An organic photodetector based on small-molecule layer modification and a preparation method thereof

Abstract

The application relates to an organic ultrathin photodetector based on small-molecule layer modification and a preparation method thereof, and belongs to the technical field of organic photodetector preparation. Organic small-molecule material rubrene is selected as a third material to undertake the role of an ultrathin modification layer. A device structure from bottom to top comprises a transparent conductive substrate ITO, a hole transport layer, an organic photosensitive layer, an organic small-molecule modification layer and an electrode. Compared with polymer materials commonly applied in organic photodetectors, the organic small-molecule material has advantages in preparation and price. The application prepares a 2nm-thick rubrene ultrathin modification layer by means of organic vapor deposition, fully utilizes the characteristics of the material, such as strong crystallinity, excellent compatibility and wide absorption range, obviously enhances the absorption coefficient of the photosensitive layer in a wide spectral range after modification, fully compensates for the common shortcomings in the ultrathin organic photodetector, and has a good commercial application prospect.

Description

Technical Field

[0001] This invention relates to an organic ultrathin photodetector based on small molecule layer modification and its preparation method, belonging to the field of organic photodetector preparation technology. Background Technology

[0002] In a broad sense, any device that converts optical signals into other easily measurable electrical quantities (such as current and voltage) for output is called a photodetector. In principle, photodetectors are divided into two main categories. One category is thermal detectors, which indirectly achieve optical measurement using the thermoelectric effect or pyroelectric effect. The other category is photodetectors, which achieve optical measurement using the photoelectric effect, including diode-type photodetectors and multiplier tube-type photodetectors. As an important alternative to traditional inorganic photodetector technology, especially silicon-based photodetectors, organic photodetectors have advantages such as tunable detection wavelength, simple synthesis, low manufacturing cost, large-area production, lightweight design, and flexible compatibility. However, under normal circumstances, an external bias voltage is required to drive the device and enhance the photocurrent in the organic photodetector, which greatly limits the operating conditions and environment of related devices. Therefore, developing self-powered photodetectors is crucial for low-energy optoelectronic devices that can operate independently, wirelessly, and sustainably. Currently, self-powered organic photodetectors are typically constructed using photovoltaic technology, converting photon energy into usable electrical energy to support self-operation.

[0003] In previous work, most photovoltaic-mode organic photodetectors were based on bulk heterojunction (BHJ) structures, aiming to fabricate devices with high photocurrents by spin-coating a mixed solution of donor and acceptor materials. However, the simultaneous presence of donor and acceptor components near the anode and cathode interfaces in conventional organic devices leads to unfavorable charge injection, resulting in severe contact with the semiconductor and directly causing high dark current density and low detectivity (D*). Related research results indicate that the sequential deposition (SD) method improves the vertical phase separation structure of the photosensitive layer, achieving effective dark current suppression and improving device performance. Furthermore, for self-powered photodetectors, to achieve sufficient absorption of probe light and obtain better device performance, a photosensitive layer with a thickness greater than 150 nm is typically required during fabrication. However, a relatively thick photosensitive layer usually leads to a higher density of defect states, which traps more free carriers under device operating conditions and limits the improvement of device performance. To address these issues, the construction of ultrathin organic photodetectors can effectively reduce defect density and broaden the operating environment of the corresponding devices. However, it cannot achieve efficient absorption and utilization of detection light. Therefore, constructing absorption-optimized ultrathin organic structures to improve device performance is a key means to overcome these problems. Summary of the Invention

