High-temperature-resistant PbS colloidal quantum dot photodiode and preparation method thereof

Abstract

The invention belongs to the field of quantum dot infrared detectors, and discloses a high-temperature-resistant PbS colloidal quantum dot photodiode and a preparation method thereof, and the preparation method comprises the following steps: S1, forming a first PbS colloidal quantum dot solution; s2, adding n-octylamine and an anti-solvent; s3, obtaining a PbS colloidal quantum dot solid of which the surface is modified with the n-octylamine ligand; s4, forming a second PbS colloidal quantum dot solution; s5, forming a thiol ligand solution; s6, a nickel oxide layer is formed, and spin coating is carried out; s7, heating the PbS colloidal quantum dot coating; s8, spin coating is conducted; s9, the multiple PbS colloidal quantum dot coatings are heated; s11, enabling the number of layers of the PbS colloidal quantum dot coating to reach a set number; s12, preparing a fullerene film; s13, preparing a tin oxide layer; and S14, preparing an ITO layer. According to the invention, the high-temperature dark current out-of-control of the PbS colloidal quantum dot photodiode can be greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot infrared detectors, and more specifically, relates to a high-temperature resistant PbS colloidal quantum dot photodiode and its preparation method. Background Technology

[0002] PbS colloidal quantum dots (PbS CQDs) are an important semiconductor nanomaterial with broad application prospects in the field of infrared photodetectors due to their unique photoelectric properties.

[0003] PbS colloidal quantum dots possess solution-processable properties, giving them significant advantages in large-scale fabrication and device integration. Simultaneously, their broad-spectrum infrared photoelectric response enables them to effectively absorb infrared light, demonstrating significant potential in infrared detection and imaging. However, PbS colloidal quantum dots face several key challenges in practical applications, limiting their use in high-performance infrared PbS colloidal quantum dot photodiodes.

[0004] PbS colloidal quantum dots are typically modified with long-chain ligands, such as oleic acid and oleylamine. These long-chain ligands are bonded to the quantum dot surface via lead carboxylate. While this provides good surface passivation at room temperature, this bonding method suffers from severe stability issues at high temperatures. When the temperature exceeds 100°C, the bonds between the long-chain ligands and the quantum dot surface easily dissociate, leading to the exposure of lead atoms and the formation of surface defect states. These surface defect states induce nonradiative recombination of charge carriers, causing a continuous increase in the dark current of the device, severely affecting its performance and stability. Furthermore, the absence of ligands can also promote the ripening of quantum dots, further exacerbating the degradation of electrical performance. Therefore, a key step in realizing high-performance PbS colloidal quantum dot photodiodes is to replace these long-chain ligands with short-chain ligands while maintaining good surface passivation.

[0005] Currently, the main ligand exchange methods for PbS colloidal quantum dots include liquid-phase ligand exchange and solid-phase ligand exchange. Liquid-phase ligand exchange is a common method, which involves dispersing lead sulfide quantum dots with long-chain ligands in a solution containing short-chain ligands, allowing the short-chain ligands to exchange with the long-chain ligands. However, traditional liquid-phase exchange methods have some problems. First, the metal halides used for the short-chain ligands have extremely poor stability at high temperatures of 125°C, leading to severe runaway dark current. Second, during liquid-phase exchange, the short-chain ligands cannot fully penetrate into the dense layer formed by the long-chain ligands, resulting in incomplete ligand exchange. The remaining long-chain ligands are prone to decomposition at high temperatures, further exacerbating the degradation of device performance.

[0006] Solid-phase ligand exchange is another method, involving ligand exchange reactions on lead sulfide quantum dots under solid-state conditions. Although the solid-phase exchange scheme performs slightly better at 125°C, the exchange efficiency is insufficient due to the steric hindrance effect of the dense oleic acid long-chain layer, and the problem of residual ligand decomposition at high temperatures persists. These issues lead to dark current runaway in PbS colloidal quantum dot photodiode devices at 125°C, failing to meet the requirements of high-performance infrared photodetectors.

[0007] Furthermore, existing ligand exchange methods have other drawbacks. For example, during ligand exchange, the ligand layer on the surface of lead sulfide quantum dots may undergo uneven exchange, leading to the generation of surface defect states. These defect states affect carrier transport efficiency and reduce the optoelectronic performance of the device. Simultaneously, the quantum dot film after ligand exchange is prone to structural changes at high temperatures, further impacting device stability. Therefore, maintaining the stability and good optoelectronic performance of PbS colloidal quantum dots at high temperatures is an important current research direction.

[0008] In summary, existing ligand exchange methods for PbS colloidal quantum dots have significant shortcomings in terms of high-temperature stability. These issues limit the application of PbS colloidal quantum dots in high-performance infrared PbS colloidal quantum dot photodiodes. Summary of the Invention

[0009] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a high-temperature resistant PbS colloidal quantum dot photodiode and its fabrication method. By optimizing the ligand exchange process and device structure, the stability and photoelectric performance of the PbS colloidal quantum dot photodiode under high-temperature environments are significantly improved.

[0010] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode is provided, comprising the following steps: S1. Dissolve the PbS colloidal quantum dot solid with the first ligand on its surface in a first nonpolar solvent to form a first PbS colloidal quantum dot solution; S2. Add n-octylamine to the first PbS colloidal quantum dot solution to form a first mixed solution. After the n-octylamine ligand exchanges with the first ligand, add an antisolvent to form a second mixed solution. S3. Centrifuge the second mixed solution, discard the supernatant, and vacuum dry the precipitate to obtain PbS colloidal quantum dot solids with surface-modified n-octylamine ligands; S4. Dissolve the PbS colloidal quantum dot solid with n-octylamine ligands on its surface in a second nonpolar solvent to form a second PbS colloidal quantum dot solution. S5. Dissolve the thiol ligand in the first polar solvent to form a thiol ligand solution; S6. Prepare a nickel oxide layer on ITO glass, spin-coat a second PbS colloidal quantum dot solution onto the nickel oxide layer to form a PbS colloidal quantum dot coating, spin-coat a thiol ligand solution onto the PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the PbS colloidal quantum dot coating. S7. Place the PbS colloidal quantum dot coating on a heating table and heat it for a period of time, then cool it. S8. Spin-coat the second PbS colloidal quantum dot solution onto the PbS colloidal quantum dot coating to form a new PbS colloidal quantum dot coating. Spin-coat the thiol ligand solution onto the new PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the surface of the new PbS colloidal quantum dot coating. S9. Place the multilayer PbS colloidal quantum dot coatings together on a heating table and heat for a period of time, then cool. S10: Repeat steps S8 and S9 until the PbS colloidal quantum dot coating reaches the set number of layers, then all the PbS colloidal quantum dot coatings together form a PbS colloidal quantum dot film. S11. Fullerene films are prepared on PbS colloidal quantum dot films; S12. Prepare a tin oxide layer on a fullerene film; S13. An ITO layer is formed on the tin oxide layer.

[0011] Preferably, in step S2, the mass concentration of the first PbS colloidal quantum dot solution is 30 mg / mL to 50 mg / mL, the purity of n-octylamine is above 99%, and the volume ratio of the first PbS colloidal quantum dot solution to n-octylamine is 1:1 to 1:3.

