CN111740018B - Cascade structure organic photoelectric detector and preparation method thereof - Google Patents

Abstract

A wideband, low-noise, ultra-fast response cascade structure organic photodetector and a preparation method thereof belong to the technical field of organic photoelectric devices. Consists of ITO conductive glass cathode, ZnO cathode buffer layer, PTB7‑Th:ITIC bottom active layer, MoO3/ _Ag /PEIE inner recombination region, PTB7‑Th:FOIC top active layer, MoO3 anode buffer layer and _Ag anode . Under the condition of full-color light irradiation, the internal recombination area forms a recombination center, which ensures the normal operation of the photodetection of the cascade structure; when the monochromatic light is irradiated, only the bottom or top subunits in the device exhibit the characteristics of p‑i‑n junctions. The other subunit is equivalent to a conductor for carrier transport, which reduces the trapping effect of the interface in the device and improves the response speed of the device; under dark state conditions, MoO ₃ and PEIE block the electrons from the top layer and the holes from the bottom layer respectively, effectively Improve the injection barrier/well of electrons and holes, so that the dark current is reduced.

Description

A cascade structure organic photodetector and preparation method thereof

technical field

The invention belongs to the technical field of organic photoelectric devices, in particular to a cascade structure organic photoelectric detector and a preparation method thereof.

Background technique

Solution-fabricated organic photodetectors (OPDs) have attracted much attention due to their low cost, light weight, ease of processing, and bendability. The ultra-fast response and high-sensitivity detection of organic photodetectors for visible and near-infrared light is a necessary condition for medical detection, artificial intelligence and other fields. Up to now, organic photodetectors have achieved wide-band and highly sensitive detection of ultraviolet-visible-near-infrared light, respectively, but the slow response speed (microsecond level) still limits the development of organic photodetectors. This is mainly due to the low carrier mobility of most organic materials, insufficient absorption range, large resistance-capacitance (RC) time constant, and interfacial trapping effect of the device. The absorbed organic material is used as the active layer. By optimizing the thickness of the active layer and replacing the appropriate photodetector structure, the RC time constant of the device is reduced, and the interface trapping effect of the device is reduced through the structural design to effectively improve the response speed of the photodetector and achieve high sensitivity. , Wide-range ultrafast organic photodetectors.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a wide-band, low-noise, ultra-fast response cascading structure organic photodetector with a simple process and a preparation method thereof.

From bottom to top, the cascade organic photodetector consists of ITO conductive glass cathode, ZnO cathode buffer layer, PTB7-Th:ITIC bottom active layer, MoO ₃ /Ag/PEIE inner recombination region, PTB7-Th:FOIC top Active layer, MoO3 anode buffer layer, _Ag anode composition. The selected donor material PTB7-Th(poly[4,8-bis(5(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiopheneco-3 -fluorothieno[3,4-b]thiophene-2-carboxylate]) and acceptor material ITIC(3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5 ,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene) Absorbing visible light, the non-fullerene material FOIC mainly absorbs near-infrared light, and the acceptor material with complementary absorption spectrum provides the basic conditions for realizing broadband detectors. In the MoO ₃ /Ag/PEIE internal recombination region, MoO ₃ acts as an electron blocking layer, and PEIE acts as a hole blocking layer. Under the condition of full-color light irradiation, the internal recombination region forms a recombination center, and there are equal amounts of electrons on both sides of the internal recombination region. and holes recombine in the internal recombination region to ensure the normal operation of the organic photodetector. Under dark _- state conditions, MoO3 and PEIE in the inner recombination region can block electrons from the top active layer and holes from the bottom active layer, respectively, effectively improving the injection barrier/well of electrons and holes, enabling dark current. reduction, resulting in lower noise current, which can effectively improve the sensitivity of the device.

