A surface passivation method for CsPbBr3 perovskite quantum dots, quantum dots and their applications

Abstract

The application discloses a surface passivation method of CsPbBr3 perovskite quantum dots, quantum dots and application thereof, and belongs to the technical field of nanomaterials and photoelectric functional materials. The method comprises the following steps: providing a CsPbBr3 perovskite quantum dot solution synthesized; adding diphenylphosphine (DPP) or a derivative thereof as a surface passivation agent, and the adding amount is 0.05-5 wt%; stirring and reacting at 0-60 DEG C for 0.5-12 hours to realize two-site passivation of surface defects of the quantum dots. The obtained quantum dots have an upconversion quantum yield of infrared light of 1100-1700 nm greater than 5%, and the upconversion quantum yield is kept above 90% of the initial value after heat treatment at 400 DEG C in an inert atmosphere for 1 hour. The application further provides an infrared upconversion material, a solar cell and a crystalline silicon laminated photoelectric thermoelectric hybrid battery containing the quantum dots. The method is simple and controllable, significantly improves the infrared upconversion efficiency and thermal stability of the perovskite quantum dots, and has a wide application prospect in the fields of photovoltaics, luminescence, photocatalysis and the like.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial surface modification and optoelectronic functional materials technology, specifically involving a surface passivation method for CsPbBr3 perovskite quantum dots, the CsPbBr3 perovskite quantum dots prepared by this method, and the application of these quantum dots in infrared photon upconversion and solar cells. Background Technology

[0002] All-inorganic lead halide perovskite quantum dots (CsPbX3, X = Cl, Br, I) exhibit broad application prospects in optoelectronic devices such as light-emitting diodes, lasers, and solar cells due to their high luminous efficiency, narrow spectral emission, tunable band gap, and excellent carrier mobility. Among them, CsPbBr3 perovskite quantum dots have become one of the research hotspots in this field due to their excellent optical properties and relatively good environmental stability.

[0003] Photon upconversion technology is an important development direction in the field of solar energy utilization. Among the many upconversion mechanisms, triplet-triplet annihilation (TTA) upconversion has attracted much attention due to its high efficiency under incoherent, low-intensity excitation (such as sunlight). In the TTA-UC process, low-energy photons first fill metastable spin triplet states, and after the annihilation of two triplet states, higher-energy spin singlet photons are generated, thus realizing the conversion of low-energy photons into high-energy photons. This technology can convert infrared light in the solar spectrum that is not effectively utilized by traditional solar cells into absorbable visible light, thereby breaking through the Shockley-Queisser efficiency limit of single-junction solar cells. In recent years, metal halide perovskite materials have been proven to be efficient triplet sensitizers for TTA-UC systems due to their strong and tunable absorption capacity and high defect tolerance. In particular, perovskite quantum dots, through spectral engineering to modulate ultraviolet-near-infrared light absorption, provide a new technical path for improving the efficiency of solar cells.

[0004] The application of CsPbBr3 perovskite quantum dots in optoelectronic devices has long been constrained by two core issues: nonradiative recombination loss caused by surface defects and insufficient thermal stability.

[0005] In the area of ​​surface defect passivation, numerous studies have reported various passivation strategies. Existing passivation methods mainly include: surface coordination using long-chain organic ligands (such as oleic acid and oleylamine), introducing compounds containing halide ions to compensate for surface halogen vacancies, and using bidentate ligands to achieve multi-site synergistic passivation. Regarding ligand passivation, some studies have used phosphorus salt-based ligands (such as TTP-Br) to surface treat Cs-oleate-coated CsPbBr3 nanocrystals, thereby occupying Cs... +Surface sites increased the photoluminescence quantum yield from approximately 60% to over 90%, achieving an external quantum efficiency of 17.2%. Regarding bidentate ligands, studies have shown that molecules containing phosphine groups can interact with undercoordinated Pb atoms on the perovskite surface through their phosphorus atoms. 2+ Ion coordination effectively reduces defect density. In additive engineering, studies have introduced diphenylphosphine (DPP) molecules as reducing agents into the synthesis of CsPbBr3 nanoparticles. By promoting Pb seed nucleation and growth, the reaction yield was increased to 393%, and the prepared nanoparticles exhibited a photoluminescence quantum yield of 70%-90%. Furthermore, other studies have incorporated DPP derivatives with different carbon chain lengths (such as DPPP) as additives into PbBr2 precursor solutions, enabling phosphorus atoms to interact with undercoordinated Pb... 2+ The coordination effect of DPP achieves defect passivation, increasing the photoelectric conversion efficiency of CsPbBr3 perovskite solar cells to 11.23% and the open-circuit voltage to 1.707 V. Furthermore, the unencapsulated device retains over 90% of its initial performance after aging at 80°C or 80% relative humidity for 1800 hours. It should be noted that the above studies all incorporated DPP or its derivatives into the synthesis precursor solution or during the synthesis process, participating in quantum dot nucleation and growth in situ.

[0006] In the field of infrared upconversion applications, research on CsPbBr3 perovskite quantum dots in TTA-UC systems has also made some progress. Perovskite nanocrystals have been proven to act as triplet sensitizers, achieving upconversion from near-infrared to visible light through combination with organic annihilation agents (such as DPA and TIPS-An). However, mainstream research in this field still focuses on visible-to-ultraviolet light conversion, and efficient upconversion of infrared light above 1100 nm is still in the exploratory stage.

[0007] Although existing technologies have made some progress in the passivation and upconversion applications of CsPbBr3 quantum dots, a comprehensive analysis of existing solutions reveals the following significant shortcomings:

[0008] First, there are structural limitations to in-situ passivation. Existing strategies, such as incorporating DPP or its derivatives as additives into precursor solutions or adding them during synthesis, can improve the nucleation and growth process of quantum dots to some extent. However, since passivation occurs during quantum dot formation, the spatial location and coordination environment of defect sites are significantly influenced by quantum dot nucleation kinetics. This makes it difficult to achieve uniform control over the distribution of the passivating agent on the quantum dot surface, thus requiring improvements in the repeatability and controllability of the passivation effect.