[0004] To address the key limitations of existing technologies, this invention provides an organic ultrathin photodetector based on small molecule layer modification, using rubrene, an organic small molecule material, as the tertiary material to serve as the ultrathin modification layer. The bottom-up device structure includes a transparent conductive substrate ITO, a hole transport layer PEDOT:PSS, a photosensitive layer, a small molecule modification layer, and electrodes. Compared to polymer materials commonly used in organic photodetectors, organic small molecule materials offer advantages in preparation and price. Rubrene, as a low-cost and easily prepared organic small molecule material, is currently widely used in the field of organic optoelectronics. This invention creatively utilizes organic vapor deposition to prepare a 2nm thick rubrene ultrathin modification layer, fully leveraging the material's strong crystallinity, excellent compatibility, and wide absorption range. This results in a significant enhancement of the absorption coefficient of the modified photosensitive layer over a broad spectral range. Furthermore, the introduction of the small molecule modification layer can significantly suppress the dark current of the organic photodetector, enabling the modified self-powered ultrathin device to achieve further breakthroughs in device performance. This effectively compensates for the common shortcomings of ultrathin organic photodetectors and has promising commercial application prospects.

[0005] The present invention also provides a method for fabricating the above-mentioned ultrathin organic photodetector structure.

[0006] Terminology Explanation: 1. Rubrene is a small molecule organic material with the molecular formula 5,6,11,12-tetraphenyltetracene, which is mainly used as a donor material for organic photodetectors.

[0007] 2. PTB7 is a polymer donor with the molecular formula poly[[4,8-bis[(2ethylhexyl)oxy]-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno-[3,4b]thiophenediyl]. It is mainly used as a donor material for organic photodetectors.

[0008] 3. PC 71 BM is a fullerene derivative with the molecular formula [6,6]-phenyl C71 butyric acidmethyl ester, which is mainly used as the acceptor material for organic photodetectors.

[0009] 4. Dark current density (J) dark ): The current flowing through an organic photodetector under reverse bias in darkness.

[0010] 5. Photocurrent density (J)light ): The current flowing through the OPD when a voltage is applied under illumination.

[0011] 6. Spectral responsivity (R): The ratio of the generated photocurrent to the incident light intensity.

[0012] 7. Detectability (D*): The sensitivity of a photodetector to weak light signals.

[0013] The technical solution of the present invention is as follows: An organic ultrathin photodetector based on small molecule layer modification comprises, from bottom to top, a glass substrate, a transparent conductive film (anode), a hole transport layer, an organic photosensitive layer, an organic small molecule modification layer, and a top electrode (cathode). The organic photosensitive layer includes a polymer donor and a polymer acceptor material; the organic small molecule modification layer material is the organic material Rubrene.

[0014] According to a preferred embodiment of the present invention, the organic photodetector polymer donor material is PTB7, and the organic photodetector acceptor material is PC. 71 BM.

[0015] According to a preferred embodiment of the present invention, the thickness of the organic photosensitive layer is 10-20 nm, the thickness of the organic small molecule modification layer is 1-5 nm, and the organic photodetector device prepared by the organic small molecule layer modification-assisted deposition method contains PTB7:PC. 71 The mass ratio of BM is 100:1. Under this optimal active layer blend film thickness and component ratio, the photoelectric conversion capability of the organic photodetector is maximized.

[0016] More preferably, the glass substrate with the transparent conductive film is a transparent conductive substrate, which is ITO conductive glass with a thickness of 130 nm; the hole transport layer material is PEDOT:PSS with a thickness of 30 nm; the organic photosensitive layer has a thickness of 10 nm; the organic small molecule modification layer material is Rubrene with a thickness of 2 nm; and the top electrode material is aluminum (Al) with a thickness of 80 nm.

[0017] A method for fabricating an organic ultrathin photodetector based on small molecule layer modification is disclosed. This invention utilizes the organic small molecule layer modification-assisted deposition technique to fabricate organic photovoltaic devices using the aforementioned organic materials. The method involves fabricating a transparent conductive film and a hole transport layer on a glass substrate using a one-step solution deposition method, first mixing PTB7 with PC... 71 A blended solution of BM was spin-coated to form an organic photosensitive layer, followed by a layer of PTB7 and PC. 71 An organic small molecule modification layer was prepared on the BM blend film using physical vapor deposition to obtain the organic photodetector device.

