are similar to those of Example 1.

[0056] Example 3 X-ray detector of a photodiode type based on a CsCu2I3 wafer

[0057] comprising the following steps:

[0058] Step one, weigh 3.8971 g of CsI and 5.7135 g of CuI powder raw materials, place them in a ball mill jar, add 30 g of agate balls, and perform ball milling at a speed of 400 rpm for 2 h to obtain a total amount of 9.61 g of microcrystalline powder;

[0059] Step two, uniformly mix the powder in step one with 0.3 g of black phosphorus additive, and the microcrystalline powder changes from milky white to brown;

[0060] Step three, weigh 0.6 g of the powder in step three, select a mold with a circular hole diameter size of 10 mm, and use a press to press the wafer under the conditions of 160 ℃ and 10 MPa for 4 h;

[0061] Step four, prepare a hole transport layer for the wafer obtained in step three, weigh 12 mg of Poly-TPD and dissolve it in 2 mL of chlorobenzene solution, place the CsCu2I3 wafer in a spin coater in a glove box, then spin coat at 2000 rpm for 45 s to obtain a hole transport layer Poly-TPD film, and anneal the spin-coated Poly-TPD film at 120 ℃ for 20 min to obtain a CsCu2I3 wafer coated with Poly-TPD.

[0062] Step five, place the CsCu2I3 wafer coated with Poly-TPD obtained in step four on an electrode mask and in a vacuum evaporation machine to prepare a 150 nm Cu electrode.

[0063] Step six, take out the CsCu2I3 wafer with the prepared Cu electrode and Poly-TPD layer obtained in step five from the evaporation box, place it on the mask after turning over and place it in the vacuum evaporation machine, evaporate to prepare a 150 nm Ag electrode, and complete the preparation of the X-ray detector;

[0064] The detector prepared in the present example has a good response to X-rays. Its dark current, current response under 25 V bias, and current response under different doses of X-ray irradiation under 25 V bias are similar to those of Example 1.

[0065] Example 4 X-ray detector of a photodiode type based on a CsCu2I3 wafer

[0066] comprising the following steps:

[0067] Step one, weigh 3.8971 g of CsI and 5.7135 g of CuI powder raw materials, place them in a ball mill tank, add 30 g of agate balls, and mill at a speed of 400 rpm for 2 h to obtain a total of 9.61 g of microcrystalline powder;

[0068] Step two, uniformly mix the powder in step one with 0.3 g of C60 additive, and the microcrystalline powder changes from milky white to brown;

[0069] Step three, weigh 0.3 g of the powder in step three, select a mold with a model circular hole diameter size of 10 mm, and use a press to press the wafer under the conditions of 150°C and 12 MPa for 4 h;

[0070] Step four, prepare a hole transport layer for the wafer obtained in step three, weigh 12 mg of Poly-TPD and dissolve it in 2 mL of chlorobenzene solution, place the CsCu2I3 wafer in the spin coater in the glove box, then spin coat at 2000 rpm for 45 s to obtain a Poly-TPD thin film, and then anneal the Poly-TPD thin film at 120°C for 20 min to obtain a CsCu2I3 wafer coated with a Poly-TPD film.

[0071] Step five, place the CsCu2I3 wafer coated with a Poly-TPD film obtained in step four on an electrode mask and place it in a vacuum evaporation machine to prepare a 150 nm Cu electrode.

[0072] Step six, take out the CsCu2I3 wafer with a prepared Cu electrode and Poly-TPD layer obtained in step five from the evaporation box, place it on the mask after turning it over and place it in a vacuum evaporation machine, and evaporate to prepare a 150 nm Ag electrode to complete the preparation of the X-ray detector;

[0073] The detector prepared in this example has a good response to X-rays, and its dark current, current response at 25V bias, and current response under different dose X-ray irradiation at 25V bias are similar to those of Example 1.

[0074] Example 5 CsCu2I3 wafer-based photodiode type X-ray detector

[0075] comprising the following steps:

[0076] Step one, weigh 3.8971 g of CsI and 5.7135 g of CuI powder raw materials, place them in a ball mill tank, add 30 g of agate balls, and mill at a speed of 350 rpm for 3 h to obtain a total of 9.61 g of microcrystalline powder;

[0077] Step two, the powder in step one is mixed with 0.3g black phosphorus additive, the microcrystalline powder changes from milky white to brown;

[0078] Step three, 0.45g of the powder in step three is weighed, a mold with a circular hole diameter of 10mm is selected, and the wafer is pressed by a press at 165℃ and 15MPa for 10h;

[0079] Step four, a hole transport layer is prepared for the wafer obtained in step three, 12mg of Poly-TPD is dissolved in 2mL of chlorobenzene solution, the CsCu2I3 wafer is placed in the spin coater in the glove box, and then spin-coated at 2000rpm for 45s to obtain a hole transport layer Poly-TPD film, and the Poly-TPD film obtained by spin coating is annealed at 120℃ for 20min to obtain a CsCu2I3 wafer coated with Poly-TPD.

[0080] Step five, the CsCu2I3 wafer coated with Poly-TPD obtained in step four is placed on an electrode mask plate and placed in a vacuum evaporation machine to prepare a 150nm Cu electrode.

