An organic two-dimensional charge transfer co-crystal-based light detection device and a preparation method thereof

Abstract

A photodetector based on an organic two-dimensional charge-transfer eutectic and its fabrication method are disclosed. The photodetector includes an organic two-dimensional charge-transfer eutectic photosensitive layer (2). The organic two-dimensional charge-transfer eutectic photosensitive layer (2) is located on an electrode (3) and electrically connected between two electrodes (3) for collecting photogenerated electrical signals. The organic two-dimensional charge-transfer eutectic photosensitive layer (2) is composed of organic donor molecules and organic acceptor molecules. The method includes the selection and solution preparation of organic donor molecules and organic acceptor molecules, substrate preparation and electrode fabrication, drop-coating of the eutectic precursor solution and two-dimensional self-assembly growth, and device construction. This invention can significantly improve the separation and transport efficiency of photogenerated charge carriers in the photodetector and enhance the synergistic efficiency of light absorption and charge transfer. In addition, it can improve the compatibility of the two-dimensional eutectic structure in this invention with the device fabrication process. The photodetector obtained by the invention can have higher tunability.

Description

Technical Field

[0001] This invention relates to the fields of organic micro / nano optoelectronic crystal materials, polarization optical properties, and photodetectors, specifically to a photodetector device based on an organic two-dimensional charge-transfer eutectic and its fabrication method. Background Technology

[0002] Photodetectors are devices that convert incident light signals into electrical signals. Their core performance indicators include photoresponsivity, detectivity, linear dynamic range, response speed, and stability. Traditional photodetectors mostly use inorganic semiconductor materials such as silicon, gallium arsenide, and lead sulfide. However, these materials typically suffer from high manufacturing costs, complex processes, and poor flexibility and stretchability, making it difficult to meet the development needs of flexible electronics and wearable devices. Organic photodetectors, due to their advantages such as designable molecular structures, solution-processable nature, ease of large-area fabrication, and flexibility, are gradually becoming an important research direction in the field of photodetection. Common organic photosensitive materials include small organic molecules, conjugated polymers, and donor-acceptor organic semiconductor systems.

[0003] Organic charge-transfer eutectics are a very important and special type of donor-acceptor organic semiconductor materials. They are organic crystal materials formed by non-covalent interactions such as π–π stacking and charge transfer interactions between electron donor and acceptor molecules. These materials typically possess the following well-known characteristics: stable charge-transfer states are formed between donor and acceptor molecules, which is beneficial for the separation and transport of photogenerated carriers; the energy level structure can be controlled by molecular selection and proportioning; they exhibit strong absorption capabilities in the visible to near-infrared wavelength range; and they can be prepared using low-cost methods such as solution methods and growth methods. In recent years, some studies have reported the application of organic charge-transfer eutectic materials in photoconductive or photovoltaic devices to improve photoelectric conversion efficiency.

[0004] Two-dimensional organic crystal materials typically exhibit anisotropic carrier transport properties and high mobility in the planar direction, which is beneficial for constructing high-performance optoelectronic devices. Existing micro-nano fabrication techniques (such as photolithography, flexible electrode transfer, and patterned electrode fabrication) have been used to improve device electrode contacts and device structures, but their system application in organic charge-transfer eutectic photodetectors remains relatively limited.

[0005] Existing photodetectors based on organic donor-acceptor heterojunctions typically employ the following technical approach: ① Selecting organic donor materials (such as pentanebenzene derivatives) and organic acceptor materials (such as fullerenes or non-fullerene acceptors); ② Forming a hybrid thin film on a rigid or flexible substrate using solution processes such as spin coating or drop coating; ③ Fabricating metal electrodes on both sides of the thin film to construct a planar or vertically oriented photodetector; ④ Relying on the donor-acceptor interface to achieve the separation and transport of photogenerated electron-hole pairs. This approach is characterized by mature material systems and relatively simple fabrication processes. However, the donors and acceptors often exist in a disordered mixed state or in the form of amorphous or polycrystalline thin films, lacking long-range order in molecular arrangement. This results in discontinuous carrier transport paths, high dark current, and limited stability. This type of existing technology does not utilize charge-transfer eutectic materials with a clearly defined two-dimensional ordered structure, nor does it systematically regulate the charge transfer mechanism and band structure, thus limiting further improvements in photodetector performance.