The cascaded organic photodetector is equivalent to a circuit consisting of two pin junctions in series, the visible light part and the near-infrared light part are equivalent to two pin junctions, each junction includes a junction resistance and a junction capacitance; the parasitic capacitance of the device It is represented by C _p ; the equivalent cascade resistance of the device is represented by R _s , which includes the bulk resistance of organic materials, electrode resistance and contact resistance between layers. When the monochromatic light is incident from the ITO side, one of the visible light part and the near-infrared light part effectively absorbs the monochromatic light in this band to generate carriers, showing the characteristics of a pin junction. The other of the two cannot generate carriers because there is no corresponding light absorption. It is equivalent to a plate capacitor in the circuit. The carriers do not need to pass through the interface to be collected by the corresponding electrodes, which greatly reduces the interface trapping effect. Enables ultra-fast response of cascaded devices.

The method for preparing a cascade-structured organic photodetector with broadband, low noise and ultra-fast response according to the present invention, the steps are as follows:

1) The ITO conductive glass is ultrasonically cleaned with isopropanol, acetone, ethanol, and deionized water for 15-30 minutes in turn, then dried with nitrogen for 20-40 minutes, and then treated with ultraviolet ozone for 10-15 minutes, as cathode 1;

2) Dissolve 15-30 g of zinc acetate in 145-290 μL of dimethoxyethanol solution, add 5-10 μL of ethanolamine to prepare a ZnO solution with a ZnO solution concentration of 50-200 mg/mL, and stir for 8-12 h at room temperature. Spin-coating on the cathode 1, the spin-coating speed is 3000-4000 rpm, and the spin-coating time is 30-40 s, to obtain a ZnO cathode buffer layer 2 with a thickness of 30-40 nm;

3) The bottom active layer adopts the polymer donor material and the non-fullerene small molecule acceptor material to prepare the form of bulk heterojunction: the donor material PTB7-Th and the acceptor material with a mass ratio of 1:1 to 1.4 are used After mixing, ITIC was dissolved in chlorobenzene (CB) solution. The total concentration of donor material and acceptor material was 15-20 mg/mL. After stirring evenly at 20-25 °C, spin-coated on ZnO cathode buffer layer 2. The spin-coating speed is 800-1500rpm, and the spin-coating time is 40-60s to obtain the bottom active layer 3 with a thickness of 100-120nm;

4) Preparation of the inner recombination region 4 on the bottom active layer 3 by the vacuum evaporation method of the vapor deposition system: in the multi-source organic vapor phase molecular deposition system, under the condition of 2×10 ⁻⁴ to 6×10 ⁻⁵ Pa, A MoO ₃ layer with a thickness of 8 to 12 nm was prepared on the bottom active layer 3 by thermal evaporation, and then an ultra-thin Ag layer with a thickness of 8 to 12 nm was evaporated on the MoO ₃ layer; PEIE aqueous solution with a concentration of 37 wt% was used Dissolved in dimethoxyethanol solution with a concentration of 0.1-0.2v%, the PEIE solution was spin-coated on the ultra-thin Ag layer by spin-coating method, the rotation speed was 4000-6000rpm, and the spin-coating time was 30-40s to obtain A PEIE layer with a thickness of 10 to 15 nm is formed to form a MoO ₃ /Ag/PEIE internal recombination region 4;

5) The top active layer also uses polymer donor materials and non-fullerene small molecule acceptor materials to prepare bulk heterojunctions: the donor material PTB7-Th and the acceptor with a mass ratio of 1:1.5-2 are used The material FOIC is mixed and dissolved in chloroform (CF) solution. The total concentration of the donor material and the acceptor material is 6-10 mg/mL. After stirring evenly at 20-25 °C, spin-coat on the inner composite area 4, spin The coating speed is 1000-2500 rpm, and the spin coating time is 40-60 s to obtain the top active layer 5 with a thickness of 80-110 nm;

6) An anode buffer layer 6 is prepared on the top active layer 5 by a vacuum evaporation method of a vapor deposition system: in a multi-source organic vapor phase molecular deposition system, under the condition of 2×10 ⁻⁴ to 6×10 ⁻⁵ Pa, A layer of MoO ₃ with a thickness of 3.5-5 nm is prepared on the top active layer 5 by thermal evaporation to obtain an anode buffer layer 6;

7) Preparation of anode 7 on anode buffer layer 6 by vacuum evaporation in a vapor deposition system: in a multi-source organic vapor phase molecular deposition system, under the condition of 2×10 ⁻⁴ to 6×10 ⁻⁵ Pa Ag with a thickness of 60-80 nm is evaporated on the layer 6 to obtain an anode 7, thereby preparing a cascade structure organic photodetector with broadband, low noise and ultrafast response.

