Method for reducing NIR-OPD dark current based on bipolar carrier barrier construction and NIR-OPD device

Abstract

The invention discloses a method for reducing dark current of a near-infrared organic photoelectric detector (NIR-OPD) based on bipolar carrier barrier construction and an NIR-OPD device, and belongs to the technical field of organic semiconductor film near-infrared photoelectric detectors. The bipolar carrier potential barrier is constructed by adjusting the energy level structure of an anode interface layer, and 15 mg / ml of a salt solution containing Cu or Co metal ions and 5 mg / ml of a D149 small organic molecule solution are mixed according to the mass ratio of (100-25): 1 and fully hybridized; the surface of a conductive anode is coated with the coating through a solution method, and thermal annealing treatment is conducted at the temperature of 100-200 DEG C, so that the electrode is obtained. Through combination of organic and inorganic components, on one hand, flexible regulation and control of a material energy level structure are realized, so that a transmission barrier of a thermal excitation hole and an injection barrier of external circuit electrons are respectively constructed at an active layer / anode interface layer and an anode interface layer / anode; on the other hand, close contact between the functional layers is promoted; the dark current of the NIR-OPD is significantly reduced through the synergistic effect, and the device is endowed with high specific detection rate.

Description

Technical Field

[0001] This invention belongs to the field of near-infrared organic photodetector (NIR-OPD) technology, specifically involving a method for reducing dark current in NIR-OPD by constructing a dark-state carrier transport and injection barrier based on the design of interface layer energy level structure. Background Technology

[0002] Near-infrared light, with its advantages of penetrating deeper into biological tissues and exhibiting low optical loss in optical fibers, has demonstrated immense potential in industrial, military, and scientific fields. With the development of industrial intelligence, inorganic-based NIR photodiodes are increasingly unable to meet the diverse market demands of emerging fields such as implantable / wearable optical fidelity systems, soft robotics, and optical communication systems. Therefore, organic near-infrared photosensitive materials, possessing biocompatibility, mechanical flexibility, and tunable photoelectric properties, have naturally attracted significant attention from the scientific community.

[0003] In recent years, significant progress has been made in the design and structural innovation of near-infrared photosensitive materials. However, effectively suppressing the dark current density of NIR-OPD (NIR-OPD) remains a challenge. J d This remains a key challenge hindering its commercialization. Unlike photoresponse, J d The values ​​can span multiple orders of magnitude depending on material properties and device architecture. This means reducing... J d To improve the signal-to-noise ratio, linear dynamic range, and specific detection efficiency in photodetectors ( D* This is crucial. The inherent dark current of NIR-OPD mainly originates from two parts: the drift and collection of carriers injected by the external circuit, and the collection of carriers generated by thermal activation within the photosensitive layer under an applied electric field; while the dark current structure of visible light OPD based on wide-bandgap photosensitive materials only considers carrier injection from the external circuit. Compared to the active layer structure design, introducing an interface layer to increase the carrier injection barrier and suppress OPD... J d Widely used due to its simplicity and efficiency. For example, patent application CN 118139505A reports a method for reducing bidirectional dark current in OPD based on interface layer energy level and trap modulation. This method utilizes the electron transfer (chelation reaction) between N and O elements in the polymer PEIE and metal ions in a metal acetate solution to prepare an organometallic anode interlayer with tunable energy levels and abundant traps. This significantly reduces the bidirectional bias dark current of visible light OPD by blocking the injection of charge carriers from the external circuit. However, the above method and anode interface layer structure design do not consider the crucial component of thermally excited charge carrier transport in NIR-OPD dark current, thus failing to effectively suppress the dark current of NIR-OPD. Summary of the Invention

[0004] This invention addresses the problems in the prior art by proposing a method and device for reducing dark current in NIR-OPD based on the construction of a bipolar carrier barrier. By introducing metal ions into the narrow-bandgap organic molecule D149, the metal ions fully hybridize with the S, N, and O atoms in D149, respectively. The energy level structure and optical bandgap of the hybrid material are precisely controlled by adjusting the ratio of the two components, achieving flexible and tunable bandgap. This aims to construct a transport barrier for thermally excited holes and an injection barrier for electrons into the external circuit at the hybrid active layer / anodine interface and the anode interface / anodine interface, respectively. The construction of this bipolar carrier barrier effectively blocks the generation path of dark current in NIR-OPD, thereby effectively reducing its dark current.

