Broadband quantum dot / organic bipolar photoelectric detector and preparation method thereof

Abstract

The invention discloses a broadband quantum dot / organic bipolar photoelectric detector and a preparation method thereof, and belongs to the technical field of photoelectric detection.The broadband quantum dot / organic bipolar photoelectric detector comprises a substrate, a transparent electrode layer, a first photosensitive layer, an electron transport layer, a second photosensitive layer, a hole transport layer and a metal electrode layer which are sequentially stacked from bottom to top; the first photosensitive layer is made of an organic donor-acceptor mixed material, and the second photosensitive layer is made of a quantum dot material. According to the invention, broadband light response in a range from ultraviolet to short wave infrared can be realized, the characteristics of low dark current, high responsivity, fast response speed and the like are realized, external bias voltage is not needed, and the energy consumption is low. More importantly, the photoelectric current polarity inversion can be induced under the adjustment of the irradiation light wavelength, the integration of five logic gate functions is realized, and the optical communication encryption device has safer optical communication encryption capability when being applied to image coding communication encryption.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric detection, and in particular relates to a wide-band quantum dot / organic bipolar photoelectric detector and a preparation method thereof. Background Art

[0002] Due to the inherent output characteristics, traditional photodetectors maintain fixed responsivity and response polarity after preparation, which limits their ability to process complex optical information. With the development of photodetector technology, bipolar photodetectors, due to their special adjustable light response polarity that can be affected by factors such as light wavelength, light intensity and operating voltage, provide a new solution for improving the information processing capabilities of photodetectors and promoting the development of new multifunctional optoelectronic devices. They have broad application prospects in application fields such as optical communications, logical operations and visual imaging. However, the photoelectric performance of most bipolar photodetectors is weak and it is difficult to meet the needs of practical applications. For example, the perovskite-based bipolar photodetector (CN117460269A) invented by Cao Guoyang and others from Soochow University has a small response range and is difficult to cover the short-wave infrared communication band with strong anti-interference ability. Therefore, current research mainly focuses on improving the detection range, response speed, responsivity and reducing noise current. In addition, for example, the bipolar photodetector composed of two-dimensional α-phase indium selenide and topological insulator molybdenum telluride materials invented by Zhang Jiazhen and others from the Yangtze River Delta Research Institute (Huzhou) of the University of Electronic Science and Technology of China (CN117650194A), most of the current bipolar photodetectors are generally prepared by mechanically peeling off two-dimensional materials for transfer. The mechanical peeling process will limit the large-area preparation of the device, which is not conducive to large-scale integration and cannot meet the current requirements for high integration of optoelectronic devices. In view of this, it is urgent to improve the performance of bipolar photodetectors and optimize the process, and finding new materials is one of the effective ways to solve the problem.

[0003] Organic materials are easy to process, highly flexible, and highly responsive in the visible light band, and can be used to prepare photodetectors. Due to the inherent properties of organic semiconductors, such as low carrier mobility and high exciton binding energy, photodetectors based on such materials exhibit dark currents as low as 10 -11 A / cm 2 , but its response speed is slow compared with commonly used inorganic materials.

[0004] In order to expand the response range of bipolar photodetectors based on organic materials and improve the response speed, the present invention proposes a bipolar photodetector combined with quantum dots, which is expected to become an excellent photoelectric detection device with the characteristics of wide response range, low dark current, high responsiveness and fast response speed. Summary of the invention

[0005] In view of the problems of slow response speed and narrow response range of existing bipolar photodetectors based on organic materials, the present invention provides a wide-band quantum dot / organic bipolar photodetector and a preparation method thereof, which can achieve broadband light response in the ultraviolet to short-wave infrared range, and has the characteristics of low dark current, high responsiveness, fast response speed, etc., and has application prospects in the field of image coding, communication and encryption.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A wide-band quantum dot / organic bipolar photodetector, comprising a substrate, a transparent electrode layer, a first photosensitive layer, an electron transport layer, a second photosensitive layer, a hole transport layer and a metal electrode layer stacked in sequence from bottom to top;