[0081] Step six, the CsCu2I3 wafer with prepared Cu electrode and Poly-TPD layer obtained in step five is taken out of the evaporation box, placed on the mask plate after turning over, and placed in the vacuum evaporation machine to evaporate and prepare a 150nm Ag electrode, completing the preparation of the X-ray detector;

[0082] The detector prepared in this example has good response to X-rays, and its dark current, current response at 25V bias, and current response under different dose X-ray irradiation at 25V bias are similar to those of Example 1.

[0083] Example 6: X-ray photodiode detector based on CsCu2I3 wafer

[0084] Comprising the following steps:

[0085] Step one, 3.8971g of CsI and 5.7135g of CuI powder raw materials are weighed and placed in a ball mill jar, 30g of agate balls are added, and ball milling is carried out at a speed of 280rpm for 4h to obtain a total amount of 9.61g of microcrystalline powder;

[0086] Step two, 0.45g of the powder in step one is weighed, a mold with a circular hole diameter of 10mm is selected, and the wafer is pressed by a press at 160℃ and 10MPa for 8h;

[0087] Step three, a hole transport layer was prepared on the wafer obtained in step two, 12 mg of Poly-TPD was dissolved in 2 mL of chlorobenzene solution, the CsCu2I3 wafer was placed in the spin coater in the glove box, then spin coated at 2000 rpm for 45 s to obtain a Poly-TPD thin film, and the Poly-TPD thin film obtained by spin coating was annealed at 120 °C for 20 min to obtain a CsCu2I3 wafer coated with a Poly-TPD thin film.

[0088] Step four, the CsCu2I3 wafer coated with a Poly-TPD thin film obtained in step three was placed on an electrode mask and placed in a vacuum evaporation machine to prepare a 150 nm Cu electrode.

[0089] Step five, the CsCu2I3 wafer with the prepared Cu electrode and Poly-TPD layer obtained in step four was taken out of the evaporation box, placed on the mask after turning over, and placed in a vacuum evaporation machine to prepare a 150 nm Ag electrode, and the preparation of the X-ray detector was completed;

[0090] The detector prepared in this example has poor performance, and the large defect density of the wafer leads to short circuit of the device, and the size of the light dark current is consistent as shown in Figure 6 ​

Claims

1. A method for producing a CsCu2I3 wafer-based photodiode type X-ray detector, characterized by, It comprises the following steps: Step one, weigh the CsI and CuI powder raw materials, put them in a ball mill tank, and obtain uniformly ground microcrystalline powder by mechanical grinding; Step two, weigh the solid additives and uniformly mix them with the microcrystalline powder; Step three, weigh the solid additives and the microcrystalline powder mixture, add them to the tablet press mold, and prepare CsCu2I3 crystal sheets after hot pressing; Step four, place the CsCu2I3 crystal sheet in a spin coater, spin coat to obtain a hole transport layer film, and anneal to prepare a hole transport layer; Step five, place the prepared hole transport layer CsCu2I3 crystal sheet on an electrode mask plate and place it in a vacuum evaporation machine, and evaporate to prepare a Cu electrode; Step six, take out the CsCu2I3 crystal sheet with the prepared Cu electrode and hole transport layer from the evaporation box, place it on the mask plate after turning it over, and place it in a vacuum evaporation machine to evaporate to prepare an electron transport layer and an electrode.

2. The production method according to claim 1, characterized by, In step one, the molar ratio of the CsI and CuI powder raw materials is 1:2, the ball-to-material ratio is 1:1-1:5, the ball milling speed is 200-1000 rpm, and the ball milling time is 1-6 h.

3. The preparation method according to claim 1, characterized in that, In step two, the solid additives are one or more of C60, graphite, and black phosphorus.

4. The preparation method according to claim 1, characterized in that, In step two, the amount of solid additives added is 1wt%-20wt% of the content of CsCu2I3 powder raw materials.

5. The method of claim 1, wherein, In step three, the pressure is 5-40 MPa, the temperature is 80-250℃, and the pressure holding time is 2-10 h.

6. The method of claim 1, wherein, In step four, the hole transport layer can be made of one or more of Poly-TPD, PEDOT:PSS, PTAA, and TAPC, or a multilayer structure composed of one or more of the above materials, and the thickness can be 1nm-100nm.

7. The preparation method according to claim 1, characterized in that, In step six, the electron transport layer can be made of one or more of C60, BCP, PCBM, V2O5, and WO3, or a multilayer structure composed of one or more of the above materials, and the thickness is 1nm-100nm.

8. The method of claim 1, wherein, In steps four and six, the electrode materials used are Cu, Ag, Au, Al, Cr, or carbon electrodes, and the thickness is 50-200nm.

9. A photodiode type X-ray detector, characterized by Obtained by the preparation method of any one of claims 1-8; The detector has a photodiode type device structure, and the device structure is cathode / hole transport layer / CsCu2I3 crystal sheet / electron transport layer / anode.

10. Use of the photodiode type X-ray detector of claim 9 in the field of X-ray detection.

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