[0018] Compared with traditional photodetector organic systems (PTB7: PC) 71 Compared to the relatively high dark current in BM (Browser-Based Photodetector), photodetectors prepared using the organic small molecule layer-assisted deposition method exhibit a more ideal component distribution. Specifically, the organic small molecule layer modification promotes a more ideal crystalline state on the structural surface, and its presence further enhances the energy transfer efficiency between donor and acceptor layers, thus significantly suppressing dark current in organic photodetectors. The organic small molecule modification layer constitutes an ideal charge transport channel, achieving more ideal carrier transport behavior in the active layer. According to a preferred embodiment of the present invention, the photodetector prepared using the organic small molecule layer-assisted deposition method not only possesses a more ideal crystalline state, but also, under the modification of the small molecule layer, the device's dark current value at 0V is significantly reduced by nearly two orders of magnitude compared to the unmodified layer. This effectively reduces the leakage current of the device, significantly increases the number density of photogenerated carriers in the photoexcited state, and thus enhances the photoelectric conversion capability of the photodetector. This fabrication process not only achieves a more ideal crystalline state but also significantly suppresses the device's dark current value and effectively increases the number density of photogenerated carriers under the modification of the small molecule layer. Furthermore, the modification with organic small molecule layers effectively improved the energy transfer efficiency between organic donor and acceptor materials, further enhancing the exciton dissociation rate and promoting the formation of more carrier transport channels. This ultimately enabled more efficient extraction and collection of photogenerated carriers by the electrodes, thereby improving the photoelectric conversion capability of the organic photodetector. Device testing results showed that the photodetector fabricated by the organic small molecule layer-assisted deposition method suppressed the dark current to 7.45 × 10⁻⁶ under 0V conditions. -11 A, and the responsivity was improved to 0.42 A / W, while the device specific detectivity was also effectively improved to 1.25 × 10⁻⁶. 12 J.

[0019] The fabrication method of the above-mentioned organic solar cell structure includes the following steps: (1) Clean the transparent conductive substrate; (2) A hole transport layer PEDOT:PSS thin film is prepared on the transparent conductive substrate obtained in step (1); (3) Preparation of organic photosensitive layer thin film, including: a. Weigh 10-20 mg Rubrene, 5-10 mg PTB7, and 0.2-1 mg PC using a high-precision electronic analytical balance. 71 BM, then add 1-2 mL of high-purity chlorobenzene solvent (AR > 99%) to the weighed PTB7, PC 71After weighing BM, add 50-100 μL of high-purity chlorobenzene solvent (AR > 99%). Store Rubrene in a clean material bottle. Add the weighed material to the accurate solvent and place the bottle on a heatable magnetic stirrer. Stir for 6-8 h at 30-50℃ to obtain a pure PTB7 solution with a concentration of 5-10 mg / mL and PC. 71 BM solution; b. After stirring thoroughly on a heatable magnetic stirrer for 6-8 hours, add 1% pure PC to the obtained pure PTB7 solution using a high-precision pipette. 71 After stirring the BM solution for another 60 minutes, PTB7:PC was obtained. 71 A mixed solution with a BM mass ratio of 100:1; c. In an inert gas (preferably N2) glove box, place the PTB7:PC prepared in step a. 71 Spin-coat the BM solution onto the substrate with hole transport layer obtained in step (2), wait 30s, and then place the substrate with the photosensitive layer material attached to it on an annealing table at 100°C and anneal it in an inert gas for 5-10 min. (4) An organic small molecule modified layer Rubrene is obtained on the organic photosensitive layer by means of physical vapor deposition; (5) The metal electrode material is vapor-deposited on the organic small molecule modification layer.

[0020] Most preferably, in step (3)a, 1 mL of high-purity chlorobenzene solvent (AR > 99%) is added to the 5 mg PTB7 obtained by weighing, and the mixture is placed on a heatable magnetic stirrer and stirred at 50 °C for 8 h to obtain a pure PTB7 solution with a concentration of 5 mg / mL; 0.2 mg PC 71 20 μL of high-purity chlorobenzene solvent (AR > 99%) was added to BM, and the mixture was placed on a heatable magnetic stirrer and stirred at 40 °C for 8 h to obtain pure PC with a concentration of 10 mg / mL. 71 Using a high-precision pipette, 5 μL of pure PC was added to pure PTB7 solution to obtain BM solution. 71 PTB7:PC in the blended solution obtained from BM solution 71 The mass ratio of BM is 100:1. At this solution concentration and corresponding stirring temperature, all components can be fully dissolved in the chlorobenzene solvent, and the organic small molecule modified layer material can achieve effective vapor deposition at 220-260℃.

