A multiplication type photodetector based on an organic-perovskite quantum dot active layer and a preparation method thereof

Abstract

A kind of multiplication type photoelectric detector based on organic-perovskite quantum dot active layer and preparation method thereof belong to organic photoelectric device technical field.It is successively composed of ITO conductive glass anode, poly (2, 3-dihydrothiophene and-1, 4-dioxane) hole transport layer, organic-perovskite quantum dot active layer and aluminum metal cathode.The application proposes the strategy of introducing CsPbBr3 perovskite quantum dot into P3HT organic material, quantum dot can effectively be used as electron trap in organic material, photo-generated electron of organic electron donor material under illumination is captured by quantum dot electron trap, the electron density captured by trap at the interface of active layer and cathode increases, resulting in band bending downward, barrier width decreases.At the same time, as P-type material, a large number of holes produced by P3HT under illumination are difficult to be captured by quantum dot electron trap, and a large number of holes pass through the barrier with reduced width to form multiplication current under the action of external electric field due to tunneling effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic optoelectronic devices, and particularly relates to a multiplication type photodetector based on an organic-perovskite quantum dot active layer and a preparation method thereof. BACKGROUND

[0002] As a device for directly converting optical signals into electrical signals by using photoelectric effect, photodetectors are widely used in various fields such as military defense, environmental monitoring, medical communication and industrial production. The multiplication type photodetector is a kind of photodetector device that can convert weak optical signals into electrical signals and amplify the signals through internal multiplication mechanism. Its high sensitivity detection characteristics for weak light have important applications in the fields of astronomy observation, biomedical science, industrial detection, radiation measurement and chemical analysis.

[0003] With the continuous progress of science and technology, new demands for the spectral range and performance of the multiplication type photodetector have been put forward. Most of the commercial multiplication type photodetectors on the market are composed of silicon or germanium materials, and their working voltage is usually tens to hundreds of volts. The high working voltage makes it difficult to meet the requirements of miniaturization and flexible use of the multiplication type photodetector. Therefore, it is necessary to develop new multiplication type photodetectors to make up for the shortcomings of traditional photodetectors.

[0004] The multiplication type photodetector is a kind of device based on organic semiconductor materials, which realizes high-sensitivity light detection by using a unique photoelectric multiplication mechanism. Based on the interface trap-induced quantum tunneling mechanism, the multiplication type photodetector has a smaller working voltage than the traditional silicon-germanium photodetector. When the metal electrode contacts the organic semiconductor layer, a Schottky junction is formed at the interface due to the difference in Fermi level between the two. When there are a large number of hole or electron traps in the organic semiconductor material, the photo-generated electrons or holes under light are trapped by the traps. When a bias is applied at the electrode end, the trapped carriers are transported to the Schottky junction area under the action of the external electric field, causing the Schottky junction area to narrow, thereby causing a large number of carriers in the external circuit to be injected back into the circuit under the influence of the external electric field, realizing current multiplication.

[0005] Perovskite quantum dots are a new type of nanomaterial composed of semiconductor crystals with perovskite structure, with a size of several nanometers to several tens of nanometers. They have good photoelectric properties, and their spectral line tunability allows us to change their energy level structure by adjusting the size of the quantum dots, thereby better adapting the energy levels of the organic donor material as electron traps and improving their performance. Higher conductivity also allows it to better trap photo-generated electrons in the organic donor material, promote the narrowing of the Schottky junction area, and increase the current multiplication effect. SUMMARY

[0006] The application aims to provide a multiplication type photodetector based on an organic-perovskite quantum dot active layer and a preparation method thereof, wherein the organic-perovskite quantum dot active layer is composed of poly-3-hexylthiophene-2,5-diyl (P3HT) organic material and CsPbBr3 perovskite quantum dots (QDs), the poly-3-hexylthiophene-2,5-diyl (P3HT) organic material serves as an electron donor, and the CsPbBr3 perovskite quantum dots (QDs) serve as an electron acceptor.