[0012] If the concentration of the first PbS colloidal quantum dot solution is below 30 mg / mL, the number of quantum dots per unit volume will be too small, resulting in a sparse dispersion of quantum dots in the solution. This significantly reduces the contact probability between the n-octylamine ligand and the first ligand on the quantum dot surface. In this case, some of the first ligands on the quantum dot surface cannot effectively contact the n-octylamine, leading to incomplete pre-exchange. The remaining first ligands are prone to dissociation under subsequent heating, exposing lead atoms on the quantum dot surface, forming defect states, and inducing nonradiative recombination of charge carriers, ultimately causing an increase in the device's dark current. If the concentration of the first PbS colloidal quantum dot solution is above 50 mg / mL, the intermolecular forces between quantum dots, such as van der Waals forces, will be significantly enhanced, making irreversible aggregation more likely. The aggregated quantum dots form cluster structures, where the surface ligands of the internal quantum dots are encapsulated and cannot contact the n-octylamine ligand, forming exchange dead zones. Simultaneously, the aggregates are prone to precipitate together with unaggregated quantum dots during the centrifugation process in subsequent step S3, resulting in aggregated particles in the final PbS colloidal quantum dot solid with surface-modified n-octylamine ligands. These agglomerated particles are difficult to disperse evenly during the dissolution process in the subsequent step S4, resulting in an uneven PbS colloidal quantum dot coating in the spin coating stages of steps S6 and S8. This causes the PbS colloidal quantum dot coating to be excessively thick in some areas or to have gaps, which not only affects the light absorption efficiency, but also exacerbates the curing of quantum dots at high temperatures due to uneven stress, forming local current channels and causing uncontrolled dark current.

[0013] Therefore, a first PbS colloidal quantum dot solution with a concentration range of 30 mg / mL to 50 mg / mL ensures a moderate quantum dot density in the solution, allowing each quantum dot surface to be fully exposed to the n-octylamine ligand environment. This significantly increases the exchange probability between n-octylamine and the first ligand, minimizing long-chain ligand residue. The 30 mg / mL to 50 mg / mL concentration balances quantum dot dispersion and density, preventing aggregation while ensuring exchange efficiency, laying the foundation for the subsequent preparation of a uniform and dense PbS colloidal quantum dot coating.

[0014] The purity of n-octylamine in PbS colloidal quantum dots (PbS) must be above 99%. High-purity n-octylamine can effectively participate in ligand exchange reactions because it acts as a short-chain ligand, replacing the first ligand on the surface of PbS colloidal quantum dots. If the purity of n-octylamine is insufficient, impurities may interfere with the ligand exchange reaction, reducing exchange efficiency. High-purity n-octylamine ensures sufficient contact with the long-chain ligands on the PbS colloidal quantum dot surface and facilitates the exchange reaction, thereby improving the efficiency and uniformity of ligand exchange. High-purity n-octylamine can also reduce the adsorption of impurities on the PbS colloidal quantum dot surface, preventing impurities from introducing additional defect states. These defect states may lead to nonradiative recombination of charge carriers, increasing dark current and affecting device performance. At high temperatures, impurities may cause ligand bonding instability on the PbS colloidal quantum dot surface, leading to lead atom exposure and the formation of surface defect states. High-purity n-octylamine ensures more stable ligand bonding on the PbS colloidal quantum dot surface at high temperatures, reducing the generation of defect states and thus improving the high-temperature stability of the device. High-purity n-octylamine ensures a uniform and stable ligand layer on the surface of PbS colloidal quantum dots, which helps improve carrier transport efficiency, reduce nonradiative recombination, and thus enhance the optoelectronic performance of the device. If the purity of n-octylamine is insufficient, impurities may cause quantum dots to aggregate in solution. Aggregated quantum dots are difficult to disperse uniformly during subsequent spin coating, forming an uneven PbS colloidal quantum dot coating, which affects device performance. High-purity n-octylamine ensures uniform dispersion of quantum dots in solution, avoiding aggregation.

[0015] A volume ratio of 1:1 to 1:3 provides sufficient n-octylamine molecules for PbS colloidal quantum dots, enabling efficient contact and exchange between n-octylamine and the first ligand on the quantum dot surface, minimizing the residue of long-chain ligands. If the n-octylamine ratio is too low (volume ratio less than 1:1), insufficient n-octylamine molecules will lead to incomplete exchange, and the remaining long-chain ligands will easily dissociate during subsequent heating, exposing lead atoms on the quantum dot surface to form defect states, triggering nonradiative recombination of charge carriers, and ultimately causing an increase in the device's dark current. If the n-octylamine ratio is too high (volume ratio greater than 1:3), although sufficient exchange can be ensured, excessive n-octylamine may remain during subsequent centrifugation and drying, forming impurities, which will interfere with subsequent thiol ligand exchange and the uniformity of the PbS colloidal quantum dot coating. A volume ratio of 1:1 to 1:3 ensures that the quantum dot surface is uniformly covered by n-octylamine, avoiding the situation where some areas still retain long-chain ligands and have high steric hindrance due to insufficient n-octylamine. This allows thiol ligands to more easily penetrate to the quantum dot surface in subsequent steps, further exchange with n-octylamine, form a stable Pb-S covalent bond and a fully covalent bond network, and improve the high-temperature stability of the device.

[0016] Preferably, in step S4, the concentration of the second PbS colloidal quantum dot solution is 30 mg / mL to 50 mg / mL; in step S5, the volume ratio of the liquid thiol ligand to the first polar solvent is 1:80 to 1:100.

[0017] If the concentration of the second PbS colloidal quantum dot solution is below 30 mg / mL, the number of quantum dots per unit volume is too small. During spin coating, the sparse dispersion of quantum dots can easily lead to gaps or insufficient thickness in the PbS colloidal quantum dot coating, resulting in insufficient absorption of infrared light and a significant decrease in the photoelectric response sensitivity of the device. If the concentration is above 50 mg / mL, the intermolecular forces between quantum dots (such as van der Waals forces) are significantly enhanced, making irreversible aggregation more likely. The resulting aggregated particles will cause unevenness on the surface of the PbS colloidal quantum dot coating after spin coating, which not only destroys the uniformity of light absorption but also forms carrier transport traps inside the PbS colloidal quantum dot coating. At high temperatures, these traps will further intensify nonradiative recombination of carriers, leading to an increase in dark current.

[0018] The core function of thiol ligands is to exchange with n-octylamine ligands on the surface of PbS colloidal quantum dot coatings to form stable Pb-S covalent bonds. If the volume ratio is greater than 1:80 (i.e., the thiol ligand is too concentrated), the excess thiol ligands cannot be completely exchanged with n-octylamine, and the residual thiol ligands will form a sticky impurity layer on the surface of the PbS colloidal quantum dot coating. This impurity layer not only hinders the interfacial contact between the subsequent fullerene film and the PbS colloidal quantum dot film, but also decomposes at high temperatures to generate sulfur free radicals, destroying the surface structure of the quantum dots. If the volume ratio is less than 1:100 (i.e., the thiol ligand is too dilute), the insufficient ligand concentration leads to incomplete exchange, and the residual n-octylamine exceeds 5%. At high temperatures (e.g., 125℃), the residual n-octylamine is easily desorbed, exposing lead atoms on the quantum dot surface, forming a large number of defect states, inducing nonradiative recombination of charge carriers, and increasing the dark current by 2 to 3 orders of magnitude compared to the ideal state. The limited volume ratio of 1:80 to 1:100 ensures that the thiol ligand dissolves uniformly in the first polar solvent and can fully exchange with the n-octylamine ligand after spin coating.

[0019] The concentration of the second PbS colloidal quantum dot solution and the volume ratio of thiol ligands to the first polar solvent have a synergistic effect: the former ensures a dense and uniform physical structure of the PbS colloidal quantum dot coating, while the latter ensures sufficient exchange of chemical ligands in the PbS colloidal quantum dot coating. Together, they provide the prerequisite for the subsequent layer-by-layer heating to form a fully covalent network. If only the solution concentration is controlled while the volume ratio of thiol ligands to the first polar solvent is ignored, even if the PbS colloidal quantum dot coating is dense, insufficient ligand exchange will lead to an increase in defect states at high temperatures. If only the ligand ratio is controlled while the solution concentration is inappropriate, the physical defects of the PbS colloidal quantum dot coating will offset the advantages of ligand exchange.

[0020] Preferably, in step S5, the thiol ligand is one or more of 1,3-benzenedithiol and ethylenedithiol.