[0008] Among them, the material of the first photosensitive layer is an organic donor-acceptor mixed material, specifically P3HT:PC71BM, PBDB-T:ITIC-Th, PBDB-T:Y6, PM6:Y6 or PCE10:IEICO-4F; the material of the second photosensitive layer is a quantum dot material, specifically lead sulfide quantum dots, lead selenide quantum dots, mercury selenide quantum dots, mercury telluride quantum dots, silver sulfide quantum dots, silver selenide quantum dots or silver telluride quantum dots.

[0009] Furthermore, the molar ratio of the donor to the acceptor in the first photosensitive layer is 1:1 to 1.5.

[0010] Furthermore, the thickness of the first photosensitive layer is 30-200 nm.

[0011] Furthermore, the thickness of the second photosensitive layer is 100-300 nm.

[0012] Furthermore, the material of the substrate is glass or quartz; the material of the transparent electrode layer is silver, aluminum, gold, indium tin oxide or fluorine-doped indium tin oxide; the material of the electron transport layer is titanium oxide, tin oxide or zinc oxide; the material of the hole transport layer is molybdenum trioxide, PEDOT:PSS, Spiro-OMeTAD or LiF; the material of the metal electrode layer is silver, aluminum or gold.

[0013] Furthermore, the thickness of the transparent electrode layer is 100-200 nm; the thickness of the electron transport layer is 10-80 nm; the thickness of the hole transport layer is 10-40 nm; and the thickness of the metal electrode layer is 100-200 nm.

[0014] A method for preparing a wide-band quantum dot / organic bipolar photodetector comprises the following steps:

[0015] Step 1, pre-treating the substrate covered with the transparent electrode layer;

[0016] Step 2, preparing an organic donor-acceptor mixed solution, spin coating it on the surface of the transparent electrode layer, and annealing it at 100-120° C. for 10-20 min to obtain a first photosensitive layer;

[0017] Step 3, preparing an electron transport layer on the surface of the first photosensitive layer;

[0018] Step 4: prepare a quantum dot solution, spin-coat it on the surface of the electron transport layer to obtain a quantum dot film to be treated, and after solid-phase ligand exchange, obtain a layer of quantum dot film, and repeat the preparation of multiple layers of quantum dot film to obtain a second photosensitive layer;

[0019] Step 5: Prepare a hole transport layer and a metal electrode layer in sequence on the surface of the second photosensitive layer, and finally obtain a wide-band quantum dot / organic bipolar photodetector.

[0020] Furthermore, the solvent of the organic donor-acceptor mixed solution in step 2 is toluene, chlorobenzene or o-dichlorobenzene.

[0021] Furthermore, in step 2, the concentration of the organic donor-acceptor mixed solution is 5 to 25 mg / mL, the spin coating speed is 2000 to 12000 rpm, and the spin coating time is 20 to 60 s.

[0022] Furthermore, the solvent of the quantum dot solution in step 4 is n-octane, n-hexane or toluene.

[0023] Furthermore, the concentration of the quantum dot solution in step 4 is 50-100 mg / mL, the spin coating speed is 2000-6000 rpm, and the spin coating time is 20-40 s.

[0024] Furthermore, the specific process of the solid phase ligand exchange in step 4 is:

[0025] Step 4.1, preparing a ligand solution by mixing 1,2-ethanedithiol (EDT) and an organic solvent in a volume ratio of 1:50 to 100, wherein the organic solvent is isopropanol (IPA) or acetonitrile (ACN);

[0026] Step 4.2, coating the surface of the quantum dot film to be treated with the ligand solution, leaving it to stand for 30 to 60 seconds for ligand exchange, and then removing the excess ligand solution by high-speed spin coating to obtain the quantum dot film to be cleaned;

[0027] Step 4.3, applying the same organic solvent as in step 4.1 to the surface of the quantum dot film to be cleaned, leaving it to stand for 10 to 20 seconds to clean the surface residue, and then removing the excess organic solvent by high-speed spin coating to complete a cleaning process;

[0028] Step 4.4: After repeating the cleaning process for several times, anneal at 50-100° C. for 10-20 minutes to obtain a quantum dot film.