[0006] In existing technologies, photoconductive or photovoltaic devices based on organic charge transfer eutectic typically employ the following technical approaches: ① Select specific donor and acceptor molecules to form a charge-transfer eutectic through slow evaporation of solution or solvent diffusion; ② The obtained eutectic often exhibits a one-dimensional needle-like, bulk, or thick-film structure; ③ The eutectic is directly placed or transferred between prefabricated electrodes to construct a photoresponse device; ④ The charge-transfer state is used to achieve a response to light in a specific wavelength band. Although this technical solution has recognized the application potential of charge-transfer eutectic in optoelectronic devices, its implementation method still has significant shortcomings: the eutectic structure is mostly one-dimensional or bulk, lacking two-dimensional confinement effect, making it difficult to balance high absorption and high in-plane transport; the interface engineering research between the eutectic and the substrate / electrode is insufficient, resulting in high contact resistance; the device structure is relatively simple, without combining micro / nano fabrication methods to optimize the internal structure; it is mostly concentrated on rigid substrate devices, with less research on flexible devices. This type of existing technology has not systematically introduced organic two-dimensional charge-transfer eutectic into the research of photodetector performance, nor has it improved photodetector performance from the perspective of charge transfer mechanism, bandgap modulation, and synergistic optimization of device structure.

[0007] In the field of organic donor-acceptor heterojunction photodetectors, existing technologies generally employ organic donor-acceptor materials to form hybrid thin films or heterojunction structures to achieve photodetection functionality. However, this approach suffers from several technical drawbacks in practical applications, such as disordered internal material structures limiting carrier transport efficiency; interface-dependent charge separation resulting in high recombination losses; and limited band structure modulation methods, leading to a restricted spectral response range. Based on these shortcomings, the technical problem this application aims to solve is: how to construct efficient carrier transport channels, reduce recombination losses, and achieve tunable band structure in photodetectors by introducing organic two-dimensional materials with ordered molecular arrangement and stable charge transfer mechanisms, thereby improving photodetection performance.

[0008] In the field of one-dimensional or bulk organic charge-transfer eutectic optoelectronic devices, some existing technologies have used organic charge-transfer eutectic materials in photoconductive or photoresponse devices. However, these technologies still have some shortcomings, such as limited eutectic dimensionality, insufficient in-plane carrier transport capability, poor interface matching between the eutectic and the substrate / electrode, and simple device structure, making it difficult to further improve performance. Based on these shortcomings, the technical problem this application aims to solve is: how to construct organic charge-transfer eutectic materials with two-dimensional confinement characteristics, and through interface engineering and device structure optimization, improve in-plane carrier transport capability and reduce contact resistance, thereby achieving high-performance photodetectors. Summary of the Invention

[0009] The purpose of this invention is to provide a photodetector device based on an organic two-dimensional charge-transfer eutectic and its fabrication method. This method can significantly improve the separation and transport efficiency of photogenerated carriers in the photodetector device and enhance the synergistic efficiency of light absorption and charge transfer. In addition, it can also improve the compatibility of the two-dimensional eutectic structure in this invention with the device fabrication process. The photodetector device obtained by the invention can have higher tunability.