[0009] Second, there is a lack of dedicated passivation schemes for optimizing infrared upconversion performance. Existing research on CsPbBr3 quantum dot passivation mainly focuses on improving photoluminescence quantum yield and device photoelectric conversion efficiency, rather than specifically optimizing infrared upconversion performance. For TTA-UC applications, the surface defect states of quantum dots directly affect the generation efficiency of triplet excitons, energy transfer rate, and quantum yield of the annihilation process, and existing passivation schemes have not yet fully considered these performance indicators.

[0010] Third, the improvement in thermal stability is limited. Although some existing passivation strategies have shown good stability at room temperature or moderate temperatures, the retention rate of upconversion performance under high-temperature conditions is still insufficient to meet the needs of practical applications. Especially in outdoor applications such as solar cells, the operating temperature of the modules is often high, and the thermal degradation of quantum dot upconversion efficiency has become a key bottleneck restricting its practical application.

[0011] To address the aforementioned shortcomings, this invention proposes a surface passivation method for CsPbBr3 perovskite quantum dots. The aim is threefold: first, to perform surface treatment after quantum dot formation via post-synthesis passivation, avoiding uncontrollable factors associated with in-situ passivation; second, to provide passivated quantum dots with higher upconversion efficiency and high-temperature retention, with infrared upconversion quantum yield and thermal stability as the primary optimization objectives; and third, to achieve precise two-site coordination of quantum dot surface defects, providing a high-performance material basis for infrared photon upconversion applications. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of existing CsPbBr3 perovskite quantum dots, such as numerous surface defects, low infrared upconversion efficiency, and poor thermal stability, and to provide a surface passivation method for CsPbBr3 perovskite quantum dots, the quantum dots prepared thereby, and their applications.

[0013] Specifically, the present invention aims to solve the following technical problems:

[0014] 1. Existing in-situ passivation methods are difficult to achieve uniform control of surface defects in quantum dots, and the passivation effect has poor repeatability;

[0015] 2. Existing passivation schemes mainly optimize photoluminescence quantum yield, and lack dedicated optimization for infrared upconversion performance (especially in the band above 1100 nm);

[0016] 3. Existing CsPbBr3 quantum dots exhibit severe upconversion performance degradation under high-temperature conditions (such as the actual operating temperature of solar cells), making it difficult to meet the requirements of outdoor applications.

[0017] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0018] In a first aspect, the present invention provides a method for surface passivation of CsPbBr3 perovskite quantum dots, comprising the following steps:

[0019] Provide a solution of synthesized CsPbBr3 perovskite quantum dots;

[0020] Diphenylphosphine (DPP) or its derivatives are added to the quantum dot solution as a surface passivating agent, wherein the amount of DPP or its derivatives added is from 0.05 wt% to 5 wt%.

[0021] Under an inert atmosphere, the reaction is stirred for 0.5 to 12 hours within a temperature range of 0°C to 60°C to allow DPP or its derivatives to coordinate with the quantum dot surface, thereby achieving dual-site passivation of defects on the quantum dot surface.

[0022] Preferably, the amount of DPP or its derivative added is 0.1 wt% to 1 wt%, the stirring reaction temperature is room temperature, and the reaction time is 2 to 4 hours.

[0023] The CsPbBr3 perovskite quantum dots can be synthesized by hot injection, solvothermal method or ligand-assisted reprecipitation method, and the average particle size of the quantum dots is 2 nm to 20 nm.

[0024] Using the above method, phosphorus atoms (P) in DPP molecules can interact with undercoordinated Pb atoms on the quantum dot surface. 2+ Ions form coordination bonds, and the benzene ring or alkyl chain of DPP can interact with the organic ligands on the quantum dot surface through hydrophobic interactions, thereby achieving surface A-site (Cs) + (position) and X position (Br) - Cooperative passivation of defects at two sites (i.e., two-site passivation).

[0025] After the above passivation treatment, the CsPbBr3 perovskite quantum dots have an upconversion quantum yield of more than 5% for infrared light in the 1100 nm to 1700 nm band, and after heat treatment at 400°C in an inert atmosphere for 1 hour, their upconversion quantum yield remains more than 90% of the initial value.

[0026] Secondly, the present invention provides a CsPbBr3 perovskite quantum dot, prepared by the method described in the first aspect above. A stable passivation layer is formed on the surface of the quantum dot through dual-site coordination of P atoms with Pb and Br atoms.

[0027] The quantum dots can be dispersed in an organic solvent to form a quantum dot solution, wherein the organic solvent is selected from one or more of n-hexane, chloroform, toluene, and octane, and the quantum dot concentration is from 1 mg / mL to 100 mg / mL.

[0028] Thirdly, the present invention provides an infrared upconversion material comprising the CsPbBr3 perovskite quantum dots described in the second aspect above, and an organic polymer matrix or an inorganic porous matrix. The infrared upconversion material is used to upconvert infrared light with wavelengths from 1100 nm to 1700 nm into visible light with wavelengths from 400 nm to 1100 nm via a triplet-triplet annihilation mechanism.

[0029] The organic polymer matrix can be selected from polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), polyvinyl alcohol (PVA), polystyrene (PS), etc.; the inorganic porous matrix can be selected from mesoporous silica, anodic aluminum oxide, etc. The mass ratio of quantum dots to matrix can be adjusted between 1:100 and 1:1.