[0021] The 1,3-phenyldithiol molecule contains two symmetrically distributed thiol groups (-SH) linked by a rigid benzene ring backbone. Compared to commonly used monothiol ligands in existing technologies (such as mercaptoethanol, which has only one -SH group), the dual thiol groups of 1,3-phenyldithiol can react with PbS on the surface of colloidal quantum dots. 2+ The formation of bidentate coordination bonds (Pb-SS-Pb) is much higher than that of monothiol ligands with Pb. 2+ The formed monodentate bond and the rigid structure of the benzene ring restrict the thermal motion of the ligand molecules, preventing ligand desorption from the quantum dot surface at high temperatures (e.g., 125°C). In the subsequent ligand exchange processes S6 and S8, the dithiol group of 1,3-benzenedithiol can efficiently replace the n-octylamine ligand on the PbS colloidal quantum dot surface: on the one hand, the dithiol reacts with Pb... 2+ The multi-site binding reduces the activation energy of ligand exchange, and the exchange efficiency can reach more than 98% (far higher than the less than 80% of single-thiol ligands); on the other hand, the benzene ring skeleton can form a rigid ligand layer on the surface of quantum dots, which prevents the aggregation of quantum dots due to intermolecular forces, keeps the PbS colloidal quantum dot coating uniformly dispersed, and avoids carrier transport traps formed by aggregation.

[0022] The dithiol groups of a 1,3-phenyldithiol molecule not only bind to a single quantum dot, but can also form bridging bonds across quantum dots. That is, the two -SH groups of a 1,3-phenyldithiol molecule bind to the Pb groups on the surfaces of two adjacent PbS colloidal quantum dots, respectively. 2+ This process combines to form a fully covalent network of Pb-S-benzene ring-S-Pb in the multilayer PbS colloidal quantum dot coating. In this fully covalent network structure, the conjugated system of the benzene ring disperses bond energy, reducing the probability of covalent bond breakage by more than 60% even at 125°C, thus preventing the exposure of Pb atoms on the quantum dot surface. Furthermore, the fully covalent network structure encapsulates the quantum dots, suppressing their ripening at high temperatures (i.e., abnormal increase in quantum dot size; ripening is one of the core causes of increased dark current in existing devices).

[0023] Ethylene dithiol molecules have a straight-chain structure, with carbon chain lengths much shorter than those of commonly used long-chain thiol ligands in existing technologies (such as butanethiol, with 4 carbon chains), and even shorter than those of n-octylamine ligands. This short-chain structure results in extremely low steric hindrance, allowing ethylene dithiol molecules to easily penetrate into the dense layer formed by the n-octylamine ligand during the spin-coating ligand exchange process in steps S6 and S8, interacting with the Pb on the quantum dot surface. 2+ Sufficient contact is necessary to avoid exchange dead zones caused by steric hindrance (i.e., areas on the quantum dot surface that are not covered by ligands).

[0024] Preferably, in steps S6 and S8, the area of ​​the PbS colloidal quantum dot coating layer is 6 cm². 2 ~7cm 2 The thickness is 17nm~20nm, and the volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating is 0.3mL~0.5mL.

[0025] The core function of the thiol ligand solution is to exchange with the n-octylamine ligands on the surface of the PbS colloidal quantum dot coating. Its volume must be matched to the area × thickness of the PbS colloidal quantum dot coating: if the volume is less than 0.3 mL, it is difficult to completely cover a 6 cm² area. 2 ~7cm 2 On the surface of the PbS colloidal quantum dot coating, in some areas (such as the edges), insufficient ligand solution leads to inadequate exchange. Residual n-octylamine is easily desorbed at high temperatures, exposing Pb atoms on the quantum dot surface and forming defect states. If the volume is greater than 0.5 mL, the excess solution will overflow the substrate edge during spin coating, which not only wastes ligands but also contaminates the spin coating equipment. Furthermore, the excess ligands are difficult to completely remove by subsequent cleaning with the first polar solvent. Residual thiols decompose at high temperatures to generate sulfur free radicals, which damage the surface structure of the quantum dots.

[0026] Preferably, in step S7, the heating temperature is 50℃~70℃, the heating time is 17min~20min, and the cooling time is 8min~10min; in step S9, the heating temperature is 50℃~70℃, the heating time is 17min~20min, and the cooling time is 8min~10min.

[0027] If the heating temperature is below 50℃, sufficient energy cannot be provided to drive the complete desorption of n-octylamine ligands from the PbS colloidal quantum dot surface: the large proportion of residual n-octylamine, and its competitive adsorption with thiol ligands, will hinder the adsorption of thiols and PbS from the quantum dot surface. 2+ The bonding between Pb and styrene cannot form a stable dithiol bridging structure (Pb-SS-Pb). If the temperature exceeds 70℃, it will trigger the thermal decomposition of the thiol ligands. For example, 1,3-phenyldithiol is prone to thiol cleavage above 80℃, generating phenylthio radicals. These radicals attack the quantum dot surface lattice, causing Pb atoms to detach and form defect states. Simultaneously, the quantum dots are prone to ripening, compromising the density of the PbS colloidal quantum dot coating. Energy above 50℃ can efficiently break the bond between n-octylamine and Pb. 2+ The coordination bonds have a high desorption rate, which frees up binding sites for thiol ligands; on the other hand, temperatures below 70°C can prevent the decomposition of thiols, ensuring that their dithiol groups form stable crosslinks with adjacent quantum dots.

[0028] Heating for 17 to 20 minutes allows for a complete crosslinking reaction. Cooling for 8 to 10 minutes releases the thermal stress of the PbS colloidal quantum dot coating.

[0029] Preferably, in step S11, the thickness of the fullerene film is 10nm-40nm, and the evaporation rate of the thermal evaporation coating is 0.05 Å / s to 0.2 Å / s.

[0030] A thickness range of 10nm~40nm can achieve complete coverage of PbS colloidal quantum dot films (pinhole density less than 2 / cm). 2 At the same time, it takes into account electron transport efficiency: a thickness of 10nm can fill the microscopic protrusion gaps on the PbS surface, and a thickness of 40nm can avoid excessive loss of electron transport path.

[0031] Fullerene molecules can passivate the interface and reduce surface defect states by binding with dangling bonds on the surface of PbS colloidal quantum dots via π electrons. However, if the thickness is less than 10 nm, there are insufficient passivation sites, and the defect state density on the PbS surface remains higher than 3 × 10⁻⁶. 15 cm -2 At high temperatures, nonradiative recombination of charge carriers is easily induced; if the thickness is greater than 40 nm, the difference in the coefficient of thermal expansion between the fullerene film and the PbS film and tin oxide layer (the coefficient of thermal expansion of fullerene is approximately 4 × 10⁻⁶) is significant. -6 / ℃, PbS approximately 7×10⁻⁶ -6 / ℃, tin oxide approximately 5×10 -6 A temperature of 100°C or higher can cause stress accumulation within the film layer (stress value exceeding 150MPa), making the film layer prone to cracking or peeling during high-temperature aging, and device failure can occur within 100 hours.

[0032] If the deposition rate exceeds 0.2 Å / s, the fullerene molecules deposit too quickly on the substrate surface, and the atoms do not have enough time to arrange themselves in an orderly manner, easily forming amorphous or polycrystalline structures. This results in poor film density and a large number of grain boundaries and voids within the film. Electrons are scattered at the grain boundaries during transport, reducing mobility. If the deposition rate is less than 0.05 Å / s, the deposition process takes too long, not only reducing mass production efficiency but also causing water vapor to adsorb onto the film surface due to prolonged exposure. This water vapor disrupts the interfacial bonding between fullerene and PbS, leading to an increased interfacial barrier and hindering electron injection. A limited deposition rate range of 0.05 Å / s to 0.2 Å / s allows for the orderly stacking of fullerene molecules: the lower limit ensures sufficient time for molecules to arrange themselves into a dense single-crystal structure (density reaching 92% to 95%), avoiding disordered molecular stacking.

[0033] Preferably, steps S1 to S14 are all performed in an inert environment.