[0005] The technical solution adopted in this invention is as follows: A method for reducing the dark current of NIR-OPD based on the construction of a bipolar carrier barrier is achieved by controlling the optical band gap and energy level structure of the anode interface layer. The anode interface layer is an organic-inorganic hybrid material, and its preparation process includes: A 15 mg / ml metal salt solution and a 5 mg / ml D149 solution were mixed at a mass ratio of 100 to 25:1, coated onto the surface of a conductive anode, and then subjected to a heat annealing treatment at 100 to 200°C to obtain an organic-inorganic hybrid anode interface layer; wherein the metal ions in the metal salt solution are Cu or Co.

[0006] Furthermore, the metal salt solution is specifically a Cu(CH3COO)2·H2O solution or a Co(CH3COO)2·4H2O solution.

[0007] Furthermore, the solvent for the metal salt solution and the D149 solution is dimethoxyethanol.

[0008] Furthermore, the thickness of the organic-inorganic hybrid anode interface layer is 15~100 nm.

[0009] Furthermore, the heat annealing is achieved by one or more of the following methods: constant temperature hot table heating, oven heating, far-infrared heating, and hot air heating, at a temperature of 80~150℃ and a time of 10~30 min.

[0010] Furthermore, the duration of the thermal annealing treatment is 10 to 60 minutes.

[0011] Furthermore, the coating is any one of spin coating, blade coating, or spray coating.

[0012] A NIR-OPD device comprises, from bottom to top, a substrate, a conductive anode, an anode interface layer, a photoactive layer, a cathode interface layer, and a metal cathode; wherein the anode interface layer is constructed by the method described above.

[0013] Furthermore, the material of the conductive anode is one of ITO (indium tin oxide), FTO (fluorine-doped SnO2 conductive glass), and PEDOT:PSS, with a thickness of 135~300 nm.

[0014] Furthermore, the donor material of the photoactive layer is PM6, PCE-10, or PBDB-T, and the acceptor material is ITIC-Th, COTIC-4F, or Y6, TQ. PP 2FIC, thickness 150~500 nm.

[0015] Furthermore, the preparation process of the photoactive layer is as follows: the donor and acceptor are mixed at a mass ratio of 1:0.01~100, dissolved in a solvent, and then spin-coated onto the surface of the anode interface layer, and then annealed to obtain the final product.

[0016] Furthermore, the annealing is solvent annealing, using one or more of chlorobenzene, chloroform, methanol, and o-dichlorobenzene as the organic solvent, at room temperature, for 10-120 min.

[0017] Furthermore, the cathode interface layer is made of one or more of ZnO, PFN, PFN-Br, PFNOH, and PEO, and has a thickness of 10–30 nm.

[0018] Furthermore, the substrate is made of a transparent polymer material or quartz glass, wherein the transparent polymer material is one or more of polyethylene, polymethyl methacrylate, polycarbonate, polyurethane, polyimide, and polyacrylic acid.

[0019] Furthermore, the metal cathode is made of one or more of Al, Ag, and Au, and has a thickness of 100~300 nm.

[0020] The beneficial effects of this invention are as follows: 1. The method for reducing dark current of NIR-OPD based on the construction of bipolar carrier barrier proposed in this invention effectively reduces the roughness of conductive anode (1.19nm) by adding organic small molecule D149, promotes close contact between interfaces and the preparation of high-quality photosensitive layer film.

[0021] 2. The organic-inorganic dual-phase hybridization method proposed in this invention endows the anode interface layer with a flexible and tunable optical bandgap and band structure, thereby successfully constructing a bipolar carrier barrier highly compatible with the active layer and the anode; that is, a transport barrier for thermally excited holes and an injection barrier for electrons from the external circuit are established at the active layer / anode interface layer and the anode interface layer / electrode, respectively. Compared with the traditional unipolar carrier barrier, this bipolar carrier barrier significantly reduces the dark current of NIR-OPD, achieving a high specific detectivity.