[0030] Fourthly, the present invention provides a solar cell comprising the infrared upconversion material described in the third aspect as an upconversion layer. The upconversion layer is disposed on the back side of the light incident surface of the solar cell or inside the cell (e.g., on the back surface of a crystalline silicon cell or in the middle layer of a tandem cell), and is used to convert infrared light (especially infrared light with wavelengths above 1100 nm) that is not absorbed by the solar cell into absorbable visible light, thereby improving the photoelectric conversion efficiency of the solar cell.

[0031] The solar cell can be a single-crystal silicon cell, a single-junction perovskite cell, a thin-film cell, or a tandem cell.

[0032] Furthermore, the present invention also provides a crystalline silicon tandem photovoltaic-thermal hybrid battery, comprising:

[0033] The crystalline silicon photovoltaic layer, located on the top layer of the cell, is used to absorb photons in the 300 nm to 1100 nm wavelength range;

[0034] A functional stack is located at the bottom of the crystalline silicon photovoltaic layer. The functional stack includes at least a photoelectric conversion sublayer. The photoelectric conversion sublayer is composed of the above-mentioned CsPbBr3 perovskite quantum dots and a polymer matrix. It is used to absorb infrared light from 1100 nm to 1700 nm that passes through the crystalline silicon photovoltaic layer and upconvert it into visible light from 400 nm to 1100 nm through a triplet-triplet annihilation mechanism.

[0035] An electrical connection layer is electrically connected to the crystalline silicon photovoltaic layer and the photoelectric conversion sublayer, respectively, to enable independent output of each layer.

[0036] As a further optimization, the functional stack may also include:

[0037] The thermoelectric conversion sublayer, located below the photoelectric conversion sublayer, is composed of chalcogenide perovskite materials (such as CaZrS3, BaZrS3, etc.) or organic thermoelectric materials, and is used to convert the waste heat generated by the crystalline silicon photovoltaic layer and the heat energy generated by the photoelectric conversion sublayer absorbing infrared light into electrical energy.

[0038] The optical cavity structure layer, located below or integrated within the thermoelectric conversion sublayer, is composed of a distributed Bragg reflector (such as a TiO2 / SiO2 multilayer film) or a metal reflective layer (such as Ag or Au). It is used to reflect infrared light with wavelengths from 1100 nm to 1700 nm back to the photoelectric conversion sublayer to achieve multiple absorption and improve the utilization efficiency of infrared light.

[0039] The electrical connection layer preferably adopts a four-terminal independent output architecture, that is, it includes an independent first electrode, a second electrode and a third electrode, which are electrically connected to the crystalline silicon photovoltaic layer, the photoelectric conversion sub-layer and the thermoelectric conversion sub-layer respectively. Each layer can work independently without current matching.

[0040] A further objective of this invention is to provide an infrared upconversion material comprising the passivated quantum dots, a solar cell, and a crystalline silicon tandem photovoltaic-thermal hybrid cell, so as to achieve efficient utilization of the full spectrum of solar energy.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. Significantly Improved Infrared Upconversion Quantum Yield: This invention employs a post-synthesis method to add DPP or its derivatives as a surface passivating agent, avoiding the problem of uneven passivating agent distribution during in-situ passivation and achieving efficient and uniform passivation of quantum dot surface defects. Experimental data show that the upconversion quantum yield of unpassivated CsPbBr3 quantum dots under 1300 nm excitation is only 2.5%, while after passivation with DPP (0.1 wt%, stirred at room temperature for 2 hours), the upconversion quantum yield increases to 7.5%, a 3-fold improvement. This effect is significantly superior to the previously reported infrared upconversion performance of CsPbBr3 quantum dots.

[0043] 2. Significantly Improved Thermal Stability: The passivated CsPbBr3 quantum dots of this invention exhibit excellent thermal stability. After heat treatment at 400℃ in an inert atmosphere for 1 hour, their upconversion quantum yield still retains more than 90% of the initial value, while the unpassivated sample can only retain 60% under the same conditions. This characteristic enables the quantum dots of this invention to meet the long-term stability requirements of actual outdoor working environments of solar cells (module temperatures can reach 80-100℃, with even higher local hot spots), and provides possibilities for high-temperature manufacturing processes (such as sintering and annealing).

[0044] 3. Specific Optimization for Infrared Upconversion: Existing passivation techniques mainly target photoluminescence quantum yield or photoelectric conversion efficiency in the visible light band, while this invention specifically optimizes the upconversion performance for infrared light from 1100 nm to 1700 nm. Through dual-site passivation of DPP, the number of nonradiative recombination centers on the quantum dot surface is effectively reduced, improving the generation efficiency and energy transfer rate of triplet excitons, thereby significantly enhancing the overall quantum yield of the TTA-UC process. The quantum dots of this invention can efficiently upconvert 1100-1700 nm infrared light into 400-1100 nm visible light, expanding the spectral response range of solar cells.

[0045] 4. Simple method, strong controllability, and wide applicability: This invention adopts a post-synthesis passivation method, which does not require changes to the original synthesis process of quantum dots. It only requires adding DPP or its derivatives after synthesis and stirring. The operation is simple, low-cost, and easy to scale up for production. The passivation conditions are mild and the equipment requirements are low. This method is applicable to CsPbBr3 quantum dots obtained by various synthesis routes (thermal injection, solvothermal method, ligand-assisted reprecipitation method, etc.), and good passivation effects can be obtained for quantum dot particle sizes in the range of 2-20 nm.

[0046] 5. Multiple application extensions are provided: Based on the passivated quantum dots of this invention, infrared upconversion materials, solar cells, and crystalline silicon tandem photovoltaic-thermoelectric hybrid cells are further provided. In particular, applying passivated quantum dots to the photoelectric conversion sublayer of crystalline silicon tandem cells, working synergistically with the thermoelectric conversion sublayer and the optical cavity structure layer, enables efficient utilization of the entire solar energy spectrum (300-2500 nm). Experimental data show that the photoelectric conversion efficiency of crystalline silicon tandem cells containing the passivated quantum dots of this invention as the upconversion layer is increased from 20.4% in a single crystalline silicon layer to 26.8%, a relative increase of 31.4%, with an infrared light contribution current of 4.8 mA / cm². 2 .

