Quantum dot photovoltaic detector with dual gradient regulation and its preparation method

Abstract

The disclosed embodiments relate to a dual-gradient controlled quantum dot photovoltaic detector, comprising: a substrate; a first electrode disposed on one side of the substrate; a quantum dot layer disposed on a side of the first electrode facing away from the substrate; and a second electrode disposed on a side of the quantum dot layer facing away from the first electrode. The quantum dot layer comprises at least one first-type quantum dot layer, at least one weak first-type quantum dot layer, at least one intrinsic-type quantum dot layer, at least one weak second-type quantum dot layer, and at least one second-type quantum dot layer, stacked sequentially along the direction from the first electrode to the second electrode. The first type is N-type, and the second type is P-type. The band gaps of the quantum dot layers of each type increase sequentially along the direction from the first electrode to the second electrode. Thus, by vertically stacking colloidal quantum dots of different types, a PIN homojunction based on dual-gradient control of band gap and doping is formed, which facilitates improving device performance and realizing an ultra-wide spectrum photovoltaic photodetector.

Description

Technical Field

[0001] The present disclosure relates to the field of optoelectronic sensing technologies, and particularly to a quantum dot photovoltaic detector with dual-gradient regulation and a preparation method thereof. Background Art

[0002] In the field of optoelectronic detection, infrared optoelectronic detectors are widely used in fields such as thermal imaging, material spectral analysis, autonomous driving assistants, monitoring, and biological health monitoring.

[0003] Among them, in traditional infrared commercial optoelectronic detectors, molecular beam epitaxy technology is mainly used for preparation, and then coupled with a silicon-based readout circuit through flip-chip bonding. However, such a processing method results in a long preparation cycle, slow production rate, and high material processing cost. At the same time, the flip-chip bonding method has a low bonding success rate. Therefore, due to its high preparation complexity, low yield, and high cost, its application range is limited, generally limited to military and scientific research, and cannot be applied on a large scale. In this regard, for short-wave and mid-wave photovoltaic infrared detectors prepared by using mercury telluride (HgTe) colloidal quantum dots to replace epitaxial semiconductors, due to doping with heterojunctions, the doping layer and the quantum dot layer material in the heterojunction have different types, resulting in problems of lattice mismatch and interface transmission, which will affect the transport efficiency of photo-generated carriers and thus affect the performance of the device. Summary of the Invention

[0004] In order to solve the above technical problems or at least partially solve the above technical problems, the present disclosure provides a quantum dot photovoltaic detector with dual-gradient regulation and a preparation method thereof.

[0005] The present disclosure provides a quantum dot photovoltaic detector with dual-gradient regulation, including:

[0006] A substrate;

[0007] A first electrode disposed on one side of the substrate;

[0008] A quantum dot layer disposed on a side of the first electrode away from the substrate;

[0009] A second electrode disposed on a side of the quantum dot layer away from the first electrode;

[0010] Wherein, the quantum dot layer includes at least one first-type quantum dot layer, at least one weak first-type quantum dot layer, at least one intrinsic-type quantum dot layer, at least one weak second-type quantum dot layer, and at least one second-type quantum dot layer stacked in sequence along a direction from the first electrode to the second electrode;

[0011] The first type is N-type, the second type is P-type, and along the direction from the first electrode to the second electrode, the band gaps of the quantum dot layers of each type increase in sequence; or, the first type is P-type, the second type is N-type, and along the direction from the first electrode to the second electrode, the band gaps of the quantum dot layers of each type decrease in sequence.

[0012] The present disclosure also provides a preparation method of a quantum dot photovoltaic detector with dual-gradient regulation for preparing any one of the above detectors; the method includes:

[0013] Providing a substrate; a first electrode is formed on one side of the substrate;

[0014] Based on liquid-phase ligand exchange, preparing at least one first-type quantum dot, at least one weak first-type quantum dot, at least one intrinsic-type quantum dot, at least one weak second-type quantum dot, and at least one second-type quantum dot;

[0015] Using the quantum dots prepared by liquid-phase ligand exchange, forming quantum dot layers in sequence on the side of the first electrode facing away from the substrate, and performing solid-phase ligand exchange; the quantum dot layers include at least one first-type quantum dot layer, at least one weak first-type quantum dot layer, at least one intrinsic-type quantum dot layer, at least one weak second-type quantum dot layer, and at least one second-type quantum dot layer;

[0016] Forming a second electrode on the side of the quantum dot layer facing away from the first electrode.

[0017] The technical solutions provided by the embodiments of the present disclosure have the following advantages compared with the prior art:

[0018] The dual-gradient-regulated quantum dot photovoltaic detector provided by the embodiments of the present disclosure includes: a substrate; a first electrode disposed on one side of the substrate; a quantum dot layer disposed on the side of the first electrode facing away from the substrate; and a second electrode disposed on the side of the quantum dot layer facing away from the first electrode; wherein the quantum dot layer includes at least one first-type quantum dot layer, at least one weak first-type quantum dot layer, at least one intrinsic-type quantum dot layer, at least one weak second-type quantum dot layer, and at least one second-type quantum dot layer stacked in sequence along the direction from the first electrode to the second electrode; the first type is N-type, the second type is P-type, and along the direction from the first electrode to the second electrode, the band gaps of the quantum dot layers of each type increase in sequence. Thus, by vertically stacking the colloidal quantum dots of each type in sequence, a PIN homojunction based on dual-gradient regulation of band gap and doping is formed. Compared with the photodetectors based on heterojunctions in the related art, there are no problems of different material types and lattice mismatch. Therefore, the lattice matching between different layers is better, the interfacial transport of photo-generated carriers between different layers is better, enabling the device to collect more photo-generated carriers to enhance the photocurrent, which is beneficial to improving the device performance and further realizing a photovoltaic photodetector with an ultra-wide spectrum. Description of the Drawings

[0019] The drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present disclosure and, together with the specification, are used to explain the principles of the present disclosure.

[0020] To more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a schematic structural diagram of a quantum dot photovoltaic detector provided by the embodiments of the present disclosure;

[0022] Figure 2 It is a schematic structural diagram of another quantum dot photovoltaic detector provided by the embodiments of the present disclosure;

[0023] Figure 3 It is a schematic diagram of the FET (field effect transistor) doping test results of a quantum dot photovoltaic detector provided by the embodiments of the present disclosure;

[0024] Figure 4 It is a schematic diagram of the energy band structure of a quantum dot photovoltaic detector provided by the embodiments of the present disclosure;

[0025] Figure 5 It is a schematic diagram of the optical absorption spectrum of a quantum dot photovoltaic detector provided by the embodiments of the present disclosure;

[0026] Figure 6 Schematic diagram of the IV curve corresponding to the PIN homojunction with dual-gradient regulation of bandgap and doping provided by the embodiments of the present disclosure;

[0027] Figure 7 Schematic diagram of the normalized spectral response of a quantum dot photovoltaic detector provided by the embodiments of the present disclosure;

[0028] Figure 8 Schematic flow chart of a preparation method of a quantum dot photovoltaic detector provided by the embodiments of the present disclosure;

[0029] Figure 9 For Figure 8 In the method shown, it is a schematic diagram of a refined process for forming a quantum dot layer in S24;

[0030] Figure 10 Schematic flow chart of the preparation of doping-regulated quantum dots provided by the embodiments of the present disclosure.

[0031] Among them, 110 is the substrate; 120 is the first electrode; 130 is the quantum dot layer; 140 is the second electrode; 131 is the first type quantum dot layer; 132 is the weak first type quantum dot layer; 133 is the intrinsic type quantum dot layer; 134 is the weak second type quantum dot layer; 135 is the second type quantum dot layer; 136 is the first intrinsic type quantum dot layer; 137 is the second intrinsic type quantum dot layer; 138 is the third intrinsic type quantum dot layer. Detailed implementation manners

[0032] In order to be able to more clearly understand the above-mentioned objects, features and advantages of the present disclosure, the solutions of the present disclosure will be further described below. It should be noted that, without conflict, the embodiments of the present disclosure and the features in the embodiments may be combined with each other.

[0033] Many specific details are set forth in the following description in order to fully understand the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present disclosure, rather than all of the embodiments.

[0034] First, in combination with the relevant background and the solutions of the embodiments of the present disclosure proposed for improvement thereof, a brief description will be given.

[0035] In the field of optoelectronic sensing technology, infrared detectors are widely used in thermal imaging, material spectral analysis, autonomous driving assistants, monitoring, and biological health monitoring. With the increasing demand for high-sensitivity, low-cost, and scalable devices capable of distinguishing consistent spectral information, infrared multispectral imaging technology has attracted great interest. Therefore, driven by the requirements of fast response and high sensitivity, photon detectors have gradually occupied the dominant position in infrared detection technology. However, the widespread use of such detectors is still limited by high-cost epitaxial semiconductors. These devices have high manufacturing complexity, low yield, and high cost. For example, the current main commercial infrared optoelectronic detectors are based on some mature epitaxial materials, such as mercury cadmium telluride (MCT), InSb, quantum wells, and type-II superlattices, and mainly use molecular beam epitaxy technology. First, indium columns are grown by epitaxy, and then they are coupled with a silicon-based readout circuit through flip-chip bonding. Such a processing method has a long cycle, slow productivity, and high material processing cost. At the same time, the flip-chip bonding method has a low bonding success rate. Due to the defects such as difficult growth of bulk materials, high technical requirements, and high cost, it limits its application range and prevents large-scale civilian production. Therefore, its application is limited to scientific research and military-related research.