[0022] 3. The anode interface layer based on organic-inorganic dual-phase hybrid proposed in this invention has the advantages of high stability / high conductivity of inorganic phase and high flexibility / high biocompatibility of organic phase, and can be used for the fabrication of high-performance wearable organic electronic devices. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the OPD proposed in an embodiment of the present invention.

[0024] Figure 2 The NIR-OPD prepared in Examples 1-4 of this invention JV (Current density-voltage) curve.

[0025] Figure 3 The D-CoO proposed in Embodiment 2 of this invention x XPS curves compared with D149 and CoO; where (a) is Co2p, (b) is N 1s, (c) is S 2p, (d) is O 1s of CoO, and (e) is D-CoO. x O 1s; Figure 4 The anode is ITO(a) and the D-CoO proposed in Example 2 of this invention. x (b) AFM surface morphology diagram; Figure 5 The D-CoO proposed in Embodiment 2 of this invention x UPS test curve (a) and UV-vis test curve (b); Figure 6 This is a schematic diagram of the OPD reducing dark current obtained in Embodiment 2(a), Comparative Example 1(c), and Comparative Example 2(b) of the present invention.

[0026] Figure 7 The EQE-λ curve and D*-λ curve of OPD obtained in Embodiment 2 and Comparative Examples 1 and 2 of the present invention are shown. Among them, (a) is JV (a) Current density-voltage curve; (b) EQE-λ curve; (c) D*-λ curve.

[0027] The attached figures are labeled as follows: 1-Substrate, 2-Conductive anode, 3-Anode interface layer, 4-Photoactive layer, 5-Hole transport layer, 6-Metal cathode. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] This embodiment provides a method for reducing the dark current of NIR-OPD based on the construction of a bipolar carrier barrier, wherein the structure of the OPD is as follows: Figure 1 As shown, it includes a substrate 1, a conductive anode 2, an anode interface layer 3, a photoactive layer 4, a cathode interface layer 5, and a metal cathode 6 arranged sequentially from bottom to top.

[0031] In this embodiment, the substrate 1 is made of quartz glass; the conductive anode 2 is made of ITO with a thickness of 135 nm; and the anode interface layer 3 is an organic-inorganic anode interlayer (D-CoO2). x The thickness is approximately 25 nm; the material of photoactive layer 4 is PCE10:TQ. PP 2FIC, with a thickness of approximately 180 nm; cathode interface layer 5 is made of ZnO, with a thickness of approximately 20 nm; metal cathode 6 is made of Al, with a thickness of 100 nm.

[0032] The method for preparing the OPD includes the following steps: Step 1: The quartz glass substrate 1 and the ITO conductive anode 2 together form a substrate. The substrate is then sequentially cleaned, dried with nitrogen, and cleaned with ultraviolet light. Step 2: Mix 15 mg / ml Co(CH3COO)2·4H2O solution with 5 mg / ml D149 solution at a mass ratio of 100:1 to obtain D-CoO x The mixed solution was then spin-coated onto the surface of conductive anode 2 at 4000 rpm for 40 s. After heat annealing at 110 ℃ for 15 min, the anode interface layer 3 was obtained, which is a D-CoO layer with a thickness of approximately 30 nm. x ; Step 3: Transfer PCE10:TQ PP 2FIC (laboratory synthesis) was prepared into a mixed solution with a concentration of 15 mg / mL (solvent is chlorobenzene) at a mass ratio of 1:1. It was then spin-coated onto the surface of the anode interface layer 3 at a speed of 2000 rpm for 40 s using a thermal spin method. After heat annealing at 110℃ for 15 min, the photoactive layer 4 was obtained. Step 4: In 10 -4Under a vacuum of Pa and a temperature of 650℃, ZnO was deposited on the surface of the photoactive layer 4 to obtain a 20 nm thick cathode interface layer 5. Then, a 100 nm thick Al was deposited on the surface of the cathode interface layer 5 to serve as the metal cathode 6. Finally, the OPD was encapsulated.

[0033] Example 2

[0034] This embodiment provides a method for reducing the dark current of NIR-OPD based on the construction of a bipolar carrier barrier. The only difference from Embodiment 1 is that the mass ratio of Co(CH3COO)2·4H2O solution to D149 solution in step 2 is 75:1; the other structures and steps are exactly the same.

