Laminated triple heterojunction low dark current all-polymer organic photoelectric detector and preparation method thereof

Abstract

The invention discloses a laminated triple heterojunction low dark current all-polymer organic photoelectric detector and a preparation method thereof, and belongs to the technical field of organic photoelectric detectors. According to the detector, on the basis of a traditional bulk heterojunction (BHJ) layer, a pure acceptor layer is introduced between the traditional BHJ layer and a cathode, and a pure donor layer is introduced between the traditional BHJ layer and an anode, so that a laminated triple heterojunction structure is constructed. The bulk heterojunction (BHJ) layer and the donor layer are prepared through a water transfer printing process, the acceptor layer and the bulk heterojunction (BHJ) layer are in Van der Waals contact, and the bulk heterojunction (BHJ) layer and the donor layer are in Van der Waals contact. According to the structure, dark current can be effectively reduced, and the specific detection rate (D *) and the signal-to-noise ratio of the device are improved. Compared with a traditional BHJ structure, the BHJ structure has the advantages that the dark current suppression capability is remarkably improved while high light response performance is maintained, and the BHJ structure has better comprehensive photoelectric performance. The technical scheme is suitable for the application fields of high-sensitivity photoelectric detection, near-infrared imaging, low-power-consumption biological signal monitoring, optical wireless communication and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic photodetectors, and in particular relates to a low dark current all-polymer organic photodetector based on a van der Waals contact stacked triple heterojunction (LTHJ) and a preparation method thereof. Background Art

[0002] Organic photodetectors (OPDs) have shown broad application prospects in the fields of biomedical sensing, optical communications, night vision imaging, artificial intelligence sensing, etc. due to their flexibility, low-cost preparation process, wide spectral response range and excellent adjustability. Among them, near-infrared OPDs have become a research hotspot in this field because they can perform efficient detection in the non-visible light range and are suitable for low-power biological signal monitoring (such as photoplethysmography (PPG) sensing), invisible optical communications and security monitoring. However, existing OPDs still face many challenges in performance, mainly including high dark current, low specific detection rate (D*), limited responsiveness and insufficient noise suppression capabilities, which severely limit their application in high-sensitivity detection scenarios.

[0003] At present, the bulk heterojunction (BHJ) structure is one of the most widely used structures in organic photodetectors because of its large donor-acceptor interface, which helps to improve the exciton dissociation efficiency. However, in the BHJ structure, both the donor phase and the acceptor phase can be in direct contact with the electrode, resulting in electrons and holes being directly injected into the LUMO energy level of the acceptor or the HOMO energy level of the donor, which will lead to a higher dark current, thereby affecting the signal-to-noise ratio and specific detectivity (D*) of the device. On the other hand, although the planar heterojunction can effectively suppress the unnecessary injection of carriers, due to its small donor-acceptor interface area, the exciton dissociation efficiency is limited, resulting in a lower photocurrent, thereby reducing the overall performance of the detector. Therefore, how to maintain a high light response while reducing the dark current is still a key issue that needs to be solved in the field of organic photodetectors. Summary of the invention

[0004] In order to solve the problems of high dark current and low specific detection rate in existing organic photodetectors, the present invention proposes a low dark current all-polymer organic photodetector based on a stacked triple heterojunction (LTHJ) with van der Waals contact. Based on the traditional bulk heterojunction (BHJ), this structure introduces a layer of pure acceptor material between it and the cathode as an electron blocking layer, and at the same time introduces a layer of pure donor material between it and the anode as a hole blocking layer, thereby effectively suppressing unnecessary injection of carriers, reducing the dark current of the device and improving its specific detection rate.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A stacked triple heterojunction low dark current all-polymer organic optoelectronic detector, which comprises, stacked in sequence: a transparent substrate and electrode layer, an electron transport layer, a polymer acceptor layer, a polymer bulk heterojunction layer, a polymer donor layer, a hole transport layer, and a top electrode layer;

[0007] The thickness of the polymer acceptor layer is 15 - 50 nm, the thickness of the polymer bulk heterojunction layer is 50 - 250 nm, and the thickness of the polymer donor layer is 15 - 50 nm;

[0008] The material of the polymer acceptor layer is an organic polymer acceptor material, including: N2200, PY-IT, PYF-T-o, or PNDI. It has a lower HOMO energy level compared to the donor material and can effectively block the injection of hole carriers from the external circuit.