[0036] In response to this, mercury telluride colloidal quantum dots (HgTe CQD) can be used as a substitute for epitaxial semiconductors because of their advantages such as synthetic scalability, mechanical flexibility, and broad-spectrum tunability, and their absorption edge covers the main atmospheric windows, including short-wave infrared (SWIR, wavelength 1.5 - 2.5 μm), mid-wave infrared (MWIR, wavelength 3 - 5 μm), and long-wave infrared (LWIR, wavelength 8 - 12 μm). In the research progress of colloidal quantum dot photovoltaic infrared detectors in the past decade, colloidal quantum dots have been successfully applied to short-wave and mid-wave infrared light detection, realizing photoconductors, phototransistors, heterojunction photovoltaic devices, optically structured enhanced devices, and dual-band photovoltaic devices with multiple junctions.

[0037] However, current multispectral infrared detectors mainly focus on dual-band detection. For example, the short wave detected by the fabricated dual-band photovoltaic device is 2.3 μm, and the mid-wave is 4 μm. In the dual-band photovoltaic infrared detector prepared based on colloidal quantum dots, by stacking the quantum dots corresponding to these two wavelengths, namely short wave (2.3 μm) and mid-wave (4 μm), vertically, the detector can detect the light detection information of these two bands, and two reverse PN junctions (p-n junction) are realized through heterojunction doping. Among them, the main doping methods for the heterojunction are to use silver telluride (Ag2Te) for P-type doping and bismuth selenide (Bi2Se3) for N-type doping. Here, taking Ag2Te as an example, Ag2Te is spin-coated on the mercury telluride colloidal quantum dot thin film, and then silver ions (Ag +) can diffuse to the thin film surface of mercury telluride colloidal quantum dots. After spin-coating Ag2Te, it is further treated with a 10 mM mercury chloride / methanol (HgCl2 / MeOH) solution to promote the diffusion of Ag + , and this method is the solid-state cation exchange method. However, there will be problems with interface transport and lattice structure mismatch in this heterojunction doping.

[0038] In addition, in the photovoltaic infrared detector mentioned above, mercury telluride colloidal quantum dots (HgTe CQD) adopt a traditional synthesis method and combine it with a solid-state ligand exchange method to treat the thin film surface. The specific methods include:

[0039] Traditional synthesis method: In a glove box under a nitrogen atmosphere, mercury chloride (HgCl2) is added to oleylamine (OAM) to obtain a mixture; the mixture is heated under a hot plate until all the mercury chloride is dissolved to form a transparent light yellow solution, and the temperature is adjusted to the required reaction temperature, and then TOPTe solution is quickly injected. Among them, by controlling the reaction time and temperature differently, the size of the quantum dots can be controlled. After the reaction is completed, a quenching solution composed of tri-n-octylphosphine (TOP), tetrachloroethylene (TCE), and dodecanethiol (DDT) is quickly added to carry out a cooling reaction.

[0040] Traditional "solid-state ligand exchange" method: After the quantum dots form a film, the film layer is immersed in an ethanedithiol / hydrochloric acid / isopropanol (EdT / HCl / IPA) (the volume ratio of the three is 1:1:20) solution for 10 s. Then it is rinsed with isopropanol (IPA) to displace the ligands on the surface of the quantum dot film.

[0041] In summary, the following defects exist in the prior art and are summarized as follows.

[0042] First: For commercial infrared photodetectors prepared by molecular beam epitaxy technology, the epitaxial materials such as mercury cadmium telluride (MCT), InSb, quantum wells, and type-II superlattices used are expensive, require high preparation technology, and have a long production cycle, thus limiting the application scope of this detector.

[0043] Second: The preparation of mercury telluride colloidal quantum dots is simple and low-cost. Although photovoltaic infrared detectors have developed rapidly in the past decade, the detection bands of current multi-spectral infrared detectors are still limited to dual bands, and there is still great research potential in infrared multi-spectra such as the 1-2.5 um short-wave range, 3-5 um mid-wave range, and 8-12 um long-wave range.

[0044] Third: The photovoltaic infrared detector for dual-band detection uses heterojunction doping. Since the doping layer and the quantum dot layer materials in the heterojunction are of different types, it will cause the problem of lattice mismatch, thereby affecting the carrier transport efficiency.

[0045] Fourthly: The current infrared detectors are only prepared by traditional synthesis methods and the "solid-state ligand exchange" method, but this will result in low mobility and responsivity, thus affecting the performance of the device, and it is difficult to change the doping state of the quantum dots after the quantum dot film is formed.

[0046] Based on this, it can be seen that using surface ligand modification of quantum dots synthesized traditionally to control the arrangement and transport characteristics of colloidal quantum dots, such as the type of charge carriers, is a key development direction for realizing a super-wide spectral detector that can work in multiple bands and distinguish multiple spectral information.

[0047] To address at least one of the above defects, the embodiments of the present disclosure propose a quantum dot photovoltaic detector with dual-gradient regulation and its preparation method. The photovoltaic detector includes a substrate; a first electrode disposed on one side of the substrate; a quantum dot layer disposed on the side of the first electrode facing away from the substrate; a second electrode disposed on the side of the quantum dot layer facing away from the first electrode; wherein the quantum dot layer includes at least one first-type quantum dot layer, at least one weak first-type quantum dot layer, at least one intrinsic-type quantum dot layer, at least one weak second-type quantum dot layer, and at least one second-type quantum dot layer stacked in sequence along the direction from the first electrode to the second electrode; the first type is N-type, the second type is P-type, and along the direction from the first electrode to the second electrode, the band gaps of the quantum dot layers of each type increase in sequence. Thus, by vertically stacking the colloidal quantum dots of each type in sequence, a PIN homojunction based on dual-gradient regulation of band gap and doping is formed, which is beneficial to improving the device performance and realizing a super-wide spectral photovoltaic photodetector.

[0048] Next, with reference to the accompanying drawings, the quantum dot photovoltaic detector with dual-gradient regulation and its preparation method provided by the embodiments of the present disclosure will be described by way of example.

[0049] In some embodiments, Figure 1 is a schematic structural diagram of a quantum dot photovoltaic detector provided by an embodiment of the present disclosure. Referring to Figure 1 , the detector includes: a substrate 110; a first electrode 120 disposed on one side of the substrate 110; a quantum dot layer 130 disposed on the side of the first electrode 120 facing away from the substrate 110; a second electrode 140 disposed on the side of the quantum dot layer 130 facing away from the first electrode 120;

[0050] Among them, the quantum dot layer 130 includes at least one first-type quantum dot layer 131, at least one weak first-type quantum dot layer 132, at least one intrinsic-type quantum dot layer 133, at least one weak second-type quantum dot layer 134, and at least one second-type quantum dot layer 135 that are sequentially stacked in the direction from the first electrode 120 to the second electrode 140; the first type is N-type, the second type is P-type, and along the direction from the first electrode 120 to the second electrode 140, the band gaps of the quantum dot layers of each type increase in sequence; or, the first type is P-type, the second type is N-type, and along the direction from the first electrode 120 to the second electrode 140, the band gaps of the quantum dot layers of each type decrease in sequence.

[0051] Exemplarily, when the first type is N-type, correspondingly, the second type is P-type; the corresponding stacked structure is: N-type quantum dot layer, weak N-type quantum dot layer, intrinsic-type quantum dot layer, weak P-type quantum dot layer, P-type quantum dot layer. Or, when the first type is P-type, correspondingly, the second type is N-type; the corresponding stacked structure is: P-type quantum dot layer, weak P-type quantum dot layer, intrinsic-type quantum dot layer, weak N-type quantum dot layer, N-type quantum dot layer.

[0052] In this way, on the basis of doping the same type of quantum dots to form quantum dots of different doping types, a homogeneous gradient junction is formed based on the quantum dots of different doping types.

[0053] Among them, the substrate 110 is a substrate for preparing a PV-type device. Exemplarily, the substrate 110 can be an aluminum oxide (Al2O3) substrate. The first electrode 120 is formed on one side of the substrate 110. Exemplarily, taking the Figure 1 shown orientation as an example, the first electrode 120 is formed above the substrate 110; on this basis, the quantum dot layer 130 is formed above the first electrode 120, and the second electrode 140 is formed above the formed quantum dot layer 130 to form a quantum dot photovoltaic photodetector. Exemplarily, the first electrode 120 can be an indium tin oxide (ITO) electrode, and the second electrode 140 can be a gold layer, which is prepared by means of magnetron sputtering, evaporation, etc. In other embodiments, it can also be other electrode materials and electrode formation methods known to those skilled in the art, which are not limited herein.

