Photovoltaic-multiplication dual-mode photoelectric detector based on bias voltage regulation and control and preparation method thereof

Abstract

The invention provides a photovoltaic-multiplication dual-mode photoelectric detector based on adjustable bias polarity and a preparation method thereof, the photovoltaic-multiplication dual-mode photoelectric detector adopts a multi-layer structure design, and specifically comprises a transparent substrate, a first conductive electrode layer, an electron transport layer, a photosensitive active layer, a hole transport layer and a second conductive electrode layer from bottom to top in sequence; the photosensitive active layer is a heterojunction formed by an organic polymer donor and a fullerene acceptor. Under forward bias voltage, the electron trap captures photo-induced electrons and triggers energy band bending, so that holes can be tunneled and injected from an external circuit, and a high-gain photomultiplication type detection mode is realized; under reverse bias voltage, photo-generated holes and electrons in the heterojunction are respectively collected by the hole transport layer and the electron transport layer, and a photovoltaic detection mode is realized. Through the cooperative detection capability of the double working modes, the detector has the advantages of a photovoltaic mechanism and a multiplication mechanism, has tunable dark current and photoelectric gain, and can ensure the flexible detection of the photoelectric detector on strong light or weak light.

Description

Technical Field

[0001] This invention relates to the field of photodetector technology, and specifically to a method for fabricating a photovoltaic-multiplication dual-mode photodetector based on bias control. Background Technology

[0002] Photodetectors are semiconductor devices that convert optical signals into electrical signals, and are widely used in optical communication, sensing, imaging, environmental monitoring, and military fields. With the rise of organic semiconductor materials, their tunable spectral absorption range, the flexibility they offer due to their low hardness, and the reduced production costs resulting from solution-based processes, demonstrate promising application prospects in the field of photodetectors.

[0003] For diode-type photodetectors, which typically operate in photovoltaic mode, the photocurrent is generated by photogenerated carriers collected by the electrodes at both ends of the device. In practical applications, losses occur at each step of the process: photon absorption by the photosensitive active layer, exciton dissociation, and collection of free electrons and holes by the electrodes. These inherent loss mechanisms result in the external quantum efficiency (EQE) of diode-type photodetectors always being less than 100%, which is detrimental to weak light detection. As Professor Zhang Fujun described in "Adv. Funct. Ma ter. 2021, 31, 2106009," a multiplication photodetector was fabricated using an electron trap introduced by an unbalanced donor-acceptor material ratio strategy. This significantly increased the photocurrent density under high bias voltage, resulting in excellent weak light detection capabilities. However, Professor Cui Yanxia also mentioned in "Research Progress of Organic Photomultiplication Detectors" that the response speed and stability of multiplication photodetectors still require further in-depth research. In addition, it generally operates under a high bias voltage and is prone to saturation and severe heat generation under strong light, which is not conducive to the detection of strong light signals. Summary of the Invention

[0004] The purpose of this invention is to provide a photovoltaic-multiplication dual-mode photodetector based on bias control and its fabrication method, which can achieve photovoltaic and photomultiplication dual-mode operation under reverse bias and forward bias respectively.

[0005] The technical solution for realizing the present invention is as follows: a photovoltaic-multiplication dual-mode photodetector based on bias control, comprising, from bottom to top, a transparent substrate, a first conductive electrode layer, an electron transport layer, a photosensitive active layer, a hole transport layer, and a second conductive electrode layer; wherein, the photosensitive active layer is a bulk heterojunction formed by fully mixing organic donor materials and organic acceptor materials.

[0006] Furthermore, the transparent substrate is a rigid substrate, and a first conductive electrode layer is fabricated on the transparent substrate; the material of the first conductive electrode layer is indium tin oxide, and the thickness is 100nm to 150nm.

[0007] Furthermore, the organic donor material is PTB7-Th, and the organic acceptor material is PC. 71 BM; organic donors and organic acceptors mix to form bulk heterojunctions, and the response wavelength range of bulk heterojunctions is 400nm-900nm.