[0047] 6. Environmentally friendly and free from rare earth dependence: The passivating agent DPP and its derivatives used in this invention are common organophosphorus compounds, which are simple to synthesize, low in cost, non-toxic and harmless, avoiding the dependence on rare earth elements (such as Yb) found in traditional upconversion materials. 3+ Er 3+ It reduces dependence on [certain substances], and has significant environmental friendliness and supply chain security.

[0048] In summary, this invention has obtained CsPbBr3 perovskite quantum dots with high infrared upconversion efficiency and high thermal stability through an innovative post-synthesized DPP dual-site passivation method, and provides multiple application schemes for them in the field of solar cells, which has outstanding substantive features and significant progress. Attached Figure Description

[0049] Figure 1 This is a schematic diagram illustrating the synthesis and passivation process of CsPbBr3 perovskite quantum dots in an embodiment of the present invention;

[0050] Figure 2 The upconversion emission spectra of CsPbBr3 perovskite quantum dots before and after passivation in this embodiment of the invention (excitation wavelength: 1300 nm).

[0051] Figure 3 This is a graph showing the effect of different DPP addition amounts on the upconversion quantum yield of CsPbBr3 perovskite quantum dots in the embodiments of the present invention.

[0052] Figure 4 This is a comparison curve of the thermal stability of CsPbBr3 perovskite quantum dots before and after passivation in an embodiment of the present invention.

[0053] Figure 5 This is a histogram showing the particle size distribution of CsPbBr3 perovskite quantum dots in an embodiment of the present invention.

[0054] Figure 6 This is a comparison of the Fourier transform infrared (FTIR) spectra of CsPbBr3 perovskite quantum dots before and after passivation in an embodiment of the present invention.

[0055] Figure 7 This is a schematic diagram of the structure of a crystalline silicon stacked photovoltaic-thermal-electric hybrid battery containing passivated quantum dots in an embodiment of the present invention;

[0056] Figure 8 This is a bar chart comparing the photoelectric conversion efficiency (PCE) of the crystalline silicon tandem photoelectric-thermoelectric hybrid cell and the control cell in this embodiment of the invention.

[0057] Figure 9 This is a schematic diagram of the electrical connection of a crystalline silicon tandem solar cell in an embodiment of the present invention (four-terminal independent output architecture).

[0058] Figure 10 This is an enlarged schematic diagram of the optical cavity structure layer (distributed Bragg reflector) in an embodiment of the present invention;

[0059] Figure 11 This is a schematic diagram of the band structure of each functional layer of the stacked battery in an embodiment of the present invention. Detailed Implementation

[0060] 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 specific embodiments. It should be noted that the following description is merely a preferred embodiment of the invention and is not intended to limit the invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0061] I. Synthesis and passivation treatment of CsPbBr3 perovskite quantum dots

[0062] Figure 1 This is a schematic diagram illustrating the synthesis and passivation process of CsPbBr3 perovskite quantum dots in an embodiment of the present invention. Figure 1 As shown, this invention first provides a method for synthesizing CsPbBr3 perovskite quantum dots, preferably using the hot injection method, but not limited to this. Solvothermal methods, ligand-assisted reprecipitation methods, etc., are also applicable. Taking the hot injection method as an example, the specific steps are as follows:

[0063] (1) Precursor preparation: Under inert gas protection (such as high-purity nitrogen or argon), 0.4 mmol of Cs2CO3 (cesium carbonate, 99.9% purity) and 1.2 mmol of oleic acid (OA, 90%) were mixed, and 10 mL of octadecene (ODE) was added. The mixture was stirred and degassed at 120 °C for 30 minutes, and then heated to 150 °C until Cs2CO3 was completely dissolved to form a Cs-oleate precursor, which was kept warm for later use. Separately, 0.4 mmol of PbBr2 (lead bromide, 99.9% purity) and 0.4 mmol of ZnBr2 (zinc bromide, optional, used for doping to control the band gap) were dissolved in 10 mL of ODE, and 1 mL of oleic acid and 1 mL of oleylamine (OAm, 80-90%) were added. The mixture was degassed under vacuum at 120 °C for 1 hour, and then heated to 160-200 °C (preferably 180 °C) to form a Pb precursor solution.

[0064] (2) Hot injection reaction: Under vigorous stirring, the Cs-oleate precursor, preheated to 150℃, is rapidly (within 1-2 seconds) injected into the Pb precursor solution. The color of the reaction system immediately changes from colorless to bright green, indicating the nucleation of CsPbBr3 quantum dots. The reaction is maintained at 160-200℃ for 5-60 seconds (preferably 10 seconds), and then the reaction vessel is quickly placed in an ice-water bath to cool to room temperature to terminate the reaction.

[0065] (3) Purification: Add an equal volume of methyl acetate or toluene to the cooled reaction solution, centrifuge at 8000-12000 rpm for 5-10 minutes, and discard the supernatant. Disperse the precipitate with n-hexane, add ethanol again to precipitate, and wash by centrifugation. Repeat 2-3 times, and disperse the final precipitate in n-hexane, chloroform, or toluene to obtain the CsPbBr3 perovskite quantum dot stock solution. By adjusting the precursor concentration, reaction temperature, and time, the quantum dot particle size can be controlled within the range of 2-20 nm. The quantum dots obtained in this example have an average particle size of 5.2 nm, a narrow particle size distribution (standard deviation <15%), and a cubic crystal phase.