[0029] Furthermore, by adjusting the wavelength of the irradiated light, the polarity reversal of the photocurrent of the wide-band quantum dot / organic bipolar photodetector can be achieved.

[0030] Furthermore, a beam of modulated light and two beams of signal light are simultaneously irradiated on the wide-band quantum dot / organic bipolar photodetector, and the logic gate operations of OR, AND, NOR and NAND are realized by controlling the switching state of the two signal light beams, and adjusting the wavelength of the modulated light, the intensity of the modulated light and the wavelength of the signal light; a beam of modulated light and a beam of signal light are simultaneously irradiated on the wide-band quantum dot / organic bipolar photodetector, and the logic gate operation of NOT is realized by controlling the switching state of the signal light.

[0031] Furthermore, in the case where the illumination light that outputs negative photocurrent is used as the modulated light and the illumination light that outputs positive photocurrent is used as the signal light, the OR or AND logic gate operation is realized by controlling the switching state of the two signal light beams and adjusting the intensity of the modulated light.

[0032] Furthermore, in the case where the illumination light that outputs a positive photocurrent is used as the modulated light and the illumination light that outputs a negative photocurrent is used as the signal light, the logic gate operation of NOR or NAND is realized by controlling the switching states of the two signal light beams and adjusting the intensity of the modulated light.

[0033] Furthermore, the wide-band quantum dot / organic bipolar photodetector is simultaneously irradiated with two laser beams of different wavelengths and corresponding to different photocurrent polarities. By controlling the switching states of the two laser beams, the photoresponse current output by the wide-band quantum dot / organic bipolar photodetector is encoded to achieve optical communication encryption.

[0034] The beneficial effects of the present invention are:

[0035] 1. The present invention proposes a wide-band quantum dot / organic bipolar photodetector and a preparation method thereof, which can achieve broadband light response in the range of ultraviolet to short-wave infrared, and has the characteristics of low dark current, high responsiveness, fast response speed, etc.; at the same time, it adopts a self-powered working mode, does not require external bias, and has low energy consumption; the preparation process only involves simple solution spin coating and evaporation process, which is conducive to large-area preparation and large-scale integration, and reduces production costs;

[0036] 2. The wide-band quantum dot / organic bipolar photodetector obtained by the present invention can induce photocurrent polarity reversal under the regulation of the wavelength of the irradiated light. On the one hand, by simultaneously irradiating the modulated light and the signal light, the integrated integration of five logic gate functions can be realized; on the other hand, by simultaneously irradiating two laser beams of different wavelengths corresponding to different photocurrent polarities, the output light response current is encoded, and image coding communication encryption can be realized. Compared with the traditional unipolar photodetector, it has a more secure optical communication encryption capability; and further, the wide-band quantum dot / organic bipolar photodetector obtained by the present invention is conducive to simplifying the structure of the dual-band encrypted optical communication system, improving the integration of the dual-band encrypted optical communication system, and increasing the security of information transmission;

[0037] 3. The wide-band quantum dot / organic bipolar photodetector obtained by the present invention has excellent broadband light field modulation function and can be further used in bionic vision, intelligent robots, unmanned driving technology and other artificial intelligence fields in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the three-dimensional structure of the wide-band quantum dot / organic bipolar photodetector in Example 1 of the present invention;

[0039] Figure 2 This is a schematic diagram of the cross-sectional planar structure of the wide-band quantum dot / organic bipolar photodetector in Example 1 of the present invention;

[0040] Figure 3 The photoelectric test results of the wide-band quantum dot / organic bipolar photodetector under zero bias in Example 1 of the present invention;