[0007] The multiplication type photodetector designed by the application is sequentially composed of an ITO conductive glass anode, a poly(2,3-dihydrothieno-1,4-dioxin) (PEDOT:PSS) hole transport layer, an organic-perovskite quantum dot active layer and an aluminum metal cathode from bottom to top. The application proposes a strategy of introducing CsPbBr3 perovskite quantum dots into P3HT organic material, the quantum dots can effectively serve as electron traps in the organic material, the photo-generated electrons of the organic electron donor material under irradiation are captured by the quantum dot electron traps, the electron density captured by the traps at the organic-cathode interface increases, resulting in the downward bending of the energy band and the reduction of the potential barrier width. Meanwhile, a large number of holes generated by P3HT as a P-type material under irradiation are difficult to be captured by the quantum dot electron traps, and the holes pass through the reduced-width potential barrier to form a multiplication current under the action of an external electric field due to the tunneling effect.

[0008] The application further provides a preparation method of the multiplication type photodetector based on the organic-perovskite quantum dot active layer.

[0009] (1) In a reaction container, 1-3 mmol of CsCO3, 1-3 mL of oleic acid and 10-20 mL of octadecene are mixed, vacuumized at 450-550 rpm, the obtained mixed solution is heated to 95-105 DEG C and maintained for 30-40 min, nitrogen is then introduced and vacuumized again, and the process is repeated for 3-4 times, and then the obtained solution is heated to 145-155 DEG C and maintained for 1-3 h to obtain a cesium oleate solution;

[0010] (2) In a reaction vessel, 0.1-0.5 mmol PbBr2, 0.5-2.0 mL oleic acid, 0.5-2.0 mL oleylamine, 8-15 mL octadecene were mixed and vacuumized at 450-550 rpm, the resulting mixed solution was heated to 90-100 °C and lasted for 30-40 min until the solution was clear; then nitrogen was introduced and vacuumized again, this process was repeated for 3-4 times; the resulting solution was heated to 180-190 °C, then nitrogen was introduced and 1-2 mL of the cesium oleate solution prepared in step (1) was quickly injected thereinto, 10-15 s later the reaction vessel was quickly cooled in ice water; the resulting solution was centrifuged at 8000-10000 rpm for 8-10 min, the precipitate obtained after centrifugation was taken and 4-5 mL of toluene was added to the precipitate, to obtain a CsPbBr3 QDs toluene solution;

[0011] (3) ITO conductive glass (250-350 mm 2 ) was cleaned with acetone, anhydrous ethanol and deionized water respectively, then dried with nitrogen, and then treated with ozone ultraviolet to optimize the hydrophobicity of the surface, to obtain an ITO conductive glass anode;

[0012] (4) A PEDOT:PSS aqueous solution with a mass fraction of 1.3-1.7% was filtered; in an air environment, the filtered PEDOT:PSS aqueous solution was uniformly spin-coated on the ITO conductive glass anode at a speed of 4500-5500 rpm for 35-50 s, then placed on a hot stage at 110-120 °C for annealing for 8-10 min, to obtain a PEDOT:PSS hole transport layer with a thickness of 20-40 nm on the ITO conductive glass anode;

[0013] (5) 12-20 mg of P3HT was placed in 1-2 mL of 1,2-dichlorobenzene solvent and stirred for 20-30 h to obtain a P3HT dichlorobenzene solution with a concentration of 6-12 mg / mL; the CsPbBr3 QDs toluene solution obtained in step (2) was ultrasonically treated in 8-12 °C cold water for 1-3 min, then mixed with the P3HT dichlorobenzene solution at a volume ratio of 1:90-110 to obtain a mixed solution; then 20-30 μL of the mixed solution was added dropwise on the PEDOT:PSS hole transport layer and spin-coated for 15-25 s under the conditions of being filled with nitrogen, water oxygen content being less than 0.01 ppm and 700-1000 rpm, the device was transferred to a hot stage at 50-60 °C for annealing for 4-6 min, to obtain an organic-perovskite quantum dot active layer with a thickness of 180-200 nm on the PEDOT:PSS hole transport layer, which has a high quality and a good film forming type;