[0034] The inert gas isolates oxygen, resulting in a low oxidation rate of thiol ligand mercapto groups. This ensures that during ligand exchange, the n-octylamine on the surface of each quantum dot is replaced by thiol with a high efficiency. On the other hand, the inert environment has extremely low water vapor content and a low hydrolysis rate of n-octylamine. After pre-exchange, the surface of the quantum dots is filled with pure n-octylamine ligands without the interference of octanol impurities, thus clearing the way for the full penetration of subsequent thiol ligands.

[0035] Preferably, in step S6, after the thiol ligand exchanges with the n-octylamine ligand on the PbS colloidal quantum dot coating, the PbS colloidal quantum dot coating is washed multiple times with a first polar solvent. In step S8, after the thiol ligands exchange with the n-octylamine ligands on the PbS colloidal quantum dot coating, the PbS colloidal quantum dot coating is washed multiple times with a first polar solvent.

[0036] Preferably, in step S6, a nickel oxide layer is prepared on the ITO glass by magnetron sputtering.

[0037] Preferably, in step S11, a fullerene film is prepared by thermal evaporation coating.

[0038] Preferably, in step S12, an atomic layer deposition method is used to prepare a tin oxide layer on the fullerene film.

[0039] Preferably, in step S13, an ITO layer is formed on the tin oxide layer by magnetron sputtering.

[0040] Preferably, in step S1, the first ligand is selected from one or more of oleic acid and oleylamine, and the first nonpolar solvent is selected from one or more of n-hexane, n-octane, or toluene; In step S2, the antisolvent is one or more of isopropanol, chloroform, and acetone; In step S4, the second nonpolar solvent is selected from one or more of n-hexane, n-octane, and toluene; In step S5, the first polar solvent is one or more of acetonitrile and methanol; In steps S6 and S8, the spin coating parameters are as follows: rotation speed 3000 r / min~4000 r / min, and standing time for both PbS colloidal quantum dot solution and thiol ligand solution 25s~30s. In step S10, the number of PbS colloidal quantum dot coatings is 8 to 10 layers.

[0041] According to another aspect of the present invention, a high-temperature resistant PbS colloidal quantum dot photodiode is also provided, which is prepared by the aforementioned preparation method.

[0042] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1) The method for preparing the high-temperature resistant PbS colloidal quantum dot photodiode of the present invention achieves pre-exchange of ligands on the PbS colloidal quantum dot surface by exchanging ligands between n-octylamine ligand and a first ligand modified on the PbS colloidal quantum dot surface. In this invention, the pre-exchange of the first ligand with n-octylamine ligand, due to the short carbon chain of n-octylamine, effectively reduces the steric hindrance on the PbS colloidal quantum dot surface, making it easier for subsequent thiol ligands to penetrate and exchange, significantly improving the efficiency and uniformity of ligand exchange. Conventional ligand exchange methods directly use thiol ligands (such as mercaptoethanol or butanethiol) to exchange ligands with long-chain ligands (such as oleic acid) on the PbS colloidal quantum dot surface. Because the original long-chain ligands form a dense layer on the quantum dot surface, the steric hindrance effect is significant, making it difficult for thiol ligands to fully penetrate and exchange, resulting in low exchange efficiency.

[0043] (2) The method for preparing the high-temperature resistant PbS colloidal quantum dot photodiode of the present invention firstly achieves ligand exchange between the n-octylamine ligand and the first ligand modified on the surface of the PbS colloidal quantum dots, thus realizing the pre-exchange of ligands on the surface of the PbS colloidal quantum dots. Then, by heating each layer of PbS colloidal quantum dots individually, a more stable fully covalent network structure can be formed between the PbS colloidal quantum dots and the thiol ligands at high temperature. During the process of heating each layer of PbS colloidal quantum dot coating individually, the high temperature provides sufficient energy to make the covalent bond formation between the thiol group and the lead atom more complete and stable. At the same time, the thiol groups between the thiol ligand molecules can also undergo cross-linking reaction to form a three-dimensional fully covalent network.

[0044] Fully covalent networks exhibit higher thermal stability, maintaining structural integrity at high temperatures. This network structure effectively suppresses lead atom exposure and defect state formation on the quantum dot surface, thereby reducing dark current generation. Fully covalent networks also improve the mechanical stability of PbS colloidal quantum dot films, making them less prone to structural collapse or cracking at high temperatures, further enhancing device reliability. Fully covalent networks effectively passivate the quantum dot surface, reducing the number of surface defect states. These defect states are one of the main causes of increased dark current; reducing defect states significantly reduces dark current generation. Fully covalent networks effectively suppress nonradiative recombination of charge carriers, improving carrier transport efficiency and thus enhancing the optoelectronic performance of the device.

[0045] Conventionally, after forming a PbS colloidal quantum dot film with a multilayer PbS colloidal quantum dot coating, the PbS colloidal quantum dot film is heated as a whole. During the heating process, due to incomplete ligand exchange, the remaining long-chain ligands are prone to decomposition at high temperatures, leading to an increase in defect states on the quantum dot surface, an increase in dark current, and a deterioration in device performance.

[0046] 3) The method for preparing the high-temperature resistant PbS colloidal quantum dot photodiode of the present invention involves liquid-phase ligand pre-exchange of PbS colloidal quantum dots, layer-by-layer spin coating, solid-phase ligand exchange, and individual heating of each PbS colloidal quantum dot coating layer. This method enables the thiol ligands on the surface of the PbS colloidal quantum dots to have a more stable structure at high temperatures, effectively suppressing the decomposition of thiol ligands and the ripening of quantum dots at high temperatures, thereby improving the runaway of dark current at high temperatures. Specifically, the present invention forms a solid-phase PbS colloidal quantum dot coating by layer-by-layer spin coating of PbS colloidal quantum dot solution and then coats the solid-phase PbS colloidal quantum dot coating with a thiol ligand solution. The ligand-exchanged PbS colloidal quantum dot coating is then individually heated, ensuring that the ligand exchange in each layer of the PbS colloidal quantum dot coating is more thorough and uniform. This layer-by-layer processing method ensures that the surface of each quantum dot layer is in full contact with the thiol ligands and undergoes an exchange reaction, further enhancing the thermal stability and interface integrity of the ligand layer on the quantum dot surface. Meanwhile, heating each layer of PbS colloidal quantum dot coating individually can promote the formation of a more stable structure between PbS colloidal quantum dots and thiol ligands at high temperatures, effectively inhibiting the decomposition of thiol ligands and the ripening of quantum dots at high temperatures, thereby significantly improving the stability of PbS colloidal quantum dot photodiodes in high-temperature environments.

[0047] 4) The method for preparing the high-temperature resistant PbS colloidal quantum dot photodiode of the present invention utilizes a layer-by-layer spin-coating and heating process to ensure that each layer of the PbS colloidal quantum dot coating possesses excellent photoelectric performance. Optimizing the ligands on the quantum dot surface through layer-by-layer exchange and heating effectively improves the light absorption efficiency and carrier transport efficiency of the PbS colloidal quantum dots. Simultaneously, layer-by-layer heating also promotes the crystallization of the PbS colloidal quantum dots, further enhancing their photoelectric performance. This layer-by-layer optimization method enables the PbS colloidal quantum dot photodiode to maintain good photoelectric performance under high-temperature conditions, improving the overall performance and stability of the device. Attached Figure Description

[0048] Figures 1-4 The current-voltage relationship curve of the PbS colloidal quantum dot photodiode prepared by the preparation method of Example 4 of the present invention after aging at 125°C. Figures 5-6 The current-voltage relationship curve of the PbS colloidal quantum dot photodiode prepared by the preparation method of Example 5 of the present invention after aging at 125°C. Figure 7 The current-voltage relationship curve of the PbS colloidal quantum dot photodiode prepared by the preparation method of Example 6 of the present invention after aging at 125°C; Figures 8-9The current-voltage relationship curve of the PbS colloidal quantum dot photodiode prepared by the preparation method of Comparative Example 1 of the present invention after aging at 125°C. Figure 10 The current-voltage relationship curve of the PbS colloidal quantum dot photodiode prepared by the preparation method of Comparative Example 2 of the present invention after aging at 125°C. Figure 11 The current-voltage relationship curve of the PbS colloidal quantum dot photodiode prepared by the preparation method of Comparative Example 3 of the present invention after aging at 125°C. Figure 12 This is a process flow diagram of the preparation method of the high-temperature resistant PbS colloidal quantum dot photodiode of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0050] Example 1 A method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode includes the following steps: S1. Dissolve the PbS colloidal quantum dot solid with the first ligand on its surface in a first nonpolar solvent to form a first PbS colloidal quantum dot solution; the first ligand is selected from oleic acid, and the first nonpolar solvent is selected from n-hexane.