[0041] Figure 4 Truth tables and schematic diagrams of five photoelectric logic gates "AND", "OR", "NAND", "NOR", and "NOT" of the wide-band quantum dot / organic bipolar photodetector in Example 1 of the present invention under visible light and infrared light;

[0042] Figure 5 This is a graph of the instantaneous photocurrent of the “AND” logic gate operation of the wide-band quantum dot / organic bipolar photodetector in Example 1 of the present invention;

[0043] Figure 6 This is a graph of the instantaneous photocurrent of the “OR” logic gate operation of the wide-band quantum dot / organic bipolar photodetector in Example 1 of the present invention;

[0044] Figure 7 This is a graph of the instantaneous photocurrent of the “NAND” logic gate operation of the wide-band quantum dot / organic bipolar photodetector in Example 1 of the present invention;

[0045] Figure 8This is a graph of the instantaneous photocurrent of the “NOR” logic gate operation of the wide-band quantum dot / organic bipolar photodetector in Example 1 of the present invention;

[0046] Fig. 9 This is a graph of the instantaneous photocurrent of the “NOT” logic gate operation of the wide-band quantum dot / organic bipolar photodetector in Example 1 of the present invention;

[0047] Fig.10 This is a schematic diagram of image encryption transmission of a wide-band quantum dot / organic bipolar photodetector under visible light and infrared light in Example 2 of the present invention;

[0048] The descriptions of the symbols in the accompanying drawings are as follows:

[0049] 1 is a substrate; 2 is a transparent electrode layer; 3 is a first photosensitive layer; 4 is an electron transport layer; 5 is a second photosensitive layer; 6 is a hole transport layer; and 7 is a metal electrode layer. DETAILED DESCRIPTION

[0050] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Although limited embodiments are described below, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0051] Example 1

[0052] This embodiment provides a broadband quantum dot / organic bipolar photodetector, the structure of which is as follows: Figure 1 and Figure 2 As shown, it includes a substrate 1, a transparent electrode layer 2, a first photosensitive layer 3, an electron transport layer 4, a second photosensitive layer 5, a hole transport layer 6 and a metal electrode layer 7 which are stacked in sequence from bottom to top.

[0053] Among them, the material of the substrate 1 is glass; the material of the transparent electrode layer 2 is indium tin oxide (ITO) with a thickness of 130nm; the material of the first photosensitive layer 3 is PBDB-T:Y6, the molar ratio of the donor PBDB-T to the acceptor Y6 is 1:1.5, and the thickness is 50nm; the material of the electron transport layer 4 is ZnO with a thickness of 40nm; the material of the second photosensitive layer 5 is HgTe quantum dots with a thickness of 100nm; the material of the hole transport layer 6 is MoO3 with a thickness of 10nm; the material of the metal electrode layer 7 is Ag with a thickness of 100nm.

[0054] The preparation process of the broadband quantum dot / organic bipolar photodetector described in this embodiment is as follows:

[0055] Step 1, cleaning the substrate 1 covered with the transparent electrode layer 2, and then pre-treating the substrate 1 covered with the transparent electrode layer 2 with ultraviolet ozone, the treatment time being 20 minutes;

[0056] Step 2, PBDB-T:Y6 was prepared at a molar ratio of 1:1.5, and dissolved in o-dichlorobenzene to prepare a 20 mg / ml organic donor-acceptor mixed solution. After stirring overnight, the solution was spin-coated on the surface of the transparent electrode layer 2 at a spin-coating speed of 4000 rpm for 40 seconds, and then annealed at 120° C. for 15 minutes to obtain a first photosensitive layer 3;

[0057] Step 3: using an evaporation process to evaporate ZnO on the surface of the first photosensitive layer 3 to obtain an electron transport layer 4;

[0058] Step 4, adding HgTe quantum dot material to n-octane to prepare a quantum dot solution of 80 mg / mL, and spin coating it on the surface of the electron transport layer 4 at a spin coating speed of 2000 rpm for 20 seconds to obtain a quantum dot film to be treated; then, solid-phase ligand exchange is performed on the quantum dot film to be treated to obtain a layer of quantum dot film, and 10 layers of quantum dot film are repeatedly prepared to obtain a second photosensitive layer 5;