[0021] Preferably, in step (3)c, the spin coating speed of the active layer solution is: PTB7: PC 71The BM blend solution was spin-coated in a single step at a speed of 3500-4500 rpm, yielding PTB7:PC. 71 The thickness of the BM layer is 10-20 nm.

[0022] More preferably, in step (3)c, PTB7: PC 71 The BM blend solution was spin-coated at 4000 rpm, yielding PTB7:PC. 71 The BM layer has a thickness of 10 nm. In a photodetector device with donor-acceptor and small molecule modified layers of this size, not only can the ideal crystalline distribution of the donor and acceptor components be fully achieved, but also, especially with the modification of the organic small molecule layer, sufficient absorption of the probe light can be achieved. Simultaneously, under 0V conditions, the device's dark current is significantly suppressed, reducing leakage current loss. The annealing temperature of the active layer is 70 °C, and the annealing time is 10 min. This annealing temperature allows residual solvent in the active layer film to evaporate and improves the crystallinity of the donor and acceptor phases, thereby enhancing the carrier transport capacity.

[0023] Preferably, in step (1), the transparent conductive substrate (i.e., the glass substrate with ITO transparent conductive film) is ultrasonically cleaned in an ultrasonic machine in a water bath for 20 min with detergent, deionized water, acetone, anhydrous ethanol and isopropanol in sequence. After cleaning, it is dried with high-purity nitrogen (>99%). The dried transparent conductive substrate is placed in an ultraviolet irradiation machine and irradiated with ultraviolet light for 15 min.

[0024] Preferably, in step (2), a hole transport layer material PEDOT:PSS with a thickness of 30 nm is spin-coated onto a transparent conductive substrate treated with ultraviolet light in air using a spin coater, and then the substrate with the spin-coated hole transport layer material is placed on an annealing table at 150°C and annealed for 15 min.

[0025] Preferably, in step (4), the weighed organic small molecule material Rubrene (10-20 mg) is placed in the evaporation container, and the substrate with the hole transport layer / organic photosensitive layer obtained in step (3) is transferred into the physical vapor deposition chamber. After starting the vacuum system, the chamber pressure is allowed to drop to 2.5 × 10⁻⁶. -4 Pa, heat the evaporation container, and evaporate stably for 5-15 min at 220-260℃ to deposit an organic small molecule modified layer with a thickness of 1-5 nm.

[0026] The advantages of photodetector fabrication technology using organic small molecule layer modification-assisted deposition lie in further achieving sufficient absorption of probe light, while enhancing the ideal crystallization state of the donor and acceptor components, significantly suppressing device dark current and reducing device leakage current loss. Furthermore, the introduction of the organic small molecule modification layer enhances the energy transfer efficiency between the donor and acceptor, further promoting efficient exciton dissociation, achieving efficient carrier transport and extraction, and ultimately improving the photoelectric conversion capability of the organic photodetector.

