CN118475138A - N-i-p-i-n type visible-infrared dual-band photoelectric detector and preparation method thereof - Google Patents

Abstract

The present invention discloses a n‑i‑p‑i‑n type visible‑infrared dual-band photodetector and a preparation method thereof, and belongs to the field of photoelectric detection technology. The method comprises: growing a _TiO2 film on a substrate as a first electron transport layer; growing _{a Sb2S3} film on the first electron transport layer as a first intrinsic absorption layer; forming a PbS‑EDT quantum dot film on the first intrinsic absorption layer as a hole transport layer based on a solid phase ligand exchange method; forming a PbS‑IBr quantum dot film on the hole transport layer as a second intrinsic absorption layer based on a liquid phase ligand exchange method; depositing a ZnO film on the second intrinsic absorption layer as a second electron transport layer; exposing a portion of a conductive glass substrate to prepare two groups of metal electrodes contacting the second electron transport layer and the substrate, respectively. The present invention realizes visible and infrared dual-band photoelectric detection with voltage bias adjustment switching in a single device, which greatly broadens the spectral detection range and its application field.

Description

A n-i-p-i-n type visible-infrared dual-band photoelectric detector and its preparation method

Technical Field

The present invention belongs to the technical field of photoelectric detection, and in particular relates to an n-i-p-i-n type visible-infrared dual-band photoelectric detector and a preparation method thereof.

Background Art

Visible light and infrared dual-band photodetectors have very broad application prospects in signal detection, biological imaging, optical communications and security monitoring. At present, silicon-based photodetectors, as the main force of visible light and near-infrared band detection devices, have the advantages of high efficiency and low power consumption and are widely used in various fields.

However, the bandgap width of silicon is about 1.1eV, and photon energy less than 1.1eV cannot be absorbed by silicon, resulting in essentially zero light absorption of silicon-based detectors in the near- and mid-infrared bands, which greatly limits the development of silicon-based detectors in the near-infrared and mid- and far-infrared bands with wavelengths greater than 1100nm. Moreover, the existing silicon-based detectors on the market mainly perform single-band spectral detection, which has limitations in wide-band detection, limiting their application in some fields. When faced with new demands such as narrow bandgap detection and multi-color imaging, silicon-based detectors often need to integrate filters, additional optical interfaces, and complex structural designs to achieve detection functions, thereby reducing the resolution of photoelectric detection imaging arrays.

Compared with the shortcomings of silicon-based detectors, quantum dot materials have been widely used in the field of photoelectric detection and solar cells in recent years due to their advantages such as quantum confinement effect, multi-exciton generation effect, diversified film preparation, low cost, and adaptability to flexible substrates. Lead sulfide colloidal quantum dots (PbS CQDs) can be sized and regulated during solution synthesis so that their absorption band edge can be adjusted within the range of 400nm~3000nm, covering the entire short-wave infrared region. In addition, PbSCQDs have a high absorption coefficient and are therefore often used as the light-absorbing layer of infrared devices. At present, although there are some reports on PbSCQDs near-infrared photodetectors, they are all single-light-absorbing layer strategies. It is challenging for these photodetection devices to respond to light in various bands and achieve switchable light detection.

In contrast, strategies based on multiple photosensitive materials have attracted increasing attention because they can selectively activate one of the photoresponsive channels by applying different bias voltages, thus achieving switchable dual-band photodetection in a single device.

In view of the above-mentioned deficiencies in the prior art, there is an urgent need to develop a new visible light-infrared dual-band photodetector that is a combination of multiple photosensitive materials with adjustable voltage bias.

Summary of the invention

In view of this, the object of the present invention is to provide an n-i-p-i-n type visible-infrared dual-band photoelectric detector and a preparation method thereof, aiming to solve at least one technical problem among the background technology.

The present invention is achieved in that:

The first aspect of the present invention provides an n-i-p-i-n type visible-infrared dual-band photodetector, which adopts a vertical n-i-p-i-n structure based on two photosensitive materials;

The photodetector comprises:

substrate;

A first electron transport layer, a first intrinsic absorption layer made of a visible light-sensitive material, a hole transport layer, a second intrinsic absorption layer made of an infrared light-sensitive material, and a second electron transport layer are sequentially grown on the substrate;

A first metal electrode contacts the second electron transport layer and a second metal electrode contacts the substrate.

Preferably, the substrate is a conductive glass substrate;

The first electron transport layer is a _TiO2 thin film;

The first intrinsic absorption layer is a Sb ₂ S ₃ thin film made of visible light sensitive material;

The hole transport layer adopts PbS-EDT quantum dot film;

The second intrinsic absorption layer is a PbS-IBr quantum dot film made of infrared photosensitive material;

The second electron transport layer is made of ZnO thin film;

The materials of the first metal electrode and the second metal electrode are selected from gold, aluminum or titanium.

The second aspect of the present invention provides a method for preparing the above-mentioned n-i-p-i-n type visible-infrared dual-band photoelectric detector, comprising the following steps:

Providing a conductive glass substrate;

Growing a _TiO2 thin film on a conductive glass substrate as the first electron transport layer;

Growing a Sb ₂ S ₃ thin film on the first electron transport layer as a first intrinsic absorption layer for absorbing visible light;

A PbS-EDT quantum dot film is formed on the first intrinsic absorption layer based on a solid phase ligand exchange method as a hole transport layer;

Based on the liquid phase ligand exchange method, a PbS-IBr quantum dot film is formed on the hole transport layer as a second intrinsic absorption layer for absorbing infrared light;

A ZnO film is deposited on the second intrinsic absorption layer as a second electron transport layer;

A portion of the conductive glass substrate is exposed to prepare two groups of metal electrodes, wherein the first metal electrode contacts the second electron transport layer; and the second metal electrode contacts the conductive glass substrate.