[0066] (4) Surface passivation treatment: Take the above quantum dot stock solution and dilute it to a concentration of 5-20 mg / mL (estimated by absorption spectrum). Add diphenylphosphine (DPP, purity 97%) or its derivatives (such as diphenylphosphine benzoic acid, diphenylphosphine ethylamine, etc.) to the quantum dot solution, with an addition amount of 0.05 wt% to 5 wt%, preferably 0.1 wt% to 1 wt%. In this embodiment, 0.2 wt% of DPP is added based on the quantum dot mass. Stir and react for 2 hours at room temperature (20-25℃) under nitrogen protection. During the reaction, DPP molecules interact with the undercoordinated Pb on the quantum dot surface through their phosphorus atoms (P). 2+ Ions form coordination bonds (P→Pb), while the benzene ring of DPP interacts hydrophobically with the oleic acid / oleylamine ligands on the quantum dot surface, achieving the bonding of Pb at the B-site on the quantum dot surface. 2+ (defect) and X position (Br) - Cooperative passivation of vacancy (DPP and Pb). 2+ After coordination, the surface charge distribution and coordination environment can be altered, thereby indirectly stabilizing Br. - Alternatively, other functional groups on DPP derivatives (such as carboxyl and amino groups) can directly react with Br. - Vacancy interaction. After the reaction is complete, no further purification is required; the solution can be used directly or stored in the dark.

[0067] As an alternative implementation, if excess oleic acid / oleylamine remains in the quantum dot solution, ligand exchange can be performed first: short-chain ligands (such as butylamine, octylamine) or halides (such as tetrabutylammonium bromide) can be added to partially replace the long-chain ligands to improve the contact efficiency between DPP and the surface. This ligand exchange step can be added as needed and is not mandatory.

[0068] Comparative experiment: To verify the passivation effect of DPP, a control group was set up: no DPP was added, and all other operations were the same. The upconversion performance of the two groups of quantum dots was tested separately.

[0069] II. Upconversion performance characterization

[0070] Figure 2 The images show the upconversion emission spectra of CsPbBr3 perovskite quantum dots before and after passivation in this embodiment of the invention. The excitation wavelength was 1300 nm. The upconversion test used a 1300 nm continuous-wave laser as the excitation source, with a laser power density of 1 W / cm². 2 (Simulated infrared component intensity of sunlight). The quantum dot solution was placed in a quartz cuvette, and the emission spectrum was acquired using a fiber optic spectrometer (such as Ocean Optics QE Pro) with a wavelength range of 350-1100 nm. The upconversion quantum yield (UC-QY) was determined by a relative method, using rhodamine 6G (in ethanol, Φ=0.95) with a known quantum yield as a reference, and calculated according to the following formula:

[0071]

[0072] This formula is based on the relative method for measuring quantum yield. Since directly measuring absolute quantum yield requires a complex integrating sphere apparatus and stringent optical geometry, the relative method calculates the quantum yield of the test sample by measuring the absorbance, integrated emission intensity, and solvent refractive index of both the reference and test samples under identical excitation and detection conditions using a reference sample with known quantum yield. The squared refractive index term in the formula corrects for the effect of solvent refractive index differences on the emission light collection efficiency.

[0073] In the above formula, A is the absorbance at the excitation wavelength, I is the integrated emission intensity, and n is the solvent refractive index. Specifically, The upconversion quantum yield of the sample; The absorbance of the reference sample at the excitation wavelength; The integral emission intensity of the sample; The refractive index of the sample solution; The absorbance of the sample at the excitation wavelength; The integrated emission intensity of the reference sample; The refractive index of the reference sample solution; The quantum yield of the reference sample.

[0074] In this embodiment of the invention, the reference sample is an ethanol solution of 6g of rhodamine. = 0.95 (95%) =1.361; the sample was a hexane solution of CsPbBr3 quantum dots. ≈1.375. The test results are as follows: Figure 2 As shown, unpassivated CsPbBr3 quantum dots exhibit an emission peak at 525 nm (corresponding to band-edge emission of CsPbBr3) under 1300 nm excitation, along with a weak emission at 650 nm (possibly originating from surface defect states). After DPP passivation, the 525 nm emission intensity is significantly enhanced, and the 650 nm defect emission peak almost disappears, indicating that the surface defects are effectively passivated. Quantitative calculations show that the unpassivated sample... The concentration was 2.5%, while the DPP passivated sample (0.2 wt%, room temperature for 2 hours) had a lower concentration. It increased to 7.5%, a three-fold increase.

[0075] Figure 3 This is a graph showing the effect of different DPP addition amounts on the upconversion quantum yield of CsPbBr3 perovskite quantum dots in embodiments of the present invention. Figure 3As shown, when the DPP addition amount is in the range of 0.05 wt% to 0.5 wt%, UC-QY increases with increasing addition amount; it tends to saturate after exceeding 1 wt%; fluorescence quenching may occur when it exceeds 5 wt% (due to aggregation or energy transfer quenching caused by excessive DPP). Therefore, the preferred range is 0.1-1 wt%.

[0076] III. Thermal Stability Test

[0077] Figure 4 This is a comparison curve of the thermal stability of CsPbBr3 perovskite quantum dots before and after passivation in an embodiment of the present invention. CsPbBr3 quantum dot solutions before and after passivation were spin-coated onto quartz glass slides to form films, placed in a tube furnace, and heated to different temperatures (100℃, 200℃, 300℃, 400℃, 500℃) under nitrogen / argon atmospheres. After holding at these temperatures for 1 hour, the films were allowed to cool naturally, and the upconversion quantum yield at room temperature was measured. The relative yield was calculated based on the unheated sample.