[0027] The beneficial effects of this invention are as follows: Compared with current device fabrication technology, the present invention deposits an organic small molecule modification layer on an organic photosensitive layer, which has the following advantages: (1) The organic small molecule material is low in cost, which can effectively reduce the manufacturing cost; (2) The entire fabrication process is simple, requiring only a simple organic small molecule layer modification; (3) The organic small molecule layer modification enhances the absorption of the probe light, making it easier to apply to future commercial production; (4) It solves the leakage current loss of the device itself to a certain extent and significantly suppresses the dark current density of the device; (5) The introduction of the organic small molecule modification layer enhances the energy transfer efficiency between the photosensitive layer and the acceptor; (6) The modification effect of the organic small molecule layer further promotes effective exciton dissociation, realizes efficient carrier transport and extraction, and ultimately improves the photoelectric conversion capability of the organic photodetector. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the photodetector fabrication technology using organic small molecule layer modification-assisted deposition in this invention; Figure 2 To prepare the molecular structure of materials for photodetector devices with organic small molecule modified layers; Figure 3 The steady-state absorption spectra of each component material of the photodetector device with an organic small molecule modification layer; Figure 4 This is a schematic diagram showing the thickness of the photosensitive layer during device fabrication. Figure 5 A schematic diagram showing the changes in photocurrent between a photodetector device with an organic small molecule modification layer and a traditional photodetector device. Figure 6 A schematic diagram showing the functional parameters of a photodetector device with an organic small molecule modification layer and a traditional photodetector device. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0030] Example 1

[0031] A photodetector device fabricated using organic small molecule layer modification-assisted deposition comprises, from bottom to top, a transparent conductive substrate, a hole transport layer, an organic photosensitive layer, an organic small molecule modification layer, and a metal electrode, such as... Figure 1 As shown, the organic small molecule modified layer is prepared by the physical vapor deposition method described in this invention. The organic photosensitive layer includes a polymer donor and a fullerene acceptor.

[0032] The transparent conductive substrate is ITO conductive glass, wherein the ITO thickness is 130 nm and the sheet resistance is <15 Ω cm. -2 The hole transport layer is a polymer PEDOT:PSS with a thickness of 30 nm, the organic small molecule modification layer is Rubrene with a thickness of 2 nm, and the metal electrode is aluminum (Al) with a thickness of 80 nm.

[0033] The polymer donor is PTB7, and the fullerene acceptor material is PC. 71 BM, related molecular structures such as Figure 2 As shown. Physical vapor deposition is a strategy for preparing organic small molecule modified layers. The preparation process includes: a) spin-coating PTB7:PC onto the hole transport layer. 71 a) A 10 nm thick organic photodetector photosensitive layer film was formed by depositing a BM blend solution; b) In PTB7:PC 71 A small molecule modification layer with a thickness of 2 nm was formed on the BM blend photosensitive layer film using physical vapor deposition. The total thickness of the organic photosensitive active layer and the organic small molecule modification layer was 12 nm. The corresponding results are as follows: Figure 3 As shown.

[0034] The PTB7:PC 71 The mass ratio of the two organic donor and acceptor materials in the BM blend solution is 100:1.

[0035] In the fabrication of organic photodetectors, an ultrathin organic small molecule layer deposition modification strategy was adopted to form an ideal crystalline state of donor and acceptor components. This significantly suppressed the device's dark current, reduced leakage current loss, and further promoted effective exciton dissociation, achieving efficient carrier transport and extraction. This provides a new approach for the future industrialization of organic optoelectronics.