[0008] Furthermore, the electron transport layer is made of zinc oxide with a thickness of 40 nm to 60 nm; the hole transport layer is made of molybdenum trioxide with a thickness of 12 nm to 15 nm; and the second conductive electrode is made of metallic silver with a thickness of 100 nm to 150 nm.

[0009] Furthermore, the dual-mode photodetector operates in photovoltaic detection mode under zero bias or reverse bias, responding to the visible light band of 400-760nm; and operates in photomultiplication detection mode under forward bias, exhibiting a significant narrowband response to the near-infrared band of 760-900nm.

[0010] A method for fabricating a photovoltaic-multiplication dual-mode photodetector based on bias voltage control includes the following steps:

[0011] Step 1: ITO is etched on the upper surface of the transparent substrate. The transparent substrate with indium tin oxide is ultrasonically cleaned in a series of detergents, deionized water, acetone and isopropanol. Then it is dried under a nitrogen flow to obtain the first conductive electrode layer with surface impurities removed.

[0012] Step 2: Spin-coat the ZnO solution onto the first conductive electrode layer and perform thermal annealing to obtain the electron transport layer.

[0013] Step 3: Prepare the photosensitive active layer solution: Combine the organic donor PTB7-Th and the organic acceptor PC. 71 BM was mixed at a mass ratio of 1:1 and ground thoroughly into powder to obtain a bulk heterojunction. The bulk heterojunction was transferred to a reagent bottle and dissolved by adding an organic solvent to obtain an organic solution with a total mass concentration of 40 mg / mL. The organic solution was sealed and heated at 100-120°C, and stirred by a magnetic rotor to promote dissolution. After heating and stirring for at least 6 hours, a photosensitive active layer solution was obtained.

[0014] Step 4: In a nitrogen atmosphere, spin-coat the photosensitive active layer solution onto the upper surface of the electron transport layer. After spin-coating, perform thermal annealing to obtain the photosensitive active layer.

[0015] Step 5: Molybdenum trioxide is deposited on the upper surface of the photosensitive active layer using a vacuum thermal evaporation method to obtain a hole transport layer.

[0016] Step 6: Deposit metallic silver on the upper surface of the hole transport layer using a vacuum thermal evaporation method to obtain a second conductive electrode, thereby obtaining a photovoltaic-multiplication dual-mode photodetector based on bias control.

[0017] Step 7: In a nitrogen atmosphere, encapsulate the bias-controlled photovoltaic-multiplication dual-mode photodetector using optical adhesive and grooved glass.

[0018] Furthermore, in step 2, the ZnO solution is prepared as follows:

[0019] Zinc acetate dihydrate was dissolved in a mixture of ethanolamine and 2-methoxyethanol to obtain a ZnO solution with a total mass concentration of 15 mg / ml.

[0020] When spin-coating the ZnO solution onto the first conductive electrode layer, the spin-coating speed is 1500-2000 rpm, the acceleration is 600 rpm / s, the spin-coating time is 50-60 s, the heat annealing temperature is 100-130℃, and the heat annealing time is 3-5 min.

[0021] Further, in step 3, the organic solvent is chlorobenzene or o-dichlorobenzene; in step 4, the spin coating speed of the photosensitive active layer is 1000 rpm, the acceleration is 400 rpm / s, the spin coating time is 50-60 s, the heat annealing temperature is 100-130℃, and the heat annealing time is 10-15 min.

[0022] Furthermore, in step 5, when preparing the hole transport layer using vacuum thermal evaporation, the evaporation rate is...

[0023] Furthermore, in step 6, when preparing the second conductive electrode layer using vacuum thermal evaporation, the evaporation rate is [value missing] for the first 10 nm. The evaporation rate of the remaining thickness is This forms a dense second conductive electrode layer.