[0059] Among them, the specific process of solid phase ligand exchange is:

[0060] Step 4.1, prepare a ligand solution by mixing 1,2-ethanedithiol and isopropanol in a volume ratio of 1:100;

[0061] Step 4.2, coating the surface of the quantum dot film to be treated with the ligand solution, leaving it to stand for 30 seconds for ligand exchange, and then removing the excess ligand solution by high-speed spin coating to obtain the quantum dot film to be cleaned;

[0062] Step 4.3, applying isopropanol to the surface of the quantum dot film to be cleaned, leaving it for 10 seconds to clean the surface residue, and then removing the excess isopropanol by high-speed spin coating to complete a cleaning process;

[0063] Step 4.4, after repeating the cleaning process for several times, annealing at 50°C for 15 minutes to obtain a quantum dot film;

[0064] Step 5: Using an evaporation process, evaporating MoO3 on the surface of the second photosensitive layer 5 to obtain a hole transport layer 6;

[0065] Step 6: Using an evaporation process, Ag is evaporated on the surface of the hole transport layer 6 to obtain a metal electrode layer 7, and finally a wide-band quantum dot / organic bipolar photodetector is obtained.

[0066] The broadband quantum dot / organic bipolar photodetector prepared in this embodiment was irradiated with ultraviolet-shortwave infrared light (300-1800nm) without external bias. The photoelectric test results are as follows: Figure 3 As shown, when the wavelength of the irradiated light is between 300 and 900 nm, the device outputs a positive photocurrent, and when the wavelength of the irradiated light is between 1000 and 1800 nm, the polarity of the device photocurrent reverses and a negative photocurrent is output.

[0067] The wide-band quantum dot / organic bipolar photodetector prepared by this embodiment can induce the characteristic of photocurrent polarity reversal under the adjustment of the wavelength of irradiated light. The device is irradiated with modulated light and signal light at the same time. By controlling the switching state of the signal light, and adjusting the wavelength of the modulated light, the intensity of the modulated light and the wavelength of the signal light, five logic gate operations of OR, AND, NOR, NAND and NOT are realized.

[0068] Figure 4 The truth tables and simulation diagrams corresponding to the five logic gate operations of OR, AND, NOR, NAND and NOT are as follows:

[0069] 1) When a beam of 1550nm infrared light is used as the modulated light and two beams of 400nm visible light are used as the signal light, the photocurrent output by the device is binarized: the positive photocurrent greater than 0A is set to "1", and the negative photocurrent less than 0A is set to "0".

[0070] When the power density of 1550nm infrared light modulation is 100μW / cm 2 The power density of the two 400nm visible light signal beams is 10μW / cm 2 By changing the switch state of the two visible light signal beams, the four-state input of "00", "01", "10" and "11" is realized. Under the modulation of infrared light modulation light, the four-state input corresponds to the four-state output of "0", "0", "0" and "1", thereby realizing the "AND" logic gate operation. The corresponding photocurrent output curve is shown in Figure 5 shown.

[0071] When the power density of 1550nm infrared light modulation is reduced to 50μW / cm 2 When the same four-state input operation corresponds to the four-state output of "0", "1", "1" and "1", thus realizing the "OR" logic gate operation, the corresponding photocurrent output curve is as follows: Figure 6 shown.

[0072] 2) When a beam of 400nm visible light is used as the modulated light and two beams of 1550nm infrared light are used as the signal light, the photocurrent output by the device is binarized: the positive photocurrent greater than 0A is set to "0", and the negative photocurrent less than 0A is set to "1".