In the inner recombination region 4 prepared by the present invention, MoO ₃ is used as an electron blocking layer, and PEIE is used as a hole blocking layer, and also has the effect of reducing the work function. Under full-color light irradiation, the MoO ₃ /Ag/PEIE composite junction layer exists in the photodetector as a recombination center, and equal amounts of electrons and holes on both sides of the inner recombination region meet and recombine in the inner recombination region, as shown in Fig. 4.

As shown in Fig. 5, in the dark state, the electron injection barrier of the photodetector without internal recombination region is the difference between the LUMO energy level of the acceptor material and the work function of the Ag electrode, and the hole injection potential well is expressed as the donor material The difference between the HOMO energy level and the work function of ITO, and for photodetectors with an internal recombination region, _MoO3 and PEIE in the internal recombination region can effectively block electrons from the top layer and holes from the bottom layer, respectively, forming a higher The low dark current reduces the noise current of the device, thereby obtaining higher detection sensitivity; at the same time, the design of the cascade structure reduces the interface trapping effect and makes the device The response speed has been effectively improved.

Description of drawings

Figure 1: Schematic diagram of a cascade structure organic photodetector with broadband, low noise and ultrafast response according to the present invention; the names of the parts are: ITO conductive glass 1, ZnO cathode buffer layer 2, PTB7-Th:ITIC Bottom active layer ₃ , MoO3/Ag/PEIE inner recombination region 4, PTB7-Th:FOIC top active layer ₅ , MoO3 anode buffer layer 6, Ag anode 7; inner recombination region ₄ consists of MoO3 electron blocking layer 41 , Ag metal layer 42 and PEIE hole blocking layer 43 are composed.

FIG. 2 : Absorption spectra of active layer materials in Examples 1 to 3. FIG. As a typical non-fullerene electron acceptor material, ITIC has a spectral range of 300-800 nm, with a visible peak at 705 nm, while FOIC has a strong light-harvesting ability in the near-infrared region, with a peak at 820 nm. near-infrared peaks. Furthermore, PTB7-Th showed stronger visible absorption in the spectrum from 300 nm to 700 nm. Since light with a longer wavelength has a greater penetration depth in the photoactive layer, PTB7-Th:ITIC, which mainly absorbs visible light, is selected as the bottom active layer, and PTB7-Th:FOIC, which absorbs near-infrared light, is selected as the top active layer. Benefiting from the complementary absorption spectrum, the organic photodetector based on the cascade structure has a broad absorption in the 300-1000 nm region, which ensures the theoretical feasibility of the cascaded device to realize broadband detection in the ultraviolet-visible-near-infrared.

FIG. 3 : Equivalent circuit diagram of a cascade-structured organic photodetector with broadband, low noise and ultrafast response prepared in Example 3. FIG. As shown in the figure, the entire cascaded organic photodetector is equivalent to a cascade of two separate devices. When monochromatic light is incident from the ITO side, one of the visible light part and the near-infrared light part is effective for the monochromatic light in this band. Absorption generates charge carriers, exhibiting the properties of a p-i-n junction. The other of the two cannot generate carriers because there is no corresponding light absorption. It is equivalent to a plate capacitor in the circuit. The carriers do not need to pass through the interface to be collected by the corresponding electrodes, which greatly reduces the interface capture effect, thereby reducing the trapping effect. Enables ultra-fast response of cascaded devices.