[0054] Among them, the first-type quantum dot layer 131, the weak first-type quantum dot layer 132, the intrinsic-type quantum dot layer 133, the weak second-type quantum dot layer 134, and the second-type quantum dot layer 135 are the film layers of various types included in the quantum dot layer 130, and when light is incident, a photoelectric reaction will occur in the quantum dot layer 130. It should be noted that the film layers of various types are both bandgap and doping dual-regulated film layers, that is, when the first type is N-type and the second type is P-type, an N-type quantum dot layer, a weak N-type quantum dot layer, an intrinsic-type quantum dot layer, a weak P-type quantum dot layer, and a P-type quantum dot layer are sequentially stacked above the first electrode 120, and the response wavelengths of the film layers of various types are different, and the bandgaps of the film layers increase sequentially in the direction from the first electrode 120 to the second electrode 140, thereby forming a PIN homojunction based on dual-gradient regulation of bandgap and doping.

[0055] The quantum dot photovoltaic detector provided by the embodiments of the present disclosure includes a substrate, a first electrode, a quantum dot layer formed above the first electrode, and a second electrode, and the quantum dot layer includes at least one first-type quantum dot layer, at least one weak first-type quantum dot layer, at least one intrinsic-type quantum dot layer, at least one weak second-type quantum dot layer, and at least one second-type quantum dot layer sequentially stacked in the direction from the first electrode to the second electrode, where the first type is N-type and the second type is P-type, and along the direction from the first electrode to the second electrode, the bandgaps of the quantum dot layers of various types increase sequentially. Thus, the colloidal quantum dots of various types are sequentially vertically stacked to form a PIN homojunction based on dual-gradient regulation of bandgap and doping, which is beneficial to improving the optoelectronic performance of the device and further realizing a photovoltaic photodetector with an ultra-wide spectrum.

[0056] In some embodiments, Figure 2 is a schematic structural diagram of another quantum dot photovoltaic detector provided by the embodiments of the present disclosure. Referring to Figure 2 , the response band of at least one first-type quantum dot layer 131 is long wave, and the response band of at least one weak first-type quantum dot layer 132 is medium wave; at least one intrinsic-type quantum dot layer 133 includes a first intrinsic-type quantum dot layer 136, a second intrinsic-type quantum dot layer 137, and a third intrinsic-type quantum dot layer 138 sequentially stacked in the direction from the first electrode to the second electrode. The response bands of the first intrinsic-type quantum dot layer 136 and the second intrinsic-type quantum dot layer 137 are both medium wave, and the response band of the third intrinsic-type quantum dot layer 138 is short wave; the response bands of at least one weak second-type quantum dot layer 134 and at least one second-type quantum dot layer 135 are both short wave; where the wavelength corresponding to the long wave is equal to or greater than 5 microns, the wavelength corresponding to the medium wave is less than 5 microns and equal to or greater than 3 microns, and the wavelength corresponding to the short wave is less than 3 microns.

[0057] Among them, at least one layer of first-type quantum dot layer 131, at least one layer of weak first-type quantum dot layer 132, at least one layer of intrinsic-type quantum dot layer 133, at least one layer of weak second-type quantum dot layer 134, and at least one layer of second-type quantum dot layer 135 are vertically stacked according to the wavelength range and doping state.

[0058] Exemplarily, referring to Figure 2 the orientation shown, when performing the stacking setting, the overall film layer forms quantum dot layers with different doping states corresponding to long wave, medium wave, and short wave response bands on the first electrode 120 in sequence from bottom to top according to the wavelength range, and N-type, weak N-type, intrinsic-type, weak P-type, and P-type colloidal quantum dots are formed correspondingly according to the wavelength range, that is, on one side of the intrinsic-type quantum dot layer 133 ( Figure 2 above the intrinsic-type quantum dot layer in Figure 2 ), a weak P-type quantum dot layer and a P-type quantum dot layer are sequentially formed in a stacked manner, and on the other side of the intrinsic-type quantum dot layer 133 (

[0059] below the intrinsic-type quantum dot layer in

[0060] ), a weak N-type quantum dot layer and an N-type quantum dot layer are sequentially formed in a stacked manner, thereby forming a PIN homogenous gradient junction in the photovoltaic detector. It should be noted that the specific doping regulation process for regulating quantum dot layers with different doping states corresponding to long wave, medium wave, and short wave response bands will be described in detail later. Figure 2 the orientation shown, they are sequentially stacked on the first electrode 120 in the order from bottom to top.

[0061] Exemplarily, Figure 3Schematic diagram of the doping test results of a quantum dot photovoltaic detector FET (field effect transistor) provided by an embodiment of the present disclosure, showing the doping effects of each thin film in the device. Refer to Figure 3 , where the horizontal axis X1 represents voltage, with the unit of volt (V); the vertical axis Y1 represents current, with the unit of ampere (A); L41, L42, L43, L44, L45, L46, L47 respectively represent the IV curves corresponding to 1.5um P-type quantum dots, 2um weakly P-type quantum dots, 2um intrinsic quantum dots, 3um intrinsic quantum dots, 5um intrinsic quantum dots, 5um weakly N-type quantum dots, and 10um N-type quantum dots. It can be seen from Figure 3 that by adding mercury chloride or not adding such salts in the liquid-phase ligand exchange, quantum dots of different wavelengths can be regulated to the desired doping states.

[0062] Exemplarily, Figure 4 Schematic diagram of the energy band structure of a quantum dot photovoltaic detector provided by an embodiment of the present disclosure. Refer to Figure 4 , where 51 represents the bottom energy level of the conduction band (E C ), 52 represents the top energy level of the valence band (E v ), and the difference between these two energy levels is the energy band gap. 53 represents the Fermi level (E F ), 54 represents the conduction band and valence band corresponding to the 10um N-type quantum dot layer, 55 represents the conduction band and valence band corresponding to the 5um weakly N-type quantum dot layer, 56 represents the conduction band and valence band corresponding to the 5um intrinsic quantum dot layer, 57 represents the conduction band and valence band corresponding to the 3um intrinsic quantum dot layer, 58 represents the conduction band and valence band corresponding to the 2um intrinsic quantum dot layer, 59 represents the conduction band and valence band corresponding to the 2um weakly P-type quantum dot layer, and 60 represents the conduction band and valence band corresponding to the 1.5um P-type quantum dot layer. It can be seen from Figure 4It can be seen that, exemplarily, the energy levels between 54 and 56 are divided into smaller gradient energy levels by 55, and so on for other quantum dot layers. The relationship between the positions of the conduction band and the valence band indicates that the band gaps of various types of quantum dot layers increase successively from left to right, and the doping states of the quantum dots also show a gradient effect, that is, quantum dots with different doping states such as N-type, weakly N-type, intrinsic type, P-type, and P-type are represented. In addition, this schematic diagram of the energy band structure shows that the holes generated in the quantum dot layer can be transmitted in one direction, and the electrons are transmitted in another direction, which is equivalent to setting two transmission paths for the carriers (holes and electrons), that is, facilitating the transmission of the carriers in the directions of the two electrodes (the second electrode and the first electrode). Specifically, since the holes and electrons in the carriers will recombine, the electrical signal generated after recombination will disappear accordingly. For this schematic diagram of the energy band structure, the electrons travel in the conduction band and the holes travel in the valence band. In the embodiments of the present disclosure, by stacking different quantum dot layers and obtaining the schematic diagram of the energy band structure, the transmission paths of the electrons and the holes are separated, so that the electrons and the holes will not meet and recombine, and at the same time, the transmission distances of the two can be long enough, which is conducive to the separation and transmission of the carriers.

[0063] Exemplarily, Figure 5 is a schematic diagram of the light absorption spectrum of a quantum dot photovoltaic detector provided by an embodiment of the present disclosure. As can be Figure 5 seen, where the horizontal axis X2 represents the wave number (i.e., the reciprocal of the wavelength), and the unit is cm -1 , and the vertical axis Y2 represents the absorbance, which is a dimensionless unit and is represented by a.u. (abbreviation of arbitrary units); L61, L62, L63, L64, and L65 respectively represent the absorption spectral curves of quantum dots with wavelengths of 1.5um, 2um, 3um, 5um, and 12um. As can be Figure 5 seen, through the curves of the quantum dot absorption spectrum in this figure, it can be shown that quantum dots of different bands can be synthesized when preparing a photovoltaic photodetector; it should be noted that when measuring the quantum dot absorption spectrum in an actual scenario, L65 corresponds to the synthesis of a 12um long-wave N-type quantum dot, and there are parts of intraband transitions at the curve, that is, the two small peaks on the rightmost side, indicating that the actual wavelength covers 12um. However, since the intraband transitions in this part do not show spectral response, the detection spectrum of the detector during testing can only reach 10um, and finally a photovoltaic photodetector with a spectral detection range of 1-10um is realized.

[0064] It should be noted that by vertically stacking quantum dots with different wavelengths and doping states, a long-wave, mid-wave, and short-wave infrared ultra-wide spectral photovoltaic detector formed by vertically stacking and accumulating a 10-μm long-wave N-type quantum dot, a 5-μm mid-wave weakly N-type quantum dot, a 5-μm mid-wave intrinsic quantum dot, a 3-μm mid-wave intrinsic quantum dot, a 2-μm short-wave intrinsic quantum dot, a 2-μm short-wave weakly P-type quantum dot, and a 1.5-μm short-wave P-type quantum dot can achieve responses in multiple infrared bands of short-wave, mid-wave, and long-wave, that is, it can achieve detection of an ultra-wide spectrum of 1-10 μm.