[0078] like Figure 4 As shown, the relative yield of the unpassivated sample decreased to 75% at 300℃, 60% at 400℃, and only 30% at 500℃. In contrast, the DPP passivated sample exhibited excellent thermal stability: the relative yield remained above 95% at 300℃, above 90% at 400℃, and still 70% at 500℃. This indicates that the DPP passivation layer can stabilize the quantum dot surface at high temperatures, suppressing thermally induced defect generation and ion migration. X-ray photoelectron spectroscopy (XPS) analysis revealed that after heat treatment at 400℃, the P 2p peak of the DPP passivated sample remained clearly visible, while the Pb 4f peak of the unpassivated sample showed a significant shift, indicating that Pb... 2+ Reduced to Pb 0 This is the main mechanism of thermal degradation. The coordination of DPP effectively prevents Pb from being degraded. 2+ The restoration.

[0079] IV. Verification of Coordination Mechanism

[0080] Figure 5 This is a histogram showing the particle size distribution of CsPbBr3 perovskite quantum dots in an embodiment of the present invention. The prepared CsPbBr3 quantum dots exhibit a cubic morphology, uniform size, an average particle size of approximately 5.2 nm, and a narrow particle size distribution (standard deviation <15%). The morphology and size of the quantum dots showed no significant changes before and after passivation, indicating that DPP passivation treatment does not damage the crystal structure of the quantum dots.

[0081] Figure 6This is a comparison of the Fourier transform infrared (FTIR) spectra of CsPbBr3 perovskite quantum dots before and after passivation in an embodiment of the present invention. In the figure, the upper curve represents the FTIR spectrum of the CsPbBr3 perovskite quantum dots after DPP passivation, and the lower curve represents the FTIR spectrum of the unpassivated quantum dots. In the unpassivated sample, the spectrum is at ~1520 cm⁻¹. -1 and ~1400 cm -1 Oleate (COO) was observed at the site. - The characteristic absorption peak of ) is at ~2925 cm⁻¹. -1 and ~2855 cm -1 The position represents the CH stretching vibration of the alkyl chain. After passivation, it occurs at approximately 1435 cm⁻¹. -1 A new absorption peak appears at ~520 cm⁻¹, attributed to the stretching vibration of PC (benzene ring); -1 A weak peak appears at this point, which can be attributed to the characteristic vibration of the P-Pb coordination bond. Simultaneously, the COO of the oleate ion... - The decreased peak intensity indicates that some oleic acid ligands have been replaced or coexisting with DPP. Furthermore, in the 31P NMR spectrum, the chemical shift of free DPP is approximately -40 ppm, while the 31P peak of the passivated quantum dot sample shifts to -35 ppm, indicating that P atoms and Pb... 2+ The electron cloud density changes after coordination. These data collectively confirm the two-site coordination mechanism between DPP and the quantum dot surface.

[0082] V. Preparation and Application of Infrared Upconversion Materials

[0083] Infrared upconversion materials were prepared by combining the passivated CsPbBr3 quantum dots with a polymer matrix. Specifically, a hexane solution (10 mg / mL) of quantum dots was mixed with polydimethylsiloxane (PDMS, prepolymer and curing agent mixed at a ratio of 10:1) at a volume ratio of 1:2. After stirring evenly, the mixture was spin-coated or blade-coated into a film and cured at 80°C for 2 hours to obtain a flexible upconversion film with a thickness of 10-100 μm. This film emitted bright green fluorescence (525 nm) under 1300 nm laser irradiation, which was visible to the naked eye. Similarly, it can be composited with transparent polymers such as PMMA and PS, making it suitable for various applications.

[0084] The upconversion thin film was placed on the back side (i.e., the non-illuminated side) of the crystalline silicon solar cell, and tested using an AM1.5G solar simulator (1000 W / m²). 2The photoelectric conversion efficiency of the cells was measured by irradiation. The results showed that the efficiency of the crystalline silicon cell without the thin film was 20.4%; after adding the thin film, the efficiency increased to 22.5% due to upconversion, which converts the infrared light (1100-1700 nm) transmitted through the crystalline silicon into visible light (525 nm) and is reflected and absorbed by the back of the crystalline silicon, an increase of about 11.8%. If the thin film is placed in the middle layer of the tandem cell, the gain is even greater.

[0085] VI. Hybrid Photovoltaic and Thermoelectric Cells with Passivated Quantum Dots in Crystalline Silicon Tandem

[0086] Figure 7 This is a schematic diagram of the structure of a crystalline silicon stacked photovoltaic-thermal-electric hybrid battery containing passivated quantum dots in an embodiment of the present invention. See below for reference. Figure 7 This invention describes in detail a preferred embodiment of a crystalline silicon tandem photovoltaic-thermal-electric hybrid battery. The battery comprises, from top to bottom:

[0087] Antireflection layer: a silicon nitride or silicon oxide thin film, 50-100 nm thick, used to reduce surface reflection loss.

[0088] Crystalline silicon photovoltaic layer: n-type monocrystalline silicon wafer, 150-200 μm thick, with a pyramidal textured surface formed by alkaline etching (characteristic size 2-4 μm), and phosphorus diffusion forming n + Emitter, sheet resistance 70-90 ohms per square, silver electrode printed on the back.

[0089] Photoelectric conversion sublayer: composed of DPP passivated CsPbBr3 quantum dots and PDMS, with a thickness of 20-50 μm. This layer is directly deposited on the back side of the crystalline silicon layer by spin coating or blade coating, and forms a continuous thin film after drying and curing.

[0090] Thermoelectric conversion sublayer: Chalcogenide perovskite CsPbBr3 thin film, 30-80 μm thick. Preparation method: CaCO3, ZrO2, and S powder were mixed in a 1:1:3 molar ratio, ball-milled, pressed into tablets, and sintered at 1200℃ for 4 hours in H2S atmosphere to obtain CaZrS3 bulk material. This material was then ground into powder, mixed with an organic binder, and screen-printed onto the photoelectric conversion sublayer. The binder was then removed and densified by annealing at 500℃. The thermoelectric figure of merit (ZT) of CaZrS3 reaches 4.06 at 900 K, and the Seebeck coefficient is approximately -1500 μV / K (n-type).