[0014] (6) A multi-source organic vapor phase molecular deposition system was used, the pressure was not higher than 7 x 10 -4Under the condition of Pa, an aluminum cathode with a thickness of 80-90 nm is deposited on the organic-perovskite quantum dot active layer to prepare the multiplication photodetector based on the organic-perovskite quantum dot active layer of the present invention. Attached Figure Description

[0015] Figure 1 : A schematic diagram of the structure of the multiplication-type photodetector described in this invention; as shown Figure 1 As shown, from bottom to top, the structure consists of an ITO conductive glass anode, a PEDOT:PSS hole transport layer, an organic-perovskite quantum dot active layer, and an Al metal cathode.

[0016] Figure 2 A schematic diagram of the energy level structure of the multiplication-type photodetector described in this invention; as shown. Figure 2 As shown, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the perovskite quantum dot electron acceptor material in the active layer are both lower than those of the P3HT organic electron donor material. Due to the energy level difference between the two, electrons in the active layer will accumulate at the quantum dots, and a small number of perovskite quantum dots can exist as electron traps in the organic donor. At the same time, the large electronic barrier (~1.9 eV) between PEDOT:PSS and the ITO anode can make PEDOT:PSS act as an electron blocking layer to inhibit electron transport to the ITO anode;

[0017] Figure 3 The absorption spectrum of CsPbBr3 QDs prepared in this invention and its image under ultraviolet light irradiation (illustration); as shown in the illustration, the perovskite quantum dots prepared in this invention emit green light under ultraviolet light irradiation; Figure 3 As shown, the light absorption edge of the perovskite quantum dots prepared by this invention is around 528 nm, which is consistent with the characteristics of CsPbBr3 quantum dots, proving the successful synthesis of quantum dots;

[0018] Figure 4 Scanning electron microscope images of the organic-perovskite quantum dot active layer prepared in this invention; such as Figure 4 As shown, the thickness of the spin-coated active layer is approximately 190 nm, with a dense composition and a relatively smooth surface, proving that the active layer has been successfully formed.

[0019] Figure 5 The external quantum efficiency (EQE) curves of the multiplication photodetector prepared in this invention under different bias voltages; for example... Figure 5 As shown, the device achieves an EQE exceeding 100% for ultraviolet light (~350nm) at a bias voltage of -0.5V and an EQE exceeding 3600% for ultraviolet light (~350nm) at a bias voltage of -5.0V. Its ability to multiply the photocurrent at relatively low external bias voltages is beneficial for the miniaturization and portability of multiplication detectors.

[0020] Figure 6 The light switch current-time spectrum of the prepared multiplication type photoelectric detector within 30 min; as shown in the figure, the device has good stability, and has good time stability under the irradiation of switch light with a frequency of 0.5 Hz within 30 min; Figure 6

[0021] Figure 7 The calculation result curve of the detection sensitivity of the multiplication type photoelectric detector prepared by the application; the detection sensitivity is an important parameter for indicating the detection ability of the device, and the specific detection sensitivity (D*) of the photoelectric detector based on the application can be obtained through the following equation:

[0022]

[0023] In the formula, A is the area of the active layer, Δf is the bandwidth, NEP is the noise equivalent power, which can be measured by an experimental instrument, and the unit of the specific detection sensitivity is cm Hz -1 / 2 W -1 (Jones). The detection sensitivity (D*) of the device prepared based on the method is more than 2.4*10 11 Jones (-0.3 V bias), which indicates that the multiplication type photoelectric detector based on perovskite quantum dots as electron acceptors has good detection ability for weak light at low bias. DETAILED DESCRIPTION

[0024] Example 1:

[0025] (1) Put 1.23 mmol of CsCO3, 1.25 mL of oleic acid, 15 mL of octadecene and a rotor into a three-necked flask, stir the flask on a stirring table at a speed of 500 rpm and pump the flask to make it enter a vacuum state until there is no bubble in the solution, then heat the solution to 100℃ and maintain for 30 min; then fill the flask with nitrogen and pump it to vacuum, repeat the process for 3 times; finally heat it to 150℃, maintain this temperature for at least 1 h, and maintain this temperature before the end of the next step, to obtain a cesium oleate solution;

[0026] ​(2) Put 0.36 mmol of PbBr2, 1 mL of oleic acid, 1 mL of oleylamine, 10 mL of octadecene and a rotor into a three-necked flask, place the flask on a stirring table to stir at a speed of 500 rpm and pump air out of the flask to make it in a vacuum state, heat it to 100°C for 30 min until the solution is clear; then fill the flask with nitrogen and pump it to vacuum again, repeat this process for 3 times; after 3 times of nitrogen filling and pumping, heat the solution to 180°C, then pass nitrogen into the flask, quickly inject 1 mL of cesium oleate prepared in step (1) (150°C) into the three-necked flask, and after 10 s, quickly put the flask into ice water for rapid cooling; take out the solution in the three-necked flask, centrifuge it in a centrifuge at a speed of 9000 rpm for 10 min; take the precipitate after centrifugation and put it into the refrigerator after adding 4 mL of toluene to the precipitate, to obtain a toluene solution of CsPbBr3 QDs;

[0027] (3) The ITO conductive glass (300 mm 2 ) was cleaned with acetone, anhydrous ethanol and deionized water for 25 min respectively, then dried with nitrogen, and then treated with ozone ultraviolet for 30 min to obtain an ITO conductive glass anode;

[0028] (4) A 1.5% by mass fraction of PEDOT:PSS aqueous solution (PEDOT:PSS aqueous solution is purchased from Xi'an Yuriguang Energy Technology Co., Ltd.) was filtered through a 0.22 μm water filter. In an air environment, the filtered PEDOT:PSS aqueous solution was uniformly spin-coated on the ITO conductive glass anode using a spin coater at a speed of 5000 rpm for 40 s, and then annealed on a hot table at 120°C for 10 min to obtain a 30 nm PEDOT:PSS hole transport layer on the ITO conductive glass anode;

[0029] (5) 12 mg of P3HT solid was weighed by a balance and placed in 1 mL of 1,2-dichlorobenzene solvent, and stirred for 22 h to obtain a P3HT dichlorobenzene solution with a concentration of 12 mg / mL; the CsPbBr3 QDs toluene solution obtained in step (2) was ultrasonically treated in 10°C cold water for 2 min, then mixed with the P3HT dichlorobenzene solution at a volume ratio of 1:100 to obtain a mixed solution; then 30 μL of the mixed solution was added dropwise on the PEDOT:PSS hole transport layer on a spin coater in a glove box filled with nitrogen with a water oxygen content of less than 0.01 ppm under the condition of 800 rpm, and spin-coated for 20 s, then the device was transferred to a hot table at 50°C for annealing for 5 min, to obtain a high-quality, well-filmed organic-perovskite quantum dot active layer with a thickness of 190 nm on the PEDOT:PSS hole transport layer;

[0030] (6) A multi-source organic vapor phase molecular deposition system was used, and the pressure was not higher than 7 x 10-4 The multiplication type photoelectric detector is prepared by evaporating 80 nm thick aluminum cathode on the active layer under the condition of 1.5 Pa.