[0035] Example 3

[0036] This embodiment provides a method for reducing the dark current of NIR-OPD based on the construction of a bipolar carrier barrier. Compared with Embodiment 1, the only difference is that the mass ratio of Co(CH3COO)2·4H2O solution to D149 solution in step 2 is 50:1; the other structures and steps are exactly the same.

[0037] Example 4

[0038] This embodiment provides a method for reducing the dark current of NIR-OPD based on the construction of a bipolar carrier barrier. The only difference from Embodiment 1 is that the mass ratio of Co(CH3COO)2·4H2O solution to D149 solution in step 2 is 25:1; the other structures and steps are exactly the same.

[0039] Comparative Example 1 This embodiment provides a method for reducing the dark current of NIR-OPD based on the construction of a bipolar carrier barrier. Compared with Embodiment 1, the only difference is that the mass ratio of Co(CH3COO)2·4H2O solution to D149 solution in step 2 is 0:1; the other structures and steps are exactly the same.

[0040] Comparative Example 2 This comparative example presents a method for preparing NIR-OPD, which differs from Example 1 only in that: in step 2, PEDOT:PSS solution is spin-coated at 4000 rpm for 40 s and then heat-annealed at 110 ℃ for 15 min to obtain the anode interface layer 3; the other structures and steps are exactly the same.

[0041] The NIR-OPDs prepared in Examples 1-4 were tested under both dark and illuminated conditions (650 nm). JV (Current density-voltage) curve, such as Figure 2 As shown, D:CoO xWhen the ratio is 25-100:1, both exhibit low dark current and high photocurrent; however, when the ratio is 75:1, D:CoO... x This results in lower dark current and higher photocurrent for the device, which is the optimal ratio (subsequent analyses are based on this ratio).

[0042] Figure 3 The D-CoO proposed in Example 2 x The XPS (X-ray photoelectron spectroscopy) curves of D149 compared with those of Comparative Example 1 clarify the chemical interaction between D149 and Co ions. Figure 3 As shown in (ab), compared with D149, D:CoO x The binding energy corresponding to the N 1 core energy level shifts to a lower value, and the change in the S 2p peak indicates that N and S atoms in D149 chemically interact with Co ions to form N-Co and S-Co chemical bonds, respectively; Figure 3 As shown in (c), the 530.20 eV and 531.35 eV of the O 1s spectrum in D149 correspond to the hydroxyl (-OH) and carboxyl (-COOH) groups, respectively. D:CoO x The O 1s spectra at 529.95 eV (16.55%) and 531.16 eV (83.45%) are respectively related to Co 2+ Cation-bound O 2− The correlation between the anion and oxygen vacancy / hydroxyl group indicates that a large number of O-Co bonds are formed between the Co ion and the O atom of D149. Figure 3 (d)). In summary, this indicates that there are chemical bonds between N and Co ions, between S and Co ions, and between O and Co ions.

[0043] The anodic interface layer D:CoO prepared on ITO in Example 1 x AFM (atomic force microscopy) was performed to characterize the surface morphology, and the results are as follows: Figure 4 As shown. Compared to ITO (4.12 nm), D:CoO x The film exhibits a smooth and uniform surface morphology, and its low roughness of 1.19 nm helps to improve the tight contact between the functional layer interfaces and improve the quality of the active layer film, thereby effectively reducing leakage current and suppressing the recombination rate of photogenerated carriers.

[0044] Through such Figure 5 (a) shows the ultraviolet photoelectron spectroscopy (UPS) and as shown in the figure. Figure 5 (b) shows the UV-Vis absorption measurement of D:CoO x The lowest unoccupied orbital (LUMO), highest occupied orbital (HOMO) energy levels, and optical band gap were calculated for D:CoO.x The HOMO, LUMO, and optical band gaps are 6.03 eV, 1.91 eV, and 4.12 eV, respectively. Figure 6 As shown in (a), its shallower LUMO level forms a barrier of approximately 2.79 eV with the anode ITO, effectively preventing electron injection from external circuitry; the deeper HOMO level establishes a hole barrier of 0.81 eV with the donor material PTB7-Th, reducing the transport and collection efficiency of thermally activated holes. However, the shallower HOMO (PEDOT:PSS@5.20 eV; D149@5.22 eV) levels in the unipolar barrier structure based on PEDOT:PSS or D149 result in a lack of transport barrier for thermally activated holes in the NIR-OPD, making it difficult to effectively suppress the device's dark current. Figure 6 (bc)).