[0065] In other embodiments, quantum dots of other bands can also be used during the preparation of the detector, and their doping states can be regulated. Exemplarily, there can be 3 quantum dots of different bands, as long as these 3 bands cover the short, mid, and long bands; similarly, there can also be 4 bands, 6 bands, or other numbers of bands, which will not be elaborated or limited here. According to this extended embodiment, different values of wavelengths can also be set according to the covered band range. Exemplarily, quantum dots with the required wavelengths can be set in the short-wave range of 1-2.5 μm, the mid-wave range of 3-5 μm, and the long-wave range of 8-12 μm to regulate the formation of a PIN homogenous gradient junction, as long as the wavelength coverage range and the structure corresponding to the formation of a PIN homogenous gradient junction are satisfied. The wavelengths can also be other values or value ranges, which will not be limited here.

[0066] In some embodiments, the thickness of the N-type quantum dot layer in the photovoltaic detector is 50 nm to 70 nm; the thickness of the weakly N-type quantum dot layer is 30 nm to 50 nm; the thickness of a single-layer intrinsic quantum dot layer is 80 nm to 120 nm; the thickness of the weakly P-type quantum dot layer is 30 nm to 50 nm; the thickness of the P-type quantum dot layer is 50 nm to 70 nm.

[0067] Among them, the N-type and weakly N-type quantum dot layers in the photodetector are electron injection layers, and the P-type and weakly P-type quantum dot layers are hole transport layers. The thicknesses of the quantum dot layers of different doping types (also called doping states) can be set corresponding values according to their respective doping types (doping states) and carrier transport requirements.

[0068] Exemplarily, the first type of quantum dot layer 131 with a long wavelength of 10 μm can be set to 60 nm, the weak first type of quantum dot layer 132 with a medium wavelength of 5 μm can be set to 40 nm, the first intrinsic type quantum dot layer 136 with a medium wavelength of 5 μm can be set to 100 nm, the second intrinsic type quantum dot layer 137 with a medium wavelength of 3 μm can be set to 100 nm, the third intrinsic type quantum dot layer 138 with a short wavelength of 2 μm can be set to 100 nm, the weak second type of quantum dot layer 134 with a short wavelength of 2 μm can be set to 40 nm, and the second type of quantum dot layer 135 with a short wavelength of 1.5 μm can be set to 60 nm. In other embodiments, the film thicknesses of different wavelengths can also be other thickness values or thickness ranges, which will not be elaborated or limited herein.

[0069] In some embodiments, the substrate 110 includes a readout circuit substrate (not shown in the figure); the detector further includes: a signal processing circuit (not shown in the figure); the signal processing circuit is connected to the readout circuit substrate; the signal processing circuit is configured to determine information about the target detection object based on the optoelectronic response signal transmitted by the readout circuit substrate.

[0070] In other embodiments, the photovoltaic detector may further include other components known to those skilled in the art, which will not be elaborated or limited herein.

[0071] In some embodiments, the quantum dot layers are all mercury telluride quantum dot layers.

[0072] Exemplarily, Figure 6 is a schematic diagram of the IV curve corresponding to the PIN homojunction with bandgap and doping double gradient regulation provided by an embodiment of the present disclosure. Among them, the horizontal axis X3 represents voltage, with the unit of volt (V); the vertical axis Y3 represents current, with the unit of microampere (μA); referring to Figure 6 , the operating temperature of the device is 80K, where L71 represents the dark current curve, and L72 represents the photocurrent curve with a blackbody at 873K as the infrared light source, and it will have a relatively large response to the entire blackbody spectrum. Therefore, this figure shows that the device can work normally, the sensitivity of the prepared photovoltaic detector is relatively high, and the test results of its operation are similar to those of a normal PIN junction.

[0073] Exemplarily, Figure 7 is a schematic diagram of the normalized spectral response of a quantum dot photovoltaic detector provided by an embodiment of the present disclosure. Referring to Figure 7 , where the horizontal axis X4 represents wavenumber (i.e., the reciprocal of wavelength), with the unit of cm -1 ; the vertical axis Y4 represents the normalized spectral response; as can be seen from Figure 7 , this figure shows that the detector can cover the spectral ranges of short wave, medium wave, and long wave, and the response in the entire band is relatively balanced.

[0074] The dual-gradient-regulated quantum dot photovoltaic detector provided by the embodiments of the present disclosure includes: a substrate; a first electrode disposed on one side of the substrate; a quantum dot layer disposed on the side of the first electrode facing away from the substrate; and a second electrode disposed on the side of the quantum dot layer facing away from the first electrode. Among them, the quantum dot layer includes at least one first-type quantum dot layer, at least one weakly first-type quantum dot layer, at least one intrinsic-type quantum dot layer, at least one weakly second-type quantum dot layer, and at least one second-type quantum dot layer that are sequentially stacked along the direction from the first electrode to the second electrode. The first type is N-type, the second type is P-type, and along the direction from the first electrode to the second electrode, the band gaps of the quantum dot layers of each type increase in sequence. Thus, by sequentially vertically stacking colloidal quantum dots of each type, a PIN homojunction based on dual-gradient regulation of band gap and doping is formed, which is beneficial to improving the device performance and realizing a photovoltaic photodetector with an ultra-wide spectrum.

[0075] On the basis of the above embodiments, the embodiments of the present disclosure further provide a preparation method of a dual-gradient-regulated quantum dot photovoltaic detector. This preparation method can be used to prepare any one of the detectors provided by the above embodiments and has corresponding beneficial effects.

[0076] In some embodiments, Figure 8 is a schematic flowchart of a preparation method of a quantum dot photovoltaic detector provided by the embodiments of the present disclosure. Referring to Figure 8 , the method includes:

[0077] S21. Provide a substrate.

[0078] Among them, the substrate 110 is used to support and protect other film layers or thin films formed thereon. The substrate 110 is the substrate 110 for forming at least one first-type quantum dot layer 131, at least one weakly first-type quantum dot layer 132, at least one intrinsic-type quantum dot layer 133, at least one weakly second-type quantum dot layer 134, and at least one second-type quantum dot layer 135.

[0079] S22. A first electrode is formed on one side of the substrate.

[0080] Among them, the first electrode 120 is directly disposed on the substrate 110. In other embodiments, the first electrode 120 can also be formed on the substrate by evaporation or other process steps, which is not specifically limited herein.

[0081] Exemplarily, the material of the first electrode 120 can be indium tin oxide (i.e., Indium Tin Oxide, ITO), which is an N-type semiconductor material with high conductivity, high visible light transmittance, high mechanical hardness, and chemical stability. Exemplarily, ITO can be deposited on the substrate 110 by magnetron sputtering or physical vacuum evaporation method, that is, the first electrode 120 is an ITO conductive layer. Exemplarily, the thickness of the first electrode can be 50nm, 60nm, 40nm, 40 - 60nm, or other thickness values or thickness ranges, which are not limited here.

[0082] S23. Prepare at least one first type of quantum dot, at least one weakly first type of quantum dot, at least one intrinsic type of quantum dot, at least one weakly second type of quantum dot, and at least one second type of quantum dot based on liquid-phase ligand exchange.

[0083] Among them, the liquid-phase ligand exchange can be carried out twice; Exemplarily, the first liquid-phase ligand exchange realizes the high carrier mobility of the colloidal quantum dots; the second liquid-phase ligand exchange realizes the different doping states of the synthesized colloidal quantum dots of different bands, that is, forms the first type of quantum dot layer 131 with long waves, the weakly first type of quantum dot layer 132 with medium waves, the intrinsic type of quantum dot layer 133 with medium and short waves, the weakly second type of quantum dot layer 134 with short waves, and the second type of quantum dot layer 135 with short waves. The specific preparation process will be detailed later.

[0084] S24. Using the quantum dots prepared by liquid-phase ligand exchange, form quantum dot layers in sequence on the side of the first electrode facing away from the substrate, and perform solid-phase ligand exchange.

[0085] Among them, at least one first type of quantum dot layer, at least one weakly first type of quantum dot layer, at least one intrinsic type of quantum dot layer, at least one weakly second type of quantum dot layer, and at least one second type of quantum dot layer are prepared by performing liquid-phase ligand exchange twice, and the quantum dots of different types are laminated into a film in sequence on the side of the first electrode 120 facing away from the substrate 110.

[0086] Among them, after the film formation of each type of quantum dot layer, solid-phase ligand exchange is performed on the formed film layer, that is, surface treatment is performed on each film layer; in this step, the Fermi energy levels of each film layer are stabilized and the excess ligands on the surface of each film layer are removed through solid-phase ligand exchange, laying a foundation for the formation of short-wave, medium-wave, and long-wave infrared ultra-wide spectral photovoltaic detectors.