Preferably, the solid phase ligand exchange method is: spin coating a quantum dot PbS solution on the first intrinsic absorption layer to form a PbS film, and dropping an EDT ligand solution onto the PbS film to perform ligand exchange to form a PbS-EDT quantum dot film.

Preferably, the step of forming a PbS-EDT quantum dot film on the first intrinsic absorption layer based on a solid phase ligand exchange method comprises:

(1) preparing an EDT-acetonitrile solution and a first PbS quantum dot solution dissolved in a non-polar organic solvent;

(2) spin coating a first PbS quantum dot solution on the first intrinsic absorption layer to form a PbS thin film;

(3) Add EDT-acetonitrile solution until the PbS film is completely covered. After standing, EDT fully replaces the oleic acid on the surface of the first PbS quantum dot to achieve ligand exchange and form a PbS-EDT quantum dot film.

(4) using a protic polar solvent to wash and remove the residual solution;

(5) Repeat steps (2) to (4) at least once until the PbS-EDT quantum dot film reaches a set thickness.

Preferably, the first PbS quantum dot solution uses PbS quantum dots with an absorption peak of 880 nm.

Preferably, the step of forming a PbS-IBr quantum dot film on the hole transport layer based on a liquid phase ligand exchange method comprises:

Preparing a halogen ion IBr ligand solution dissolved in a polar organic solvent and a second PbS quantum dot solution dissolved in a non-polar organic solvent;

Adding the halogen ion IBr ligand solution dropwise to the second PbS quantum dot solution, shaking vigorously and then standing to separate layers, completing the replacement of the long-chain oleic acid ligands on the surface of the second PbS quantum dot by ^I- and Br ^- ligands;

The upper clarified liquid and the lower liquid are phase separated, and the lower liquid is washed with a non-polar organic solvent to remove the long-chain oleic acid ligand;

After adding ethyl acetate, a precipitation reaction occurs, and then a black precipitate is obtained by physical separation, and then a drying process is performed to obtain PbS-IBr quantum dot powder coated with I ^- and Br ^- ions;

The PbS-IBr quantum dot powder is dissolved in an amine mixed solvent to form a PbS-IBr solution, the PbS-IBr solution is spin-coated on the hole transport layer to form a film, and finally annealing treatment is performed to obtain a PbS-IBr quantum dot film.

Preferably, the second PbS quantum dot solution uses PbS quantum dots with an absorption peak of 1000nm~1800nm.

Preferably, the first metal electrode and the second metal electrode are prepared by vacuum thermal evaporation; and the conductive glass substrate is an ITO glass substrate or a FTO glass substrate.

Preferably, the thickness of the conductive glass substrate is 350 nm to 450 nm, preferably 400 nm;

The thickness of the _TiO2 film is 45nm~55nm, preferably 50nm;

The thickness of the ZnO film is 120nm-170nm, preferably 150nm;

The thickness of the Sb ₂ S ₃ film is 400nm~800nm;

The thickness of the PbS-EDT quantum dot film is 40nm-50nm, preferably 50nm;

The thickness of the PbS-IBr quantum dot film is 350nm-450nm, preferably 400nm.

Compared with the prior art, the present invention combines the detection capabilities of visible light and infrared light, and can perform dual detection. By simultaneously sensing visible light and infrared light, the accuracy and reliability of target detection are improved, and the false alarm rate is reduced. When the device is reverse biased, it is used for near-infrared light response, and when forward biased, it is used for visible light response. At the same time, the present invention can achieve the functions of high sensitivity, fast response, low dark current, etc. of the detector by comparing the detection information of visible light and infrared light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of an n-i-p-i-n type visible-infrared dual-band photoelectric detector according to the present invention;

FIG2 is a current density-voltage curve diagram of the dual-band photodetector prepared in Example 1 of the present invention under irradiation of light of different bands;

FIG3 is a graph showing the quantum efficiency of the dual-band photodetector obtained in Example 1 of the present invention as a function of wavelength;

FIG. 4 is a graph showing the variation of the responsivity of the dual-band photodetector obtained in Example 1 of the present invention with wavelength.

Illustration: 1-substrate, 2-first electron transport layer, 3-first intrinsic absorption layer, 4-hole transport layer, 5-second intrinsic absorption layer, 6-second electron transport layer, 7-first metal electrode, 8-second metal electrode.

DETAILED DESCRIPTION

In order to facilitate understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of the following embodiments is to make the disclosure of the present invention more thorough and comprehensive.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and/or" used herein includes any and all combinations of one or more of the related listed items.

As shown in Figure 1, an n-i-p-i-n type visible-infrared dual-band photodetector adopts a vertical n-i-p-i-n structure based on two photosensitive materials; it realizes dual-band detection in a single device, greatly broadening the spectral detection range and its corresponding fields.

Specifically, the photodetector includes: a substrate 1; a first electron transport layer 2, a first intrinsic absorption layer 3 made of a visible light-sensitive material, a hole transport layer 4, a second intrinsic absorption layer 5 made of an infrared light-sensitive material, and a second electron transport layer 6 grown in sequence on the substrate 1; a first metal electrode 7 contacting the second electron transport layer 6 and a second metal electrode 8 contacting the substrate 1.

