An organic composite flexible quantum dot detector for heart rate monitoring and a preparation method thereof

Abstract

The application discloses an organic composite flexible quantum dot detector for heart rate monitoring and a preparation method thereof, and belongs to the technical field of photoelectric detectors. The structure of the application comprises a flexible substrate, a transparent electrode, an electron transport layer, a quantum dot absorption layer, an organic polymer barrier layer, a hole transport layer and a top electrode. The organic polymer barrier layer is arranged in the device, external electron injection is enhanced, a depletion region is formed at the interface between the absorption layer and the organic layer, the conductive channel in the two layers of films is narrowed, and therefore the dark current is greatly reduced. The organic polymer barrier layer is added, the quantum dot material is combined with the flexible substrate, a low-dark-current organic composite flexible quantum dot detector is manufactured, the dark current of the device is reduced, meanwhile, the mechanical flexibility of the quantum dot material is beneficial to the preparation of wearable photoelectric detectors, and the organic composite flexible quantum dot detector has wide application prospects in human health signal detection.

Description

Technical Field

[0001] This invention belongs to the field of photodetectors, and specifically relates to a low dark current organic composite flexible quantum dot detector and its preparation method. Background Technology

[0002] The core function of photodetectors is to convert captured light signals into electrical signals that can be processed by electronic devices. Based on the range of light wavelengths detected, photodetectors can be divided into three main types: ultraviolet-response detectors, visible-response detectors, and infrared-response detectors. Traditional short-wave infrared photodetectors, such as indium gallium arsenide detectors, are difficult to apply in various fields due to their complex fabrication process and high manufacturing cost. In contrast, photodetectors based on quantum dot materials offer advantages such as low manufacturing cost, tunable detection wavelength, and compatibility with flexible and lightweight devices. Furthermore, the mechanical flexibility of quantum dot materials facilitates the fabrication of wearable photodetectors, making them promising for applications in human health signal detection.

[0003] Among numerous infrared quantum dot materials, PbSe quantum dots not only possess a narrower bandgap and a wider spectral tuning range, but also exhibit a larger exciton Bohr radius and a significant multiexciton effect. However, the quantum dot surface has numerous defects, leading to an increase in the detector's dark current. An organic polymer blocking layer is incorporated into the device to enhance the blocking of external electron injection. Simultaneously, a depletion region forms at the interface between the absorption layer and the organic layer, narrowing the conductive channels in the two films, thus significantly reducing the dark current. Summary of the Invention

[0004] Based on the above background technology, the present invention mainly introduces an organic polymer blocking layer into a flexible quantum dot detector to create a low dark current organic composite flexible quantum dot detector for heart rate monitoring.

[0005] The present invention also provides an organic composite flexible quantum dot detector for heart rate monitoring, the detector comprising, in sequence: a flexible substrate, a transparent electrode, an electron transport layer, a PbSe quantum dot absorption layer, an organic polymer blocking layer, a hole transport layer, and a top electrode;

[0006] The transparent electrode is made of indium tin oxide (ITO) with a thickness of 200 nm, and the flexible substrate is made of polyethylene terephthalate (PET) with a thickness of 0.05 mm.

[0007] A method for fabricating an organic composite flexible quantum dot detector for heart rate monitoring, the method comprising:

[0008] S1: Place the flexible substrate with its own transparent electrode in an ultraviolet ozone cleaner for cleaning;

[0009] S2: Spin-coating zinc oxide nanoparticles onto a flexible substrate to create an electron transport layer;

[0010] S3: Synthesize PbSe quantum dot materials, prepare a solution and spin-coat it onto the electron transport layer, spin-coat four layers, and prepare a PbSe quantum dot absorption layer film;

[0011] S4: An organic polymer solution was prepared using chlorobenzene and spin-coated onto the PbSe quantum dot absorption layer to obtain an organic thin film barrier layer;

[0012] S5: A hole transport layer is obtained by vacuum evaporation of molybdenum trioxide onto an organic thin film barrier layer.