[0010] This invention provides a method for realizing a two-dimensional charge-transfer eutectic photodetector based on a simple method of synthesizing organic eutectic.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a photodetector based on organic two-dimensional charge transfer eutectic, comprising a substrate, electrodes, a ceramic sheet, a metal π electrode, silver paste, gold wire, tin, and silver wire. The substrate and the metal π electrode are disposed on the ceramic sheet, and multiple electrodes are disposed on the substrate. The silver paste disposed on the metal π electrode is connected to the silver paste disposed on the electrode by gold wire. The tin disposed on the metal π electrode is connected to the silver wire. It also includes an organic two-dimensional charge transfer eutectic photosensitive layer. The organic two-dimensional charge transfer eutectic photosensitive layer is located on the electrode and electrically connected between the two electrodes for collecting photogenerated electrical signals. The organic two-dimensional charge transfer eutectic photosensitive layer is composed of organic donor molecules and organic acceptor molecules.

[0012] Preferably, the organic donor molecule is a polycyclic aromatic hydrocarbon molecule or a heterocyclic aromatic hydrocarbon molecule, and the acceptor molecule is a molecule containing electron-deficient molecules.

[0013] Preferably, the organic donor molecule is dithiophene[3,2-b:2',3'-d]thiophene, and the acceptor molecule is 7,7,8,8-tetracyanoquinone dimethane.

[0014] Preferably, the substrate is a rigid substrate or a flexible substrate, wherein the rigid substrate is made of glass, quartz, or silicon; and the flexible substrate is made of polyethylene terephthalate or polyimide.

[0015] Preferably, the electrode is a metal electrode or a transparent conductive electrode, and the material of the metal electrode is one of Au, Ag, and Cu.

[0016] To achieve the above objectives, the present invention also provides a method for fabricating the above-mentioned photodetector based on organic two-dimensional charge-transfer eutectic, comprising the following steps: S1. Selection and solution preparation of organic donor and organic acceptor molecules: Organic donor and organic acceptor molecules are added to a good organic solvent at a certain molar ratio and sonicated to obtain an organic micro / nano eutectic precursor solution containing organic donor and organic acceptor molecules. S2. Substrate preparation and electrode fabrication: After pre-cleaning the substrate, a copper mesh is attached to the substrate and thermal evaporation coating is performed to prepare the electrode. S3. Dropping and two-dimensional self-assembly growth of eutectic precursor solution: The eutectic precursor solution prepared in step S1 is dropped onto the surface of the substrate and the electrode to form an organic two-dimensional charge transfer eutectic photosensitive layer, so that the electrode and the organic two-dimensional charge transfer eutectic photosensitive layer form a stable electrical contact; by adjusting the spacing and arrangement of the electrodes, the charge carriers are transported in the two-dimensional eutectic plane, reducing the contact resistance. S4. Device Construction: Using a ceramic sheet as a substrate, attach the substrate and the metal π electrode to the ceramic sheet. The metal π electrode is located at both ends of the substrate and has a gap between it and the substrate. Apply silver paste to the two electrodes attached to the organic two-dimensional charge transfer eutectic photosensitive layer and the metal π electrode. There is a gap between the silver paste and the organic two-dimensional charge transfer eutectic photosensitive layer. Connect the silver paste on the electrode to the silver paste on the metal π electrode with gold wire. Finally, solder on the metal π electrode. The solder is connected to one end of the silver wire, and the other end of the silver wire is used to connect to the test device. The device fabrication is complete.

[0017] Preferably, in step S1, the organic donor molecule is dithiophene[3,2-b:2',3'-d]thiophene, and the acceptor molecule is 7,7,8,8-tetracyanoquinone dimethane; the molar ratio between the organic donor molecule and the organic acceptor molecule is 1:1; and the concentrations of the organic donor molecule and the organic acceptor molecule in the eutectic precursor solution are 2.5 mM.

[0018] Preferably, in step S2, the substrate (1) is a rigid substrate, and the material of the rigid substrate is silicon; the pre-cleaning process is: using acetone, isopropanol and ethanol solution to plasma clean the silicon wafer for 5 minutes each.

[0019] Preferably, in step S2, the electrode is a metal electrode made of Au; the gold plating film is 100 nm, and the copper mesh is 300 mesh square aperture.