FIG. 4 is a schematic diagram of the working principle of the organic photodetector with a cascade structure prepared in Example 3 under illumination conditions. Under full-color light irradiation, the bottom and top active layers absorb visible light and near-infrared light, respectively, to generate electrons and holes. In the bottom active layer, electrons are concentrated on the ITO side, and holes are concentrated on the inner recombination region side. . In the top active layer, holes are concentrated near the top electrode, and electrons are concentrated on the side of the inner recombination region. At this time, the MoO ₃ /Ag/PEIE internal recombination region exists in the photodetector as a recombination center, and equal amounts of electrons and holes on both sides of the internal recombination region meet and recombine in the internal recombination region.

表示为受体材料的LUMO能级与Ag电极功函数的差值，空穴注入势垒

表示为给体材料的HOMO能级与ITO功函数的差值。而对于级联结构的器件来说，内部复合区中的P型材料MoO₃和N型材料PEIE能够分别有效阻挡来自顶层的电子和来自底层的空穴，形成了较高的电子注入势垒

和空穴注入势垒

使暗电流降低。从图中我们可以清晰的比较，本发明制备的基于级联结构的有机光电探测器能够有效提升光电探测器的性能。Figure 5: Schematic diagram of the working principle of the organic photodetector with cascade structure prepared in Example 3 under dark conditions. Under dark conditions, due to the effect of external bias, the dark current of the device mainly comes from the reverse injection of charges. As shown in the figure, the electron injection barrier of the single-section device

Expressed as the difference between the LUMO energy level of the acceptor material and the work function of the Ag electrode, the hole injection barrier

Expressed as the difference between the HOMO energy level of the donor material and the ITO work function. For devices with a cascade structure, the P-type material MoO ₃ and N-type material PEIE in the internal recombination region can effectively block electrons from the top layer and holes from the bottom layer, respectively, forming a higher electron injection barrier.

and hole injection barrier

reduce the dark current. From the figure, we can clearly compare that the organic photodetector based on the cascade structure prepared by the present invention can effectively improve the performance of the photodetector.

Figure 6: Single-segment organic photodetectors based on PTB7-Th:ITIC and PTB7-Th:FOIC active layers prepared in Examples 1-2 and cascading organic photodetectors prepared in Example 3 at 100mw cm ^-2 The JV characteristic curve was measured under the AM1.5G standard sunlight, and the open circuit voltage (V _oc ) of the three devices has been indicated in the figure. As shown in the figure, the _Voc of the cascaded organic photodetector is 1.488V, which is close to the sum of the Voc of the two single-cell organic photodetectors (the _Voc of the single-cell organic photodetector is _0.738V and 0.814 V, respectively V), indicating that the organic photodetector of the cascade structure formed by the internal recombination region can work normally.

Figure 7: Single-section organic photodetectors based on PTB7-Th:ITIC and PTB7-Th:FOIC active layers prepared in Examples 1-2 and cascaded organic photodetectors prepared in Example 3 at -0.5V to Comparison of dark current in the 1.5V range. As shown in the figure, the dark current density of the organic photodetector with the cascade structure is 1.94×10 ^-9 A cm ^-2 at -0.1V, which is more than 1 order of magnitude lower than that of the single-cell photodetector, indicating that the level of The tandem organic photodetector can achieve lower noise current and higher sensitivity. From the figure, we can clearly compare that the organic photodetector based on the cascade structure prepared by the present invention can effectively improve the performance of the photodetector.

Figure 8: Single-segment organic photodetectors based on PTB7-Th:ITIC and PTB7-Th:FOIC active layers prepared in Examples 1-2 and cascade-structured organic photodetectors prepared in Example 3 under zero bias Comparison of measured EQE curves. As shown in the figure, the organic photodetector of the cascade structure realizes a wide range of detection from 300-1000nm, and the EQE value in the range of 380-450nm is improved compared with the single-section photodetector, and the photodetector of the cascade structure is improved. The highest EQE value of 54.69% is obtained at 800 nm, which proves that the carriers generated in the near-infrared region can be fully collected by the electrodes, which ensures that the organic photodetector based on the cascade structure prepared by the present invention can effectively cover the broadband of 300-1000 nm. probe.