[0051] S2. Add n-octylamine to the first PbS colloidal quantum dot solution to form a first mixed solution. After the n-octylamine ligand exchanges with the first ligand, add an antisolvent to form a second mixed solution. The mass concentration of the first PbS colloidal quantum dot solution is 42 mg / mL, the purity of n-octylamine is 99%, the antisolvent is isopropanol, and the volume ratio of the first PbS colloidal quantum dot solution to n-octylamine is 1:1.8.

[0052] S3. Centrifuge the second mixed solution, discard the supernatant, and vacuum dry the precipitate to obtain PbS colloidal quantum dot solids with surface-modified n-octylamine ligands.

[0053] S4. Dissolve the PbS colloidal quantum dot solid with n-octylamine ligands on its surface in a second nonpolar solvent to form a second PbS colloidal quantum dot solution; the concentration of the obtained second PbS colloidal quantum dot solution is 30 mg / mL, and the second nonpolar solvent is selected from n-hexane.

[0054] S5. Dissolve the thiol ligand in a first polar solvent to form a thiol ligand solution; the volume ratio of the liquid thiol ligand to the first polar solvent is 1:95, wherein the thiol ligand is 1,3-benzenedithiol (BDT), and the first polar solvent is acetonitrile.

[0055] S6. A nickel oxide layer is formed on ITO glass by magnetron sputtering. A second PbS colloidal quantum dot solution is spin-coated onto the nickel oxide layer to form a PbS colloidal quantum dot coating. A thiol ligand solution is then spin-coated onto the PbS colloidal quantum dot coating, allowing the thiol ligands to exchange with the n-octylamine ligands on the PbS colloidal quantum dot coating. The PbS colloidal quantum dot coating is then repeatedly cleaned using a first polar solvent. The area of ​​one PbS colloidal quantum dot coating layer is 6 cm². 2 The thickness was 17 nm, and the volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating was 0.3 mL. The spin coating parameters were as follows: spin speed 3000 r / min, and the standing time of both the PbS colloidal quantum dot solution and the thiol ligand solution was 26 s.

[0056] S7. Place the PbS colloidal quantum dot coating on a heating table and heat it for a period of time, then cool it down. The heating temperature is 50℃, the heating time is 17min, and the cooling time is 8min.

[0057] S8. Spin-coat the second PbS colloidal quantum dot solution onto the PbS colloidal quantum dot coating to form a new PbS colloidal quantum dot coating. Spin-coat the thiol ligand solution onto the new PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the surface of the new PbS colloidal quantum dot coating. Then, wash the PbS colloidal quantum dot coating multiple times with the first polar solvent. The area, thickness, volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating, and spin-coating parameters of the PbS colloidal quantum dot coating are the same as in step S6. The heating temperature parameters are the same as in step S7.

[0058] S9. Place the multilayer PbS colloidal quantum dot coatings together on a heating table and heat for a period of time, then cool.

[0059] S10: Repeat steps S8 and S9 until the PbS colloidal quantum dot coating reaches the set number of layers. Then all the PbS colloidal quantum dot coatings together form a PbS colloidal quantum dot film; the number of PbS colloidal quantum dot coatings is 8 layers.

[0060] S11. A fullerene film is formed on a PbS colloidal quantum dot film by thermal evaporation deposition; the thickness of the fullerene film is 10 nm, and the evaporation rate of the thermal evaporation deposition is 0.05 Å / s.

[0061] S12. A tin oxide layer is deposited on the fullerene film using atomic layer deposition.

[0062] S13. An ITO layer is formed on the tin oxide layer by magnetron sputtering.

[0063] Example 2 A method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode includes the following steps: S1. Dissolve the PbS colloidal quantum dot solid with the first ligand on its surface in a first nonpolar solvent to form a first PbS colloidal quantum dot solution; the first ligand is selected from oleylamine, and the first nonpolar solvent is selected from n-octane.

[0064] S2. Add n-octylamine to the first PbS colloidal quantum dot solution to form a first mixed solution. After the n-octylamine ligand exchanges with the first ligand, add an antisolvent to form a second mixed solution. The mass concentration of the first PbS colloidal quantum dot solution is 30 mg / mL, the purity of n-octylamine is 99.5%, the antisolvent is chloroform, and the volume ratio of the first PbS colloidal quantum dot solution to n-octylamine is 1:1.

[0065] S3. Centrifuge the second mixed solution, discard the supernatant, and vacuum dry the precipitate to obtain PbS colloidal quantum dot solids with surface-modified n-octylamine ligands.

[0066] S4. Dissolve the PbS colloidal quantum dot solid with n-octylamine ligands on its surface in a second nonpolar solvent to form a second PbS colloidal quantum dot solution; the concentration of the obtained second PbS colloidal quantum dot solution is 45 mg / mL, and the second nonpolar solvent is selected from n-octane.

[0067] S5. Dissolve the thiol ligand in a first polar solvent to form a thiol ligand solution; the volume ratio of the liquid thiol ligand to the first polar solvent is 1:100, wherein the thiol ligand is ethylenedithiol, and the first polar solvent is methanol.

[0068] S6. A nickel oxide layer is formed on ITO glass by magnetron sputtering. A second PbS colloidal quantum dot solution is spin-coated onto the nickel oxide layer to form a PbS colloidal quantum dot coating. A thiol ligand solution is then spin-coated onto the PbS colloidal quantum dot coating to allow the thiol ligands to exchange with the n-octylamine ligands on the PbS colloidal quantum dot coating. The PbS colloidal quantum dot coating is then repeatedly cleaned using a first polar solvent. The area of ​​one PbS colloidal quantum dot coating layer is 7 cm². 2 The thickness was 17 nm, and the volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating was 0.5 mL. The spin coating parameters were as follows: spin speed 4000 r / min, and the standing time of both the PbS colloidal quantum dot solution and the thiol ligand solution was 25 s.

[0069] S7. Place the PbS colloidal quantum dot coating on a heating table and heat it for a period of time, then cool it down. The heating temperature is 65℃, the heating time is 20min, and the cooling time is 10min.

[0070] S8. Spin-coat the second PbS colloidal quantum dot solution onto the PbS colloidal quantum dot coating to form a new PbS colloidal quantum dot coating. Spin-coat the thiol ligand solution onto the new PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the surface of the new PbS colloidal quantum dot coating. Then, wash the PbS colloidal quantum dot coating multiple times with the first polar solvent. The area, thickness, volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating, and spin-coating parameters of the PbS colloidal quantum dot coating are the same as in step S6. The heating temperature parameters are the same as in step S7.

[0071] S9. Place the multilayer PbS colloidal quantum dot coating together on a heating table and heat for a period of time, then cool; the heating parameters are the same as in step S7.

[0072] S10: Repeat steps S8 and S9 until the PbS colloidal quantum dot coating reaches the set number of layers. Then all the PbS colloidal quantum dot coatings together form a PbS colloidal quantum dot film; the number of PbS colloidal quantum dot coatings is 9 layers.

[0073] S11. A fullerene film is formed on a PbS colloidal quantum dot film by thermal evaporation deposition; the thickness of the fullerene film is 30 nm, and the evaporation rate of the thermal evaporation deposition is 0.15 Å / s.

[0074] S12. A tin oxide layer is deposited on the fullerene film using atomic layer deposition.

[0075] S13. An ITO layer is formed on the tin oxide layer by magnetron sputtering.

