An organic photodetector with wide spectral response and a preparation method thereof

Abstract

The application provides an organic photoelectric detector with a wide spectrum response and a preparation method thereof, and belongs to the technical field of organic photoelectric detectors. 11 The photoelectric detector has an excellent response to a visible-short-wave infrared wide band of 0.3-1.6 microns, and the specific detectivity at a 1.5-micron band can reach 10 Jones; the structure and preparation process of the device are simple, the working voltage is small, the device can be applied to large-area devices, the cost is low, and the application range is wide.

Description

Technical Field

[0001] This invention belongs to the field of organic photodetector technology, specifically relating to an organic photodetector with a wide spectral response and its fabrication method. Background Technology

[0002] As core components of optoelectronic systems, photodetectors have wide applications in civilian and military fields such as optical imaging, optical communication, environmental monitoring, and biomedicine. Among these, devices capable of effectively detecting short-wave infrared (SWIR, typically 0.9-1.7 μm) light signals have become a research hotspot due to their unique advantages in areas such as smoke penetration, camouflage identification, and night vision imaging. Currently, commercially available short-wave infrared detectors are mainly based on inorganic semiconductor materials, such as InGaAs and HgCdTe. However, these inorganic detectors typically require stringent fabrication processes (such as molecular beam epitaxy) and expensive substrate materials, resulting in high costs. Furthermore, their integration with silicon-based readout circuits is challenging, limiting their widespread adoption in portable, flexible, and low-cost devices.

[0003] Organic semiconductor materials offer significant advantages such as solution-processability, high mechanical flexibility, suitability for large-area fabrication, and low cost, providing a novel approach for developing next-generation high-performance, low-cost, and large-area short-wave infrared detectors. In recent years, organic photodetectors have made significant progress in the visible to near-infrared bands, with some performance indicators approaching or even exceeding those of inorganic detectors. However, limited by the band structure of organic materials, most conventional organic semiconductors typically have narrow absorption spectra, covering only the visible light band and struggling to respond to longer wavelengths of infrared light. Therefore, to achieve short-wave infrared detection, it is necessary to introduce narrow bandgap materials or utilize charge-transfer complex absorption to broaden the spectral range. Patent CN115377290A discloses a broadband organic photodetector with short-wave infrared response. Although the device's response cutoff wavelength extends to 1.4 μm, the specific detectivity of the device significantly decreases as the wavelength approaches 1.4 μm, dropping to 10. 11 The Jones value below indicates that the device's detection capability in the 1.4 μm band is significantly weakened.

[0004] Therefore, developing organic photodetectors that can simultaneously achieve high absorption, low noise, and high specific detectivity in the 1.4 μm and longer wavelength ranges remains a significant challenge. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention aims to provide an organic photodetector with a short-wave infrared broadband spectral response and its fabrication method. The photosensitive layer of this photodetector is fabricated based on a novel narrowband small molecule acceptor material, and the device can achieve a broadband spectral response in the visible-short-wave infrared range with a specific detectivity of 10-1.12 Jones devices have simple structures and fabrication processes, low operating voltages, can be applied to large-area devices, are low in cost, and have a wide range of applications.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] An organic photodetector with a broad spectral response includes a transparent substrate, a first electrode, a first modification layer, a photosensitive layer, a second modification layer, and a second electrode arranged sequentially. The first electrode is a transparent conductive electrode. The photosensitive layer is characterized by being made of an organic donor material and an organic small molecule acceptor material, COTCNTTM, wherein COTCNTTM is a narrow bandgap small molecule acceptor material, and its molecular structure is shown in Formula I.

[0008]

[0009] (Formula I)

[0010] Furthermore, the thickness of the first electrode is 100–150 nm; the thickness of the first modification layer is 5–40 nm; the thickness of the photosensitive layer is 50–500 nm; the thickness of the second modification layer is 5–40 nm; and the thickness of the second electrode is 100–150 nm.

[0011] Furthermore, the device structure of organic photodetectors includes positive-type devices and inverted-type devices;

[0012] When the device is a positive device, the first electrode is the anode, and its material is any one of ITO, PEDOT:PSS, graphene, and silver nanowires; the first modification layer is the anode modification layer, and its material is any one of MePACz, P-4PACz, P-2PACz, PEDOT:PSS, MoO3, NPB, PVK, and NiO; the second modification layer is the cathode modification layer, and its material is PNDIT-F3N, ZnO, LiF, PFN-Br, BCP, or C. 60 The first electrode is any one of SnO2, Ca, and Mg; the second electrode is the cathode, and its material is any one of Ag, Al, Au, and PEDOT:PSS.