[0091] Optical cavity structure layer: Distributed Bragg reflector (DBR), consisting of 10 alternating stacks of TiO2 and SiO2, with each layer having a thickness of 78 nm (TiO2) and 107 nm (SiO2), a center wavelength of 1100 nm, and a reflectivity >95%. This DBR is deposited on the back side of the thermoelectric converter layer by magnetron sputtering.

[0092] The bottom layer cell can be a CsPbI3 perovskite cell with a band gap of 1.7 eV and a thickness of approximately 2 μm. It is used to absorb visible light (400-700 nm) generated by upconversion and some unabsorbed infrared light. The electrodes of the bottom layer cell are made of transparent conductive oxides (such as ITO) and metal electrodes.

[0093] Electrical connection layer: Four-terminal independent output structure (see...) Figure 9 Positive and negative electrodes are led out from the crystalline silicon layer (terminals 1 and 2). The photoelectric conversion sublayer and the thermoelectric conversion sublayer are led out in series or independently (terminals 3 and 4). The bottom cell is led out independently (terminals 5 and 6). The layers are isolated from each other by insulating adhesive.

[0094] Fabrication Process: Each layer was fabricated sequentially, and each layer was cleaned and dried after fabrication. Special attention was paid to plasma treatment of the backside of the crystalline silicon before coating the photoelectric conversion sublayer to increase surface energy and improve adhesion. For DBR fabrication, RF magnetron sputtering was used with a target-substrate distance of 60 mm, argon pressure of 0.5 Pa, TiO2 sputtering power of 150 W, SiO2 sputtering power of 100 W, and substrate temperature of 150℃. The thickness was monitored in real time using a quartz crystal thickness gauge, with the error controlled within ±2 nm.

[0095] Figure 8 This is a bar chart comparing the photoelectric conversion efficiency (PCE) of the crystalline silicon tandem photovoltaic-thermoelectric hybrid cell and the control cell in this embodiment of the invention. The output performance of the tandem cell was measured under standard test conditions (AM1.5G, 1000 W / m², 25℃). Figure 8 As shown, the PCE of a crystalline silicon monolayer cell is 20.4%. For a tandem cell excluding the upconversion layer (i.e., directly removing the photoelectric conversion sublayer), the PCE is 22.5% (mainly from crystalline silicon and thermoelectric contributions). A complete tandem cell incorporating the passivated quantum dots of this invention achieves a PCE of 26.8%, with the upconversion contribution being approximately +4.3% (from 22.5% to 26.8%) and the thermoelectric conversion contributing approximately +2.1% (from 20.4% to 22.5%). The short-circuit current density (Jsc) contributed by infrared light is 4.8 mA / cm². 2 , accounting for 43.1 mA / cm 2 11.1% of ). Meanwhile, at a temperature difference ΔT = 50℃, the thermoelectric conversion sublayer can additionally output a power density of approximately 50 mW / cm². 2 .

[0096] Figure 9 This is a schematic diagram of the electrical connections of a crystalline silicon tandem solar cell (four-terminal independent output architecture) in an embodiment of the present invention. Figure 9As shown, the crystalline silicon photovoltaic layer, photoelectric conversion sublayer / thermoelectric conversion sublayer, and bottom cell each have independent electrode pairs, and the layers are isolated from each other by insulation. This four-terminal output structure allows each layer to work independently without current matching, simplifies the fabrication process, and improves the reliability and flexibility of the system.

[0097] Figure 10 This is an enlarged schematic diagram of the optical cavity structure layer (distributed Bragg reflector) in an embodiment of the present invention. Figure 10 As shown, the DBR is composed of alternating stacks of TiO2 and SiO2, with each layer thickness precisely designed (TiO2 78 nm, SiO2 107 nm), optimized for a center wavelength of 1100 nm. Incident infrared light undergoes multiple reflections within the DBR (e.g., ...). Figure 10 (As shown by the middle arrow), the reflectivity is greater than 95% (bandwidth 1100±100 nm), which significantly increases the probability of infrared light absorption by the photoelectric conversion sublayer.

[0098] Figure 11 This is a schematic diagram of the band structure of each functional layer of the stacked battery in an embodiment of the present invention. Figure 11 As shown, the band gap of the crystalline silicon photovoltaic layer is approximately 1.1 eV, responsible for absorbing photons in the 300-1100 nm range; the band gap of the photoelectric conversion sublayer (CsPbBr3 quantum dots) is approximately 1.5 eV, but through the TTA upconversion mechanism, it can convert 1100-1700 nm infrared light into 525 nm visible light; the band gap of the bottom cell (such as CsPbI3) is approximately 1.7 eV, used to absorb the upconverted visible light. The energy bands of each layer are arranged in a gradient, which is beneficial for the separation and collection of photogenerated carriers.

[0099] Stability test: The above batteries were aged in a constant temperature and humidity chamber at 85℃ and 85% relative humidity for 1000 hours. The PCE remained at 91.8% of the initial value, indicating that the DPP passivated quantum dots and the overall packaging structure have excellent long-term stability.

[0100] In alternative embodiments of the present invention, DPP derivatives may also be used. Besides DPP itself, its derivatives such as 4-(diphenylphosphine)benzoic acid (DPPBA) and diphenylphosphine ethylamine (DPPEA) can also be used as passivating agents. This is because the carboxyl or amino groups can additionally react with surface Cs. + or Br - The passivation effect may be better. Experiments show that using 0.1 wt% DPPBA under the same conditions, UC-QY can reach 8.2%, and its thermal stability is slightly better than that of DPP.

[0101] Furthermore, the quantum dot concentration can be optimized. The concentration of the quantum dot solution affects the adsorption kinetics of DPP. When the quantum dot concentration is below 1 mg / mL, too many DPP molecules contact the surface of a unit quantum dot, which may lead to multilayer adsorption and quenching; when it is above 100 mg / mL, the system viscosity is too high, resulting in uneven passivation. A concentration of 5-20 mg / mL is preferred.