[0076] Example 3 A method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode includes the following steps: S1. Dissolve the PbS colloidal quantum dot solid with the first ligand on its surface in a first nonpolar solvent to form a first PbS colloidal quantum dot solution; the first ligand is selected from oleic acid, and the first nonpolar solvent is selected from toluene.

[0077] S2. Add n-octylamine to the first PbS colloidal quantum dot solution to form a first mixed solution. After the n-octylamine ligand exchanges with the first ligand, add an antisolvent to form a second mixed solution. The mass concentration of the first PbS colloidal quantum dot solution is 50 mg / mL, the purity of n-octylamine is 99.5%, the antisolvent is acetone, and the volume ratio of the first PbS colloidal quantum dot solution to n-octylamine is 1:3.

[0078] S3. Centrifuge the second mixed solution, discard the supernatant, and vacuum dry the precipitate to obtain PbS colloidal quantum dot solids with surface-modified n-octylamine ligands.

[0079] S4. Dissolve the PbS colloidal quantum dot solid with n-octylamine ligands on its surface in a second nonpolar solvent to form a second PbS colloidal quantum dot solution; the concentration of the obtained second PbS colloidal quantum dot solution is 50 mg / mL, and the second nonpolar solvent is selected from toluene.

[0080] S5. Dissolve the thiol ligand in a first polar solvent to form a thiol ligand solution; the volume ratio of the liquid thiol ligand to the first polar solvent is 1:80, wherein the thiol ligand is ethylenedithiol, and the first polar solvent is methanol.

[0081] S6. A nickel oxide layer is formed on ITO glass by magnetron sputtering. A second PbS colloidal quantum dot solution is spin-coated onto the nickel oxide layer to form a PbS colloidal quantum dot coating. A thiol ligand solution is then spin-coated onto the PbS colloidal quantum dot coating, allowing the thiol ligands to exchange with the n-octylamine ligands on the PbS colloidal quantum dot coating. The PbS colloidal quantum dot coating is then repeatedly cleaned using a first polar solvent. The area of ​​one PbS colloidal quantum dot coating layer is 6.25 cm². 2 The thickness was 20 nm, and the volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating was 0.4 mL. The spin coating parameters were as follows: spin speed 3600 r / min, and standing time for both the PbS colloidal quantum dot solution and the thiol ligand solution was 30 s.

[0082] S7. Place the PbS colloidal quantum dot coating on a heating table and heat it for a period of time, then cool it down. The heating temperature is 70℃, the heating time is 18min, and the cooling time is 9min.

[0083] S8. Spin-coat the second PbS colloidal quantum dot solution onto the PbS colloidal quantum dot coating to form a new PbS colloidal quantum dot coating. Spin-coat the thiol ligand solution onto the new PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the surface of the new PbS colloidal quantum dot coating. Then, wash the PbS colloidal quantum dot coating multiple times with the first polar solvent. The area, thickness, volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating, and spin-coating parameters of the PbS colloidal quantum dot coating are the same as in step S6. The heating temperature parameters are the same as in step S7.

[0084] S9. Place the multilayer PbS colloidal quantum dot coating together on a heating table and heat for a period of time, then cool; the heating parameters are the same as in step S7.

[0085] S10: Repeat steps S8 and S9 until the PbS colloidal quantum dot coating reaches the set number of layers. All the PbS colloidal quantum dot coatings together form a PbS colloidal quantum dot film; the number of PbS colloidal quantum dot coatings is 10 layers.

[0086] S11. A fullerene film is formed on a PbS colloidal quantum dot film by thermal evaporation deposition; the thickness of the fullerene film is 40 nm, and the evaporation rate of the thermal evaporation deposition is 0.2 Å / s.

[0087] S12. A tin oxide layer is deposited on the fullerene film using atomic layer deposition.

[0088] S13. An ITO layer is formed on the tin oxide layer by magnetron sputtering.

[0089] Example 4 This embodiment, as a typical example, describes a method for preparing PbS colloidal quantum dot photodiodes using a method of pre-exchanging oleic acid on the surface of a PbS colloidal quantum dot film with n-octylamine ligand, followed by "1,3-benzenedithiol solid-phase exchange-separate annealing". All steps are performed in an inert environment.

[0090] A method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode includes the following steps: S1. Dissolve the PbS colloidal quantum dot solid with the first ligand on its surface in a first nonpolar solvent to form a first PbS colloidal quantum dot solution; the first ligand is selected from oleic acid, and the first nonpolar solvent is selected from toluene.

[0091] S2. Add n-octylamine to the first PbS colloidal quantum dot solution to form a first mixed solution. After the n-octylamine ligand exchanges with the first ligand, add an antisolvent to form a second mixed solution. The mass concentration of the first PbS colloidal quantum dot solution is 50 mg / mL, the purity of n-octylamine is 99%, the antisolvent is isopropanol, and the volume ratio of the first PbS colloidal quantum dot solution to n-octylamine is 1:1.

[0092] S3. Centrifuge the second mixed solution, discard the supernatant, and vacuum dry the precipitate to obtain PbS colloidal quantum dot solids with surface-modified n-octylamine ligands.

[0093] S4. Dissolve the PbS colloidal quantum dot solid with n-octylamine ligands on its surface in a second nonpolar solvent to form a second PbS colloidal quantum dot solution; the concentration of the obtained second PbS colloidal quantum dot solution is 50 mg / mL, and the second nonpolar solvent is selected from n-octane.

[0094] S5. Dissolve the thiol ligand in a first polar solvent to form a thiol ligand solution; the volume ratio of the liquid thiol ligand to the first polar solvent is 1:100, wherein the thiol ligand is 1,3-benzenedithiol, and the first polar solvent is acetonitrile.

[0095] S6. A nickel oxide layer is formed on ITO glass by magnetron sputtering. A second PbS colloidal quantum dot solution is spin-coated onto the nickel oxide layer to form a PbS colloidal quantum dot coating. A thiol ligand solution is then spin-coated onto the PbS colloidal quantum dot coating, allowing the thiol ligands to exchange with the n-octylamine ligands on the PbS colloidal quantum dot coating. The PbS colloidal quantum dot coating is then repeatedly cleaned using a first polar solvent. The area of ​​one PbS colloidal quantum dot coating layer is 6.25 cm². 2 The thickness was 20 nm, and the volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating was 0.4 mL. The spin coating parameters were as follows: spin speed 4000 r / min, and the standing time of both the PbS colloidal quantum dot solution and the thiol ligand solution was 30 s.

[0096] S7. Place the PbS colloidal quantum dot coating on a heating table and heat it for a period of time, then cool it down. The heating temperature is 50℃, the heating time is 20min, and the cooling time is 10min.

[0097] S8. Spin-coat the second PbS colloidal quantum dot solution onto the PbS colloidal quantum dot coating to form a new PbS colloidal quantum dot coating. Spin-coat the thiol ligand solution onto the new PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the surface of the new PbS colloidal quantum dot coating. Then, wash the PbS colloidal quantum dot coating multiple times with the first polar solvent. The area, thickness, volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating, and spin-coating parameters of the PbS colloidal quantum dot coating are the same as in step S6. The heating parameters are the same as in step S7.

[0098] S9. Place the multilayer PbS colloidal quantum dot coating together on a heating table and heat for a period of time, then cool; the heating parameters are the same as in step S7.

[0099] S10: Repeat steps S8 and S9 until the PbS colloidal quantum dot coating reaches the set number of layers. All the PbS colloidal quantum dot coatings together form a PbS colloidal quantum dot film; the PbS colloidal quantum dot coating has 10 layers.

[0100] S11. A fullerene film is formed on a PbS colloidal quantum dot film by thermal evaporation deposition; the thickness of the fullerene film is 40 nm, and the evaporation rate of the thermal evaporation deposition is 0.2 Å / s.

[0101] S12. A tin oxide layer is deposited on the fullerene film using atomic layer deposition.

[0102] S13. An ITO layer is formed on the tin oxide layer by magnetron sputtering.