The substrate 1 is a conductive glass substrate, such as an indium tin oxide ITO glass substrate, a fluorine tin oxide FTO glass substrate, etc. The first electron transport layer 2 is a _TiO2 film; the first intrinsic absorption layer 3 is _{a Sb2S3} film made of a visible light sensitive material; the hole transport layer 4 is a PbS-EDT quantum dot film; the second intrinsic absorption layer 5 is a PbS-IBr quantum dot film made of an infrared light sensitive material; the second electron transport layer 6 is a ZnO film. Among them, metal oxides such as _TiO2 film and ZnO film can be prepared by physical deposition film methods, including but not limited to radio frequency magnetron sputtering, molecular beam epitaxy, spray pyrolysis, etc. _{The Sb2S3} film as a visible light absorption layer is prepared by rapid thermal evaporation, and the PbS-EDT quantum dot film as a hole transport layer and the PbS-IBr quantum dot film as an infrared light absorption layer are prepared by chemical spin coating. The materials of the first metal electrode 7 and the second metal electrode 8 are selected from gold, aluminum, titanium, etc., and are prepared by vacuum thermal evaporation.

The present invention is based on two photosensitive materials and combines a unique optical device structure (n-i-p-i-n structure) to achieve voltage-biased adjustable visible light-infrared dual-band photoelectric detection in a single device. Compared with traditional detectors, the photoelectric detector of the present invention greatly broadens the spectral detection range and its application field.

The principle of the dual-wave photoelectric detector of the present invention is:

First, two different electron transport layers are introduced: a first electron transport layer 2 composed of a _TiO2 thin film and a second electron transport layer 6 composed of a ZnO thin film, which can form a good energy level matching interface with the conductive film (such as ITO, FTO) of the conductive glass substrate and the first metal electrode 7, respectively, which is helpful to effectively transmit and collect photogenerated electrons;

Secondly, under forward voltage, that is, the second metal electrode 8 on the conductive glass substrate is connected to the negative pole of the power supply, and the first metal electrode 7 at the front end is connected to the positive pole of the power supply, the front heterojunction such as _{the Sb2S3} film is in a reverse bias state, and can generate photocurrent under visible light irradiation, while the back heterojunction such as the PbS-IBr quantum dot film is in a forward bias conduction state. At this time, the device behaves as the front heterojunction working and can perform visible light detection; on the contrary, under reverse voltage, that is, the second metal electrode 8 on the conductive glass substrate is connected to the positive pole of the power supply, and the first metal electrode 7 at the front end is connected to the negative pole of the power supply, the front heterojunction is in a forward bias state and has a conduction function, and the back heterojunction is in a reverse bias state, and can generate photocurrent under infrared light irradiation. At this time, it behaves as the back heterojunction working and can perform near-infrared light detection.

Therefore, the independent carrier transfer process of the visible light-infrared light photodetection mode gives the device of the present invention a voltage-biasable dual-band detection function.

A method for preparing an n-i-p-i-n type visible-infrared dual-band photoelectric detector comprises the following steps:

S100, providing a conductive glass substrate with a thickness of 350nm-450nm;

Specifically, a physical deposition method such as radio frequency magnetron sputtering, molecular beam epitaxy, etc. is used to sputter-deposit an indium tin oxide ITO or fluorine tin oxide FTO thin film on a transparent glass as a substrate, and the estimated thickness of the substrate is about 350nm~450nm.

S200, growing a _TiO2 thin film with a thickness of 45nm-55nm on a conductive glass substrate as a first electron transport layer;

Specifically, a _TiO2 thin film is deposited on a substrate by using a spray pyrolysis method or other deposition methods in the art; the spray pyrolysis method in the present invention can adopt a method commonly used in the art, such as:

(1) Diisopropyl di(acetylacetonate)titanate and anhydrous ethanol were mixed in a volume ratio of 1:9, 20 mL of the mixed liquid was taken out and subjected to electromagnetic stirring for 48 hours, and the obtained solution was used as a precursor solution for spraying;

(2) The conductive glass substrate is cleaned by an ultrasonic cleaner and then heated to 450°C, and then the precursor solution is sprayed on the surface of the conductive glass substrate several times by an air compressor;

(3) After spraying, anneal at about 500°C for about 30 minutes, and then naturally cool to obtain a _TiO2 film of a certain thickness.

The parameters of the above-mentioned spray pyrolysis method can be adjusted according to actual needs and are not specifically limited here.

S300, growing a visible light absorption layer Sb ₂ S ₃ thin film with a thickness of 400nm-800nm on the first electron transport layer as a first intrinsic absorption layer;

Specifically, _{the Sb2S3} film placed on the surface of the _TiO2 film is prepared by a rapid thermal evaporation method, and the steps are as follows:

(1) Disperse about 0.4 g of Sb ₂ S ₃ powder evenly on a clean glass sheet of the same size as the conductive glass, and then place the glass sheet containing Sb ₂ S ₃ powder on a silicon nitride support sheet in a rapid annealing furnace as an evaporation source;

(2) Place the conductive glass substrate with the _TiO2 film deposited in a rapid annealing furnace, heat it to about 300°C for 30 seconds and keep it at a constant temperature for about 20 minutes, then continue to heat it to 550°C, at which time _{the Sb2S3} powder begins to evaporate gradually and keeps the temperature constant for 30-60 seconds. After the time is up, _{a Sb2S3} film with a thickness of about 400nm~800nm is obtained. The vacuum degree must be maintained at less than ^10-3 Torr during the entire evaporation process;

The Sb ₂ S ₃ thin film can also be prepared by other methods in the art. The parameters of the above-mentioned rapid thermal evaporation method can be adjusted according to actual needs and are not specifically limited here.