[0036] Example 2

[0037] A method for preparing the organic ultrathin photodetector based on small molecule layer modification as described in Example 1 includes the following steps: (1) Cleaning the transparent conductive substrate: The transparent conductive substrate (i.e., the glass substrate with ITO transparent conductive film) is ultrasonically cleaned in a water bath for 20 min in sequence with detergent, deionized water, acetone, anhydrous ethanol and isopropanol. After cleaning, it is dried with high-purity nitrogen (>99%). The dried transparent conductive substrate is placed in a UV irradiation machine and irradiated with UV light for 15 min. (2) Preparation of hole transport layer: In air, using a spin coater, a hole transport layer material PEDOT:PSS with a thickness of 30 nm was spin-coated on a transparent conductive substrate treated with ultraviolet light. Then, the substrate with the hole transport layer material was placed on an annealing table at 150°C and annealed for 15 min. PEDOT:PSS was purchased from Xi'an Baolai Technology Co., Ltd. Before use, PEDOT:PSS was diluted with ultrapure water at a ratio of 1:1 and stirred on a magnetic stirrer at 30°C for 30 min. (3) Preparation of organic photosensitive layer: PTB7: PC 71 The BM blend dissolved in high-purity chlorobenzene solvent (AR > 99%, concentration 5-10 mg / mL) -1 PTB7 and PC 71 In a BM mass ratio of 100:1, the organic small molecule material Rubrene was weighed and placed in a clean storage bottle. The preliminarily prepared PTB7:PC mixture was then added. 71 The BM blend solution was placed on a magnetic stirring heating table and stirred for 6-8 hours at 30-50℃ to obtain a fully dissolved solution; then, in an inert nitrogen glove box, the PTB7:PC mixture was stirred... 71 The BM blend solution was spin-coated onto the substrate after annealing in step (2). After a 30-second solvent evaporation process, an unstable crystalline state of PTB7:PC was formed on the substrate. 71 BM blended thin films will be spin-coated with PTB7:PC. 71 The substrate of the BM blend film was placed on an annealing table at 100°C and annealed for 10 min before being removed. (4) Preparation of organic small molecule modified layer: Place the weighed organic small molecule material Rubrene (10-20 mg) into the evaporation container, and transfer the substrate with hole transport layer / organic photosensitive layer obtained in step (3) into the physical vapor deposition chamber. After starting the vacuum system, wait for the chamber pressure to drop to 2.5 × 10⁻⁶. -4 Pa, heating the evaporation vessel, and evaporating stably at 240℃ for 5-15 min, depositing a 2nm organic small molecule modification layer; the organic small molecule modification layer broadens the overall device absorption range, as shown in the material absorption spectrum. Figure 4 As shown.

[0038] (5) Preparation of metal electrode: On the substrate with hole transport layer / organic photosensitive layer / organic small molecule modification layer obtained in step (4), heat aluminum target material to prepare Al electrode on the substrate with electrode thickness of 80 nm.

[0039] The detailed steps for preparing the organic photosensitive active layer in step (3) above are as follows: a. Using a high-precision electronic balance (weighing range 0.02-30 mg), weigh the polymers. Weigh 5 mg of the polymer donor material (Solarmer, >99%) PTB7 and place it in sample vial #1. Weigh 0.2 mg of the fullerene acceptor material (Solarmer, >99%) according to the ratio and place it in sample vial #2. Weigh 20 mg of the small organic molecule material Rubrene (TCI, >99%) and place it in sample vial #3. Place the sample vials in a nitrogen-protected glove box. Under a nitrogen atmosphere, add 1 mL of high-purity chlorobenzene solvent (Sigma Aldrich, AR >99%) to sample vial #1 and heat and stir at 50 °C for 8 h on a magnetic stirrer to obtain a fully dissolved polymer donor solution with a concentration of 5 mg / mL. -1 Under a nitrogen atmosphere, 20 μL of high-purity chloroform solvent (Sigma-Aldrich, AR > 99%) was added to sample vial No. 2, and the vial was placed on a magnetic stirrer and heated and stirred at 40 °C for 8 h to obtain a fully dissolved fullerene acceptor solution with a total concentration of 10 mg / mL. -1 ; b. Under a nitrogen atmosphere, add PTB7 and PC to the obtained donor solution sample vial. 71 BM was added to the acceptor fullerene solution at a mass ratio of 100:1, and after stirring for 60 min, PTB7:PC was obtained. 71 A BM mass ratio of 100:1 mixed solution can be used for spin coating to prepare the active layer; c. Under a nitrogen atmosphere, the prepared solution was spin-coated onto the PEDOT:PSS hole transport layer using a spin coater at a speed of 4000 rpm to obtain an organic donor-acceptor blend layer with a thickness of 10 nm. Under a nitrogen atmosphere, the substrate with the obtained organic photosensitive layer was placed on an electric heating annealing stage and annealed at 100 °C for 10 min. In the traditional solution deposition strategy for preparing organic photosensitive active layers, the solubility of the solvent used in the photosensitive material is fully utilized. Taking advantage of the photosensitive material itself, such as its light weight, low cost, and simple preparation process, and combined with the thermal annealing process, a more ideal crystallization state of the donor and acceptor in the organic photosensitive active layer can be achieved, which is beneficial to the transport and extraction of charge carriers.