[0020] Preferably, in step S3, the thickness of the organic two-dimensional charge transfer eutectic photosensitive layer (2) is 20-120 nm.

[0021] The working principle of the photodetector of the present invention is as follows: Under illumination, the two-dimensional charge-transfer eutectic photosensitive layer absorbs incident photons to form an excited state, and charge transfer occurs between donor / acceptor molecules to generate free electrons and holes; the free electrons and holes move along the ordered transport channel in the plane direction of the two-dimensional eutectic and are collected by each electrode under the action of an external electric field, thereby outputting a photoelectric signal.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) Significantly improved the separation and transport efficiency of photogenerated carriers. This invention employs an organic charge-transfer eutectic with two-dimensional confinement characteristics as the photosensitive layer of a photodetector, enabling donor and acceptor molecules to form a two-dimensional ordered arrangement on the substrate surface, constructing a continuous, low-defect carrier transport channel in the planar direction. Through the synergistic effect of the two-dimensional ordered structure and the stable charge transfer mechanism, this invention significantly improves the separation efficiency and in-plane transport efficiency of photogenerated electron-hole pairs, fundamentally enhancing the photoresponse performance of the photodetector.

[0023] (2) Improved the synergistic efficiency of light absorption and charge transfer. In traditional semiconductor thin films, light absorption and charge carrier transfer processes are independent, and photogenerated excitons are prone to energy loss during transport, making efficient charge transfer difficult. This invention introduces a charge transfer eutectic structure between donor and acceptor molecules, coupling light absorption and charge transfer processes at the molecular scale, enabling simultaneous photoexcitation and charge transfer. This technique improves the matching degree between light absorption and charge transfer, allowing more photogenerated excitons to be effectively converted into transportable free charge carriers.

[0024] (3) The two-dimensional eutectic structure has better compatibility with device fabrication processes. Existing charge-transfer eutectics are mostly obtained through bulk crystallization or independent growth, making it difficult to directly form a two-dimensional ordered structure on the device substrate, thus affecting device consistency. This invention employs a solution method to directly form a two-dimensional charge-transfer eutectic structure on the device substrate surface, avoiding material transfer or secondary processing. This technique improves the consistency between the material and the device structure, facilitating the fabrication of stable photodetectors.

[0025] (4) Photodetector structure designed around the carrier transport characteristics in the two-dimensional eutectic plane In this invention, the electrode structure and arrangement are matched with the in-plane carrier transport direction of the two-dimensional charge transfer eutectic, enabling photogenerated carriers to be efficiently transported and collected along the eutectic plane. This design is an important technical means to achieve low dark current, high responsivity and high photoelectric detection performance. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the photodetector device of the present invention; Figure 2 Microscopic images of the DTT-TCNQ eutectic prepared in Example 1 of this invention; (a) is an optical microscope image, and (b) is an electron microscope image; Figure 3 The images show an AMF image (a) of the DTT-TCNQ eutectic prepared in Embodiment 1 of the present invention and an optical microscope image (b) of the DTT-TCNQ eutectic photodetector. Figure 4 shows the optical anisotropic micro-area reflectance differential spectral signal of the DTT-TCNQ eutectic prepared in Example 1 of the present invention. The test collected data once every 15° rotation to complete a 360° full-angle scan. The figure shows the second harmonic signal (a), the first harmonic signal (b), and the ordinary reflectance signal (c) plotted from the test data. Figure 5 This is a schematic diagram showing the relationship between current and voltage of the DTT-TCNQ eutectic photodetector device prepared in Embodiment 1 of the present invention under 532 nm wavelength laser irradiation; IV curves (a) and IV curves (b) of the dark current of the DTT-TCNQ eutectic device at different powers. Figure 6 This is a schematic diagram showing the relationship between current density and incident light intensity of the DTT-TCNQ eutectic photodetector device prepared in Embodiment 1 of the present invention under 532 nm wavelength laser irradiation. Figure 7 The diagram shows the responsivity (a) and specific detectivity (b) of the DTT-TCNQ eutectic photodetector prepared in Embodiment 1 of the present invention under 532 nm wavelength laser irradiation as a function of incident light intensity. Figure 8 The DTT-TCNQ eutectic photodetector prepared in Example 2 of this invention operates at a laser wavelength of 532 nm and a wavelength of 177.617 mW / cm². 2 A schematic diagram showing the change in current as a function of angle when the half-wave plate is rotated every 5° under incident light intensity; Figure 9 The DTT-TCNQ eutectic photodetector prepared in Example 2 of this invention operates at a laser wavelength of 532 nm and a wavelength of 177.617 mW / cm². 2Schematic diagram (a) and schematic diagram (b) showing the change in responsivity as a function of angle when the half-wave plate is rotated every 5° under incident light intensity. Figure 10 The DTT-TCNQ eutectic photodetectors of different thicknesses prepared in Example 2 of this invention were tested at a laser wavelength of 532 nm and a wavelength of 12.14671397 mW / cm². 2 IV curves (a) under incident light intensity and schematic diagrams (b) showing the relationship between responsivity and specific detectivity as a function of DTT-TCNQ eutectic thickness. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments.