[0103] In an inert environment, the high-temperature stability current-voltage test of the PbS colloidal quantum dot photodiode prepared in Example 4 was conducted at 125°C for different durations. Figures 1-4 As shown, the obtained PbS colloidal quantum dot photodiode maintained its stability for 436 hours after aging at 125℃, and after 72 hours, the dark current fluctuation was ≤±15%, and the current-voltage curve remained normal.

[0104] Example 5 To investigate the effect of the concentration of n-octylamine pre-exchange PbS colloidal quantum dots on the dark current of PbS colloidal quantum dot photodiodes, Example 5 was based on Example 4, except that the concentration of the second PbS colloidal quantum dot solution in step S4 was changed to 30 mg / mL, while the other steps remained the same as in Example 4.

[0105] In an inert environment, the high-temperature stability current-voltage test of the PbS colloidal quantum dot photodiode prepared in Example 5 was conducted at 125°C for different durations (the test method was the same as in Example 4). Figure 5 , Figure 6 As shown, the obtained PbS colloidal quantum dot photodiode maintained a normal current-voltage curve shape after aging at 125℃ for 436 hours, demonstrating good stability.

[0106] Example 6 To investigate the effect of heating temperature on the dark current of PbS colloidal quantum dot photodiodes, Example 6 was based on Example 4, and Example 5 was based on Example 4, except that the heating temperature of steps S7 and S9 was changed to 70°C, while the other steps remained the same as in Example 4.

[0107] In an inert environment, the high-temperature stability current-voltage test of the PbS colloidal quantum dot photodiode of Example 6 was conducted at 125°C for different durations (the test method was the same as in Example 4). Figure 7 As shown, the obtained PbS colloidal quantum dot photodiode maintained a normal current-voltage curve shape after aging at 125℃ for 436 hours, demonstrating good stability.

[0108] Comparative Example 1 This comparative example provides a method for preparing PbS colloidal quantum dot photodiodes by pre-exchanging oleic acid on the surface of PbS colloidal quantum dots with n-octylamine, followed by "1,3-benzenedithiol solid-phase exchange-overall annealing". All steps are performed in an inert environment.

[0109] The method for preparing PbS colloidal quantum dot photodiodes includes the following steps: S1~S6: Same as steps S1~S6 in Example 4.

[0110] S7. Spin-coat the second PbS colloidal quantum dot solution onto the PbS colloidal quantum dot coating to form a new PbS colloidal quantum dot coating. Spin-coat the thiol ligand solution onto the new PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the surface of the new PbS colloidal quantum dot coating. Then, wash the PbS colloidal quantum dot coating multiple times with the first polar solvent. The area, thickness, volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating, and spin-coating parameters of the PbS colloidal quantum dot coating are the same as in step S6.

[0111] S8. Repeat step S7 until the PbS colloidal quantum dot coating reaches the set number of layers. Then all the PbS colloidal quantum dot coatings together form a PbS colloidal quantum dot film; the number of PbS colloidal quantum dot coatings is 10 layers.

[0112] S9. Place the multilayer PbS colloidal quantum dot coatings together on a heating table and heat for a period of time, then cool. The heating temperature is 50℃, the heating time is 20min, and the cooling time is 10min.

[0113] S10. A fullerene film is formed on a PbS colloidal quantum dot film by thermal evaporation deposition; the thickness of the fullerene film is 40 nm, and the evaporation rate of the thermal evaporation deposition is 0.2 Å / s.

[0114] S11. A tin oxide layer is deposited on the fullerene film using atomic layer deposition.

[0115] S12. An ITO layer is formed on the tin oxide layer by magnetron sputtering.

[0116] In an inert environment, the high-temperature stability current-voltage test of the PbS colloidal quantum dot photodiode prepared in Comparative Example 1 was conducted at 125°C for different durations (the test method was the same as in Example 4). Figure 8 , Figure 9 As shown, the obtained PbS colloidal quantum dot photodiode has a short maintenance time at 125℃, and the current-voltage curve deteriorates significantly. By 72 hours, the current-voltage curve has been severely degraded.

[0117] Comparative Example 2 This comparative example provides a method for preparing PbS colloidal quantum dot photodiodes using n-octylamine to pre-exchange oleic acid on the surface of PbS colloidal quantum dots, followed by "1,3-benzenedithiol solid-phase exchange-non-annealing". Compared to Comparative Example 1, this comparative example only omits the heating step of the multilayer PbS colloidal quantum dot coating in step S9 of Comparative Example 1.

[0118] In an inert environment, the PbS colloidal quantum dot photodiode of Comparative Example 2 was subjected to high-temperature stability current-voltage tests for different durations at 125°C (the test method was the same as in Example 4). Figure 10 As shown, the dark current curve of the obtained PbS colloidal quantum dot photodiode is severely tilted upwards, and the maintenance time at 125℃ is short. The current-voltage curve deteriorates significantly. After 72 hours, the current-voltage curve has been severely degraded and cannot maintain a good state.

[0119] Comparative Example 3 This comparative example provides a method for preparing PbS colloidal quantum dot photodiodes by pre-exchanging oleic acid on the surface of PbS colloidal quantum dots with mercaptoethanol (ME) followed by "BDT solid-phase exchange-separate annealing". All steps are performed in an inert environment, and the specific steps are as follows: S1. Obtain the first PbS colloidal quantum dot solid coated with oleic acid, and dissolve the PbS colloidal quantum dot solid in the nonpolar solvent toluene to prepare a first PbS colloidal quantum dot solution with a concentration of 50 mg / mL.

[0120] S2. Take 3 mL of the first PbS colloidal quantum dot solution obtained in step S1, place it in a centrifuge tube, add 60 μL of mercaptoethanol (ME), shake, and react for 30 min; then take 5 mL of isopropanol and mix it with the quantum dot solution in the centrifuge tube, let it stand for 10 min, and the first PbS colloidal quantum dots will precipitate from the mixed solution.

[0121] S3. Centrifuge the mixed solution obtained in step S2 at a speed of 4000 r / min for 5 min, discard the supernatant, place the centrifuge tube in a vacuum chamber and evacuate for 30 min to obtain the second PbS colloidal quantum dot solid. At this time, the surface of the second PbS colloidal quantum dot solid is a thiol ligand.

[0122] S4. Dissolve the second PbS colloidal quantum dot solid from step S3 in n-octane solution to prepare a second PbS colloidal quantum dot solution with a concentration of 30 mg / mL; filter the second PbS colloidal quantum dot solution into a clean glass bottle using an organic filter head for later use.

[0123] S5. Dissolve the thiol ligand in a first polar solvent to form a thiol ligand solution; the volume ratio of the liquid thiol ligand to the first polar solvent is 1:100, wherein the thiol ligand is 1,3-benzenedithiol, and the first polar solvent is acetonitrile.

[0124] S6. A nickel oxide layer is formed on ITO glass by magnetron sputtering. A second PbS colloidal quantum dot solution is spin-coated onto the nickel oxide layer to form a PbS colloidal quantum dot coating. A thiol ligand solution is then spin-coated onto the PbS colloidal quantum dot coating, allowing the thiol ligands to exchange with the n-octylamine ligands on the PbS colloidal quantum dot coating. The PbS colloidal quantum dot coating is then repeatedly cleaned using a first polar solvent. The area of ​​one PbS colloidal quantum dot coating layer is 6.25 cm². 2 The thickness was 20 nm, and the volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating was 0.4 mL. The spin coating parameters were as follows: spin speed 4000 r / min, and the standing time of both the PbS colloidal quantum dot solution and the thiol ligand solution was 30 s.

[0125] S7. Place the PbS colloidal quantum dot coating on a heating table and heat it for a period of time, then cool it down. The heating temperature is 50℃, the heating time is 20min, and the cooling time is 10min.

[0126] S8. Spin-coat the second PbS colloidal quantum dot solution onto the PbS colloidal quantum dot coating to form a new PbS colloidal quantum dot coating. Spin-coat the thiol ligand solution onto the new PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the surface of the new PbS colloidal quantum dot coating. Then, wash the PbS colloidal quantum dot coating multiple times with the first polar solvent. The area, thickness, volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating, and spin-coating parameters of the PbS colloidal quantum dot coating are the same as in step S6. The heating temperature parameters are the same as in step S7.