[0013] When the device is an inversion device, the first electrode is the cathode, and its material is any one of ITO, PEDOT:PSS, graphene, and silver nanowires; the first modification layer is the cathode modification layer, and its material is PEIE, ZnO, LiF, PFN-Br, BCP, or C. 60 The first electrode is an anode material, which is any one of SnO2, Ca, and Mg; the second modification layer is an anode modification layer, which is any one of PEDOT:PSS, MoO3, NPB, PVK, and NiO; the second electrode is an anode material, which is any one of Ag, Al, Au, and PEDOT:PSS.

[0014] Furthermore, the photosensitive layer of the device includes a planar heterojunction and a bulk heterojunction.

[0015] The present invention also provides a method for fabricating the above-mentioned organic photodetector, which includes the following steps when the photosensitive layer of the device is a bulk heterojunction:

[0016] Step 1. Clean the transparent substrate and blow dry;

[0017] Step 2. Sequentially fabricate the first electrode and the first modification layer on a transparent substrate;

[0018] Step 3. Prepare a photosensitive layer on the surface of the first modified layer. The specific process is as follows:

[0019] Step 3.1. Preparation of photosensitive layer solution: Add the donor material and acceptor material to an organic solvent, mix, heat and stir until homogeneous to obtain the photosensitive layer solution; wherein, the acceptor material is a narrow bandgap small molecule COTCNTTM;

[0020] Step 3.2. Under a nitrogen atmosphere, spin-coat the photosensitive layer solution onto the surface of the first modified layer, and then anneal it to obtain the photosensitive layer; the spin-coating process parameters are: spin-coating speed of 1500rpm-3000rpm, spin-coating time of 20-40s;

[0021] Step 4. Sequentially prepare the second modification layer and the second electrode on the surface of the photosensitive layer to obtain the desired organic photodetector.

[0022] Furthermore, the preparation process of the narrow bandgap small molecule COTCNTTM is as follows:

[0023] The first compound, the second compound, SbCl3 and propionic anhydride were mixed to obtain a mixed solution. The mixed solution was then stirred under a nitrogen atmosphere to carry out a condensation reaction at a temperature of 45-55℃ for 2.5-3.5 h.

[0024] After the reaction was completed, methanol was added to the reactants, and the solid was stirred to precipitate. The obtained solid product was filtered and then purified by silica gel column chromatography to finally obtain the desired narrow bandgap small molecule COTCNTTM.

[0025] The molecular formula of the first compound is shown in Formula II, and the molecular formula of the second compound is shown in Formula III.

[0026]

[0027] (Formula II)

[0028]

[0029] (Formula III).

[0030] Furthermore, in the mixed solution, the molar ratio of the first compound, the second compound, and SbCl3 is 1:3:4.

[0031] Furthermore, the donor material is PTB7-Th, PBDB-T, P3HT, etc.; the mass ratio of donor to acceptor is 1:(1-2); and the total mass concentration of donor and acceptor is 12-20 mg / mL.

[0032] Furthermore, additives can be added to the photosensitive layer solution in step 3.1; the additives are TMB, 1-CN, DIO, etc.

[0033] The mechanism of this invention is as follows:

[0034] The superior broadband infrared detection performance of the narrow-bandgap organic acceptor material of this invention is primarily due to the synergistic regulation of the molecular backbone and terminal functional groups. The molecular backbone can construct a stable TM quinone conjugated backbone. This structure reduces the alternation of molecular bond lengths, promotes full delocalization of π electrons, effectively narrows the material's optical bandgap, redshifts the absorption spectrum, and extends it to the near-infrared band, achieving wide-range photon capture. Furthermore, the dicyano strong electron-withdrawing group introduced at the molecular ends further enhances intramolecular charge transfer, continuously compressing the bandgap and expanding the long-wavelength absorption boundary. Simultaneously, it lowers the HOMO energy level of the acceptor molecule, increases the difference in HOMO energy levels between the donor and acceptor in the blended active layer, provides sufficient driving force for photoexciton dissociation, reduces charge recombination losses, and allows the device to achieve efficient photoelectric response in the visible-short-wavelength infrared spectral range.

[0035] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0036] This invention utilizes the low-bandgap organic small molecule material COTCNTTM as the photosensitive layer material to fabricate an organic photodetector. The fabrication process is simple, and the device exhibits excellent response in the 0.3-1.6 μm visible-shortwave infrared broadband band, with a specific detectivity reaching 10 in the 1.5 μm band. 11 Jones, with its low operating voltage, can be applied to large-area devices, has low cost, and a wide range of applications. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the organic photodetector in Embodiment 1 of the present invention.

