Manufacturing method and application of quantum dot photovoltaic cell

Abstract

The invention discloses a manufacturing method and application of a quantum dot photovoltaic cell, and the method comprises the following steps: S1, preparation and surface modification of quantum dots, S2, pretreatment of a transparent conductive substrate, S3, gradient film formation of a quantum dot active layer, S4, plasma modification of the active layer, S5, preparation of a hole transport layer and an electrode, S6, interface optimization and packaging, and S7, detection and screening of a finished product. In the step S1, metal halide and chalcogenide with the purity larger than or equal to 99.9% serve as raw materials, the core-shell structure quantum dots are prepared through a thermal injection method under the protection of nitrogen with the purity larger than or equal to 99.999%, and in the step S2, an FTO or ITO substrate with the sheet resistance smaller than or equal to 10 omega / sq and the light transmittance larger than or equal to 85% is selected and subjected to ultrasonic treatment for 15-20 min through analytically pure acetone, absolute ethyl alcohol and deionized water with the resistivity larger than or equal to 18.2 M omega.cm in sequence. Through cooperative use of the steps, the method has the advantages of improving the energy conversion efficiency and long-term stability of the device through an integrated process of surface modification, gradient film formation, interface optimization and packaging protection.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic energy and nano-semiconductor manufacturing technology, specifically to a method for manufacturing quantum dot photovoltaic cells and their applications. Background Technology

[0002] As the core device for converting solar energy into electrical energy, the energy conversion efficiency and manufacturing cost of photovoltaic cells are key factors restricting the development of the industry. Although traditional silicon-based photovoltaic cells dominate the market, they suffer from drawbacks such as high energy consumption during the manufacturing process, poor flexibility, and insensitivity to weak light. While thin-film photovoltaic cells (such as perovskite and CIGS) have advantages in flexibility and manufacturing cost, perovskite cells lack long-term stability, and CIGS cells rely on rare metals and have complex manufacturing processes.

[0003] Quantum dots, as semiconductor nanomaterials with a particle size of 1-10 nm, have achieved precise bandgap matching of the solar spectrum through particle size control by means of unique quantum confinement effect. They have core advantages such as broad spectrum absorption, high carrier mobility, solution processability and controllable cost, and have become a key direction for breaking through efficiency bottlenecks in the photovoltaic field. However, the existing technology still has four major bottlenecks: (1) The density of dangling bonds and defect states on the surface of quantum dots is as high as 8×10¹ 5 -1×10¹ 6 (1) cm⁻³, which leads to a surge in the nonradiative recombination rate of charge carriers, and the open circuit voltage is generally lower than 0.7V; (2) Van der Waals forces between quantum dots cause the agglomerates to have a particle size of more than 50nm and a surface roughness of 12-18nm during film formation, which seriously hinders charge transport; (3) Mismatch between the energy levels of the electrode and the active layer causes the interfacial contact resistance to exceed 100Ω·cm², and the charge separation efficiency to be less than 60%; (4) Lack of encapsulation technology makes quantum dots susceptible to oxygen and water corrosion, and the efficiency retention rate is less than 60% after 1000h in an 85℃ / 85%RH environment.

[0004] To address the aforementioned problems, it is essential to invent a method for manufacturing quantum dot photovoltaic cells and their applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for manufacturing quantum dot photovoltaic cells and their applications. It has the advantages of improving the energy conversion efficiency and long-term stability of the device through an integrated process of surface modification, gradient film formation, interface optimization and encapsulation protection. It solves the problems of high carrier recombination rate, poor film quality, poor interface contact and insufficient stability in existing quantum dot photovoltaic cells.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for manufacturing quantum dot photovoltaic cells, comprising the following steps: S1: Quantum dot preparation and surface modification; S2: Pretreatment of transparent conductive substrate; S3: Gradient film formation of quantum dot active layer; S4: Plasma modification of the active layer; S5: Hole transport layer and electrode fabrication; S6: Interface optimization and encapsulation; S7: Finished product inspection and screening.