S400, forming a PbS-EDT quantum dot film on the first intrinsic absorption layer based on a solid phase ligand exchange method as a hole transport layer; specifically comprising:

(1) preparing an EDT-acetonitrile solution and a first PbS quantum dot solution dissolved in a non-polar organic solvent;

(2) spin coating a first PbS quantum dot solution on the first intrinsic absorption layer to form a PbS thin film;

(3) Add EDT-acetonitrile solution until the PbS film is completely covered. After standing, EDT fully replaces the oleic acid on the surface of the first PbS quantum dot to achieve ligand exchange and form a PbS-EDT quantum dot film.

(4) using a protic polar solvent to wash and remove the residual solution;

(5) Repeat steps (2) to (4) at least once until the PbS-EDT quantum dot film reaches a set thickness.

The first PbS quantum dot solution uses PbS quantum dots with an absorption peak of 880nm, which can achieve good band alignment and reduce interface defects; the non-polar organic solvent and the proton polar solvent in step S400 use conventional organic solvents in the technical field, such as n-octane for the non-polar organic solvent and pure acetonitrile for the proton polar solvent. The final thickness of the PbS-EDT quantum dot film is set to 40nm~50nm.

S500, forming a PbS-IBr quantum dot film on the hole transport layer based on a liquid phase ligand exchange method as a second intrinsic absorption layer; specifically comprising:

(1) preparing a halogen ion IBr ligand solution dissolved in a polar organic solvent and a second PbS quantum dot solution dissolved in a non-polar organic solvent;

(2) adding the halogen ion IBr ligand solution to the second PbS quantum dot solution, shaking vigorously and then standing to separate the layers, thereby completing the replacement of the long-chain oleic acid ligands on the surface of the second PbS quantum dots by ^I- and Br ^- ligands;

(3) separating the upper clarified liquid from the lower liquid, and washing the lower liquid with a non-polar organic solvent to remove the long-chain oleic acid ligand;

(4) After adding ethyl acetate, a precipitation reaction occurs, and then a black precipitate is obtained by physical separation, and then dried to obtain PbS-IBr quantum dot powder coated with I ^- and Br ^- ions;

(5) The PbS-IBr quantum dot powder is dissolved in an amine mixed solvent to form a PbS-IBr solution, the PbS-IBr solution is spin-coated on the hole transport layer to form a film, and finally annealed at 80°C to 90°C for several minutes to obtain a PbS-IBr quantum dot film.

The second PbS quantum dot solution uses PbS quantum dots with an absorption peak of 1000nm~1800nm, preferably 1300nm, and a band gap of 0.95eV. The polar organic solvent, non-polar organic solvent, and amine mixed solvent in step S500 use conventional organic solvents in the art, such as N-N dimethylformamide DMF as the polar organic solvent, n-octane as the non-polar organic solvent, and a mixture of n-butylamine, n-pentylamine, and n-hexylamine as the amine mixed solvent; the thickness of the PbS-IBr quantum dot film is 350nm~450nm.

The mechanism of the change in the structure and performance of the infrared absorption layer PbS quantum dot film before and after the halogen mixed ion IBr ligand exchange is:

PbS quantum dot film is composed of countless quantum dots, so it has a very large surface area, which leads to the surface properties of a single quantum dot having a great influence on the performance of the entire film; there are usually dangling bonds on the surface of quantum dots, which provide additional electronic states, and for the entire film, these electronic states may become defect states between the forbidden bands, thereby affecting the electrical properties of the entire quantum dot film. By introducing ligands to connect to the surface dangling bonds, the surface states can be passivated;

However, different ligands have different passivation effects on PbS quantum dots. The surface of PbS quantum dots is usually composed of {111} planes and {100} planes. The {111} planes are composed of densely arranged lead atoms and can be tightly combined with organic long-chain ligands. The {100} planes are composed of arranged lead atoms and sulfur atoms and are not easy to combine with organic long-chain ligands. Therefore, insufficient passivation of the {100} plane will increase the defect state density on the surface of quantum dots, which is very likely to cause etching on the surface of quantum dots and agglomeration and fusion between quantum dots, resulting in reduced device performance.

As the size of PbS quantum dots increases, the ratio of {100} plane to {111} plane increases; therefore, how to effectively passivate {100} plane and reduce the density of defect states on the surface of quantum dots becomes the key to improving the performance of quantum dot films. The present invention passivates the {100} plane on the surface of PbS quantum dots by short-chain mixed halogen ions. Small-sized halogen ions such as bromide ions can be tightly adsorbed on the {100} plane to effectively passivate the defects on its {100} plane, while large-sized halogen ions such as iodide ions passivate more {111} plane of PbS quantum dots. At the same time, inorganic halogen ion ligands have a smaller size than organic long-chain ligands, so that the spacing between quantum dots after exchange of halogen ion ligands is smaller, and the final quantum dot film has higher carrier mobility and fewer surface defects.

S600, depositing a ZnO film with a thickness of 120nm-170nm on the second intrinsic absorption layer as a second electron transport layer;

Specifically, the ZnO film is prepared by a magnetron sputtering method, for example, a radio frequency power supply is used to sputter and deposit the film at room temperature, an argon oxygen mixture (such as a volume ratio set to 99:1) is used as the sputtering gas, the equipment sputtering power is about 150W, the sputtering gas pressure is about 2.5Pa, and sputtering is performed for about 20 minutes to 30 minutes to obtain a zinc oxide ZnO film with a thickness of about 120nm to 170nm.