Figure 9: Single-segment organic photodetectors based on PTB7-Th:ITIC and PTB7-Th:FOIC active layers prepared in Examples 1-2 and cascading organic photodetectors prepared in Example 3 at different wavelengths Responsiveness curve. It can be concluded that the responsivity of the organic photodetector with cascade structure in the near-infrared region of 840nm reaches 0.36AW ^-1 .

Figure 10: Single-section organic photodetectors based on PTB7-Th:ITIC and PTB7-Th:FOIC active layers prepared in Examples 1-2 and cascaded organic photodetectors prepared in Example 3 at -0.1V bias Depress the detection sensitivity curves for different wavelengths. The detectivity of the cascade organic photodetector is greater than 2.5×10 ¹¹ Jones (cm Hz ^{-1/ 2} W ^-1 ) at 350-900 nm, and the peak value at 840 nm in the near-infrared region is 9.73×10 ¹¹ Jones. The maximum detection rate of visible light device is 1.28×10 ¹¹ Jones at 585nm, and the maximum detection rate of near-infrared device is 2.04×10 ¹¹ Jones at 805nm. Compared with single-section organic photodetectors, the detection rate of the cascaded device at different wavelengths is significantly improved, and the detection rate in the near-infrared region is increased by a factor of three. Cascaded devices show a wider light detection range, providing more opportunities for practical applications. From the figure, we can clearly compare that the organic photodetector based on the cascade structure prepared by the present invention can effectively improve the performance of the photodetector.

Figure 11: Comparison of noise currents between the single-cell organic photodetectors based on PTB7-Th:ITIC and PTB7-Th:FOIC active layers prepared in Examples 1-2 and the organic photodetectors with cascaded structures prepared in Example 3 . It can be seen from the figure that the noise current of the cascade structure organic photodetector is more than 2 orders of magnitude lower than that of the single cell organic photodetector, and the noise current is almost independent of frequency, indicating that the cascade structure organic photodetector has Higher detection sensitivity. From the figure, we can clearly compare that the organic photodetector based on the cascade structure prepared by the present invention can effectively improve the performance of the photodetector.

Figure 12: Transient photocurrents of the single-segment organic photodetectors based on PTB7-Th:ITIC and PTB7-Th:FOIC active layers prepared in Examples 1-2 and the cascading organic photodetectors prepared in Example 3 Curve comparison chart. Under the excitation of 355nm pulsed laser, the response times of visible light device, near-infrared device and cascade device are 387.74ns, 454.91ns and 146.80ns respectively, and the response speed of cascade device has been greatly improved. From the figure, we can clearly compare that the organic photodetector based on the cascade structure prepared by the present invention can effectively improve the performance of the photodetector.

Detailed ways

Example 1:

1) The ITO conductive glass was ultrasonicated with isopropanol, acetone, ethanol, and deionized water for 20 minutes in turn, then passed into nitrogen for drying for 30 minutes, and then treated with an ultraviolet ozone system for 10 minutes for use;

2) Dissolve 30 g of zinc acetate in 290 μL of dimethoxyethanol solution, add 10 μL of ethanolamine to prepare a ZnO solution with a concentration of 100 mg/mL, stir at 25 °C for 8 h, spin-coat on the cathode ITO conductive glass, spin The coating speed is 3000rpm, and the spin coating time is 30s to obtain a cathode buffer layer with a thickness of 40nm for use;

3) The donor material PTB7-Th and the acceptor material ITIC with a mass ratio of 1:1.2 were mixed and dissolved in a chlorobenzene (CB) solution with a total concentration of 20 mg/mL, stirred at 25 °C for 10 h, and spin-coated on On the cathode buffer layer ZnO, the spin coating speed is 1000rpm, the spin coating time is 60s, and the thickness of the active layer is 110nm;

4) Take out the sample, move it to a vapor deposition system, and grow a layer of MoO ₃ material on the active layer by thermal evaporation under a pressure of 5×10 ^-5 Pa; obtain a MoO ₃ anode buffer layer with a thickness of 5 nm;

5) Under the condition of 5 × 10 ^-5 Pa, a layer of Ag material was grown on the anode buffer layer as the top electrode with a thickness of 70 nm to obtain an Ag anode, thereby preparing a single-cell organic photodetector as a visible light device as a comparative device. .