[0024] Compared with the prior art, the significant advantages of this invention are:

[0025] (1) This invention employs an organic donor material of PTB7-Th (HOMO level -5.2 eV, LUMO level -3.6 eV) and an organic acceptor material of PC71BM (HOMO level -6.0 eV, LUMO level -3.9 eV). This energy level combination not only optimizes electron transport efficiency but also significantly improves the overall performance of the detector. The mass ratio of the organic donor material to the acceptor material is 1:1, and the total mass concentration of the solution is 40 mg / mL. The response wavelength range of the bulk heterojunction is 400 nm-900 nm.

[0026] (2) The dual-mode photodetector operates in photovoltaic detection mode under zero bias or reverse bias, and responds to the visible light band of 400-760nm; under forward bias, it operates in photomultiplication detection mode, and has a significant narrowband response to the near-infrared band of 760-900nm.

[0027] (3) The active layer of the photodetector provided by this invention adopts a polymer-based heterojunction structure, and an electron transport layer is introduced before and after the active layer, with a hole transport layer serving as the interface layer. Under forward bias, when the detector is illuminated, due to the disordered structural traps and the potential barrier effect of the charge blocking layer, most of the photogenerated carriers are trapped at the interface between the charge blocking layer and the photosensitive active layer. As the trapped charge and accumulated charge increase, the enhanced band bending eventually leads to charge tunneling injection. Therefore, the dual-mode photodetector operates in photomultiplication mode under forward bias. Under zero bias or reverse bias, the carrier transport channel formed by the matching energy level combination between the donor and acceptor, in the same direction as the built-in electric field, greatly improves the electron transport efficiency and promotes the movement of carriers generated by the absorption of visible light by the photosensitive active layer to the corresponding electrodes, enabling the detector to operate in photovoltaic detection mode.

[0028] (4) This invention breaks through the limitation of the single working mode of traditional organic photodetectors. Through the design of the detector interface structure, it achieves the advantages of simple structure and low cost, and can flexibly meet the needs of strong light or weak light detection. Attached Figure Description

[0029] Figure 1 This is a structural diagram of the dual-mode photodetector in this invention.

[0030] Figure 2 The graph shows the external quantum efficiency (EQE) of the photodetector as a function of the incident light wavelength; where (a) is the photodetector under a 3V bias voltage and (b) is the photodetector under a -3V bias voltage.

[0031] Figure 3 The current density-voltage characteristic curves of the photodetector in the bright and dark states are shown.

[0032] Figure 4 The graph shows the device responsivity (R) of the photodetector as a function of the incident light wavelength; where (a) is the photodetector under a 3V bias voltage and (b) is the photodetector under a -3V bias voltage.

[0033] Figure 5 This is a graph showing the specific detectivity (D*) of a photodetector as a function of the incident light wavelength. Detailed Implementation

[0034] To more clearly illustrate the technical solution, innovative advantages, and specific implementation methods of the present invention, the technical details of the present invention will be systematically described and analyzed in depth below in conjunction with the embodiments and accompanying drawings.

[0035] A photovoltaic-multiplication dual-mode photodetector based on bias control is shown in the schematic diagram below. Figure 1 As shown, from bottom to top, the layers are a transparent substrate (Glass), a first conductive electrode layer (ITO), an electron transport layer (ZnO), a photosensitive active layer (PTB7-Th:PC71BM), a hole transport layer (MoO3), and a second conductive electrode layer (Ag). In this embodiment, the organic donor material and the organic acceptor material are mixed and dissolved in an organic solvent to form a bulk heterojunction, which significantly shortens the exciton diffusion distance, significantly improves the charge separation efficiency, and effectively balances the charge generation, transport, and collection processes.

[0036] Example 1

[0037] A method for fabricating a photovoltaic-multiplication dual-mode photodetector based on bias voltage control includes the following steps:

[0038] Step 1: Etch ITO on the upper surface of the transparent substrate and perform ultrasonic cleaning on the surface;

[0039] Ultrasonic cleaning shall be performed in the following order:

[0040] (1) Wipe the transparent substrate of the etched ITO with a paper towel soaked in isopropyl alcohol and apply directional airflow with a bulb syringe to remove obvious impurities on the surface;

[0041] (2) Place the transparent substrate in an ultrasonic cleaner and add detergent; ultrasonically clean for 8 minutes.