[0087] It should be noted that the high carrier mobility of quantum dots is achieved by using a mixed-phase ligand exchange method that combines liquid-phase ligand exchange with solid-state ligand exchange, and the doping state of quantum dots in different wavelength bands can be precisely controlled in this process; for example, the embodiment of the present disclosure may include quantum dots with corresponding doping states of wavelengths of 10um, 5um, 3um, 2um, and 1.5um, and by vertically superimposing quantum dots with different wavelengths and different doping states, a 10um long-wave N-type quantum dot layer, a 5um medium-wave N-type quantum dot layer, and a 1.5um long-wave N-type quantum dot layer are formed. A weak N-type quantum dot layer, a 5um medium-wave first intrinsic type quantum dot layer, a 3um medium-wave second intrinsic type quantum dot layer, a 2um short-wave third intrinsic type quantum dot layer, a 2um short-wave weak P-type quantum dot layer, and a 1.5um short-wave P-type quantum dot layer are formed based on this, and a homojunction with dual gradient control of band gap and doping is formed, short-wave, medium-wave, and long-wave infrared ultra-wide spectrum photovoltaic detectors. Further, it provides conditions for the production of short-wave, medium-wave, and long-wave infrared ultra-wide spectrum photovoltaic detectors, and ultimately realizes ultra-wide spectrum photoelectric detection of short-wave, medium-wave, and long-wave.

[0088] In the embodiment of the present disclosure, the quantum dot layer includes at least one first type quantum dot layer, at least one weak first type quantum dot layer, at least one intrinsic type quantum dot layer, at least one weak second type quantum dot layer and at least one second type quantum dot layer.

[0089] Among them, after synthesizing quantum dots in the shortwave, mediumwave and longwave ranges, the doping states of the quantum dots in the shortwave, mediumwave and longwave ranges are changed by utilizing the second liquid-phase ligand exchange to prepare second-type quantum dots, weak second-type quantum dots and third intrinsic-type quantum dots corresponding to shortwave, second intrinsic-type quantum dots, first intrinsic-type quantum dots and weak first-type quantum dots corresponding to mediumwave, and first-type quantum dots corresponding to longwave. The quantum dot layer prepared in this process can be a preset number of film layers, that is, according to the actual application scenario, the number and type of film layers can be set according to the response wavelength requirements of the photodetector to form at least one layer of quantum dot layers with different doping states covering the shortwave, mediumwave and longwave ranges to meet the structure of the PIN homogeneous gradient junction.

[0090] S25. Form a second electrode on a side of the quantum dot layer away from the first electrode.

[0091] The second electrode 140 is disposed on the other side of the overall quantum dot layer 130 opposite to the first electrode 120 , that is, the first electrode 120 and the second electrode 140 are respectively disposed on both sides of the overall quantum dot layer 130 for outputting photoelectric signals.

[0092] Exemplarily, the material of the second electrode 140 may be gold, and the forming method may be evaporation coating, which is used as the contact point of the detector; in other embodiments, the second electrode 140 may also adopt other materials known to those skilled in the art and be formed by other processes, which will not be elaborated here.

[0093] Thus, by using liquid-phase ligand exchange in room-temperature mixed ligand exchange, doping regulation of quantum dots with different wavelengths is achieved, and at the same time, the mobility of carriers in the thin film is also improved; exemplarily, 12-μm long-wave N-type quantum dots, 5-μm medium-wave weakly N-type quantum dots, 5-μm medium-wave intrinsic quantum dots, 3-μm medium-wave intrinsic quantum dots, 2-μm short-wave intrinsic quantum dots, 2-μm short-wave weakly P-type quantum dots, and 1.5-μm short-wave P-type quantum dots are sequentially stacked on the first electrode in the order from bottom to top to form a homojunction with dual-gradient regulation of bandgap and doping. Under the condition of 0 bias, when light is incident, the 12-μm long-wave N-type quantum dot layer and the 5-μm medium-wave weakly N-type quantum dot layer are electron injection layers, and the 2-μm short-wave weakly P-type quantum dot layer and the 1.5-μm short-wave P-type quantum dot layer are hole transport layers, forming a strong built-in electric field with the 5-μm medium-wave intrinsic quantum dot layer, the 3-μm medium-wave intrinsic quantum dot layer, and the 2-μm short-wave intrinsic quantum dot layer. Electron-hole pairs are generated in the relatively thick intrinsic region (i.e., the intrinsic quantum dot layer), and the electron-hole pairs are separated under the action of the built-in electric field, thereby forming a photocurrent, and finally the detector generates light responses in infrared bands such as short wave, medium wave, and long wave.

[0094] The preparation method of the quantum dot photovoltaic detector with dual-gradient regulation provided by the embodiments of the present disclosure stacks quantum dots with different doping states corresponding to different wavelengths in the vertical direction, so that the bandgaps of each type of quantum dot layer increase in sequence, forming an infrared ultra-wide spectral photovoltaic detector that can detect short-wave, medium-wave, and long-wave ranges; thus, light responses in different infrared bands such as short wave, medium wave, and long wave can be realized, that is, a detector can be used to achieve ultra-wide spectral detection.

[0095] In some embodiments, Figure 9 is Figure 8 a schematic flow chart of a refinement process for forming a quantum dot layer in the shown method. On the basis of Figure 8 and with reference to Figure 9 , forming a quantum dot layer includes:

[0096] S31. Provide materials for quantum dot synthesis.

[0097] Among them, the materials for quantum dot synthesis include mercury chloride, oleylamine, tetrachloroethylene, tri-n-octylphosphine, tellurium, and bis(trimethylsilyl)telluride.

[0098] Among them, mercury chloride is expressed as HgCl2, which can be of ACS reagent grade, that is, the purity is ≥99.5%; oleylamine is expressed as OAM, and its technical grade is 70%; tetrachloroethylene is expressed as TCE, which meets (HPLC, 99.9%), that is, it means that its content detected by high performance liquid chromatography exceeds 99.9%; tri-n-octylphosphine is expressed as TOP, and its technical grade is 90%; tellurium is expressed as Te, which meets tellurium particles with a purity of 99.999%; bis(trimethylsilyl)telluride is expressed as TMS2Te, and its technical grade is 98%. Thus, mercury telluride (HgTe) quantum dots can be prepared and formed.

[0099] In other embodiments, when forming other types of quantum dots, the materials for synthesis can also correspond to other materials known to those skilled in the art, which are not limited herein.

[0100] S32. Form a first solution based on tellurium and tri-n-octylphosphine.

[0101] Among them, the process of forming the first solution based on tellurium and tri-n-octylphosphine can be achieved at room temperature and in an environment with an externally added protective gas. Exemplarily, it can specifically include: at room temperature, stirring tellurium (Te) particles and tri-n-octylphosphine (TOP) solution in a glove box under a nitrogen environment to prepare a Te solution dissolved in tri-n-octylphosphine (TOP) until a bright yellow solution is formed, and the prepared concentration is 1M.

[0102] S33. React mercury chloride and oleylamine under a protective gas environment to obtain a second solution.

[0103] Among them, the protective gas is a gas that can isolate the materials it surrounds from other environmental factors and is not affected by other external environmental factors; Exemplarily, the protective gas can be nitrogen.

[0104] Among them, the obtained second solution is a clear solution in which mercury chloride is completely dissolved in oleylamine under specific temperature conditions. It is not difficult to understand that the temperature required for the reaction at this time is the temperature that can accelerate the dissolution of mercury chloride in oleylamine.

[0105] S34. Mix tetrachloroethylene and tri-n-octylphosphine and cool and store to obtain a third solution.

[0106] Among them, the third solution is a prepared quenching solution, that is, the medium used when a cooling reaction is required for synthesizing quantum dots. It should be noted that some current quenching solutions can be made by adding various surfactants to polyether-based polymer materials. Due to their inverse solubility in water, they overcome the disadvantages of fast water cooling speed, easy cracking of workpieces, slow cooling speed of oils, poor quenching effect, and flammability.

[0107] Exemplarily, in this step, 500 μl of trioctylphosphine solution and 4 ml of tetrachloroethylene solution can be taken and placed in a glass bottle, and stored in a refrigerator. In other embodiments, the amounts of the trioctylphosphine solution and tetrachloroethylene taken can also be other volume values or volume ranges, which are not limited herein.

[0108] S35. Based on the first preset temperature, inject the first solution into the second solution for reaction. After the reaction ends, add the third solution to cool down to obtain the fourth solution corresponding to the short-wave quantum dots.

[0109] Thus, the short-wave quantum dots are synthesized by the hot injection method; wherein, by controlling the synthesis temperature and reaction time during the reaction process, the desired short-wave quantum dots can be obtained.

[0110] Among them, the second solution is an oleylamine solution dissolving mercury chloride. Exemplarily, in the step of preparing the second solution corresponding to the short-wave quantum dots and the mid-wave quantum dots, in a glove box with a nitrogen environment, 27 mg (0.1 mmol, stored in nitrogen) of mercury chloride can be taken, 4 ml of oleylamine is added, and after obtaining a mixture of the two, it is placed on a heating plate, a magnetic stirrer is added to accelerate dissolution and stirring is carried out. The temperature of the heating plate is adjusted to 105 °C, and it is heated at 105 °C for 1 h until a transparent, light yellow solution is formed, which is the second solution. Exemplarily, the heating duration can be 1.5 h, 2 h, 1 - 2 h or other duration values or duration ranges, which are not limited herein.