Example 2:

1) 1ITO conductive glass was ultrasonicated with isopropanol, acetone, ethanol, and deionized water for 20 minutes in turn, then passed into nitrogen to dry for 30 minutes, and then treated with an ultraviolet ozone system for 10 minutes for use;

2) Dissolve 30 g of zinc acetate in 290 μL of dimethoxyethanol solution, add 10 μL of ethanolamine to prepare a ZnO solution with a concentration of 100 mg/mL, stir at 25 °C for 8 h, spin-coat on the cathode ITO conductive glass, spin The coating speed is 3000rpm, and the spin coating time is 30s to obtain a cathode buffer layer with a thickness of 40nm for use;

3) The donor material PTB7-Th and the acceptor material FOIC with a mass ratio of 1:1.5 were mixed and dissolved in a chloroform (CF) solution with a total concentration of 6.25 mg/mL, stirred at 25 °C for 2 h, and spin-coated on On the cathode buffer layer ZnO, the spin coating speed is 1500rpm, the spin coating time is 60s, and the thickness of the active layer is 90nm;

4) Take out the sample, move it to a vapor deposition system, and grow a layer of MoO3 material on the active layer by thermal evaporation under a pressure of ₅ × ^10-5pa to obtain a MoO3 anode buffer layer with a thickness of 5nm _;

5) Under the condition of 5 × 10 ^-5 Pa, a layer of Ag material was grown on the anode buffer layer as the top electrode with a thickness of 70 nm to obtain an Ag anode, thereby preparing a single-cell organic photodetector as a comparison device for near-infrared devices. device.

Example 3:

1) The ITO conductive glass was ultrasonicated with isopropanol, acetone, ethanol, and deionized water for 20 minutes in turn, then passed into nitrogen for drying for 30 minutes, and then treated with an ultraviolet ozone system for 10 minutes for use;

2) Dissolve 30 g of zinc acetate in 290 μL of dimethoxyethanol solution, add 10 μL of ethanolamine to prepare a ZnO solution with a concentration of 100 mg/mL, stir at 25 °C for 8 h, spin-coat on the cathode ITO conductive glass, spin The coating speed is 3000rpm, and the spin coating time is 30s to obtain a cathode buffer layer with a thickness of 40nm for use;

3) The donor material PTB7-Th and the acceptor material ITIC with a mass ratio of 1:1.2 were mixed and dissolved in a chlorobenzene (CB) solution with a total concentration of 20 mg/mL, stirred at 25 °C for 10 h, and spin-coated on On the cathode buffer layer ZnO, the spin coating speed is 1000 rpm, and the spin coating time is 60 s, and the thickness of the bottom active layer is 110 nm;

4) Take out the sample, move it to the vapor deposition system, and grow a layer of MoO ₃ on the bottom active layer with a thickness of 8 nm by thermal evaporation under the pressure of 5×10 ^-5 Pa; then evaporate a layer of MoO ₃ on the MoO 3 . Ag with a layer thickness of 10 nm; then, a PEIE aqueous solution with a concentration of 37 wt% was dissolved in a dimethoxyethanol solution with a concentration of 0.2 v%, and the PEIE was spin-coated on the ultra-thin Ag layer by spin coating, and the rotation speed At 5000 rpm, the spin coating time was 30 s, and a PEIE layer with a thickness of 12 nm was obtained, thereby forming the MoO ₃ /Ag/PEIE internal recombination region;

5) The donor material PTB7-Th and the acceptor material FOIC with a mass ratio of 1:1.5 were mixed and dissolved in a chloroform (CF) solution. The total concentration of the donor material and the acceptor material was 6.25 mg/mL at 25°C After stirring for 1 h under the conditions, spin-coating on the inner recombination zone with a spin-coating speed of 1500 rpm and a spin-coating time of 60 s to obtain a top active layer with a thickness of 100 nm;