Claims

1. A method for fabricating a multiplication photodetector based on an organic-perovskite quantum dot active layer, comprising the following steps: (1) The ITO conductive glass was ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively, then dried with nitrogen, and then treated with ozone ultraviolet light to optimize the hydrophobicity of its surface to obtain the ITO conductive glass anode. (2) Filter the PEDOT:PSS aqueous solution with a mass fraction of 1.3 to 1.7%; in an air environment, uniformly spin-coat the filtered PEDOT:PSS aqueous solution onto the ITO conductive glass anode, and after annealing, obtain a PEDOT:PSS hole transport layer with a thickness of 20 to 40 nm on the ITO conductive glass anode. (3) The CsPbBr3 QDs toluene solution was ultrasonically treated in cold water at 8-12℃ for 1-3 min, and then mixed with P3HT dichlorobenzene solution at a volume ratio of 1:90-110 to obtain a mixed solution; then, under conditions of nitrogen filling, water oxygen content below 0.01 ppm and 700-1000 rpm, 90-120 μL of the mixed solution was dropped onto the PEDOT:PSS hole transport layer and spin-coated. After annealing, an organic-perovskite quantum dot active layer with a thickness of 180-200 nm was obtained on the PEDOT:PSS hole transport layer. (4) Use a multi-source organic vapor deposition system at a pressure not exceeding 7×10⁻⁶. -4 Under the condition of Pa, an aluminum cathode with a thickness of 80-90 nm is deposited on the organic-perovskite quantum dot active layer to prepare the multiplication photodetector based on the organic-perovskite quantum dot active layer.

2. The method for fabricating a multiplication photodetector based on an organic-perovskite quantum dot active layer as described in claim 1, characterized in that: In step (2), spin coating is performed at a speed of 4500-5500 rpm for 35-50 seconds, followed by annealing on a hot plate at 110-120°C for 8-10 minutes.

3. The method for fabricating a multiplication photodetector based on an organic-perovskite quantum dot active layer as described in claim 1, characterized in that: The preparation steps of the CsPbBr3 QDs toluene solution in step (3) are as follows: (1) In a reaction vessel, 1-3 mmol CsCO3, 1-3 mL oleic acid, and 10-20 mL octadecene are mixed and then evacuated at 450-550 rpm. The resulting mixed solution is heated to 95-105 °C and maintained for 30-40 min. Then nitrogen gas is introduced and evacuation is carried out again. This process is repeated 3-4 times. The resulting solution is then heated to 145-155 °C and maintained for 1-3 h to obtain a cesium oleate solution. (2) In a reaction vessel, mix 0.1–0.5 mmol PbBr2, 0.5–2.0 mL oleic acid, 0.5–2.0 mL oleylamine, and 8–15 mL octadecene, and evacuate at 450–550 rpm. Heat the resulting mixture to 90–100 °C and maintain for 30–40 min until the solution is clear. Then, purge with nitrogen and evacuate again. Repeat this process 3–4 times. Heat the resulting solution to 180–190 °C, purge with nitrogen, and weigh out 1–2 mL of the cesium oleate solution prepared in step (1) and quickly inject it into the mixture. After 10–15 seconds, the reaction vessel was placed in ice water to cool it down rapidly. The resulting solution was centrifuged at 8000–10000 rpm for 8–10 min. The precipitate obtained after centrifugation was collected and 4–5 mL of toluene was added to the precipitate to obtain a CsPbBr3 QDs toluene solution.

4. The method for fabricating a multiplication photodetector based on an organic-perovskite quantum dot active layer as described in claim 1, characterized in that: In step (3), 12-20 mg of P3HT is placed in 1-2 mL of 1,2-dichlorobenzene solvent and stirred for 20-30 h to obtain a P3HT dichlorobenzene solution with a concentration of 6-12 mg / mL.

5. The method for fabricating a multiplication photodetector based on an organic-perovskite quantum dot active layer as described in claim 1, characterized in that: The spin coating time in step (3) is 15-25s. After spin coating, the device is transferred to a hot stage at 50-60℃ for annealing for 4-6min.

6. A multiplication photodetector based on an organic-perovskite quantum dot active layer, characterized in that: It is prepared by the method described in any one of claims 1 to 5.

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