[0073] When the power density of 400nm visible light modulation is 30μW / cm 2 The power density of the two 1550nm infrared light signal beams is 50μW / cm 2 By changing the switch state of the two infrared light signal beams, the four-state input of "00", "01", "10" and "11" is realized. Under the modulation of visible light modulated light, the four-state input corresponds to the four-state output of "1", "1", "1" and "0", thereby realizing the "NAND" logic gate operation. The corresponding photocurrent output curve is shown in Figure 7 shown.

[0074] When the power density of 400nm visible light modulated light is reduced to 15μW / cm 2 When the same four-state input operation corresponds to the four-state output of "1", "0", "0" and "0", thus realizing the logic gate operation of "NOR", the corresponding photocurrent output curve is as follows Figure 8 shown.

[0075] 3) When a beam of 400nm visible light is used as the modulated light and a beam of 1550nm infrared light is used as the signal light, the photocurrent output by the device is binarized: the positive photocurrent greater than 0A is set to "0", and the negative photocurrent less than 0A is set to "1".

[0076] When the power density of 400nm visible light modulation is 5μW / cm 2 , the power density of 1550nm infrared light signal is 50μW / cm 2 By changing the switch state of the infrared light signal, the binary input of "0" and "1" is realized. Under the modulation of the visible light modulated light, the binary input corresponds to the binary output of "1" and "0", thereby realizing the logic gate operation of "NOT". The corresponding photocurrent output curve is shown in Fig. 9 shown.

[0077] In summary, the integrated integration of five logic gate functions can be successfully achieved through a single wide-band quantum dot / organic bipolar photodetector and multi-light modulation. It should be noted that the power density of the signal light and the modulated light during the logic gate function demonstration of this embodiment is determined by the performance of the wide-band quantum dot / organic bipolar photodetector actually prepared, and the above light intensity values ​​are for reference only.

[0078] Example 2

[0079] This embodiment provides a wide-band quantum dot / organic bipolar photodetector. The structure and preparation process are different from those of Embodiment 1, except that the thickness of the first photosensitive layer 3 is adjusted to 30 nm, and the concentration of the organic donor-acceptor mixed solution in step 2 is adjusted to 15 mg / mL during the preparation process. The other structures and preparation processes remain unchanged.

[0080] The wide-band quantum dot / organic bipolar photodetector obtained in this embodiment is simultaneously irradiated with two laser beams of different wavelengths and corresponding to different photocurrent polarities. By controlling the switching states of the two laser beams, the light response current output by the device is encoded to achieve optical communication encryption.

[0081] Below Fig.10 Take this as an example to illustrate:

[0082] The wide-band quantum dot / organic bipolar photodetector obtained in this embodiment is simultaneously irradiated with 400nm visible light (outputting positive photocurrent) and 1550nm infrared light (outputting negative photocurrent), and the input light off is encoded as "0", and the input light on is encoded as "1", and then the four input states of the two input light beams of visible light and infrared light correspond to "00", "10", "11" and "01".

[0083] The photocurrent output by the broadband quantum dot / organic bipolar photodetector obtained in this embodiment under four input states is encoded. The input and output states are as follows: Fig.10 As shown in (a), when the visible light is off and the infrared light is off, that is, the input state is "00", the photoresponse current of the bipolar detector is 0A, and the corresponding output state is encoded as "0"; when the visible light is on and the infrared light is off, that is, the input state is "10", the photoresponse current of the bipolar detector is encoded as "2"; when the visible light is on and the infrared light is on, that is, the input state is "11", the photoresponse current of the bipolar detector is encoded as "1"; when the visible light is off and the infrared light is on, that is, the input state is "01", the photoresponse current of the bipolar detector is encoded as "-1" in the output state.

[0084] by Fig.10 Taking the real image with the character "UESTC" shown in (b) as an example to simulate the image encoding and encryption, the "UESTC" image can be divided into an 18×17 matrix image (306 pixels), in which pixels with patterns are encoded as "1" and blank pixels are encoded as "0". Therefore, we can get a Fig.10 The 18×17 encoding matrix of “0 / 1” shown in (c).