[0111] Among them, the first solution is a solution formed based on tellurium and trioctylphosphine, and at the end of the reaction, it is cooled using the configured quenching solution, i.e., the third solution. During this process, the size of mercury telluride (HgTe) colloidal quantum dots can also be controlled by controlling the synthesis temperature and reaction time.

[0112] Among them, the first preset temperature is the synthesis temperature required for synthesizing the short-wave quantum dots; Exemplarily, in the step of synthesizing the short-wave quantum dots, after obtaining a clear second solution, when controlling the first preset temperature, the temperature is first reduced to 60 °C, and then thermally equilibrated for half an hour. After the thermal equilibration ends, 100 μl of the first solution is quickly injected, and a reaction time of 2 min can obtain 1.5 μm short-wave quantum dots; a reaction time of 9 min can obtain 2 μm short-wave quantum dots.

[0113] Among them, after synthesizing the short-wave quantum dots, after the synthesis reaction ends, the configured quenching solution, i.e., the third solution, can be added for a cooling reaction, and it is taken out from the glove box with a protective gas environment, and then water-bathed to cool down to obtain the fourth solution corresponding to the short-wave quantum dots.

[0114] S36. Based on the second preset temperature, inject the first solution into the second solution for reaction. After the reaction ends, add the third solution to cool down, and obtain the fifth solution corresponding to the mid-wave quantum dots.

[0115] Thus, the mid-wave quantum dots are synthesized by the thermal injection method; among them, by controlling the synthesis temperature and reaction time during the reaction process, the required mid-wave quantum dots can be obtained.

[0116] Among them, the second preset temperature is the synthesis temperature required for synthesizing the mid-wave quantum dots; exemplarily, in the step of synthesizing the mid-wave quantum dots, after obtaining the clear second solution, when controlling the second preset temperature, first reduce the temperature to 100 °C, then perform thermal equilibrium for half an hour. After the thermal equilibrium ends, quickly inject 100 μl of the first solution, and keep the reaction going for 4 min to obtain 3-μm mid-wave quantum dots; keep the reaction going for 20 min to obtain 5-μm mid-wave quantum dots.

[0117] Among them, after synthesizing the mid-wave quantum dots, after the synthesis reaction ends, add the pre-prepared quenching solution, i.e., the third solution, to carry out the cooling reaction, take it out from the glove box with a protective gas environment, and then perform water bath cooling to obtain the fifth solution corresponding to the mid-wave quantum dots.

[0118] S37. Based on the third preset temperature, the second solution, the bis(trimethylsilyl)telluride diluted with oleylamine, and the first solution diluted with oleylamine are reacted in sequence. After the reaction ends, add the third solution to cool down, and obtain the sixth solution corresponding to the long-wave quantum dots.

[0119] Thus, the long-wave quantum dots are synthesized by the thermal injection method; among them, by controlling the synthesis temperature and reaction time during the reaction process, the required long-wave quantum dots can be obtained.

[0120] Exemplarily, in the step of preparing the second solution corresponding to the long-wave quantum dots, take 136 mg (0.5 mmol, stored in nitrogen) of mercury chloride, add 8 ml of oleylamine, place the obtained mixture on a heating plate, add a magnetic stirrer to help accelerate dissolution and stir, adjust the temperature of the heating plate to 105 °C, and heat at 105 °C for 1 h until a transparent, light yellow solution is formed, which is the second solution.

[0121] Among them, after the bis(trimethylsilyl)telluride and the first solution are both diluted with oleylamine, they are added to the second solution in sequence for reaction to synthesize the long-wave quantum dots.

[0122] Exemplarily, in the step of diluting bis(trimethylsilyl)telluride and the first solution with oleylamine, 2 ml of oleylamine can be taken and placed in a glass bottle. After heating it on a hot plate at 120 °C for 2 hours to remove water and gas, 17.5 μl (0.0625 mmol) of bis(trimethylsilyl)telluride solution is diluted in 1 ml of dehydrated and degassed oleylamine, and 62.5 μl (0.0625 mmol) of the first solution is diluted in 1 ml of dehydrated and degassed oleylamine to obtain an oleylamine-diluted solution of bis(trimethylsilyl)telluride and the first solution.

[0123] Among them, the third preset temperature is the synthesis temperature required for synthesizing long-wave quantum dots; Exemplarily, in the step of synthesizing long-wave quantum dots, after obtaining a clear second solution, the third preset temperature is controlled to be 105 °C. In this temperature environment, 17.5 μl of the already diluted bis(trimethylsilyl)telluride is quickly injected. After the reaction lasts for 5 min, the already diluted first solution is then added drop by drop, with an average rate of dropping once every 3 s (which can be expressed as drops / 3 s). It takes 4 min to finish dropping the diluted first solution, and thus 10-μm long-wave quantum dots can be obtained.

[0124] Among them, after synthesizing long-wave quantum dots, after the synthesis reaction is completed, the prepared quenching solution, i.e., the third solution, can be added for a cooling reaction, and it is taken out from the glove box with a protective gas environment, and then water bath cooling is carried out to obtain the sixth solution corresponding to the long-wave quantum dots.

[0125] Among them, the first preset temperature is less than the second preset temperature, and the second preset temperature is less than the third preset temperature.

[0126] S38: The fourth solution, the fifth solution, and the sixth solution are respectively subjected to the first liquid-phase ligand exchange to obtain quantum dot solutions with corresponding preset carrier mobilities.

[0127] Among them, the first liquid-phase ligand exchange corresponds to the process of realizing the preset carrier mobility, and the preset carrier mobility is to achieve its high carrier mobility.

[0128] Exemplarily, this step may include:

[0129] Put the fourth solution, the fifth solution, and the sixth solution into centrifuge tubes respectively, add an appropriate amount of isopropyl alcohol (IPA) for cleaning. After stirring until it becomes turbid, place it in a centrifuge and perform centrifugal separation to precipitate. The rotation speed of the centrifuge can be 7500 r / min, and the centrifugation time can be 6 min. After centrifugation, discard the supernatant, and use a nitrogen gun to dry the precipitated quantum dots; then, redissolve the quantum dots with 6 mL of n-hexane, add 50 μL of 2-mercaptoethanol (2-me) and 15 mg of dioctadecylammonium bromide (DDAB), and then perform ultrasonic oscillation for 1 min to accelerate dissolution; then use 2.5 mL of dimethylformamide (DMF) for ultrasonic oscillation for 1 min to accelerate the transfer of quantum dots from n-hexane to DMF. When the solution shows a layering phenomenon, take out the upper layer of n-hexane, so that the quantum dots are stably distributed in DMF.

[0130] In other embodiments, the rotation speed of the centrifuge, the centrifugation time, and the time of ultrasonic oscillation are not specifically limited, and can be other values known to those skilled in the art for achieving high carrier mobility.

[0131] S39. Based on the quantum dot solution with the corresponding preset carrier mobility, perform a second liquid-phase ligand exchange, and obtain at least one preset solution corresponding to at least one first-type quantum dot, at least one weak first-type quantum dot, at least one intrinsic-type quantum dot, at least one weak second-type quantum dot, and at least one second-type quantum dot based on layering and centrifugal precipitation.

[0132] Among them, after completing the first liquid-phase ligand exchange, a quantum dot solution with the corresponding preset carrier mobility is obtained. Then, through the second liquid-phase ligand exchange, quantum dots with different doping states in different wavelength bands are realized.

[0133] Exemplarily, for obtaining at least one weak second-type quantum dot and at least one second-type quantum dot, use n-hexane and toluene for layering precipitation in the short-wave quantum dot solution stably distributed in DMF; for obtaining at least one intrinsic-type quantum dot and at least one weak first-type quantum dot, add a preset amount of mercury chloride to the short-wave and medium-wave quantum dot solutions stably distributed in DMF respectively, and perform layering precipitation; for obtaining at least one first-type quantum dot, use n-hexane and toluene for layering precipitation in the long-wave quantum dot solution stably distributed in DMF. The specific operation process will be described in detail later.

[0134] S40. Based on the preset solution, redisperse the precipitated and dried quantum dots with different doping states in dimethylformamide respectively to obtain stable quantum dot solutions with different doping states and prepare them into films.

[0135] Among them, the response wavelength bands of the quantum dots with different doping states cover short wave, medium wave, and long wave.

[0136] Among them, the preset solution is a quantum dot solution with different doping states at different wavelengths obtained after layering and centrifugal precipitation in the second liquid-phase ligand exchange. It is not difficult to understand that the quantum dots in each doping state after precipitation and drying are dispersed in dimethylformamide to obtain a stable quantum dot solution in each doping state, which is the quantum dot solution with different doping states formed by finally realizing the regulation of quantum dots at different wavelengths, and is used for the preparation of subsequent quantum dot films. Exemplarily, the quantum dots after precipitation and drying can be redispersed in 100 ul of DMF.