[0045] Figure 7 The NIR-OPD with a bipolar carrier barrier prepared in Example 2 and the NIR-OPD with a unipolar carrier barrier prepared in Comparative Examples 1-2 were compared under dark and illuminated conditions (650 nm). JV (Current density-voltage) curve. For example... Figure 7 As shown in (a), compared to PEDOT:PSS-OPD (8.30×10 -7 A cm -2 ) and D149-OPD (8.30×10 -7 A cm -2 ), D:CoO x - The dark current of the OPD was significantly reduced (1.19 × 10⁻⁶). -7 A cm -2 Furthermore, based on D:CoO x The device exhibits slightly higher photocurrent generation in the 0 V to 1 V range, giving it a higher on / off ratio. The spectral response of the example and comparative OPDs was tested under test conditions of a continuously tunable light source from 300 to 1200 nm and a bias voltage of -1 V. Figure 7 As shown in (b), the EQE-λ curve indicates that D:CoO x The EQE value of the -OPD is significantly higher than that of the comparative NIR-OPD, with a peak EQE of approximately 40%. Thanks to its lower dark current, D:CoO x -OPD exhibits a high D*, greater than 10 in the 500-1100 nm range. 12 Jones, as Figure 7 As shown in (c).

[0046] The above embodiments are only for illustrating the principles and advantages of the present invention, and are not intended to limit the present invention. They are only for helping to understand the principles of the present invention. The scope of protection of the present invention is not limited to the above configurations and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the disclosed technology without departing from the essence of the present invention, but they are still within the scope of protection of the present invention.

Claims

1. A method for constructing a reduced NIR-OPD dark current based on a bipolar carrier barrier, characterized in that, The bipolar carrier barrier is constructed by adjusting the energy level structure of the anode interface layer, which is an organic-inorganic hybrid material prepared by a process comprising: 15 mg / ml of a metal salt solution and 5 mg / ml of a D149 dye solution are mixed in a mass ratio of 100-25:1, coated on the surface of a conductive anode, and then subjected to a heat annealing treatment at 100-200 DEG C to obtain an organic-inorganic hybrid anode interface layer; wherein the metal ion in the metal salt solution is Cu or Co.

2. The method of claim 1, wherein, The metal salt solution is specifically a Cu(CH3COO)2·H2O solution or a Co(CH3COO)2·4H2O solution.

3. The method of claim 2, wherein, The solvent of the metal salt solution and the D149 solution is dimethoxyethanol.

4. The method of claim 1, wherein, The thickness of the organic-inorganic hybrid anode interface layer is 15-100 nm.

5. The method of claim 1, wherein, The heat annealing treatment is performed for 10-60 min.

6. The method of claim 1, wherein, The coating is any one of spin coating, blade coating or spraying.

7. A NIR-OPD device comprising, from bottom to top, a substrate, a conductive anode, an anode interface layer, a photoactive layer, a cathode interface layer and a metal cathode, wherein the anode interface layer is constructed by the method of any one of claims 1-6.

8. The NIR-OPD device of claim 7, wherein, The material of the conductive anode is ITO, FTO or PEDOT:PSS, and the thickness is 100-300 nm.

9. The NIR-OPD device of claim 7, wherein, The donor material of the photoactive layer is PM6, PCE-10 or PBDB-T, and the acceptor material is ITIC-Th, COTIC-4F, Y6 or TQ PP 2FIC, thickness 150-500 nm.

10. The NIR-OPD device of claim 7, wherein, The material of the substrate is a transparent polymer material or quartz glass, and the transparent polymer material is one or more of polyethylene, polymethyl methacrylate, polycarbonate, polyurethane, polyimide, polyacrylic acid; preferably, the material of the metal cathode is one or more of Al, Ag and Au, and the thickness is 100-300 nm.

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