[0028] Example 1 like Figure 1 As shown, a photodetector based on an organic two-dimensional charge-transfer eutectic includes a substrate 1, electrodes 3, a ceramic sheet 4, a metal π electrode 5, silver paste 6, gold wire 7, tin 8, and silver wire 9. The substrate 1 and the metal π electrode 5 are disposed on the ceramic sheet 4, and multiple electrodes 3 are disposed on the substrate 1. The silver paste 6 disposed on the metal π electrode 5 is connected to the silver paste 6 disposed on the electrode 3 via the gold wire 7. The tin 8 disposed on the metal π electrode 5 is connected to the silver wire 9. The device also includes an organic two-dimensional charge-transfer eutectic photosensitive layer 2. The organic two-dimensional charge-transfer eutectic photosensitive layer 2 is located on the electrode 3 and electrically connected between two electrodes 3 for collecting photogenerated electrical signals. The organic two-dimensional charge-transfer eutectic photosensitive layer 2 is composed of organic donor molecules and organic acceptor molecules. The organic donor molecule is dithiophene[3,2-b:2',3'-d]thiophene, and the acceptor molecule is 7,7,8,8-tetracyanoquinone dimethane; the substrate 1 is a rigid substrate made of silicon; the electrode is a metal electrode made of Au.

[0029] The above-mentioned method for fabricating photodetectors based on organic two-dimensional charge-transfer eutectic includes the following steps: S1. Selection of organic donor and acceptor molecules and solution preparation: 0.98 mg of dithiophene[3,2-b:2',3'-d]thiophene (DTT) and 1.02 mg of 7,7,8,8-tetracyanoquinone dimethyl ether (TCNQ) (sublimed and purified) were added to 2 mL of dichloromethane (DCM) and sonicated for 5 min to obtain DTT-TCNQ dichloromethane stock solution; S2. Substrate preparation and electrode fabrication: After pre-cleaning substrate 1, a copper mesh is attached to substrate 1 and thermally evaporated to deposit a film to obtain electrode 3; substrate 1 is a rigid substrate made of silicon; the pre-cleaning process is as follows: the silicon wafer is plasma-cleaned for 5 min each with acetone, isopropanol, and ethanol solutions; electrode 3 is a metal electrode made of Au; the gold film is 100 nm thick, and the copper mesh has a 300-mesh square aperture. S3. Dropping and two-dimensional self-assembly growth of the eutectic precursor solution: Take 2 mL of the DTT-TCNQ dichloromethane stock solution prepared in step S1 and add it to 1 mL of n-hexane. Shake well, then drop it onto the surface of substrate 1 and electrode 3. After the organic solvent has completely evaporated, heat at 20°C for 5 min to obtain square organic micron-shaped eutectic sheets. Figure 2 An organic two-dimensional charge transfer eutectic photosensitive layer 2 is formed, enabling the electrode 3 to form a stable electrical contact with the organic two-dimensional charge transfer eutectic photosensitive layer 2; by adjusting the spacing and arrangement of the electrodes 3, the charge carriers can be transported within the two-dimensional eutectic plane, reducing the contact resistance; From scanning electron microscope images (SEM, Figure 3 (b) It can also be seen that the surface of the two-dimensional charge-transfer eutectic photosensitive layer 2 prepared in this invention is very clean, without obvious defects. Then, it is further examined using an atomic force microscope (AFM). Figure 3 Analysis of image a) reveals that the prepared two-dimensional charge-transfer eutectic photosensitive layer 2 has a very thin thickness of 90 nm. These conditions result in a closer contact between the crystal and the electrode, thereby promoting charge transport. Subsequently, micro-area reflectance differential spectroscopy was used to test the DTT-TCNQ eutectic sample, acquiring data every 15° rotation to complete a 360° full-angle test; from the second harmonic signal diagram (… Figure 4a ) and the first harmonic signal diagram ( Figure 4b The inversion of the signal can be observed in the ordinary reflected signal diagram ( ). Figure 4c The absence of this phenomenon confirms that the DTT-TCNQ eutectic exhibits optical anisotropy.