[0013] S6: A flexible quantum dot detector is obtained by preparing a top electrode silver on the surface of the hole transport layer using a vacuum evaporation method.

[0014] Specifically, the spin-coated zinc oxide nanoparticle film is rotated at 3000 rpm for 60 seconds, and then annealed at 100°C for 1 hour, wherein the zinc oxide nanoparticles have a mass percentage of 2.5 wt.%.

[0015] Specifically, the preparation method of the PbSe quantum dot material in step S3 is as follows:

[0016] Step a: Selenium precursor preparation: 0.64 g (8 mmol) of selenium powder and 6.4 ml of tri-n-octylphosphine were mixed and stirred for 12 h in a sealed environment, wherein the concentration of the mixture of selenium powder and tri-n-octylphosphine was 1.25 mmol / ml;

[0017] Step b: Preparation of lead precursor: Take 0.892 g (4 mmol) of lead oxide, 2.7 ml of oleic acid, and 16 ml of 1-octadecene and mix them. The molar ratio of lead oxide to selenium powder is 1:2, the volume ratio of oleic acid to 1-octadecene solution is 27:160, and the concentration of lead oxide and 1-octadecene mixture is 0.25 mmol / ml. Place the three-necked flask containing the lead precursor in a heating mantle, set the temperature to 30 °C, evacuate for 25 minutes, and purge with nitrogen for 15 minutes. Repeat the evacuation-nitrogen purging process three times until the mixture is completely in a nitrogen environment. Under nitrogen environment, slowly raise the temperature to 110 °C at a rate of 60 °C / h and hold at that temperature for 15 minutes.

[0018] Step c: Synthesis reaction, heating to 160℃ at a rate of 60℃ / h, injecting the selenium precursor into the mixed solution prepared in step b, reacting for 3 min and then quenching with n-hexane, wherein the ratio of n-hexane to selenium powder is 1.6 mmol / ml; after the temperature drops to 60℃, adding a 10.7 mg / ml ammonium chloride methanol solution, wherein the ratio of ammonium chloride methanol solution to selenium powder is 4 mmol / ml, and cooling to 35℃;

[0019] Step d: Separation and purification. Prepare a centrifugal solution by mixing isopropanol and acetone in a 2:1 ratio. Mix the original solution obtained in step c with the centrifugal solution in a 1:3 ratio, centrifuge again, and obtain quantum dots on the side wall of the centrifuge tank. Dissolve the quantum dots on the side wall with n-hexane, then centrifuge and dry to obtain dried PbSe quantum dots.

[0020] Step e: Prepare the solution. Use n-octane as the solvent to prepare a 50 mg / ml PbSe quantum dot solution.

[0021] Specifically, when spin-coating PbSe quantum dot material, the process involves first coating PbSe quantum dots by rotating at 1500 rpm for 60 seconds; then, a 2% EDT acetonitrile solution is dropped onto the entire surface of the device film, and allowed to stand for 45 seconds to allow the long-chain oleic acid to be fully replaced by the short-chain EDT. Afterward, the film is rotated at 1500 rpm for 30 seconds to ensure uniformity. Finally, acetonitrile is dropped onto the film surface to clean the ligands, and the film is rotated at 1500 rpm for 30 seconds. This cleaning step is repeated three times to ensure thorough removal of residual solutes. This process is repeated four times, equivalent to coating four layers of quantum dots, and finally annealed at 100°C for 5 minutes on a heating stage.

[0022] Specifically, the spin-coated organic polymer is P3HT with a concentration of 15 mg / ml, and is rotated at 3000 rpm for 60 seconds, and then annealed at 100°C for 10 minutes.

[0023] Specifically, the evaporation pressure of the vacuum evaporation is 10. -4 Pa.