[0137] Among them, after obtaining stable quantum dot solutions of various types of intrinsic states, films can be formed by the method of vertical stacking. Specifically, a 10 um long-wave N-type quantum dot layer, a 5 um medium-wave weakly N-type quantum dot layer, a 5 um medium-wave first intrinsic-type quantum dot layer, a 3 um medium-wave second intrinsic-type quantum dot layer, a 2 um short-wave third intrinsic-type quantum dot layer, a 2 um short-wave weakly P-type quantum dot layer, and a 1.5 um short-wave P-type quantum dot layer can be sequentially formed on the first electrode. Exemplarily, the formation method of the quantum dot layer can be drop coating, spin coating, or other film-forming methods known to those skilled in the art, which are not limited herein.

[0138] In some embodiments, on the basis of Figure 9 the second liquid-phase ligand exchange in S39 can specifically include:

[0139] First, obtain the preset solution corresponding to the second type of quantum dots.

[0140] Specifically: Add n-hexane to the quantum dot solution with a preset carrier mobility corresponding to the short wavelength for cleaning, take out the upper layer of n-hexane after the solution is layered, and then perform centrifugal precipitation.

[0141] Exemplarily, in this step, 6 mL of n-hexane is added to the 1.5 um short-wave colloidal quantum dot DMF solution for secondary cleaning. The solution shows a layering phenomenon. At this time, the upper layer of n-hexane after layering is taken out, and then 10 mL of toluene is added for centrifugal precipitation to obtain a short-wave second type of quantum dot.

[0142] Second, obtain the preset solution corresponding to the weakly second type of quantum dots.

[0143] Specifically: Add n-hexane to the quantum dot solution with a preset carrier mobility corresponding to the short wavelength for cleaning, take out the upper layer of n-hexane after the solution is layered, and then perform centrifugal precipitation.

[0144] Exemplarily, in this step, 6 mL of n-hexane is added to the 2 um short-wave colloidal quantum dot DMF solution for secondary cleaning. The solution shows a layering phenomenon. At this time, the upper layer of n-hexane after layering is taken out, and then 10 mL of toluene is added for centrifugal precipitation to obtain a short-wave weakly second type of quantum dot.

[0145] Thirdly, obtain the preset solution corresponding to the intrinsic quantum dots.

[0146] Specifically: Add mercury chloride to the quantum dot solutions with the preset carrier mobilities corresponding to short waves and medium waves respectively, then add n-hexane for cleaning. Take out the upper layer of n-hexane after the solution is stratified, and then perform centrifugal precipitation.

[0147] Exemplarily, in this step, add 20 mg of mercury chloride to the 2-μm short-wave colloidal quantum dot DMF solution, dissolve it by shaking, then add 6 mL of n-hexane for secondary cleaning. The solution shows a stratification phenomenon. At this time, take out the upper layer of n-hexane after stratification, and then add 10 mL of toluene for centrifugal precipitation to obtain a kind of short-wave intrinsic quantum dot.

[0148] Or, in this step, add 10 mg of mercury chloride to the 3-μm medium-wave colloidal quantum dot DMF solution, dissolve it by shaking, then add 6 mL of n-hexane for secondary cleaning. The solution shows a stratification phenomenon. At this time, take out the upper layer of n-hexane after stratification, and then add 10 mL of toluene for centrifugal precipitation to obtain a kind of medium-wave intrinsic quantum dot.

[0149] Or, in this step, add 2 mg of mercury chloride to the 5-μm medium-wave colloidal quantum dot DMF solution, dissolve it by shaking, then add 6 mL of n-hexane for secondary cleaning. The solution shows a stratification phenomenon. At this time, take out the upper layer of n-hexane after stratification, and then add 10 mL of toluene for centrifugal precipitation to obtain another kind of medium-wave intrinsic quantum dot.

[0150] Fourthly, obtain the preset solution corresponding to the weak first-type quantum dots.

[0151] Specifically: Add mercury chloride to the quantum dot solution with the preset carrier mobility corresponding to medium waves, then add n-hexane for cleaning. Take out the upper layer of n-hexane after the solution is stratified, and then perform centrifugal precipitation.

[0152] Exemplarily, in this step, add 5 mg of mercury chloride to the 5-μm medium-wave colloidal quantum dot DMF solution, dissolve it by shaking, then add 6 mL of n-hexane for secondary cleaning. The solution shows a stratification phenomenon. At this time, take out the upper layer of n-hexane after stratification, and then add 10 mL of toluene for centrifugal precipitation to obtain a kind of medium-wave weak first-type quantum dot.

[0153] Fifthly, obtain the preset solution corresponding to the first-type quantum dots.

[0154] Specifically: Add n-hexane to the quantum dot solution with the preset carrier mobility corresponding to long waves for cleaning. Take out the upper layer of n-hexane after the solution is stratified, and then perform centrifugal precipitation.

[0155] Exemplarily, in this step, 6 mL of n-hexane was added to a 10-μm long-wavelength colloidal quantum dot DMF solution for secondary cleaning. The solution showed a layering phenomenon. At this time, the upper-layer n-hexane after layering was taken out, and then 10 mL of toluene was added for centrifugal precipitation to obtain a long-wavelength first-type quantum dot.

[0156] Among them, for quantum dot solutions of each wavelength with a preset carrier mobility, in the second liquid-phase ligand exchange, different doping states can be regulated by adding or not adding salts (such as mercury chloride) to the quantum dots according to different wavelength types.

[0157] It should be noted that in the above example, the dosages of mercury chloride, n-hexane, toluene, and DMF can also be other dosage values or dosage ranges, which can be set according to the preparation method and the requirements of the corresponding photodetector, and will not be elaborated or limited here.

[0158] Exemplarily, Figure 10 This is a schematic diagram of the preparation process of doped and regulated quantum dots provided by an embodiment of the present disclosure, that is, the figure shows two liquid-phase ligand exchange processes in ambient-temperature mixed ligand exchange (including liquid-phase ligand exchange and solid-phase ligand exchange). Refer to Figure 10 , where S201, S202, and S203 are the processes for achieving high carrier mobility, and S204, S205, and S206 are the processes for achieving doping regulation. Specifically, in the process of achieving high carrier mobility, the colloidal quantum dot precipitate (solid) was redissolved by adding n-hexane to obtain a colloidal quantum dot n-hexane solution. Then, 2-me, TBABr, and DMF were added and ultrasonic oscillation was performed to form a colloidal quantum dot DMF solution and the upper-layer n-hexane. Subsequently, the upper-layer n-hexane was taken out, so that the quantum dots were stably distributed in DMF and the carrier mobility was improved. Then, in the process of achieving controllable doping, in the obtained colloidal quantum dot DMF solution, mercury chloride or no mercury chloride salt was added, and 6 mL of n-hexane was added. After that, ultrasonic oscillation was performed, the upper-layer n-hexane was taken out, and then 10 mL of toluene was added to the remaining colloidal quantum dot DMF solution and centrifuged to obtain a colloidal quantum dot precipitate (solid). Then, DMF was added and dried to finally obtain a colloidal quantum dot DMF ink regulated to the corresponding doping state.

[0159] It can be seen from this that by adopting the method of improving room-temperature mixed ligand exchange (including liquid-phase ligand exchange and solid-phase ligand exchange), and through the regulation by adding salts such as HgCl2, the doping states of infrared quantum dots in different bands are realized. Doped long-wave N-type quantum dots (wavelength peak 12 μm), doped medium-wave weakly N-type quantum dots (wavelength peak 5 μm), doped medium-wave intrinsic quantum dots (wavelength peak 5 μm), doped medium-wave intrinsic quantum dots (wavelength peak 3 μm), doped short-wave intrinsic quantum dots (wavelength peak 2 μm), doped short-wave weakly P-type quantum dots (wavelength peak 2 μm), and doped short-wave P-type quantum dots (wavelength peak 1.5 μm) are successively formed in the vertical direction, forming a homojunction with dual-gradient regulation of bandgap and doping, and realizing a photovoltaic infrared photodetector that can detect ultra-wide spectra in short-wave, medium-wave, and long-wave bands, which is beneficial to further realizing an ultra-wide spectrum photodetector with light response in the infrared spectral range of 1 μm - 20 μm.

[0160] In some embodiments, solid-phase ligand exchange is performed, including: providing a treatment solution for solid-phase ligand exchange; wherein, the treatment solution includes ethanedithiol, hydrochloric acid, and isopropanol; for the formed quantum dot layer, each layer of thin film is immersed in the treatment solution, and then washed and dried.

[0161] Among them, the treatment solution includes ethanedithiol, hydrochloric acid, and isopropanol; that is, the treatment solution for performing solid-phase ligand exchange is a mixed solution of ethanedithiol, hydrochloric acid, and isopropanol, and the volume ratio of the three can be 1:1:20.

[0162] Among them, immersing each prepared thin film in the treatment solution corresponds to the process of performing solid-phase ligand exchange on the outermost layer of the film, that is, surface solid-phase ligand exchange treatment is performed on each quantum dot layer corresponding to each wavelength and doping state.