[0038] Figure 2 This is the chemical structural formula of the organic small molecule acceptor material COTCNTTM of the present invention.

[0039] Figure 3This is a schematic diagram of the energy levels of COTCNTTM, the organic small molecule acceptor material of this invention.

[0040] Figure 4 This is the normalized absorption spectrum of the COTCNT™ thin film, an organic small molecule acceptor material of this invention.

[0041] Figure 5 The image shows the dark current density-voltage (JV) curve of the organic photodetector prepared in Example 1.

[0042] Figure 6 The image shows the specific detectivity (D*) spectral response of the organic photodetector prepared in Example 1. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0044] An organic photodetector with a short-wave infrared broadband response has an inversion structure, as shown in the schematic diagram below. Figure 1 As shown, it includes a transparent substrate, a transparent conductive cathode, a cathode modification layer, a photosensitive layer, an anode modification layer, and an anode layer; wherein, the photosensitive layer is prepared from a mixed solution containing an organic donor material and an organic small molecule acceptor material COTCNTTM, wherein COTCNTTM is a narrow-band small molecule acceptor material, and its chemical structure is shown in the figure. Figure 2 As shown.

[0045] Example 1

[0046] A method for fabricating an organic photodetector with a short-wave infrared broadband response includes the following steps:

[0047] Step 1. Clean the transparent glass substrate and dry it with nitrogen. Prepare a transparent conductive cathode ITO with a thickness of 100 nm on the surface of the transparent substrate by magnetron sputtering. Clean the substrate with deposited ITO sequentially with detergent, acetone and isopropanol by ultrasonic cleaning. After drying with nitrogen, clean it with ultraviolet ozone for 15 min.

[0048] Step 2. Prepare a cathode modification layer, wherein the cathode modification layer is a ZnO thin film; prepare a ZnO precursor solution on an ITO cathode by spin coating at a speed of 4000 rpm for 40 s; after spin coating, perform thermal annealing in an atmospheric environment at a temperature of 200℃ and a time of 30 min; the thickness of the prepared ZnO thin film is approximately 30 nm.

[0049] Step 3. Prepare a photosensitive layer on the surface of the cathode-modified layer. The photosensitive layer is a bulk heterojunction. The specific process is as follows:

[0050] Step 3.1. Preparation of the photosensitizing layer solution: The donor material PTB7-Th and the acceptor material COTCNTTM are added to chloroform organic solvent to obtain solution A; wherein the mass ratio of the donor material to the acceptor material is 1:1.2, and the total concentration of solution A is 15 mg / ml; then TMB is added to solution A as an additive to obtain the photosensitizing layer solution; the concentration of the additive in the photosensitizing layer solution is 10 mg / ml;

[0051] Step 3.2. Place the photosensitive layer solution on a heated stirring table at 65°C and stir for more than 6 hours to ensure that all components of the solution are mixed evenly;

[0052] Step 3.3. Preparation of photosensitive layer: Under nitrogen atmosphere, a photosensitive layer is prepared on the surface of ZnO film by spin coating process. The spin coating speed and time are 1500 rpm and 40s, respectively. After spin coating, the film is heat annealed at 150℃ for 10min to obtain a photosensitive layer with a thickness of about 200nm.

[0053] Step 4. Prepare an anode modification layer on the surface of the photosensitive layer using vacuum evaporation, with a evaporation pressure of 10. -4 Pa; The anode modification layer material is MoO3, with a thickness of 10 nm;

[0054] Step 5. Deposit the anode onto the surface of the anode modification layer by vapor deposition. The anode material is metallic Ag, and the vapor deposition pressure is 10. -4 Pa, thickness is

[0055] The required organic photodetector can be obtained at 100nm.

[0056] Figure 3 shows a schematic diagram of the HOMO / LUMO energy levels of the acceptor material COTCNTTM in this embodiment. Test results show that the HOMO energy level of this material is -5.22 eV, the LUMO energy level is -4.28 eV, and the optical band gap is 0.94 eV. This material possesses a deep HOMO energy level, which can effectively improve the environmental stability of the device and increase the HOMO energy level difference with the donor, providing sufficient driving force for hole transfer. Simultaneously, its LUMO energy level can form an effective energy level difference with the donor material, which is beneficial for exciton dissociation and charge transport, providing an energy level basis for realizing high-performance organic photoelectric detection.