[0024] The beneficial effects of this invention are:

[0025] This invention proposes a low dark current organic composite flexible quantum dot detector and its fabrication method. An organic polymer barrier layer is added to reduce the dark current of the device through organic-inorganic composite. Zinc oxide nanoparticles are used to increase the carrier lifetime, thereby improving the gain of the device. PbSe quantum dots are used as the absorption layer of the device, and the absorption wavelength can be tuned to broaden the detection wavelength. A flexible substrate is used, which can be applied to wearable devices for heart rate monitoring. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the low dark current organic composite flexible quantum dot detector of the present invention.

[0027] Figure 2 This is the absorption spectrum of the PbSe quantum dots synthesized in this invention.

[0028] Figure 3 This is a dark current test diagram of the low dark current organic composite flexible quantum dot detector of the present invention.

[0029] Figure 4This is the current-voltage test diagram of the low dark current organic composite flexible quantum dot detector of the present invention.

[0030] Figure 5 This is a heart rate monitoring image from the low dark current organic composite flexible quantum dot detector developed in this invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and beneficial effects of this invention clearer and more complete, the following embodiments and accompanying drawings further illustrate this invention.

[0032] Example 1

[0033] This invention provides a low dark current organic composite flexible quantum dot detector and its fabrication method. The specific fabrication method includes the following steps:

[0034] S1: Place the flexible substrate with transparent electrodes in an ultraviolet ozone cleaner for 20 minutes. The transparent electrodes are indium tin oxide (ITO) with a thickness of 200nm, and the flexible substrate is polyethylene terephthalate (PET) with a thickness of 0.05mm.

[0035] S2: Fabrication of the electron transport layer: Spin-coating zinc oxide nanoparticles at 3000 rpm for 60 seconds, followed by annealing at 100°C for 1 hour. The zinc oxide nanoparticles have a mass percentage of 2.5 wt.% (crystalline ZnO in 2-propanol).

[0036] S3: Fabrication of the absorption layer film: PbSe quantum dot material was synthesized and prepared as a solution for spin-coating onto the electron transport layer. During spin-coating, the PbSe quantum dots were first coated and rotated at 1500 rpm for 60 seconds. Then, a 2% EDT acetonitrile solution was added dropwise to cover the entire surface of the device film, and allowed to stand for 45 seconds to allow the long-chain oleic acid to be fully replaced by the short-chain EDT. Afterward, the film was rotated at 1500 rpm for 30 seconds to ensure uniformity. Finally, acetonitrile was added dropwise to the film surface to clean the ligands, and the film was rotated at 1500 rpm for 30 seconds. This cleaning step was repeated three times to ensure thorough removal of residual solutes. The above process was repeated four times, equivalent to coating four layers of quantum dots. Finally, the film was annealed at 100°C for 5 minutes on a heating stage.

[0037] S4: To prepare the barrier layer, P3HT was selected as the organic polymer and chlorobenzene was selected as the solvent. The solution concentration was 15 mg / ml. When spin-coating the film, the rotation speed was 3000 rpm and the rotation time was 60 seconds. Then, the film was annealed at 100℃ for 10 minutes.

[0038] S5: The electron blocking layer, molybdenum trioxide, was fabricated using vacuum evaporation. The evaporation pressure during vacuum evaporation was 10. -4 Pa, with an electron blocking layer thickness of 10 nm;

[0039] S6: Fabricate the top electrode silver using vacuum evaporation, with a evaporation pressure of 10. -4 Pa, with a thickness of 100 nm, yielded a flexible quantum dot detector.

[0040] In s3, the synthesis of PbSe quantum dot materials specifically includes:

[0041] For the preparation of the selenium precursor, 0.64 g of selenium powder (8 mmol) and 6.4 ml of tri-n-octylphosphine were mixed and stirred overnight in a glove box. For the preparation of the lead precursor, 0.892 g (4 mmol) of lead oxide was mixed with 2.7 ml of oleic acid and 16 ml of 1-octadecene. The mixture was then evacuated at 30 °C for 25 min and purged with nitrogen for 15 min. This step was repeated 3 times. Under nitrogen atmosphere, the temperature is slowly increased to 110℃ every 20℃ and held for 10 min; for the synthesis reaction, the temperature is increased to 160℃ every 20℃, the selenium precursor is injected, the reaction is quenched with 5 ml of n-hexane after 3 min, and when the temperature drops to 60℃, 2 ml of 10.7 mg / ml ammonium chloride methanol solution is added, and the mixture is cooled to 35℃; for separation and purification, isopropanol and acetone are mixed in a 2:1 ratio to prepare a centrifugal buffer, and 2 ml of the stock solution + 6 ml of the centrifugal buffer is used for centrifugation. The sidewall quantum dots are dissolved in n-hexane, centrifuged 3-4 times and dried; for solution preparation, n-octane is used to prepare a 50 mg / ml PbSe quantum dot solution.

[0042] The performance characterization tests of the device fabricated in this embodiment are as follows:

[0043] A schematic diagram of a low dark current organic composite flexible quantum dot detector structure is shown below. Figure 1 As shown, the structure comprises (1) a flexible substrate, (2) a transparent electrode, (3) an electron transport layer, (4) a PbSe quantum dot absorption layer, (5) an organic polymer blocking layer, (6) a hole transport layer, and (7) a top electrode. The organic polymer blocks electrons from the top electrode, reducing the dark current of the device. The organic-inorganic composite, with the organic polymer spin-coated onto the quantum dot absorption layer, forms a depletion region at the interface between the absorption layer and the organic layer, resulting in narrowing of the conductive channels in the two films, thus significantly reducing the dark current. The heterojunction is constructed using wide-bandgap zinc oxide nanoparticles and quantum dots prepared through surface ligand modification. Simultaneously, the zinc oxide nanoparticles can be annealed at a lower temperature, allowing them to be fabricated on a flexible substrate. The introduced zinc oxide nanoparticles can increase carrier lifetime, thereby improving the device gain. The photodetector is fabricated using a flexible substrate, and each layer in the device can be annealed at low temperatures, enabling heart rate monitoring.

[0044] The absorption spectrum of PbSe quantum dots is as follows: Figure 2 As shown, its absorption peak is at 1700 nm.

[0045] The dark current characteristics of the detector are as follows Figure 3 As shown, the addition of an organic polymer barrier layer reduces the dark current by an order of magnitude.

[0046] The detector's current JV characteristics are as follows Figure 4 As shown, under reverse bias, the photocurrent density at a wavelength of 1550 nm is 5.7 × 10⁻⁶. -3 A·cm -2 The dark current density is 1.2 × 10⁻⁶. -5 A·cm -2 .

[0047] Figure 5 The image shows the heart rate monitoring data of the flexible device, displaying the heart rate fluctuations over 10 seconds.

[0048] This invention incorporates an organic polymer barrier layer to combine quantum dot materials with a flexible substrate, thereby fabricating a low dark current organic composite flexible quantum dot detector. This reduces the dark current of the device, while the mechanical flexibility of the quantum dot material is beneficial for the fabrication of wearable photodetectors, making it a promising candidate for applications in human health signal detection.