[0042] (3) Place the transparent substrate in an ultrasonic cleaner and add deionized water; ultrasonically clean for 8 minutes.

[0043] (4) Place the transparent substrate in an ultrasonic cleaner and add acetone; ultrasonically clean for 8 minutes.

[0044] (5) Place the transparent substrate in an ultrasonic cleaner and add isopropanol; ultrasonically clean for 8 minutes.

[0045] The cleaned transparent substrate was placed in a drying oven and dried with nitrogen. This resulted in a first conductive electrode layer with surface impurities removed.

[0046] Step 2: Prepare an electron transport layer ZnO on the surface of the first conductive electrode layer by spin coating. Spin coat the ZnO solution onto the first conductive electrode layer. The spin coating speed is 1500 rpm, the acceleration is 600 rpm / s, the spin coating time is 60s, the heat annealing temperature is 100-130℃, and the heat annealing time is 5min to form the electron transport layer.

[0047] Step 3: Preparation of photosensitive active layer solution: PTB7-Th is used as the donor material of the photosensitive active layer, and PC71BM is used as the acceptor material of the photosensitive active layer, with a mass ratio of 1:1 and a total mass concentration of 40 mg / ml for the donor and acceptor. The organic donor and organic acceptor blend is thoroughly ground into powder, transferred to a reagent bottle, and dissolved using chlorobenzene as an organic solvent. After sealing, it is heated at 100°C and stirred with a magnetic rotor (130 r / min) to promote dissolution. After heating and stirring for 8 hours, the photosensitive active layer solution is obtained.

[0048] Step 4: In a nitrogen atmosphere, after completing step 2, a photosensitive active layer solution is spin-coated onto the upper surface of the electron transport layer using a spin coating process. The spin coating speed is 1000 rpm, the acceleration is 400 rpm / s, the spin coating time is 60 s, the heat annealing temperature is 100℃, and the heat annealing time is 10 min to obtain the photosensitive active layer.

[0049] Step 5: Prepare a hole transport layer by vacuum evaporation of MoO3 on the upper surface of the photosensitive active layer. The evaporation pressure is 10. -4 Pa, with a thickness of 12 nm;

[0050] Step 6: Prepare a second conductive electrode layer by vapor deposition of metallic silver on the surface of the hole transport layer MoO3 using a vapor deposition method. The vapor deposition pressure is 10. -4 Pa, with a thickness of 100 nm; thus, a photovoltaic-multiplication dual-mode photodetector based on bias control is obtained;

[0051] Evaporation is carried out in a vacuum evaporation furnace. The device to be treated is placed on a turntable at the top of the furnace chamber, with the side containing the interface layer facing down. The prescribed amount of evaporation material particles are placed in a tungsten boat. The vacuum degree inside the furnace is ≤10. -4 Pa, turntable speed 5 r / min; during the vapor deposition process, the growth rate of the hole transport layer MoO3 is set to be at... The rate of the second conductive electrode Ag in the first 10 nm is... The growth rate after 90nm is at

[0052] Step 7: Carefully apply the optical adhesive to the edge of the recessed glass, move it into the glove box, and encapsulate the vapor-deposited detector in a nitrogen atmosphere. Then, use an ultraviolet lamp to cure it for 5 minutes to complete the encapsulation operation.

[0053] The performance of the photodetector prepared in this embodiment was tested, analyzed, and characterized. The results are as follows: From Figure 2 The external quantum efficiency characteristic curves show that under forward bias, the detector operates in photomultiplication mode, exhibiting a significant narrowband response in the 760-900nm near-infrared band; under reverse bias or zero bias, the photodetector operates in photovoltaic mode, responding to the 400-760nm visible light band. This demonstrates that the detector can simultaneously operate in both photovoltaic and photomultiplication modes, broadening its application range.