The ZnO thin film can also be prepared by other methods in the art. The parameters of the above magnetron sputtering method can be adjusted according to actual needs and are not specifically limited here.

S700, exposing a portion of the conductive glass substrate by etching or the like, and preparing two sets of metal electrodes on the surface of the second electron transport layer and the conductive glass substrate respectively by vacuum thermal evaporation, wherein the metal electrodes are gold electrodes, aluminum electrodes or titanium electrodes, and the first metal electrode contacts the second electron transport layer; and the second metal electrode contacts the conductive glass substrate;

Specifically, the metal electrode is prepared by vacuum thermal evaporation. For example, about 0.4 g of metal particles are taken as an evaporation source, and the multilayer film sample prepared above is fixed on a tray and placed in an evaporation chamber. When the evaporation chamber is evacuated to a vacuum of less than 10 ^{- 4} Pa, the current is controlled to 80 A to start evaporation, and the evaporation is stopped when the crystal oscillator shows that the evaporation thickness reaches the standard.

The metal electrode may also be prepared by other methods in the art. The parameters of the above vacuum thermal evaporation may be adjusted according to actual needs and are not specifically limited here.

Example 1

A method for preparing an n-i-p-i-n type visible-infrared dual-band photoelectric detector comprises the following steps:

S100, providing a conductive glass substrate;

A FTO glass substrate with a thickness of 400 nm was selected, the FTO glass substrate was cleaned, and finally the surface moisture was blown off for standby use.

S200, depositing a _TiO2 thin film on a conductive glass substrate as a first electron transport layer;

A 50 nm thick _TiO2 film was deposited on the FTO glass substrate by spray pyrolysis.

S300, forming a Sb ₂ S ₃ thin film on the first electron transport layer as a first intrinsic absorption layer;

A Sb ₂ S ₃ thin film with a thickness of 400 nm was formed on the FTO glass substrate with the TiO ₂ thin film deposited thereon by rapid thermal evaporation.

S400, forming a PbS-EDT quantum dot film on the first intrinsic absorption layer based on a solid phase ligand exchange method as a hole transport layer;

PbS quantum dots after EDT ligand exchange are used as hole transport layers. The band gap is 1.4eV and the absorption peak is 880nm. It can achieve band alignment and reduce interface defects. The specific generation steps are as follows:

(1) preparing an EDT ligand solution and a first PbS quantum dot solution;

5 mL of acetonitrile was measured and placed in a glass bottle, and 50 μL of EDT (1,2-ethanedithiol) was pipetted and added thereto to prepare a 1% EDT-acetonitrile solution. 10 mL of acetonitrile was measured and placed in a clean glass bottle, and 200 μL of 1% EDT-acetonitrile solution was pipetted and added thereto to prepare a 0.02% EDT-acetonitrile solution.

10 mL of n-octane is measured with a measuring cylinder and placed in a reagent bottle, 400 mg of synthesized PbS quantum dots with an absorption peak of 880 nm are weighed and dissolved in the n-octane and mixed evenly, and the first PbS quantum dot solution is obtained after filtering with a 0.22 μm filter head;

(2) The FTO glass substrate containing the TiO ₂ film and the Sb ₂ S ₃ film was adsorbed on the center of the spin coater suction plate, and the first PbS quantum dot solution was uniformly rotated at a rate of 2500 rpm for 30 seconds;

(3) Then, add EDT-acetonitrile solution to the surface of the FTO glass substrate sample until the solution completely covers the sample. After waiting for about 60 seconds, EDT fully replaces the oleic acid on the surface of the quantum dots to achieve ligand exchange and form a PbS-EDT quantum dot film.

(4) Rotate to remove excess EDT-acetonitrile solution on the surface, and finally add pure acetonitrile solution to wash the sample twice;

(5) The thickness of the PbS-EDT quantum dot film can be controlled by the concentration of the first PbS quantum dot solution and the number of spin coating cycles. Repeat steps (2) to (4) until the thickness of the PbS-EDT quantum dot film is about 45 nm.

S500, forming a PbS-IBr quantum dot film on the hole transport layer based on a liquid phase ligand exchange method as a second intrinsic absorption layer;

PbS quantum dots after mixed halogen ion ^I- and Br ^- ligand exchange are used as infrared absorption layer, with a band gap of 0.95eV and an absorption peak of 1300nm. The generation steps are as follows:

(1) preparing a halogen ion IBr ligand solution and a second PbS quantum dot solution;

Dissolve about 692 mg of PbI ₂ (0.2 mol/L), 110 mg of PbBr ₂ (0.04 mol/L), and 45 mg of acetamide (0.08 mol/L) in a centrifuge tube filled with N,N-dimethylformamide (DMF). Seal the centrifuge tube and place it in an ultrasonic machine for 20 minutes to fully dissolve the mixture to form an IBr ligand solution. Filter the solution with a 0.22 μm filter head and place it in a clean glass bottle and seal it for later use.

Use a measuring cylinder to measure 15 mL of n-octane and put it in a reagent bottle, weigh about 140 mg of PbS quantum dots wrapped by oleic acid, dissolve them in n-octane and mix them evenly to form a second PbS quantum dot solution;

(2) Use a 0.22 μm filter head to drop the filtered second PbS quantum dot solution into a glass bottle containing the IBr ligand solution. After vigorous shaking for about 60 seconds, the solution quickly separates into layers. The second PbS quantum dots are transferred from the non-polar solvent to the polar solvent DMF. The ^I- and Br ^- ligands successfully replace the long-chain oleic acid ligands.