[0085] The combination code of each 1×2 pixel block (“00”, “10”, “11”, “01”) corresponds to the switch state of two input lights of 400nm and 1550nm, thereby forming a synchronized dual-channel input light transmission signal. The wide-band quantum dot / organic bipolar photodetector obtained in this embodiment receives the emitted dual-channel input light transmission signal and converts it into Fig.10 The photocurrent output shown in (d) is normalized to obtain a 9×17 digital coding matrix of "0 / 2 / 1 / -1". By corresponding to the code book, the 9×17 digital coding matrix is ​​decoded back to an 18×17 "0 / 1" digital coding matrix. The pixels are filled according to the digital coding matrix to obtain the image ("1" means the pixel is filled with blue, "0" means it is not filled), according to Fig.10 In (d), it can be seen that the wide-band quantum dot / organic bipolar photodetector obtained in this embodiment successfully decodes and restores an image with the characters "UESTC".

[0086] In contrast, the traditional unipolar photodetector is also irradiated with 400nm visible light and 1550nm infrared light. However, since it cannot form positive and negative photocurrents by changing the wavelength, it can only identify the presence or absence of light. Therefore, the four input states "00", "10", "11", and "01" will correspond to the output states "0", "1", "2", and "1". For the 18×17 "UESTC" image, the dual-channel input light transmission signal formed by each 1×2 pixel block will be converted and normalized into a 9×17 digital coding matrix of "0 / 2 / 1" by the traditional unipolar photodetector. This is because the traditional unipolar photodetector cannot distinguish between 400nm and 1550nm input light by the polarity of the photocurrent. Therefore, the output results corresponding to the four different optical signal input states are different only in intensity. The output results of the four input states "00", "10", "01", and "11" are "0", "1", and "2" respectively. Since the output result "1" corresponds to the input states "10" and "01", they cannot be distinguished during the decoding process, such as Fig.10 As shown in (d), the indistinguishable pixels are filled with “X”, so the real image cannot be accurately obtained.

[0087] In summary, compared with the traditional unipolar photodetector, the dual-band encrypted optical communication system based on the wide-band quantum dot / organic bipolar photodetector obtained in this embodiment has a more secure optical communication encryption capability.

[0088] Example 3

[0089] This embodiment provides a wide-band quantum dot / organic bipolar photodetector. The structure and preparation process are different from those of Embodiment 1, except that the thickness of the second photosensitive layer 5 is adjusted to 170 nm, and the concentration of the quantum dot solution in step 4 is adjusted to 100 mg / mL during the preparation process. The other structures and preparation processes remain unchanged.

[0090] The above embodiments only illustrate the principles and advantages of the present invention, and are not intended to limit the present invention. They are only intended to help understand the principles of the present invention. The protection scope of the present invention is not limited to the above configurations and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the disclosed technology without departing from the essence of the present invention, but they are still within the protection scope of the present invention.

Claims

1. A broadband quantum dot / organic bipolar photodetector, characterized in that: It includes a substrate, a transparent electrode layer, a first photosensitive layer, an electron transport layer, a second photosensitive layer, a hole transport layer and a metal electrode layer stacked in sequence from bottom to top; Among them, the material of the first photosensitive layer is an organic donor-acceptor mixed material, specifically P3HT:PC71BM, PBDB-T:ITIC-Th, PBDB-T:Y6, PM6:Y6 or PCE10:IEICO-4F; the material of the second photosensitive layer is a quantum dot material, specifically lead sulfide quantum dots, lead selenide quantum dots, mercury selenide quantum dots, mercury telluride quantum dots, silver sulfide quantum dots, silver selenide quantum dots or silver telluride quantum dots.

2. The broadband quantum dot / organic bipolar photodetector according to claim 1, characterized in that: The molar ratio of the donor to the acceptor in the first photosensitive layer is 1:1 to 1.

5.

3. The broadband quantum dot / organic bipolar photodetector according to claim 1, characterized in that: The thickness of the first photosensitive layer is 30-200 nm; the thickness of the second photosensitive layer is 100-300 nm.