[0049] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An organic composite flexible quantum dot detector for heart rate monitoring, the detector comprising, in sequence: a flexible substrate, a transparent electrode, an electron transport layer, a PbSe quantum dot absorption layer, an organic polymer blocking layer, a hole transport layer, and a top electrode; The transparent electrode is an indium tin oxide with a thickness of 200 nm, and the flexible substrate is a polyethylene terephthalate with a thickness of 0.05 mm. The method for fabricating the quantum dot detector includes: S1: Place the flexible substrate with its own transparent electrode in an ultraviolet ozone cleaner for cleaning; S2: Spin-coating zinc oxide nanoparticles onto a flexible substrate to create an electron transport layer; The spin-coated zinc oxide nanoparticle film was rotated at 3000 rpm for 60 seconds, followed by annealing at 100°C for 1 hour, wherein the zinc oxide nanoparticles accounted for 2.5 wt.% of the total mass. S3: Synthesize PbSe quantum dot materials, prepare a solution and spin-coat it onto the electron transport layer, spin-coat four layers, and prepare a PbSe quantum dot absorption layer film; The preparation method of the PbSe quantum dot material is as follows: Step a: Selenium precursor preparation: 0.64 g selenium powder and 6.4 ml tri-n-octylphosphine were mixed and stirred for 12 h in a sealed environment, wherein the concentration of the mixture of selenium powder and tri-n-octylphosphine was 1.25 mmol / ml; Step b: Preparation of lead precursor: Mix 0.892 g lead oxide, 2.7 ml oleic acid, and 16 ml 1-octadecene, wherein the molar ratio of lead oxide to selenium powder is 1:2, the volume ratio of oleic acid to 1-octadecene solution is 27:160, and the concentration of lead oxide and 1-octadecene mixture is 0.25 mmol / ml; place the three-necked flask containing the lead precursor in a heating mantle, set the temperature to 30°C, evacuate for 25 minutes, and purge with nitrogen for 15 minutes, repeating the evacuation-nitrogen purging process three times until the mixture is completely in a nitrogen environment; slowly raise the temperature to 110°C at a rate of 60 °C / h under nitrogen environment and hold at that temperature for 15 minutes; Step c: Synthesis reaction, heating to 160℃ at a rate of 60℃ / h, injecting the selenium precursor into the mixed solution prepared in step b, reacting for 3 min and then quenching with n-hexane, wherein the ratio of n-hexane to selenium powder is 1.6 mmol / ml; after the temperature drops to 60℃, adding a 10.7 mg / ml ammonium chloride methanol solution, wherein the ratio of ammonium chloride methanol solution to selenium powder is 4 mmol / ml, and cooling to 35℃; Step d: Separation and purification. Prepare a centrifugal solution by mixing isopropanol and acetone in a 2:1 ratio. Mix the original solution obtained in step c with the centrifugal solution in a 1:3 ratio, centrifuge again, and obtain quantum dots on the side wall of the centrifuge tank. Dissolve the quantum dots on the side wall with n-hexane, then centrifuge and dry to obtain dried PbSe quantum dots. Step e: Prepare the solution. Use n-octane as the solvent to prepare a 50 mg / ml PbSe quantum dot solution; S4: An organic polymer solution was prepared using chlorobenzene and spin-coated onto the PbSe quantum dot absorption layer to obtain an organic thin film barrier layer; The spin-coated organic polymer was P3HT with a concentration of 15 mg / ml. It was spin-coated at 3000 rpm for 60 seconds and then annealed at 100°C for 10 minutes. S5: A hole transport layer is obtained by vacuum evaporation of molybdenum trioxide onto an organic thin film barrier layer. S6: A flexible quantum dot detector is obtained by preparing a top electrode silver on the surface of the hole transport layer using a vacuum evaporation method.

2. The method for fabricating an organic composite flexible quantum dot detector for heart rate monitoring as described in claim 1, characterized in that, When spin-coating the PbSe quantum dot material, the PbSe quantum dots are first coated by rotating at 1500 rpm for 60 seconds. Then, a 2% EDT acetonitrile solution is dropped onto the entire surface of the device film and allowed to stand for 45 seconds to allow the long-chain oleic acid to be fully replaced by the short-chain EDT. After that, the film is rotated at 1500 rpm for 30 seconds to ensure uniformity. Finally, acetonitrile is dropped onto the film surface to clean the ligands, and the film is rotated at 1500 rpm for 30 seconds. This cleaning step is repeated three times to ensure that residual solutes are completely removed. The above process is repeated four times, which is equivalent to coating four layers of quantum dots. Finally, the film is annealed at 100°C for 5 minutes on a heating stage.

3. The method for fabricating an organic composite flexible quantum dot detector for heart rate monitoring as described in claim 1, characterized in that, The vacuum evaporation pressure is 10. -4 Pa.

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