(3) After the reagent bottle has been left to stand for a while, use a dropper to suck out the clear liquid on the top, continue to add n-octane to the solution and shake it. Repeat three times to clean the solution and ensure that the oleic acid ligand in the solution is completely removed;

(4) Gradually add 8 mL of ethyl acetate while shaking continuously. After all the addition is completed, place the mixture in a centrifuge and centrifuge at 9000 rpm for 5 min. Remove the upper brown liquid and leave black powder at the bottom. Vacuum dry the black powder for 30 min to obtain PbS-IBr quantum dot black powder coated with ^I- and ^Br- ions.

(5) Prepare 1 mL of a mixed solvent (n-butylamine: n-pentylamine: n-hexylamine = 10:3:2), dissolve about 270 mg of PbS-IBr quantum dot black powder in the mixed solvent, and oscillate with an oscillator for 2 min to obtain a quantum dot PbS-IBr solution. Then, drop the solution on the PbS-EDT quantum dot film and spin coat it at 3000 rpm to form a film. After that, anneal at 85 °C for 5 min to obtain a PbS-IBr quantum dot film with a thickness of about 400 nm.

S600, depositing a ZnO film with a thickness of about 150 nm on the second intrinsic absorption layer by a radio frequency magnetron sputtering method as a second electron transport layer.

S700, exposing a portion of the conductive glass substrate to prepare two sets of metal electrodes, wherein the first metal electrode contacts the conductive glass substrate, and the second metal electrode contacts the second electron transport layer;

Etching a portion of the first electron transport layer, the first intrinsic absorption layer, the hole transport layer, the second intrinsic absorption layer, and the second electron transport layer on the FTO glass substrate so that one side of the FTO glass substrate is partially exposed;

Two groups of metal electrodes Au electrodes with a thickness of about 60 nm were prepared on the surface of the ZnO film and the exposed part of the FTO glass substrate respectively by vacuum thermal evaporation.

The photodetector structure obtained by the above method steps is shown in Figure 1. The photodetector includes a substrate 1, a first electron transport layer 2, a first intrinsic absorption layer 3 made of a visible light-sensitive material, a hole transport layer 4, a second intrinsic absorption layer 5 made of an infrared light-sensitive material, a second electron transport layer 6, and a first metal electrode 7 contacting the second electron transport layer 6, which are stacked in sequence along the direction of the incident light, and also includes a second metal electrode 8 contacting the substrate 1.

The current density-voltage curve of the photodetector prepared in Example 1 under different wavelength light irradiation was simulated by using SCAPS-1D simulation software, as shown in FIG2 , indicating that the device responds to both visible light and infrared light, and the device open circuit voltage is the largest under 530nm wavelength irradiation, and the saturated photocurrent of the device can reach 0.6mA/cm ² under single-band irradiation.

The SCAPS-1D simulation software is used to simulate the curve of the quantum efficiency (EQE) of the device as a function of wavelength, as shown in Figure 3. This shows that the EQE of the dual-wave detection device can be as high as 82% in visible light and 75% in the infrared band.

The SCAPS-1D simulation software is used to simulate the curve of the device's response versus wavelength, as shown in Figure 4, indicating that the device has high response in both visible light and infrared bands.

Example 2

A method for preparing an n-i-p-i-n type visible-infrared dual-band photoelectric detector comprises the following steps:

S100, providing a conductive glass substrate;

An ITO glass substrate with a thickness of 350 nm was selected, the substrate was cleaned, and finally the surface moisture was blown off for standby use.

S200, depositing a _TiO2 thin film on a conductive glass substrate as a first electron transport layer;

A 45nm thick _TiO2 film was grown on an ITO glass substrate using spray pyrolysis.

S300, forming a Sb ₂ S ₃ thin film on the first electron transport layer as a first intrinsic absorption layer;

A Sb ₂ S ₃ film with a thickness of 600 nm was formed on an ITO glass substrate with a TiO ₂ film deposited thereon by a rapid thermal evaporation method.

S400, forming a PbS-EDT quantum dot film on the first intrinsic absorption layer based on a solid phase ligand exchange method as a hole transport layer;

PbS quantum dots after EDT ligand exchange are used as the hole transport layer, and its band gap is 1.4eV, and the absorption peak is 880nm, which can achieve band alignment and reduce interface defects. The specific generation steps are the same as those in Example 1. The thickness of the PbS-EDT quantum dot film can be controlled by the concentration of the quantum dot solution and the number of spin coating. The thickness of the PbS-EDT quantum dot film in this Example 2 is about 40nm.

S500. Based on the liquid phase ligand exchange method, a PbS-IBr quantum dot film is formed on the hole transport layer as a second intrinsic absorption layer; PbS quantum dots after mixed halogen ion ^I- and Br ^- ligand exchange are used as an infrared absorption layer, and its absorption peak is 1000nm. The generation steps are the same as those in Example 1. In this Example 2, a PbS-IBr quantum dot film with a thickness of about 350nm is prepared.

S600, depositing a ZnO film with a thickness of about 120 nm on the second intrinsic absorption layer by a radio frequency magnetron sputtering method as a second electron transport layer.

S700, exposing a portion of the conductive glass substrate to prepare two sets of metal electrodes, wherein the first metal electrode contacts the conductive glass substrate, and the second metal electrode contacts the second electron transport layer;

Etching a portion of the first electron transport layer, the first intrinsic absorption layer, the hole transport layer, the second intrinsic absorption layer, and the second electron transport layer on the ITO glass substrate so that one side of the ITO glass substrate is partially exposed;

Two groups of Al electrodes with a thickness of about 50 nm were prepared on the surface of the ZnO film and the exposed part of the ITO glass substrate by vacuum thermal evaporation.