[0057] Figure 4 shows the absorption spectrum of the COTCNT™ material. As can be seen from the figure, this material has a broad spectral absorption characteristic in the visible to near-infrared region (300–1800 nm), with the main absorption peak located at about 1200 nm and the absorption edge extending to about 1800 nm, indicating that it has excellent absorption capability for near-infrared light. It can be used to prepare organic photodetectors with a broad spectral response, suitable for applications such as weak light detection and near-infrared imaging.

[0058] The photo-dark state JV characteristics of the organic photodetector prepared in this embodiment were tested using a Keithley 4200 semiconductor analyzer, and the results are as follows: Figure 5 As shown. Under reverse bias, the device exhibits a low dark current density, with a dark current density of 3.07 × 10⁻⁶ at -0.5V. -6 A cm -2 This indicates that the device has good carrier blocking capability and high rectification characteristics, and can effectively prevent carriers from being injected in reverse from the electrodes.

[0059] The spectral response of the fabricated organic photodetector was measured using a DSR100 broadband photoelectric testing system. The test wavelength range was 0.3–1.5 μm, and the test bias voltage was -0.5 V. The device's D... * Spectral response such as Figure 6 As shown. Test results indicate that the device exhibits a high response over a wide wavelength range of 0.3–1.5 μm, D * Up to 10 12 Jones, D at 720nm * 1.62×10 12 Jones. D at 1.4 μm * Up to 7×10 11 Jones significantly outperforms existing organic photodetectors in this band.

[0060] Example 2

[0061] An organic photodetector with a broad visible-short-wave infrared spectral response, wherein the device is a positive device; the specific process of device fabrication is as follows:

[0062] Step 1. Clean the transparent substrate and dry it with nitrogen. Prepare a transparent conductive cathode ITO with a thickness of 100 nm on the surface of the transparent substrate by magnetron sputtering. Clean the substrate with deposited ITO sequentially with detergent, acetone and isopropanol by ultrasonic cleaning. After drying with nitrogen, clean it with ultraviolet ozone for 15 min.

[0063] Step 2. Prepare the anode modification layer, which is a MePACz film; prepare a 0.3 mg / ml MePACz solution on an ITO cathode by spin coating at a speed of 3000 rpm and a time of 40 s, using ethanol as the solvent for the MePACz solution; after spin coating, perform heat annealing in a glove box at a temperature of 100 °C and a time of 10 min, resulting in a film thickness of approximately 2 nm;

[0064] Step 3. Prepare a photosensitive layer on the surface of the anode-modified layer, the specific process is the same as step 3 in Example 1;

[0065] Step 4. A cathode modification layer is prepared on the surface of the photosensitive layer by spin coating. The cathode modification layer is a PNDIT-F3N film with a thickness of 8 nm. A 0.5 mg / ml PNDIT-F3N solution is prepared on the photosensitive layer by spin coating. The spin coating speed and time are 3000 rpm and 40 s, respectively.

[0066] Step 5. Deposit a cathode onto the surface of the cathode modification layer by vapor deposition. The anode material is metallic Ag, and the vapor deposition pressure is 10. -4 Pa, thickness is

[0067] The required organic photodetector can be obtained at 100nm.

[0068] Example 3

[0069] The organic photodetector was prepared according to the steps in Example 1, except that the preparation process of the photosensitive layer in step 3 was different; the other steps were the same. The photosensitive layer was a planar heterojunction structure, and the specific preparation process was as follows:

[0070] Step 3.1. Preparation of photosensitizing layer solution: Add the donor material PTB7-Th and the acceptor material COTCNTTM to chloroform organic solvent to prepare a PTB7-Th solution with a mass concentration of 5 mg / mL and a COTCNTTM solution with a mass concentration of 10 mg / mL, respectively.

[0071] Step 3.2. Place both the PTB7-Th solution and the COTCNTTM solution on a heated stirring table at 65°C and stir for at least 6 hours to ensure complete dissolution;

[0072] Step 3.3. Preparation of photosensitive layer: Under nitrogen atmosphere, PTB7-Th film and COTCNTTM film were sequentially spin-coated on the surface of ZnO film using spin coating process. The spin coating speed and time were 1500 rpm and 40 s, respectively. After spin coating, the film was heat-annealed at 150℃ for 10 min to obtain a photosensitive layer with a thickness of about 200 nm.