[0007] Preferably, in step S1, metal halides (CdCl2, InCl3) and chalcogenides (Se powder, S powder, ZnS) with a purity ≥99.9% are used as raw materials. Core-shell structured quantum dots are prepared by hot injection under nitrogen protection with a purity ≥99.999%. The core layer is CdSe or InP, and the shell layer is ZnS or ZnSe. The particle size of the core layer is precisely controlled by the reaction time (at 220℃, the particle size increases by approximately 0.5 nm for every 1 min increase in reaction time). The prepared quantum dots are filtered through a 0.22 μm organic filter membrane and then dispersed in a purity ≥99.999%... Prepare a 50 mg / mL dispersion in ≥99.5% anhydrous n-hexane, add a composite ligand consisting of ≥98% mercaptoacetic acid and ≥99% oleic acid (molar ratio 1:3-1:5, ligand to quantum dot mass ratio 1:10-1:20), and magnetically stir at 300-500 rpm for 2-4 hours in an oil bath at 60-80℃. After modification, centrifuge for 10-15 minutes using a high-speed refrigerated centrifuge (10000-12000 rpm, 4℃), discard the supernatant, and redissolve twice in n-hexane to obtain a final surface defect density ≤5×10¹. 5 Modified quantum dots of cm⁻³.

[0008] Preferably, in step S2, an FTO or ITO substrate with a sheet resistance ≤10Ω / sq and a transmittance ≥85% is selected. The substrate is sequentially ultrasonicated for 15-20 min each with analytical grade acetone, anhydrous ethanol, and deionized water with a resistivity ≥18.2 MΩ·cm, dried with nitrogen at 0.3-0.5 MPa, and then subjected to argon atmosphere plasma treatment for 5-8 min. A 30-50 nm dense TiO2 layer (target purity ≥99.9%) is deposited by radio frequency magnetron sputtering, followed by annealing at 300-350℃ for 1-2 h to form a water vapor transmission rate ≤1×10⁻⁻⁻⁶. 6 Electron transport layer substrate with g / (m²·d).

[0009] Preferably, in step S3, the modified quantum dots are dispersed in a chlorobenzene-n-octanol mixed solvent (volume ratio 4:1-6:1) to prepare a 20-50 mg / mL slurry, which is then ultrasonically dispersed. The slurry is then spin-coated in a clean glove box in a gradient manner (500-800 rpm / 5-10 s, 2000-3000 rpm / 20-30 s), followed by step annealing under inert gas protection (80-100℃ / 10-15 min, 150-180℃ / 20-30 min) to form an active layer with a thickness of 100-200 nm and a surface roughness of ≤5 nm.

[0010] Preferably, in step S4, the active layer substrate is placed in a plasma treatment instrument with O2 / Ar=1:4 (volume ratio) and treated for 30-60s at 80-100W power and 0.3-0.5Pa pressure to make the surface carbon content ≤3.5% and the water contact angle ≤35°.

[0011] Preferably, in step S5, P3HT with a number average molecular weight of 50,000-100,000 is dissolved in anhydrous chloroform to prepare a 5-10 mg / mL solution, which is then filtered. After spin coating, the solution is annealed at 120-140°C to form a 20-40 nm hole transport layer. After electron beam evaporation of 2-5 nm MoO3, an 80-120 nm Au or Ag electrode is evaporated, and the lead wire is welded by thermocompression welding.

[0012] Preferably, in step S6, a 50-100μm UV-curable encapsulating adhesive is coated and cured in a nitrogen glove box (oxygen content ≤10ppm, water content ≤10ppm), with an adhesion strength ≥5MPa; a 20-30μm aluminum-plastic composite film is heat-bonded, and a 0.1MPa pressure holding 30s sealing test shows no air leakage.