[0054] Figure 3 The photodetector prepared in this embodiment exhibits current density-voltage curves in both bright and dark states under irradiation conditions of 660 nm, 1.2 μW visible light and 800 nm, 0.76 μW near-infrared light. Figure 3 The bright and dark current density-voltage characteristic curves show that the photodetector has a significant bright-dark current ratio under forward and reverse bias, and has a significant light response in the corresponding wavelength band, ensuring the detection performance of the photodetector.

[0055] Furthermore, the detector's single-mode detection performance under both positive and negative bias was analyzed, specifically its responsivity R and specific detectivity D*. The results are as follows: Figure 4 , Figure 5 As shown.

[0056] from Figure 4 and Figure 5 It can be seen that the provided photodetector has high external quantum efficiency (EQE), responsivity (R), and specific detectivity (D*) in different operating modes.

[0057] Specifically, under a reverse bias of -3V, the photodetector operates in photovoltaic detection mode, achieving an external quantum efficiency (EQE) of approximately 60% and a responsivity of 0.25 A / W in the 400-760 nm visible light band, with a specific detectivity of 5.7 x 10¹¹ Jones. Under a forward bias of 3V, the photodetector operates in photomultiplication detection mode, achieving an external quantum efficiency (EQE) of 757% and a responsivity of 4.82 A / W at a wavelength of 790 nm, with a specific detectivity of 1.6 x 10¹¹ Jones. 12Jones. The higher external quantum efficiency (EQE) and responsivity (R) of photodetectors under forward bias is due to the fact that more photogenerated electrons are trapped near the interface layer under forward bias, causing the bandgap of the photoelectric modulation layer to bend, which is conducive to the tunneling injection of holes from the external circuit, thus improving the external quantum efficiency and responsivity of the photodetector.

[0058] This invention successfully developed a novel dual-mode photodetector. By precisely controlling the ratio and concentration of the active layer material, controllable defect states are innovatively introduced, breaking through the limitations of the single operating mode of traditional devices. The detector is fabricated using a solution method, which is simple, low-cost, and exhibits excellent reproducibility. The device demonstrates outstanding stability, while also possessing high external quantum efficiency and responsivity.

[0059] The specific embodiments of the present invention are not limited to the above-described examples. Without departing from the core ideas of the present invention, those skilled in the art can make various modifications and adjustments to the technical solutions. Unless otherwise specified, the technical features disclosed in the specification can be implemented using functionally equivalent alternatives; the technical features and method steps involved can be freely combined and applied, unless they are mutually exclusive.

Claims

1. A photovoltaic-multiplication dual-mode photodetector based on bias control, characterized in that: From bottom to top, the structure consists of a transparent substrate, a first conductive electrode layer, an electron transport layer, a photosensitive active layer, a hole transport layer, and a second conductive electrode layer; wherein, the photosensitive active layer is a bulk heterojunction formed by fully mixing organic donor materials and organic acceptor materials.

2. The photovoltaic-multiplication dual-mode photodetector based on bias control as described in claim 1, characterized in that: The transparent substrate is a rigid substrate, and a first conductive electrode layer is fabricated on the transparent substrate; the material of the first conductive electrode layer is indium tin oxide, and the thickness is 100nm to 150nm.

3. The photovoltaic-multiplication dual-mode photodetector based on bias control as described in claim 1, characterized in that: The organic donor material is PTB7-Th, and the organic acceptor material is PC. 71 BM; organic donors and organic acceptors mix to form bulk heterojunctions, and the response wavelength range of bulk heterojunctions is 400nm-900nm.

4. The photovoltaic-multiplication dual-mode photodetector based on bias control as described in claim 1, characterized in that: The electron transport layer is made of zinc oxide with a thickness of 40 nm to 60 nm; the hole transport layer is made of molybdenum trioxide with a thickness of 12 nm to 15 nm; and the second conductive electrode is made of metallic silver with a thickness of 100 nm to 150 nm.