[0030] S4. Device Construction: Using ceramic sheet 4 as a substrate, attach substrate 1 and metal π electrode 5 onto ceramic sheet 4. The metal π electrode 5 is located at both ends of substrate 1 and has a gap between it and substrate 1. Apply silver paste 6 to the two electrodes 3 and metal π electrode 5 attached to the organic two-dimensional charge transfer eutectic photosensitive layer 2. There is a gap between silver paste 6 and organic two-dimensional charge transfer eutectic photosensitive layer 2. Connect the silver paste 6 on electrode 3 to the silver paste 6 on metal π electrode 5 with gold wire 7. Finally, solder 8 on metal π electrode 5. Solder 8 is connected to one end of silver wire 9. The other end of silver wire 9 is used to connect to the test device. The device fabrication is complete.

[0031] As can be seen from the figure, the eutectic device exhibits a significant photocurrent response under 532 nm laser irradiation, which is significantly different from the dark current under conditions without a light source. Figure 5 By testing the photocurrent response under different incident light intensities at 532 nm, it can be seen that the current density of the DTT-TCNQ eutectic device increases with increasing incident light intensity, and the relationship is linear. Figure 6 Calculations using the formula show that the responsivity of the DTT-TCNQ eutectic device can reach 585.28 A / W, and the specific detectivity can reach 7.99 × 10⁻⁶. 13 Jones ( Figure 7 ).

[0032] Subsequently, using a macroscopic polarized photocurrent testing system, employing the half-wave plate method and lock-in amplification technology, data was collected every 5° of rotation to complete a 360° full-angle test, obtaining the photocurrent signals under different rotation angles irradiated by a 532 nm wavelength laser. The photocurrent signal at an incident light intensity of 177.617 mW / cm² was plotted. 2 Current curve ( Figure 8 The periodic variation of current can be observed directly. The responsivity and specific detectivity of the DTT-TCNQ eutectic device at 532 nm wavelength with respect to the waveplate angle are calculated using formulas. Figure 9 ).

[0033] Example 2 In this embodiment, the photodetector based on organic two-dimensional charge transfer eutectic and its preparation method are the same as in Embodiment 1, except that: in step S3, 0.45 mL of the DTT-TCNQ dichloromethane stock solution prepared in step S1 is added to 0.225 mL of n-hexane and shaken well, and then dripped onto the surface of substrate 1 and electrode 3. After the organic solvent has completely evaporated, it is heated at 20°C for 5 min to obtain a 20 nm square organic micron-shaped eutectic.