[0073] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. An organic photodetector with a broad spectral response, the organic photodetector comprising, sequentially disposed, a transparent substrate, a first electrode, a first modification layer, a photosensitive layer, a second modification layer, and a second electrode, wherein the first electrode is a transparent conductive electrode, characterized in that, The photosensitive layer is made of an organic donor material and an organic small molecule acceptor material COTCNTTM. COTCNTTM is a narrow bandgap small molecule acceptor material, and its molecular structure is shown in Formula I. ， Formula I.

2. The organic photodetector as described in claim 1, characterized in that, The thickness of the first electrode is 100–150 nm; the thickness of the first modification layer is 5–40 nm; the thickness of the photosensitive layer is 50–500 nm; the thickness of the second modification layer is 5–40 nm; and the thickness of the second electrode is 100–150 nm.

3. The organic photodetector as described in claim 1, characterized in that, Organic photodetectors can be either positive or negative devices. When the device is a positive device, the first electrode is the anode, and its material is any one of ITO, PEDOT:PSS, graphene, and silver nanowires; the first modification layer is the anode modification layer, and its material is any one of MePACz, P-4PACz, P-2PACz, PEDOT:PSS, MoO3, NPB, PVK, and NiO; the second modification layer is the cathode modification layer, and its material is PNDIT-F3N, ZnO, LiF, PFN-Br, BCP, or C. 60 The first electrode is any one of SnO2, Ca, and Mg; the second electrode is the cathode, and its material is any one of Ag, Al, Au, and PEDOT:PSS. When the device is an inversion device, the first electrode is the cathode, and its material is any one of ITO, PEDOT:PSS, graphene, and silver nanowires; the first modification layer is the cathode modification layer, and its material is PEIE, ZnO, LiF, PFN-Br, BCP, or C. 60 The first electrode is an anode material, which is any one of SnO2, Ca, and Mg; the second modification layer is an anode modification layer, which is any one of PEDOT:PSS, MoO3, NPB, PVK, and NiO; the second electrode is an anode material, which is any one of Ag, Al, Au, and PEDOT:PSS.

4. The organic photodetector as described in claim 1, characterized in that, The photosensitive layer is either a planar heterojunction or a bulk heterojunction.

5. The method for fabricating the organic photodetector as described in claim 4, characterized in that, When the photosensitive layer of the device is a bulk heterojunction, the fabrication method includes the following steps: Step 1. Clean the transparent substrate and blow dry; Step 2. Sequentially fabricate the first electrode and the first modification layer on a transparent substrate; Step 3. Prepare a photosensitive layer on the surface of the first modified layer. The specific process is as follows: Step 3.

1. Preparation of photosensitive layer solution: Add the donor material and acceptor material to an organic solvent, mix, heat and stir until homogeneous to obtain the photosensitive layer solution; wherein, the acceptor material is a narrow bandgap small molecule COTCNTTM; Step 3.

2. Under a nitrogen atmosphere, spin-coat the photosensitive layer solution onto the surface of the first modified layer, and then anneal it to obtain the photosensitive layer; the spin-coating process parameters are: spin-coating speed of 1500rpm-3000rpm, spin-coating time of 20-40s; Step 4. Sequentially prepare the second modification layer and the second electrode on the surface of the photosensitive layer to obtain the desired organic photodetector.

6. The preparation method according to claim 5, characterized in that, The preparation process of the narrow bandgap small molecule COTCNT™ is as follows: The first compound, the second compound, SbCl3 and propionic anhydride were mixed to obtain a mixed solution. The mixed solution was then stirred under a nitrogen atmosphere to carry out a condensation reaction at a temperature of 45-55℃ for 2.5-3.5 h. After the reaction was completed, methanol was added to the reactants, and the solid was stirred to precipitate. The obtained solid product was filtered and then purified by silica gel column chromatography to finally obtain the desired narrow bandgap small molecule COTCNTTM. The molecular formula of the first compound is shown in Formula II, and the molecular formula of the second compound is shown in Formula III. ， Formula II; ， Formula III.

7. The preparation method according to claim 6, characterized in that, In the mixed solution, the molar ratio of the first compound, the second compound, and SbCl3 is 1:3:

4.

8. The preparation method according to claim 5, characterized in that, The donor material is PTB7-Th, PBDB-T, or P3HT; the mass ratio of the donor material to the acceptor material is 1:(1-2); the total mass concentration of the donor and acceptor materials in the photosensitive layer solution is 12–20 mg / mL.

9. The preparation method according to claim 5, characterized in that, In step 3.1, an additive is added to prepare the photosensitive layer solution; the additive is TMB, 1-CN or DIO.

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