[0127] S9. Place the multilayer PbS colloidal quantum dot coating together on a heating table and heat for a period of time, then cool; the heating parameters are the same as in step S7.

[0128] S10: Repeat steps S8 and S9 until the PbS colloidal quantum dot coating reaches the set number of layers. All the PbS colloidal quantum dot coatings together form a PbS colloidal quantum dot film; the PbS colloidal quantum dot coating has 10 layers.

[0129] S11. A fullerene film is formed on a PbS colloidal quantum dot film by thermal evaporation deposition; the thickness of the fullerene film is 40 nm, and the evaporation rate of the thermal evaporation deposition is 0.2 Å / s.

[0130] S12. A tin oxide layer is deposited on the fullerene film using atomic layer deposition.

[0131] S13. An ITO layer is formed on the tin oxide layer by magnetron sputtering.

[0132] In an inert environment, the PbS colloidal quantum dot photodiode prepared in Comparative Example 3 was subjected to high-temperature stability current-voltage tests for different durations at 125°C (the test method was the same as in Example 4). Figure 11 As shown, the obtained PbS colloidal quantum dot photodiode has a short maintenance time at 125℃, and the current-voltage curve deteriorates significantly. By 72 hours, the current-voltage curve has deteriorated, and the turn-on voltage is delayed.

[0133] By comparing Examples 4-6 with Comparative Examples 1-3, it can be seen that the PbS colloidal quantum dot photodiode prepared by the method of the present invention uses short-chain n-octylamine to pre-replace a portion of oleic acid, reducing the steric hindrance of the quantum dot surface and improving the subsequent thiol solid-phase exchange permeability; then, by triggering the desorption of n-octylamine through layer-by-layer individual annealing, cross-linking between thiol molecules is promoted to form a fully covalent bond network, thereby enabling the PbS colloidal quantum dot photodiode to maintain a stable dark current curve of more than 400 hours at 125°C, which greatly improves the long-term dark current stability.

[0134] Note: The PbS colloidal quantum dot solids with the first ligand surface modified used in the above embodiments and comparative examples can be prepared based on the technology of patent number ZL201611050553.3 entitled "A method for preparing PbS quantum dots".

[0135] Figures 1-11 In the table, 0h, 2h, 16h, 72h, 96h, 120h, 192h, 268h, and 436h represent the aging time of the PbS colloidal quantum dot photodiode; P0, P1, P2, P3, and P4 represent different test points on the surface of the PbS colloidal quantum dot photodiode; dark field and light field represent the test environment, with dark field being a completely dark environment and light field being a standard light environment.

[0136] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode, characterized in that, Includes the following steps: S1. Dissolve the PbS colloidal quantum dot solid with the first ligand on its surface in a first nonpolar solvent to form a first PbS colloidal quantum dot solution; S2. Add n-octylamine to the first PbS colloidal quantum dot solution to form a first mixed solution. After the n-octylamine ligand exchanges with the first ligand, add an antisolvent to form a second mixed solution. S3. Centrifuge the second mixed solution, discard the supernatant, and vacuum dry the precipitate to obtain PbS colloidal quantum dot solids with surface-modified n-octylamine ligands; S4. Dissolve the PbS colloidal quantum dot solid with n-octylamine ligands on its surface in a second nonpolar solvent to form a second PbS colloidal quantum dot solution. S5. Dissolve the thiol ligand in the first polar solvent to form a thiol ligand solution; S6. Prepare a nickel oxide layer on ITO glass, spin-coat a second PbS colloidal quantum dot solution onto the nickel oxide layer to form a PbS colloidal quantum dot coating, spin-coat a thiol ligand solution onto the PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the PbS colloidal quantum dot coating. S7. Place the PbS colloidal quantum dot coating on a heating table and heat it for a period of time, then cool it. S8. Spin-coat the second PbS colloidal quantum dot solution onto the PbS colloidal quantum dot coating to form a new PbS colloidal quantum dot coating. Spin-coat the thiol ligand solution onto the new PbS colloidal quantum dot coating to allow the thiol ligand to exchange with the n-octylamine ligand on the surface of the new PbS colloidal quantum dot coating. S9. Place the multilayer PbS colloidal quantum dot coatings together on a heating table and heat for a period of time, then cool. S10: Repeat steps S8 and S9 until the PbS colloidal quantum dot coating reaches the set number of layers, then all the PbS colloidal quantum dot coatings together form a PbS colloidal quantum dot film. S11. Fullerene films are prepared on PbS colloidal quantum dot films; S12. Prepare a tin oxide layer on a fullerene film; S13. An ITO layer is formed on the tin oxide layer.

2. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S2, the mass concentration of the first PbS colloidal quantum dot solution is 30 mg / mL to 50 mg / mL, the purity of n-octylamine is above 99%, and the volume ratio of the first PbS colloidal quantum dot solution to n-octylamine is 1:1 to 1:

3.

3. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S4, the concentration of the second PbS colloidal quantum dot solution is 30 mg / mL to 50 mg / mL; in step S5, the volume ratio of the liquid thiol ligand to the first polar solvent is 1:80 to 1:

100.

4. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S5, the thiol ligand is one or more of 1,3-benzenedithiol and ethylenedithiol.

5. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S6, the area of ​​the PbS colloidal quantum dot coating layer is 6 cm². 2 ~7cm 2 The thickness is 17nm~20nm, and the volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating is 0.3mL~0.5mL; In step S8, the area of ​​a single PbS colloidal quantum dot coating layer is 6 cm². 2 ~7cm 2 The thickness is 17nm~20nm, and the volume of the thiol ligand solution dropped onto the PbS colloidal quantum dot coating is 0.3mL~0.5mL.

6. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 5, characterized in that, In step S7, the heating temperature is 50℃~70℃, the heating time is 17min~20min, and the cooling time is 8min~10min; In step S9, the heating temperature is 50℃~70℃, the heating time is 17min~20min, and the cooling time is 8min~10min.

7. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S11, the thickness of the fullerene film is 10nm-40nm, and the evaporation rate of the thermal evaporation coating is 0.05 Å / s to 0.2 Å / s.

8. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, Steps S1 to S14 are all performed in an inert environment.

9. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S6, after the thiol ligand exchanges with the n-octylamine ligand on the PbS colloidal quantum dot coating, the PbS colloidal quantum dot coating is washed multiple times with a first polar solvent. In step S8, after the thiol ligands exchange with the n-octylamine ligands on the PbS colloidal quantum dot coating, the PbS colloidal quantum dot coating is washed multiple times with a first polar solvent.

10. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S6, a nickel oxide layer is prepared on the ITO glass by magnetron sputtering.

11. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S11, a fullerene film is prepared by thermal evaporation deposition.

12. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S12, a tin oxide layer is prepared on the fullerene film by atomic layer deposition.

13. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S13, an ITO layer is formed on the tin oxide layer by magnetron sputtering.

14. The method for preparing a high-temperature resistant PbS colloidal quantum dot photodiode according to claim 1, characterized in that, In step S1, the first ligand is selected from one or more of oleic acid and oleylamine, and the first nonpolar solvent is selected from one or more of n-hexane, n-octane, or toluene; In step S2, the antisolvent is one or more of isopropanol, chloroform, and acetone; In step S4, the second nonpolar solvent is selected from one or more of n-hexane, n-octane, and toluene; In step S5, the first polar solvent is one or more of acetonitrile and methanol; In steps S6 and S8, the spin coating parameters are as follows: rotation speed 3000 r / min~4000 r / min, and standing time for both PbS colloidal quantum dot solution and thiol ligand solution 25s~30s. In step S10, the number of PbS colloidal quantum dot coatings is 8 to 10 layers.

15. A high-temperature resistant PbS colloidal quantum dot photodiode, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 14.

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