[0034] Example 3 In this embodiment, the photodetector based on organic two-dimensional charge transfer eutectic and its preparation method are the same as in Embodiment 1, except that: in step S3, 0.89 mL of the DTT-TCNQ dichloromethane stock solution prepared in step S1 is added to 0.445 mL of n-hexane and shaken well, and then dropped onto the surface of substrate 1 and electrode 3. After the organic solvent has completely evaporated, it is heated at 20°C for 5 min to obtain a 40 nm square organic micron-shaped eutectic.

[0035] Example 4 In this embodiment, the photodetector based on organic two-dimensional charge transfer eutectic and its preparation method are the same as in Embodiment 1, except that: in step S3, 1.33 mL of the DTT-TCNQ dichloromethane stock solution prepared in step S1 is added to 0.665 mL of n-hexane and shaken well, and then dripped onto the surface of substrate 1 and electrode 3. After the organic solvent has completely evaporated, it is heated at 20°C for 5 min to obtain a 60 nm square organic micron-shaped eutectic.

[0036] Example 5 In this embodiment, a photodetector based on an organic two-dimensional charge transfer eutectic and its preparation method are the same as in Embodiment 1, except that: in step S3, 2.22 mL of the DTT-TCNQ dichloromethane stock solution prepared in step S1 is added to 1.11 mL of n-hexane and shaken well, and then dropped onto the surface of substrate 1 and electrode 3. After the organic solvent has completely evaporated, it is heated at 20°C for 5 min to obtain a 100 nm square organic micron-shaped eutectic.

[0037] Example 6 In this embodiment, the photodetector based on organic two-dimensional charge transfer eutectic and its preparation method are the same as in Embodiment 1, except that: in step S3, 2.67 mL of the DTT-TCNQ dichloromethane stock solution prepared in step S1 is added to 1.335 mL of n-hexane and shaken well, and then dripped onto the surface of substrate 1 and electrode 3. After the organic solvent has completely evaporated, it is heated at 20°C for 5 min to obtain a 120 nm square organic micron-shaped eutectic.

[0038] The eutectic crystals obtained in Examples 2 to 6 were subjected to performance tests, and the test results are as follows: Figure 10 As shown in the figure. It can be seen from the figure that when the incident light intensity is 12.14671397 mW / cm², 2 Under 532 nm wavelength laser irradiation, the photocurrent of the DTT-TCNQ eutectic device increases with decreasing thickness, and the eutectic device with a thickness of 20 nm exhibits a more pronounced photocurrent response. Figure 10 a) Calculations using the formula show that the photoresponsivity significantly increases with decreasing thickness. When the thickness of the DTT-TCNQ eutectic device decreases from 120 nm to 20 nm, the responsivity increases from 14.18 A / W to 1210.81 A / W, and the specific detectivity increases from 2.35 × 10⁻⁶ A / W to 1210.81 A / W. 12 Increased to 1.65 × 10 14 Jones, respectively increased by 85 times and 70 times ( Figure 10 b).

Claims

1. A photodetector based on an organic two-dimensional charge-transfer eutectic, comprising a substrate (1), electrodes (3), a ceramic sheet (4), a metal π electrode (5), silver paste (6), gold wire (7), tin (8), and silver wire (9), wherein the substrate (1) and the metal π electrode (5) are disposed on the ceramic sheet (4), and a plurality of electrodes (3) are disposed on the substrate (1); the silver paste (6) disposed on the metal π electrode (5) is connected to the silver paste (6) disposed on the electrode (3) via gold wire (7); the tin (8) disposed on the metal π electrode (5) is connected to the silver wire (9); characterized in that, It also includes an organic two-dimensional charge transfer eutectic photosensitive layer (2); the organic two-dimensional charge transfer eutectic photosensitive layer (2) is located on the electrode (3) and electrically connected between the two electrodes (3) for collecting photogenerated electrical signals; the organic two-dimensional charge transfer eutectic photosensitive layer (2) is composed of organic donor molecules and organic acceptor molecules; the organic donor molecule is dithiophene[3,2-b:2',3'-d]thiophene, and the organic acceptor molecule is 7,7,8,8-tetracyanoquinone dimethane.