[0102] Furthermore, to extend device lifetime, an atomic layer deposition (ALD) layer of Al2O3 or SiO2 (5-20 nm) can be deposited on the quantum dot film as a barrier layer against oxygen and moisture. Experiments show that after ALD encapsulation, the stability of the upconversion film can be extended to over 2000 hours under 85℃ / 85% RH conditions.

[0103] In some implementations, if the underlying battery is not required, the optical cavity structure layer can be directly used as a reflective layer to reflect the upconverted visible light back to the crystalline silicon layer for secondary absorption. This simplified version has a PCE of approximately 25.1% and is simpler to fabricate.

[0104] The CsPbBr3 perovskite quantum dot surface passivation method provided by this invention is simple to operate, low in cost, and requires no complex equipment, making it ideal for large-scale production. The passivated quantum dots can be widely used in: infrared upconversion gain layers of crystalline silicon solar cells, intermediate layers of perovskite / crystalline silicon tandem cells, downconversion layers of light-emitting diodes, bioimaging probes, photocatalysis, and other fields. In particular, the full-spectrum utilization tandem cells formed by combining them with chalcogenide perovskite thermoelectric materials are expected to increase the conversion efficiency of solar cells to over 30%, which is of great significance to the development of the photovoltaic industry.

[0105] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for surface passivation of CsPbBr3 perovskite quantum dots, characterized in that, Includes the following steps: Provide a solution of synthesized CsPbBr3 perovskite quantum dots; Diphenylphosphine or its derivatives are added to the quantum dot solution as a surface passivating agent, wherein the amount of diphenylphosphine or its derivatives added is from 0.05 wt% to 5 wt%. Under an inert atmosphere, the reaction is stirred for 0.5 to 12 hours within a temperature range of 0°C to 60°C to allow diphenylphosphine or its derivatives to coordinate with the quantum dot surface, thereby achieving dual-site passivation of defects on the quantum dot surface.

2. The method according to claim 1, characterized in that, The amount of diphenylphosphine or its derivative added is from 0.1 wt% to 1 wt%, the stirring reaction temperature is room temperature, and the reaction time is from 2 hours to 4 hours.

3. The method according to claim 1, characterized in that, The CsPbBr3 perovskite quantum dots are synthesized by hot injection, solvothermal method or ligand-assisted reprecipitation method, and the average particle size of the quantum dots is 2 nm to 20 nm.

4. A CsPbBr3 perovskite quantum dot, characterized in that, The quantum dots are prepared by any one of claims 1 to 3, wherein a stable passivation layer is formed on the surface of the quantum dots through dual-site coordination of P atoms with Pb atoms and Br atoms; the quantum dots have an upconversion quantum yield of more than 5% for infrared light in the 1100 nm to 1700 nm band, and after heat treatment at 400 °C under an inert atmosphere for 1 hour, their upconversion quantum yield remains at more than 90% of the initial value.

5. The CsPbBr3 perovskite quantum dot according to claim 4, characterized in that, The quantum dots are dispersed in an organic solvent to form a quantum dot solution, wherein the organic solvent is selected from one or more of n-hexane, chloroform, toluene, and octane, and the quantum dot concentration is from 5 mg / mL to 20 mg / mL.

6. An infrared upconversion material, characterized in that, It comprises the CsPbBr3 perovskite quantum dots as described in claim 4 or 5, and an organic polymer matrix or an inorganic porous matrix.

7. The infrared upconversion material according to claim 6, characterized in that, The infrared upconversion material is used to upconvert infrared light with wavelengths from 1100 nm to 1700 nm into visible light with wavelengths from 400 nm to 1100 nm via a triplet-triplet annihilation mechanism.

8. A solar cell, characterized in that, The upconversion layer comprises the infrared upconversion material as described in claim 6 or 7, and is disposed on the back side of the light incident surface of the solar cell or inside the cell, for converting infrared light that is not absorbed by the solar cell into visible light that can be absorbed.

9. A crystalline silicon tandem photovoltaic-thermal hybrid battery, characterized in that, include: The crystalline silicon photovoltaic layer, located on the top layer of the cell, is used to absorb photons in the 300 nm to 1100 nm wavelength range; A functional stack, located at the bottom of the crystalline silicon photovoltaic layer, includes a photoelectric conversion sublayer composed of CsPbBr3 perovskite quantum dots as described in claim 4 or 5 and a polymer matrix, for absorbing 1100 nm to 1700 nm infrared light transmitted through the crystalline silicon photovoltaic layer and upconverting it to 400 nm to 1100 nm visible light through a triplet-triplet annihilation mechanism; And an electrical connection layer, which is electrically connected to the crystalline silicon photovoltaic layer and the photoelectric conversion sublayer, respectively.

10. The hybrid battery according to claim 9, characterized in that, The functional stack further includes: The thermoelectric conversion sublayer, located below the photoelectric conversion sublayer, is composed of chalcogenide perovskite material or organic thermoelectric material, and is used to convert the waste heat generated by the crystalline silicon photovoltaic layer and the heat energy generated by the photoelectric conversion sublayer absorbing infrared light into electrical energy. And an optical cavity structure layer, located below or integrated in the thermoelectric conversion sublayer, composed of a distributed Bragg reflector or a metal reflective layer, used to reflect infrared light with wavelengths from 1100 nm to 1700 nm back to the photoelectric conversion sublayer to achieve multiple absorptions; The electrical connection layer includes independent first, second, and third electrodes, which are electrically connected to the crystalline silicon photovoltaic layer, the photoelectric conversion sublayer, and the thermoelectric conversion sublayer, respectively, forming a four-terminal independent output architecture.

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