4. The broadband quantum dot / organic bipolar photodetector according to any one of claims 1 to 3, characterized in that: By adjusting the wavelength of the irradiated light, the photocurrent polarity reversal of the broadband quantum dot / organic bipolar photodetector can be achieved.

5. The broadband quantum dot / organic bipolar photodetector according to claim 4, characterized in that: A beam of modulated light and two beams of signal light are irradiated on the wide-band quantum dot / organic bipolar photodetector at the same time. The logic gate operations of OR, AND, NOR and NAND are realized by controlling the switching state of the two signal light beams, and adjusting the wavelength of the modulated light, the intensity of the modulated light and the wavelength of the signal light; a beam of modulated light and a beam of signal light are irradiated on the wide-band quantum dot / organic bipolar photodetector at the same time. The logic gate operation of NOT is realized by controlling the switching state of the signal light.

6. The broadband quantum dot / organic bipolar photodetector according to claim 4, characterized in that: The wide-band quantum dot / organic bipolar photodetector is simultaneously irradiated with two laser beams of different wavelengths and corresponding to different photocurrent polarities. By controlling the switching states of the two laser beams, the light response current output by the wide-band quantum dot / organic bipolar photodetector is encoded to achieve optical communication encryption.

7. A method for preparing a broadband quantum dot / organic bipolar photodetector, characterized in that: The following steps are involved: Step 1, pre-treating the substrate covered with the transparent electrode layer; Step 2, preparing an organic donor-acceptor mixed solution, spin coating it on the surface of the transparent electrode layer, and annealing it at 100-120° C. for 10-20 min to obtain a first photosensitive layer; Step 3, preparing an electron transport layer on the surface of the first photosensitive layer; Step 4: prepare a quantum dot solution, spin-coat it on the surface of the electron transport layer to obtain a quantum dot film to be treated, and after solid-phase ligand exchange, obtain a layer of quantum dot film, and repeat the preparation of multiple layers of quantum dot film to obtain a second photosensitive layer; Step 5: Prepare a hole transport layer and a metal electrode layer in sequence on the surface of the second photosensitive layer, and finally obtain a wide-band quantum dot / organic bipolar photodetector.

8. The method for preparing the broadband quantum dot / organic bipolar photodetector according to claim 7, characterized in that: The solvent of the organic donor-acceptor mixed solution in step 2 is toluene, chlorobenzene or o-dichlorobenzene, the concentration of the organic donor-acceptor mixed solution is 5-25 mg / mL, the spin coating speed is 2000-12000 rpm, and the spin coating time is 20-60 s.

9. The method for preparing the broadband quantum dot / organic bipolar photodetector according to claim 7, characterized in that: The solvent of the quantum dot solution in step 4 is n-octane, n-hexane or toluene, the concentration of the quantum dot solution is 50-100 mg / mL, the spin coating speed is 2000-6000 rpm, and the spin coating time is 20-40 s.

10. The method for preparing the broadband quantum dot / organic bipolar photodetector according to claim 7, characterized in that: The specific process of solid phase ligand exchange in step 4 is: Step 4.1, preparing a ligand solution by mixing 1,2-ethanedithiol and an organic solvent in a volume ratio of 1:50 to 100, wherein the organic solvent is isopropanol or acetonitrile; Step 4.2, coating the surface of the quantum dot film to be treated with the ligand solution, leaving it to stand for 30 to 60 seconds for ligand exchange, and then removing the excess ligand solution by high-speed spin coating to obtain the quantum dot film to be cleaned; Step 4.3, applying the same organic solvent as in step 4.1 to the surface of the quantum dot film to be cleaned, leaving it to stand for 10 to 20 seconds to clean the surface residue, and then removing the excess organic solvent by high-speed spin coating to complete a cleaning process; Step 4.4: After repeating the cleaning process for several times, anneal at 50-100° C. for 10-20 minutes to obtain a quantum dot film.

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