2. The photodetector based on an organic two-dimensional charge-transfer eutectic as described in claim 1, characterized in that, The substrate (1) is a rigid substrate or a flexible substrate. The rigid substrate is made of one of glass, quartz, or silicon. The flexible substrate is made of polyethylene terephthalate or polyimide.

3. A photodetector based on an organic two-dimensional charge-transfer eutectic according to claim 1, characterized in that, The electrode (3) is a metal electrode or a transparent conductive electrode, and the material of the metal electrode is one of Au, Ag, and Cu.

4. A method for fabricating a photodetector based on an organic two-dimensional charge-transfer eutectic as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Selection and solution preparation of organic donor and organic acceptor molecules: Organic donor and organic acceptor molecules are added to a good organic solvent at a certain molar ratio and sonicated to obtain an organic micro / nano eutectic precursor solution containing organic donor and organic acceptor molecules; the organic donor molecule is dithiophene[3,2-b:2',3'-d]thiophene, and the organic acceptor molecule is 7,7,8,8-tetracyanoquinone dimethane; S2. Preparation of substrate and preparation of electrode: After pre-cleaning the substrate (1), copper mesh is attached to the substrate (1) and thermal evaporation coating is performed to prepare electrode (3). S3. Dropping and two-dimensional self-assembly growth of eutectic precursor solution: The eutectic precursor solution prepared in step S1 is dropped onto the surface of the substrate (1) and the electrode (3) to form an organic two-dimensional charge transfer eutectic photosensitive layer (2), so that the electrode (3) and the organic two-dimensional charge transfer eutectic photosensitive layer (2) form a stable electrical contact; by adjusting the spacing and arrangement of the electrodes (3), the charge carriers are transported in the two-dimensional eutectic plane, reducing the contact resistance; S4. Device construction: Using a ceramic sheet (4) as a substrate, attach the substrate (1) and the metal π electrode (5) to the ceramic sheet (4). The metal π electrode (5) is located at both ends of the substrate (1) and there is a gap between it and the substrate (1). Apply silver paste (6) to the two electrodes (3) and the metal π electrode (5) attached to the organic two-dimensional charge transfer eutectic photosensitive layer (2). There is a gap between the silver paste (6) and the organic two-dimensional charge transfer eutectic photosensitive layer (2). Connect the silver paste (6) on the electrode (3) and the silver paste (6) on the metal π electrode (5) with gold wire (7). Finally, solder (8) on the metal π electrode (5). The solder (8) is connected to one end of the silver wire (9). The other end of the silver wire (9) is used to connect the test device. The device fabrication is complete.

5. The method for fabricating a photodetector based on an organic two-dimensional charge-transfer eutectic according to claim 4, characterized in that, In step S1, the molar ratio between the organic donor molecule and the organic acceptor molecule is 1:1; the concentrations of the organic donor molecule and the organic acceptor molecule in the eutectic precursor solution are 2.5 mM.

6. A method for fabricating a photodetector based on an organic two-dimensional charge-transfer eutectic according to claim 4 or 5, characterized in that, In step S2, the substrate (1) is a rigid substrate, and the material of the rigid substrate is silicon; the pre-cleaning process is: using acetone, isopropanol and ethanol solution to plasma clean the silicon wafer for 5 minutes each.

7. A method for fabricating a photodetector based on an organic two-dimensional charge-transfer eutectic according to claim 4 or 5, characterized in that, In step S2, the electrode (3) is a metal electrode, the material of which is Au; the gold plating film is 100 nm, and the copper mesh is 300 mesh square hole.

8. A method for fabricating a photodetector based on an organic two-dimensional charge-transfer eutectic according to claim 4 or 5, characterized in that, In step S3, the thickness of the organic two-dimensional charge transfer eutectic photosensitive layer (2) is 20-120 nm.

Images