[0009] The material of the polymer bulk heterojunction layer is a mixed material of an organic polymer acceptor material and a donor material. It is mainly used to absorb light energy and separate photo-generated carrier electron-hole pairs.

[0010] The material of the polymer donor layer is an organic polymer donor material, including: PM6, PTB7-TH, D18, P3HT, PBDB-T. It has a higher LUMO energy level compared to the acceptor material and can effectively block the injection of electron carriers from the external circuit.

[0011] Furthermore, both "between the polymer acceptor layer and the polymer bulk heterojunction layer" and "between the polymer bulk heterojunction layer and the polymer donor layer" are Van der Waals contacts.

[0012] A preparation method of a stacked triple heterojunction low dark current all-polymer organic optoelectronic detector, which comprises:

[0013] S1: Clean the transparent substrate and electrode layer, and perform ultrasonic cleaning with deionized water, alcohol, and acetone in sequence and then dry;

[0014] S2: Spin-coat the electron transport layer on the surface of the transparent substrate and electrode layer, and perform thermal annealing treatment;

[0015] S3: Spin-coat the polymer acceptor layer on the electron transport layer;

[0016] S4: Prepare the polymer bulk heterojunction layer on the polymer acceptor layer by water transfer printing;

[0017] S5: Transfer-print the polymer donor layer on the bulk polymer heterojunction layer by water transfer printing;

[0018] S6: Deposit the hole transport layer by vacuum evaporation;

[0019] S7: Continue to deposit the top electrode by vacuum evaporation.

[0020] Further, the water transfer printing process in step S4 includes: dropping a polymer heterojunction layer solution into a glass dish filled with deionized water. After it spreads on the water surface and dries to form a film, the device is inverted and pressed onto the film surface. After the transfer is completed, it is subjected to vacuum treatment for 1 - 10 minutes, and then thermal annealing treatment is carried out.

[0021] Further, the water transfer printing process in step S5 includes: dropping a polymer donor solution into a glass dish filled with deionized water. After it spreads on the water surface and dries to form a donor film, the device is inverted and pressed onto the film surface. After the transfer is completed, it is subjected to vacuum treatment for 1 - 10 minutes, and then thermal annealing treatment is carried out.

[0022] By constructing a stacked triple heterojunction structure composed of a pure acceptor layer, a bulk heterojunction layer, and a pure donor layer, the present invention effectively improves the exciton dissociation efficiency while forming a carrier blocking interface, significantly reducing the dark current and enhancing the specific detectivity (D*) and signal-to-noise ratio. This device combines the advantages of high efficiency of bulk heterojunctions and low noise of planar heterojunctions, and is particularly suitable for fields such as near-infrared high-sensitivity photodetection, low-power consumption biological signal reading, and optical communication, having good industrialization and application prospects. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of a photodetector with a stacked triple heterojunction (LTHJ) structure proposed by the present invention.

[0024] Figure 2 It is a schematic structural diagram of a photodetector with a traditional bulk heterojunction (BHJ) structure.

[0025] Figure 3 It is a schematic energy band diagram of a photodetector with a stacked triple heterojunction (LTHJ) structure proposed by the present invention.

[0026] Figure 4 It is a schematic energy band diagram of a photodetector with a traditional bulk heterojunction (BHJ) structure.

[0027] Figure 5 It is a comparative curve graph of the dark current density between the LTHJ photodetector of the present invention and the traditional BHJ photodetector.

[0028] Figure 6 It is a comparative curve graph of the specific detectivity (D*) between the LTHJ photodetector of the present invention and the traditional BHJ photodetector. Detailed Embodiments

[0029] To make the objectives, technical solutions, and beneficial effects of the present invention clearer, in combination with the accompanying drawings, the present invention is further described below through the following embodiments. The technical solutions of the present invention are not limited to the following embodiments.