Example 3

A method for preparing an n-i-p-i-n type visible-infrared dual-band photoelectric detector comprises the following steps:

S100, providing a conductive glass substrate;

A FTO glass substrate with a thickness of 450 nm was selected, the substrate was cleaned, and finally the surface moisture was blown off for standby use.

S200, depositing a _TiO2 thin film on a conductive glass substrate as a first electron transport layer;

A 55nm thick _TiO2 film was grown on FTO glass substrate by spray pyrolysis.

S300, forming a Sb ₂ S ₃ thin film on the first electron transport layer as a first intrinsic absorption layer;

A Sb ₂ S ₃ thin film with a thickness of 800 nm was formed on the FTO glass substrate with the TiO ₂ thin film deposited thereon by rapid thermal evaporation.

S400, forming a PbS-EDT quantum dot film on the first intrinsic absorption layer based on a solid phase ligand exchange method as a hole transport layer;

PbS quantum dots after EDT ligand exchange are used as the hole transport layer, and its band gap is 1.4eV, and the absorption peak is 880nm, which can achieve band alignment and reduce interface defects. The specific generation steps are the same as those in Example 1. The thickness of the PbS-EDT quantum dot film can be controlled by the concentration of the quantum dot solution and the number of spin coating. The thickness of the PbS-EDT quantum dot film in this Example 3 is about 50nm.

S500. Based on the liquid phase ligand exchange method, a PbS-IBr quantum dot film is formed on the hole transport layer as a second intrinsic absorption layer; PbS quantum dots after mixed halogen ion ^I- and Br ^- ligand exchange are used as an infrared absorption layer, and its absorption peak is 1800nm. The generation steps are the same as those in Example 1. This Example 3 prepares a PbS-IBr quantum dot film with a thickness of about 450nm.

S600, depositing a ZnO film with a thickness of about 170 nm on the second intrinsic absorption layer by a radio frequency magnetron sputtering method as a second electron transport layer.

S700, exposing a portion of the conductive glass substrate, and preparing two sets of metal electrodes, wherein the first metal electrode contacts the conductive glass substrate, and the second metal electrode contacts the second electron transport layer;

Etching a portion of the first electron transport layer, the first intrinsic absorption layer, the hole transport layer, the second intrinsic absorption layer, and the second electron transport layer on the FTO glass substrate so that one side of the FTO glass substrate is partially exposed;

Two sets of Ti electrodes with a thickness of about 60 nm were prepared on the surface of the ZnO film and the exposed part of the FTO glass substrate by vacuum thermal evaporation.

Comparative Example 1

The PbS-EDT quantum dot film with an exciton absorption peak of about 880nm (band gap of about 1.4eV) in Example 1 was replaced with a PbS-EDT quantum dot film with a narrower band gap (band gap of about 1.0eV, exciton absorption peak of about 1240nm), and the other parameters were the same as in Example 1.

When the PbS-EDT quantum dot film with a wider band gap is used as the common P-type layer of the device, the wider band gap of this film mainly comes from the upward shift of the conduction band, resulting in the conduction band of the hole transport layer (PbS-EDT quantum _dot film) being larger than the conduction band of the first intrinsic absorption layer ( _Sb2S3 film) and the second intrinsic absorption layer (PbS-IBr quantum dot film), giving the PbS-EDT quantum dot film a higher photogenerated electron blocking barrier, so that the photogenerated electrons generated by the corresponding absorption layer can be correctly transmitted to the corresponding electron transport layer when the device is working, effectively improving the collection efficiency of photogenerated carriers and significantly improving the device performance.

On the other hand, when a PbS-EDT quantum dot film with a narrower band gap (1.0 eV) is used, due to the narrow band gap, the conduction band of the hole transport layer (PbS-EDT quantum dot film) may be lower than the conduction band of the first _intrinsic absorption layer ( _Sb2S3 film) and the second intrinsic absorption layer (PbS-IBr quantum dot film), resulting in the photogenerated electrons generated by the corresponding light-absorbing layer to cross the blocking barrier of the PbS-EDT quantum dot film and cannot be normally transmitted to the corresponding electron transport layer. This heterogeneous interface forms an inappropriate energy band alignment, which will reduce the device performance and even affect the normal operation of the device.

Comparative Example 2

When preparing the PbS-EDT quantum dot film, the EDT ligand solution and the first PbS quantum dot solution are mixed and then directly spin-coated to form the PbS-EDT quantum dot film. Other parameters and steps are the same as those in Example 1.

Through testing and research, it is found that, although the steps of Comparative Example 2 are much simpler than the solid-phase ligand exchange process in Example 1 of the present invention, and there is no need to repeatedly spin-coat the film, the process easily leads to fusion, etching and agglomeration between quantum dots, and it is difficult to obtain colloidally stable quantum dot ink. Therefore, when spin-coating the hole transport layer PbS-EDT quantum dot film, Example 1 is superior to the method of Comparative Example 2 in terms of quantum dot size distribution control and repeatability.