[0163] Exemplarily, the immersion time of each layer of thin film in the treatment solution can be 10 s, and then it is rinsed with isopropanol (IPA) solution and dried with a nitrogen gun. Exemplarily, the immersion time can be 10 s, 8 s, 12 s, 8 s - 12 s, or other time values or time ranges, which are not limited here.

[0164] It should be noted that in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising said element.

[0165] The above are only specific embodiments of the present disclosure, enabling those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but rather will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A quantum dot photovoltaic detector with dual-gradient regulation, characterized in that, Comprising: A substrate; A first electrode disposed on one side of the substrate; A quantum dot layer disposed on the side of the first electrode facing away from the substrate; A second electrode disposed on the side of the quantum dot layer facing away from the first electrode; Wherein, the quantum dot layer includes at least one first type quantum dot layer, at least one weak first type quantum dot layer, at least one intrinsic type quantum dot layer, at least one weak second type quantum dot layer, and at least one second type quantum dot layer stacked in sequence along the direction from the first electrode to the second electrode; The first type is N-type, the second type is P-type, and along the direction from the first electrode to the second electrode, the band gaps of the quantum dot layers of each type increase in sequence; or, the first type is P-type, the second type is N-type, and along the direction from the first electrode to the second electrode, the band gaps of the quantum dot layers of each type decrease in sequence; Wherein, the response band of the at least one first type quantum dot layer is long wave, and the response band of the at least one weak first type quantum dot layer is medium wave; The at least one intrinsic type quantum dot layer includes a first intrinsic type quantum dot layer, a second intrinsic type quantum dot layer, and a third intrinsic type quantum dot layer stacked in sequence along the direction from the first electrode to the second electrode. The response bands of the first intrinsic type quantum dot layer and the second intrinsic type quantum dot layer are both medium wave, and the response band of the third intrinsic type quantum dot layer is short wave; The response bands of the at least one weak second type quantum dot layer and the at least one second type quantum dot layer are both short wave; Wherein, the wavelength corresponding to the long wave is equal to or greater than 5 microns, the wavelength corresponding to the medium wave is less than 5 microns and equal to or greater than 3 microns, and the wavelength corresponding to the short wave is less than 3 microns, so as to form a photovoltaic photodetector with an ultra-wide spectrum based on the vertically stacked quantum dot layers.

2. The detector according to claim 1, wherein The response wavelength of the N-type quantum dot layer is 10 microns; the response wavelength of the weak N-type quantum dot layer is 5 microns; The response wavelength of the first intrinsic type quantum dot layer is 5 microns, the response wavelength of the second intrinsic type quantum dot layer is 3 microns, and the response wavelength of the third intrinsic type quantum dot layer is 2 microns; The response wavelength of the weak P-type quantum dot layer is 2 microns; the response wavelength of the P-type quantum dot layer is 1.5 microns.

3. The detector according to claim 2, wherein The thickness of the N-type quantum dot layer is 50 nm to 70 nm; The thickness of the weak N-type quantum dot layer is 30 nm to 50 nm; The thickness of a single layer of the intrinsic type quantum dot layer is 80 nm to 120 nm; The thickness of the weak P-type quantum dot layer is 30 nm to 50 nm; The thickness of the P-type quantum dot layer is 50 nm to 70 nm.

4. The detector according to claim 1, wherein The substrate includes a readout circuit substrate; The detector further includes: a signal processing circuit; the signal processing circuit is connected to the readout circuit substrate; The signal processing circuit is configured to determine information about a target detection object based on the optoelectronic response signal transmitted by the readout circuit substrate.

5. The detector according to claim 1, wherein The quantum dot layers are all mercury telluride quantum dot layers.

6. A preparation method of a quantum dot photovoltaic detector with dual-gradient regulation, characterized in that, For preparing the detector according to any one of claims 1-5; the method includes: Provide a substrate; a first electrode is formed on one side of the substrate; Prepare at least one first type of quantum dots, at least one weakly first type of quantum dots, at least one intrinsic type of quantum dots, at least one weakly second type of quantum dots, and at least one second type of quantum dots based on liquid-phase ligand exchange; For the quantum dots prepared by liquid-phase ligand exchange, form a quantum dot layer in sequence on the side of the first electrode facing away from the substrate, and perform solid-phase ligand exchange; the quantum dot layer includes at least one first type of quantum dot layer, at least one weakly first type of quantum dot layer, at least one intrinsic type of quantum dot layer, at least one weakly second type of quantum dot layer, and at least one second type of quantum dot layer; Form a second electrode on the side of the quantum dot layer facing away from the first electrode; Wherein, the response band of the at least one first type of quantum dot layer is long wave, and the response band of the at least one weakly first type of quantum dot layer is medium wave; the at least one intrinsic type of quantum dot layer includes a first intrinsic type of quantum dot layer, a second intrinsic type of quantum dot layer, and a third intrinsic type of quantum dot layer stacked in sequence along the direction from the first electrode to the second electrode. The response bands of the first intrinsic type of quantum dot layer and the second intrinsic type of quantum dot layer are both medium wave, and the response band of the third intrinsic type of quantum dot layer is short wave; the response bands of the at least one weakly second type of quantum dot layer and the at least one second type of quantum dot layer are both short wave; wherein, the wavelength corresponding to the long wave is equal to or greater than 5 microns, the wavelength corresponding to the medium wave is less than 5 microns and equal to or greater than 3 microns, and the wavelength corresponding to the short wave is less than 3 microns, so as to form a photovoltaic photodetector with an ultra-wide spectrum based on the vertically stacked quantum dot layers.

7. The method according to claim 6, wherein The forming of the quantum dot layer includes: Provide materials for quantum dot synthesis; the materials for quantum dot synthesis include mercury chloride, oleylamine, tetrachloroethylene, tri-n-octylphosphine, tellurium, and bis(trimethylsilyl)telluride; Form a first solution based on the tellurium and tri-n-octylphosphine; React mercury chloride and oleylamine to obtain a second solution under a protective gas environment; Mix tetrachloroethylene and tri-n-octylphosphine and store them after cooling to obtain a third solution; Based on a first preset temperature, inject the first solution into the second solution for reaction. After the reaction is completed, add the third solution and cool to obtain a fourth solution corresponding to short-wave quantum dots; Based on a second preset temperature, inject the first solution into the second solution for reaction. After the reaction is completed, add the third solution and cool to obtain a fifth solution corresponding to medium-wave quantum dots; Based on a third preset temperature, the second solution reacts with bis(trimethylsilyl)telluride diluted with oleylamine and the first solution diluted with oleylamine in sequence. After the reaction is completed, add the third solution and cool to obtain a sixth solution corresponding to long-wave quantum dots; wherein, the first preset temperature is less than the second preset temperature, and the second preset temperature is less than the third preset temperature; The fourth solution, the fifth solution, and the sixth solution respectively perform the first liquid-phase ligand exchange to obtain quantum dot solutions with corresponding preset carrier mobilities; Based on the quantum dot solution with the corresponding preset carrier mobility, perform a second liquid-phase ligand exchange, and based on layering and centrifugal precipitation, obtain at least one preset solution corresponding to at least one first-type quantum dot, at least one weak first-type quantum dot, at least one intrinsic-type quantum dot, at least one weak second-type quantum dot, and at least one second-type quantum dot; Based on the preset solution, redisperse the quantum dots in each doping state after precipitation and drying in dimethylformamide to obtain stable quantum dot solutions in each doping state and form films; wherein, the response bands of the quantum dots in each doping state cover short waves, medium waves, and long waves.

8. The method according to claim 7, wherein The performing of the second liquid-phase ligand exchange includes: Obtaining the preset solution corresponding to the second-type quantum dots: adding n-hexane to the quantum dot solution with the preset carrier mobility corresponding to short waves for cleaning, taking out the upper layer of n-hexane after the solution is layered, and then performing centrifugal precipitation; Obtaining the preset solution corresponding to the weak second-type quantum dots: adding n-hexane to the quantum dot solution with the preset carrier mobility corresponding to short waves for cleaning, taking out the upper layer of n-hexane after the solution is layered, and then performing centrifugal precipitation; Obtaining the preset solution corresponding to the intrinsic-type quantum dots: adding mercury chloride to the quantum dot solutions with the preset carrier mobility corresponding to short waves and medium waves respectively, then adding n-hexane for cleaning, taking out the upper layer of n-hexane after the solution is layered, and then performing centrifugal precipitation; Obtaining the preset solution corresponding to the weak first-type quantum dots: adding mercury chloride to the quantum dot solution with the preset carrier mobility corresponding to medium waves, then adding n-hexane for cleaning, taking out the upper layer of n-hexane after the solution is layered, and then performing centrifugal precipitation; Obtaining the preset solution corresponding to the first-type quantum dots: adding n-hexane to the quantum dot solution with the preset carrier mobility corresponding to long waves for cleaning, taking out the upper layer of n-hexane after the solution is layered, and then performing centrifugal precipitation.

9. The method according to claim 6, wherein The performing of the solid-phase ligand exchange includes: Providing a treatment solution for solid-phase ligand exchange; wherein, the treatment solution includes ethanedithiol, hydrochloric acid, and isopropanol; For the formed quantum dot layer, immerse each thin film in the treatment solution, and then clean and dry.

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