[0030] As Figure 1 shown, a low dark current all-polymer organic optoelectronic detector based on van der Waals contact laminated triple heterojunction (LTHJ) provided by this implementation scheme includes, from bottom to top in sequence: a transparent glass substrate, an indium tin oxide ITO electrode, an electron transport layer of polyethoxyethyleneimine (PEIE), a receptor PY-IT layer (with a thickness of about 30 nm), a bulk heterojunction PM6:PY-IT layer (with a thickness of about 100 nm), a donor PM6 layer (with a thickness of about 25 nm), a hole transport layer of molybdenum trioxide (MoO3, 10 nm), and a top electrode of silver (Ag, 100 nm).

[0031] Example 1: Preparation method of LTHJ device

[0032] This example provides a preparation method of an LTHJ device, including the following steps:

[0033] S1: Substrate cleaning

[0034] Use a cleaning agent to scrub the surface of the ITO glass substrate, and rinse it thoroughly with ultrapure water. Subsequently, perform ultrasonic cleaning with ultrapure water, anhydrous ethanol, and acetone in sequence for 30 minutes, and finally treat it in an ultraviolet ozone cleaning machine for 30 minutes and dry it for standby.

[0035] S2: Preparation of electron transport layer

[0036] Drop a 0.1% PEIE solution by mass fraction onto the substrate surface, and form a film by spin coating (4500 rpm, 60 s), and perform thermal annealing at 95°C for 4.5 minutes to form an electron transport layer.

[0037] S3: Preparation of receptor PY-IT layer

[0038] In a nitrogen atmosphere, spin coat a 6 mg / ml PY-IT chlorobenzene solution onto the PEIE layer surface (1500 rpm, 45 s), and then perform thermal annealing at 95°C for 4.5 minutes to obtain a receptor layer with a thickness of about 30 nm.

[0039] S4: Preparation of bulk heterojunction PM6:PY-IT layer

[0040] Dissolve PM6 and PY-IT in chlorobenzene at a mass ratio of 1:1 to prepare a solution with a total concentration of 30 mg / ml. Take 35 μl of this solution and drop it into a petri dish filled with deionized water. After it spreads on the water surface and the solvent volatilizes, a film is formed. Invert the device and press it onto the film to complete the transfer, and then perform vacuum treatment at -0.1 MPa for 2 minutes and thermal annealing at 95°C for 3 minutes.

[0041] S5: Preparation of donor PM6 layer

[0042] Using a 20 mg / ml PM6 chlorobenzene solution, repeat the water transfer printing step (drop volume: 15 μl) to transfer the donor film onto the bulk heterojunction layer, and also perform vacuum treatment and thermal annealing.

[0043] S6: Preparation of the hole transport layer

[0044] Deposit MoO3 by vacuum evaporation at a vapor deposition pressure of 4×10 -4 Pa and a thickness of 10 nm.

[0045] S7: Preparation of the top electrode

[0046] Continue to deposit a silver electrode by vacuum evaporation with a thickness of 100 nm and a vapor deposition pressure of 4×10 -4 Pa to complete the construction of the device structure.

[0047] Comparative example: Preparation of a traditional BHJ device

[0048] To verify the superiority of the performance of the device of the present invention, a traditional bulk heterojunction structure is constructed for comparison. Its structure is as Figure 2 shown, from bottom to top in sequence: glass substrate, ITO electrode, PEIE layer, PM6:PY-IT bulk heterojunction layer, MoO3 hole transport layer, Ag top electrode.

[0049] Core difference: There is no separate acceptor and donor layer; the PM6:PY-IT layer is a single-layer structure with a thickness of about 155 nm.

[0050] Its preparation steps are the same as those of the present invention, except that in step S3, a PM6:PY-IT solution with a concentration of 18 mg / ml is directly spin-coated (2000 rpm, 45 s) to form the active layer, and the thermal annealing conditions are 95°C for 4.5 minutes.

[0051] As Figure 3 shown, in the device of the present invention, the introduced acceptor PY-IT layer and donor PM6 layer form electron and hole barriers in the cathode and anode directions respectively, effectively suppressing the injection of external carriers and reducing the dark current.

[0052] As Figure 4 shown, in the comparative example BHJ device, since both the donor and the acceptor can be in direct contact with the electrode, electrons can be injected into the LUMO of the acceptor and holes can be injected into the HOMO of the donor, resulting in a relatively high dark current.