The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims (10)

1. A n-i-p-i-n type visible-infrared dual-band photodetector, characterized in that the photodetector adopts a vertical n-i-p-i-n structure based on two photosensitive materials; The photodetector comprises: substrate; A first electron transport layer, a first intrinsic absorption layer made of a visible light-sensitive material, a hole transport layer, a second intrinsic absorption layer made of an infrared light-sensitive material, and a second electron transport layer are sequentially grown on the substrate; A first metal electrode contacts the second electron transport layer and a second metal electrode contacts the substrate. 2. The n-i-p-i-n type visible-infrared dual-band photoelectric detector according to claim 1, characterized in that the substrate is a conductive glass substrate; The first electron transport layer is a _TiO2 thin film; The first intrinsic absorption layer is a Sb ₂ S ₃ thin film made of visible light sensitive material; The hole transport layer adopts PbS-EDT quantum dot film; The second intrinsic absorption layer is a PbS-IBr quantum dot film made of infrared photosensitive material; The second electron transport layer is made of ZnO thin film; The materials of the first metal electrode and the second metal electrode are selected from gold, aluminum or titanium. 3. A method for preparing an n-i-p-i-n type visible-infrared dual-band photoelectric detector, characterized in that the method is used to prepare the n-i-p-i-n type visible-infrared dual-band photoelectric detector according to claim 1 or 2, comprising the following steps: Providing a conductive glass substrate; Growing a _TiO2 thin film on a conductive glass substrate as the first electron transport layer; Growing a Sb ₂ S ₃ thin film on the first electron transport layer as a first intrinsic absorption layer for absorbing visible light; A PbS-EDT quantum dot film is formed on the first intrinsic absorption layer based on a solid phase ligand exchange method as a hole transport layer; Based on the liquid phase ligand exchange method, a PbS-IBr quantum dot film is formed on the hole transport layer as a second intrinsic absorption layer for absorbing infrared light; A ZnO film is deposited on the second intrinsic absorption layer as a second electron transport layer; A portion of the conductive glass substrate is exposed to prepare two groups of metal electrodes, wherein the first metal electrode contacts the second electron transport layer; and the second metal electrode contacts the conductive glass substrate. 4. The method for preparing a n-i-p-i-n type visible-infrared dual-band photodetector according to claim 3 is characterized in that the solid-phase ligand exchange method is: spin coating a quantum dot PbS solution on the first intrinsic absorption layer to form a PbS film, and dropping an EDT ligand solution onto the PbS film to perform ligand exchange to form a PbS-EDT quantum dot film. 5. The method for preparing a n-i-p-i-n type visible-infrared dual-band photodetector according to claim 4, characterized in that the step of forming a PbS-EDT quantum dot film on the first intrinsic absorption layer based on a solid phase ligand exchange method comprises: (1) preparing an EDT-acetonitrile solution and a first PbS quantum dot solution dissolved in a non-polar organic solvent; (2) spin coating a first PbS quantum dot solution on the first intrinsic absorption layer to form a PbS thin film; (3) Add EDT-acetonitrile solution until the PbS film is completely covered. After standing, EDT fully replaces the oleic acid on the surface of the first PbS quantum dot to achieve ligand exchange and form a PbS-EDT quantum dot film. (4) using a protic polar solvent to wash and remove the residual solution; (5) Repeat steps (2) to (4) at least once until the PbS-EDT quantum dot film reaches a set thickness. 6. The method for preparing a n-i-p-i-n type visible-infrared dual-band photodetector according to claim 5, characterized in that the first PbS quantum dot solution uses PbS quantum dots with an absorption peak of 880nm. 7. The method for preparing a n-i-p-i-n type visible-infrared dual-band photodetector according to claim 3, characterized in that the step of forming a PbS-IBr quantum dot film on the hole transport layer based on a liquid phase ligand exchange method comprises: Preparing a halogen ion IBr ligand solution dissolved in a polar organic solvent and a second PbS quantum dot solution dissolved in a non-polar organic solvent; Adding the halogen ion IBr ligand solution dropwise to the second PbS quantum dot solution, shaking and then standing to separate layers, completing the replacement of the long-chain oleic acid ligands on the surface of the second PbS quantum dot by ^I- and Br ^- ligands; The upper clarified liquid and the lower liquid are phase separated, and the lower liquid is washed with a non-polar organic solvent to remove the long-chain oleic acid ligand; After adding ethyl acetate, a precipitation reaction occurs, and then a black precipitate is obtained by physical separation, and then a drying process is performed to obtain PbS-IBr quantum dot powder coated with I ^- and Br ^- ions; The PbS-IBr quantum dot powder is dissolved in an amine mixed solvent to form a PbS-IBr solution, the PbS-IBr solution is spin-coated on the hole transport layer to form a film, and finally annealing treatment is performed to obtain a PbS-IBr quantum dot film. 8. The method for preparing a n-i-p-i-n type visible-infrared dual-band photodetector according to claim 7, characterized in that the second PbS quantum dot solution uses PbS quantum dots with an absorption peak of 1000nm~1800nm. 9. The method for preparing a n-i-p-i-n type visible-infrared dual-band photoelectric detector according to claim 3 is characterized in that the first metal electrode and the second metal electrode are prepared by vacuum thermal evaporation; and the conductive glass substrate is an ITO glass substrate or a FTO glass substrate. 10. The method for preparing a nipin type visible-infrared dual-band photodetector according to any one of claims 3 to 9, characterized in that the thickness of the conductive glass substrate is 350nm~450nm, the thickness of the _TiO2 film is 45nm~55nm, and the thickness of the ZnO film is 120nm~170nm; The thickness of the Sb ₂ S ₃ film is 400nm~800nm; The thickness of the PbS-EDT quantum dot film is 40nm~50nm; The thickness of the PbS-IBr quantum dot film is 350nm~450nm.