6) Take the sample out, move it to the vapor deposition system again, and grow an anode buffer layer MoO ₃ with a thickness of 5 nm on the top active layer by thermal evaporation under a pressure of 5×10 ^-5 Pa;

7) Under the pressure of 5 × 10 ^-5 Pa, a layer of Ag material is grown on the anode buffer layer by thermal evaporation as the top electrode, with a thickness of 70 nm, to obtain an Ag anode, thereby preparing the one described in the present invention. A broadband, low-noise, ultrafast response cascaded organic photodetector.

Claims (2)

1. a preparation method of cascade structure organic photodetector, its steps are as follows: 1) The ITO conductive glass is ultrasonically cleaned with isopropanol, acetone, ethanol, and deionized water for 15 to 30 minutes in turn, then dried with nitrogen for 20 to 40 minutes, and then treated with ultraviolet ozone for 10 to 15 minutes as the cathode (1); 2) Dissolve 15-30 g of zinc acetate in 145-290 μL of dimethoxyethanol solution, add 5-10 μL of ethanolamine to prepare a zinc oxide solution with a ZnO solution concentration of 50-200 mg/mL, and stir at room temperature for 8-12 h and then spin-coated on the cathode (1), the spin-coating speed is 3000-4000 rpm, and the spin-coating time is 30-40 s to obtain a ZnO cathode buffer layer (2) with a thickness of 30-40 nm; 3) Mix the donor material PTB7-Th and the acceptor material ITIC with a mass ratio of 1:1 to 1.4 and dissolve them in a chlorobenzene solution. The total concentration of the donor material and the acceptor material is 15 to 20 mg/mL, and 20 After stirring evenly at ~25°C, spin coating on the ZnO cathode buffer layer (2) with a spin coating speed of 800 to 1500 rpm and a spin coating time of 40 to 60 s to obtain a bottom active layer (3) with a thickness of 100 to 120 nm. ); 4) Under the condition of 2 × 10 ^-4 to 6 × 10 ^-5 Pa, a MoO 3 layer (41) with a thickness of 8 to 12 nm is prepared by thermal evaporation on the bottom active layer ( ₃ ), and then a MoO ₃ layer (41) with a thickness of 8 to 12 nm is prepared on the bottom active layer (3). An Ag layer (42) with a thickness of 8 to 12 nm is evaporated on the top; the PEIE aqueous solution with a concentration of 37 wt % is dissolved in a dimethoxyethanol solution with a concentration of 0.1 to 0.2 v%, and the PEIE solution is spun by a spin coating method. Coating on the ultra-thin Ag layer, the spinning speed is 4000-6000 rpm, and the spin-coating time is 30-40 s to obtain a PEIE layer (43) with a thickness of 10-15 nm, thereby forming a MoO ₃ /Ag/PEIE internal composite region (4) ; 5) Mix the donor material PTB7-Th and the acceptor material FOIC with a mass ratio of 1:1.5-2 and dissolve them in a chloroform solution, the total concentration of the donor material and the acceptor material is 6-10 mg/mL, 20- After stirring evenly at 25°C, spin-coating on the inner recombination zone (4) at a spin-coating speed of 1000-2500 rpm and a spin-coating time of 40-60 s to obtain a top active layer (5) with a thickness of 80-110 nm; 6) under the condition of 2×10 ^-4 to 6×10 ^-5 Pa, a MoO ₃ layer with a thickness of 3.5 to 5 nm is prepared on the top active layer (5) to obtain an anode buffer layer (6); 7) Under the condition of 2×10 ^-4 to 6×10 ^-5 Pa, Ag with a thickness of 60 to 80 nm is evaporated on the anode buffer layer (6) to obtain the anode (7), thereby preparing a cascade structure Organic Photodetectors. 2. A cascade structure organic photodetector, characterized in that: it is prepared by the method of claim 1.

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