[0040] Experimental Example

[0041] An organic photodetector was fabricated according to the device structure described in Example 1 and the operation steps for preparing the photodetector by organic small molecule layer modification-assisted deposition as described in Example 2. The fabricated organic photodetector was tested under a specific wavelength of 633 nm laser detection. The specific wavelength detection light power was calibrated using a standard power meter.

[0042] Comparative Example 1 The organic photodetector prepared by organic small molecule layer modification-assisted deposition according to Example 2 differs in that: Step (4) was not performed to prepare an organic small molecule modification layer using organic vapor deposition. The resulting device structure, from top to bottom, is: metal electrode, organic photosensitive layer (approximately 12 nm), hole transport layer (PEDOT:PSS, 30 nm), ITO (130 nm), and glass substrate.

[0043] like Figure 5 As shown, the current under dark conditions was tested. A significant enhancement of dark current was observed in the organic photodetector structure without the organic small molecule modification layer prepared by organic vapor deposition in step (4), within the voltage range of -1 to 1V. This result indicates that the modification with the organic small molecule layer can significantly suppress the device's inherent dark current. Furthermore, under the same excitation light intensity, the photocurrent of the photodetector modified with the organic small molecule layer was significantly improved. This is attributed to the fact that the modification of this molecule layer further promotes the effective dissociation of excitons, achieving efficient carrier transport and extraction. (Comparison) Figure 6 In the intermediate and comparative examples, the spectral responsivity (R) and specific detection rate (D*) under weak light excitation conditions (0.08 mW / cm²) were... 2 The optoelectronic devices modified with organic small molecule layers achieved a more ideal photoelectric response, and the device parameters were significantly improved. The corresponding results show that the presence of the organic small molecule modification layer is more conducive to improving the energy transfer efficiency between the donor and acceptor, thereby achieving significant dark current suppression in organic photodetectors. The presence of the organic small molecule modification layer constitutes a more ideal charge transport channel, realizing more ideal carrier transport behavior in the photosensitive layer.

Claims

1. An organic photodetector based on small molecular layer modification, characterized in that, From bottom to top, the structure consists of a glass substrate, a transparent conductive film, a hole transport layer, an organic photosensitive layer, an organic small molecule modification layer, and a top electrode. The organic photosensitive layer comprises a polymer donor and a polymer acceptor material; the polymer donor material is PTB7, and the polymer acceptor material is PC. 71 BM; the organic small molecule modification layer material is the organic material Rubrene; the thickness of the organic photosensitive layer is 10-20 nm, the thickness of the organic small molecule modification layer is 1-5 nm, and the PTB7:PC 71 The mass ratio of BM is 100:

1.

2. The organic photodetector based on small molecule layer modification according to claim 1, characterized in that, The transparent conductive film is ITO with a thickness of 130 nm, the hole transport layer material is PEDOT:PSS with a thickness of 30 nm, the organic photosensitive layer has a thickness of 10 nm, the organic small molecule modification layer material is Rubrene with a thickness of 2 nm, and the top electrode material is aluminum with a thickness of 80 nm.

3. A method for preparing the organic photodetector based on small molecule layer modification as described in any one of claims 1-2, characterized in that, The transparent conductive film and hole transport layer are fabricated on the glass substrate using a one-step solution deposition method, first by mixing PTB7 with PC. 71 A blended solution of BM is spin-coated to form an organic photosensitive layer. Subsequently, an organic small molecule modification layer is prepared on the organic photosensitive layer using physical vapor deposition to obtain an organic photodetector based on the small molecule layer modification.