5. The photovoltaic-multiplication dual-mode photodetector based on bias control as described in any one of claims 1 to 4, characterized in that: The dual-mode photodetector operates in photovoltaic detection mode under zero bias or reverse bias, responding to the visible light band of 400-760nm; and operates in photomultiplication detection mode under forward bias, exhibiting a significant narrowband response to the near-infrared band of 760-900nm.

6. A method for fabricating a photovoltaic-multiplication dual-mode photodetector based on bias voltage control, characterized in that, Includes the following steps: Step 1: Etch indium tin oxide on the upper surface of a transparent substrate. The transparent substrate with indium tin oxide is ultrasonically cleaned in a series of detergents, deionized water, acetone and isopropanol. Then it is dried under a nitrogen flow to obtain the first conductive electrode layer with surface impurities removed. Step 2: Spin-coat the ZnO solution onto the first conductive electrode layer and perform thermal annealing to obtain the electron transport layer; Step 3: Prepare the photosensitive active layer solution: Combine the organic donor PTB7-Th and the organic acceptor PC. 71 BM is mixed at a mass ratio of 1:1 and thoroughly ground into powder. The powder is then transferred to a reagent bottle, and an organic solvent is added to dissolve it, resulting in an organic solution with a total mass concentration of 40 mg / mL. The organic solution is then sealed and heated at 100–120 °C, and stirred with a magnetic rotor to promote dissolution. After heating and stirring for at least 6 hours, a photosensitive active layer solution is obtained. Step 4: In a nitrogen atmosphere, spin-coat the photosensitive active layer solution onto the upper surface of the electron transport layer. After spin-coating, perform thermal annealing to obtain the photosensitive active layer. Step 5: Molybdenum trioxide is deposited on the upper surface of the photosensitive active layer using a vacuum thermal evaporation method to obtain a hole transport layer; Step 6: Deposit metallic silver on the upper surface of the hole transport layer using vacuum thermal evaporation to obtain the second conductive electrode, thereby obtaining a photovoltaic-multiplication dual-mode photodetector based on bias control. Step 7: In a nitrogen atmosphere, encapsulate the bias-controlled photovoltaic-multiplication dual-mode photodetector using optical adhesive and grooved glass.

7. The fabrication method of the photovoltaic-multiplication dual-mode photodetector based on bias control as described in claim 6, characterized in that, In step 2, the ZnO solution is prepared as follows: Zinc acetate dihydrate was dissolved in a mixture of ethanolamine and 2-methoxyethanol to obtain a ZnO solution with a total mass concentration of 15 mg / ml.

8. The fabrication method of the photovoltaic-multiplication dual-mode photodetector based on bias control as described in claim 7, characterized in that, In step 2, when spin-coating the ZnO solution onto the first conductive electrode layer, the spin-coating speed is 1500-2000 rpm, the acceleration is 600 rpm / s, the spin-coating time is 50-60s, the heat annealing temperature is 100-130℃, and the heat annealing time is 3-5min.

9. The fabrication method of the photovoltaic-multiplication dual-mode photodetector based on bias control as described in claim 6, characterized in that, In step 3, the organic solvent is chlorobenzene or o-dichlorobenzene; in step 4, the spin coating speed of the photosensitive active layer is 1000 rpm, the acceleration is 400 rpm / s, the spin coating time is 50-60 s, the heat annealing temperature is 100-130℃, and the heat annealing time is 10-15 min.

10. The fabrication method of the photovoltaic-multiplication dual-mode photodetector based on bias control as described in claim 6, characterized in that, In step 5, when the hole transport layer is prepared using vacuum thermal evaporation, the evaporation rate is: In step 6, when the second conductive electrode layer is prepared using vacuum thermal evaporation, the evaporation rate is [missing value] for the first 10 nm. The evaporation rate of the remaining thickness is This forms a dense second conductive electrode layer.

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