[0053] The performance characterization tests of the devices prepared in this example are as follows:

[0054] Dark current test ( Figure 5):Compare the dark current density-voltage (J-V) characteristics of the LTHJ and BHJ devices under reverse bias. The results show that the dark current of the device of the present invention is significantly lower than that of the comparative device at the same voltage, and the suppression effect is remarkable.

[0055] Specific detectivity test ( Figure 6 ):The specific detectivity (D*) curve was measured at a bias voltage of -1V. The results indicate that the D* value of the LTHJ device is significantly higher than that of the traditional BHJ device, with better signal-to-noise ratio and photodetection performance.

[0056] The present invention effectively solves the problems of high dark current and limited detection performance of traditional BHJ devices by constructing a stacked triple heterojunction structure. Its innovation in structural design realizes the coordinated optimization of dark current suppression and detectivity improvement, and is applicable to high-sensitivity optoelectronic application scenarios such as near-infrared detection, biophoto-sensing, and low-light imaging.

[0057] The above embodiments are only used to illustrate the principles and technical solutions of the present invention, and should not be used to limit the protection scope of the present invention. Any equivalent replacement or modification of the structure, method, etc. within the spirit and essence of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A stacked triple heterojunction low dark current all-polymer organic photodetector, the photodetector comprising: a transparent substrate and electrode layer, an electron transport layer, a polymer acceptor layer, a polymer body heterojunction layer, a polymer donor layer, a hole transport layer, and a top electrode layer stacked in sequence; The thickness of the polymer acceptor layer is 15-50 nm, the thickness of the polymer body heterojunction layer is 50-250 nm, and the thickness of the polymer donor layer is 15-50 nm; The material of the polymer receptor layer is an organic polymer receptor material, including: N2200, PY-IT, PYF-To or PNDI.

2. The stacked triple heterojunction low dark current all-polymer organic photodetector according to claim 1, characterized in that: The material of the polymer bulk heterojunction layer is a mixed material of an organic polymer acceptor material and a donor material.

3. The stacked triple heterojunction low dark current all-polymer organic photodetector according to claim 1, characterized in that: The material of the polymer donor layer is an organic polymer donor material, including: PM6, PTB7-TH, D18, P3HT, PBDB-T.

4. The stacked triple heterojunction low dark current all-polymer organic photodetector according to claim 1, characterized in that: The "contact between the polymer acceptor layer and the polymer bulk heterojunction layer" and the "contact between the polymer bulk heterojunction layer and the polymer donor layer" are both van der Waals contacts.

5. A method for preparing a stacked triple heterojunction low dark current all-polymer organic photodetector, the method comprising: S1: Clean the transparent substrate and electrode layer, use deionized water, alcohol and acetone to perform ultrasonic cleaning in sequence and then dry; S2: spin coating an electron transport layer on the surface of the transparent substrate and the electrode layer, and performing thermal annealing treatment; S3: spin coating a polymer acceptor layer on the electron transport layer; S4: preparing a polymer bulk heterojunction layer on the polymer receptor layer by water transfer printing; S5: transferring a polymer donor layer onto the bulk polymer heterojunction layer by a water transfer method; S6: depositing a hole transport layer by vacuum evaporation; S7: Continue to deposit the top electrode using vacuum evaporation method.

6. The method for preparing a stacked triple heterojunction low dark current all-polymer organic photodetector according to claim 5, characterized in that: The water transfer process in step S4 includes: dropping a polymer heterojunction layer solution into a glass dish filled with deionized water, and after it spreads on the water surface and dries to form a film, the device is inverted and pressed onto the surface of the film, and after the transfer is completed, vacuum treatment is performed for 1-10 minutes, and then thermal annealing is performed.

7. The method for preparing a stacked triple heterojunction low dark current all-polymer organic photodetector according to claim 5, characterized in that: The water transfer process in step S5 includes: dropping a polymer donor solution into a glass dish filled with deionized water, and after the polymer donor solution is spread on the water surface and dried to form a donor film, the device is inverted and pressed onto the film surface, and after the transfer is completed, vacuum treatment is performed for 1-10 minutes, and then thermal annealing is performed.

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