4. The preparation method according to claim 3, characterized in that, The steps include the following: (1) Clean the transparent conductive substrate; (2) A hole transport layer PEDOT:PSS thin film is prepared on the transparent conductive substrate obtained in step (1); (3) Preparation of organic photosensitive layer thin film, including: a. Weigh 10-20 mg of Rubrene, 5-10 mg of PTB7, and 0.2-1 mg of PC using a high-precision electronic analytical balance. 71 BM, then add 1-2 mL of high-purity chlorobenzene solvent (AR > 99%) to the weighed PTB7. 71 After weighing BM, add 50-100 μL of high-purity chlorobenzene solvent. Store Rubrene in a clean material bottle. Add the weighed material to the accurate solvent and place the bottle on a heatable magnetic stirrer. Stir for 6-8 h at 30-50℃ to obtain a pure PTB7 solution with a concentration of 5-10 mg / mL and PC. 71 BM solution; b. After stirring thoroughly on a heatable magnetic stirrer for 6-8 hours, add 1% pure PC to the obtained pure PTB7 solution using a high-precision pipette. 71 After stirring the BM solution for another 60 minutes, PTB7:PC was obtained. 71 A mixed solution of BM; c. In an inert gas glove box, place the PTB7:PC prepared in step a. 71 Spin-coat the BM solution onto the substrate with hole transport layer obtained in step (2), wait 30s, and then place the substrate with the photosensitive layer material attached to it on an annealing table at 100°C and anneal it in an inert gas for 5-10 min. (4) An organic small molecule modified layer Rubrene is obtained on the organic photosensitive layer by means of physical vapor deposition; (5) Evaporate the top electrode material onto the organic small molecule modified layer.

5. The preparation method according to claim 4, characterized in that, In step (3), 1 mL of high-purity chlorobenzene solvent was added to the 5 mg PTB7 obtained by weighing, and the mixture was placed on a heatable magnetic stirrer and stirred at 50 °C for 8 h to obtain a pure PTB7 solution with a concentration of 5 mg / mL; 0.2 mg PC was weighed... 71 20 μL of high-purity chlorobenzene solvent was added to BM, and the mixture was placed on a heatable magnetic stirrer and stirred at 40 °C for 8 h to obtain pure PC with a concentration of 10 mg / mL. 71 Using a high-precision pipette, 5 μL of pure PC was added to pure PTB7 solution to obtain BM solution. 71 PTB7:PC in the blended solution obtained from BM solution 71 The mass ratio of BM is 100:

1.

6. The preparation method according to claim 4, characterized in that, In step (3)c, the spin coating speed of the active layer solution is: PTB7:PC 71 The BM blend solution was spin-coated in a single step at a speed of 3500-4500 rpm, yielding PTB7:PC. 71 The thickness of the BM layer is 10-20 nm.

7. The preparation method according to claim 6, characterized in that, In step (3)c, PTB7:PC 71 The BM blend solution was spin-coated at 4000 rpm to obtain PTB7:PC. 71 The BM layer is 10 nm thick.

8. The preparation method according to claim 4, characterized in that, In step (1), the transparent conductive substrate, i.e. the glass substrate with ITO transparent conductive film, is ultrasonically cleaned in an ultrasonic machine in a water bath for 20 min in sequence with detergent, deionized water, acetone, anhydrous ethanol and isopropanol. After cleaning, it is dried with high-purity nitrogen (>99%). The dried transparent conductive substrate is placed in an ultraviolet irradiation machine and irradiated with ultraviolet light for 15 min.

9. The preparation method according to claim 4, characterized in that, In step (2), a hole transport layer material PEDOT:PSS with a thickness of 30 nm is spin-coated onto a transparent conductive substrate treated with ultraviolet light in air using a spin coater. Then, the substrate with the spin-coated hole transport layer material is placed on an annealing table at 150°C and annealed for 15 min.

10. The preparation method according to claim 4, characterized in that, In step (4), the weighed organic small molecule material Rubrene is placed in the evaporation container. The substrate with the hole transport layer / organic photosensitive layer obtained in step (3) is transferred into the physical vapor deposition chamber. After starting the vacuum system, the chamber pressure is allowed to drop to 2.5 × 10⁻⁶. -4 Pa, heat the evaporation container, and evaporate stably for 5-15 min at 220-260℃ to deposit an organic small molecule modified layer with a thickness of 1-5 nm.

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