[0013] Preferably, in step S7, samples with an initial screening efficiency of ≥18% using the AM1.5G solar simulator are sampled and aged at 85℃ / 85%RH for 100h. An efficiency decay of ≤5% is considered acceptable.

[0014] Preferably, the quantum dot photovoltaic cell has the following structure from bottom to top: transparent conductive substrate → TiO2 dense layer → quantum dot active layer → P3HT hole transport layer → MoO3 interface modification layer → metal electrode → encapsulation layer; the energy conversion efficiency of this cell is ≥18%, and the efficiency retention rate is ≥80% after aging at 85℃ and 85%RH for 1000h; the thickness of the quantum dot active layer is 100-200nm, and the surface roughness is ≤5nm; the thickness of the MoO3 interface modification layer is 2-5nm, and the thickness of the metal electrode is 80-120nm.

[0015] The application of the quantum dot photovoltaic cell manufacturing method, using the steps and methods described in claim 1, ① can prepare flexible quantum dot photovoltaic cells (using a 125μm thick flexible ITO / PET substrate). Mechanical performance tests show that the bending radius can reach 5mm, and the efficiency retention rate is ≥90% after repeated bending 1000 times (90.5% for the flexible version in Example 2); low-light power generation performance tests: under 500lux indoor natural light, the output power density reaches 5mW / cm², providing a charging current of 15mA (the standby charging current of a smartphone is about 10mA); under 1000lux fluorescent lamp, the output power density reaches... 10mW / cm², charging current increased to 30mA; in outdoor cloudy environment (light intensity 30mW / cm²), it can achieve 0.5C fast charging (charging current 1A) for smartphones, which is 150% higher than silicon-based flexible batteries (0.2C fast charging); integrated into the surface of outdoor flashlights (area 10cm²), it can output 1W power under strong light to meet the continuous lighting needs of flashlights; ② Colorization and transparency can be achieved by adjusting the particle size of quantum dots: blue with a particle size of 3nm and a light transmittance of 50%; green with a particle size of 5nm and a light transmittance of 40%; red with a particle size of 7nm and a light transmittance of 30%, which meets the requirements of architectural decoration. It is manufactured into a 1m×1m photovoltaic curtain wall module with a light transmittance of 45% (green version) and a power output of 150W. In Shanghai (with an average annual sunshine of 1400h), a 100㎡ photovoltaic curtain wall can generate 12000kWh of electricity annually, meeting 30%-40% of the electricity needs of an average household (based on an annual household electricity consumption of 3000-4000kWh). Thermal performance tests show that the heat transfer coefficient of this curtain wall is 2.8W / (m²·K), which is better than that of traditional double-glazed curtain walls (3.0-3.5W / (m²·K)). It can reduce air conditioning load by 15% in summer and reduce heat loss by 10% in winter. Weather resistance tests (1 year of outdoor exposure) show that the light transmittance decreases by ≤3% and the power generation efficiency decreases by ≤4%.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Significantly improved defect passivation efficiency: Synergistic modification with thioglycolic acid-oleic acid composite ligands reduces the surface defect density of quantum dots from 8×10¹ 5 -1×10¹ 6 cm⁻³ decreased to ≤5×10¹ 5 cm⁻³ (reduced by more than 40%); carrier lifetime increased from 1.2ns to 2.0ns, recombination rate decreased by 30%, open-circuit voltage increased from 0.6-0.7V to 0.85-1.0V, and XPS verification showed that the ligands and quantum dots formed stable chemical bonds.

[0017] 2. Optimization of film quality and charge transport: Gradient spin coating combined with stepped annealing process makes the surface roughness of the active layer ≤5nm (12-15nm in traditional process) and the particle size of agglomerates ≤20nm; the charge transport time is shortened from 800ps to 450ps, the transport efficiency is improved by 25%, and the short-circuit current density reaches 25-35mA / cm² (22-25mA / cm² in traditional process). Example 1 is 28% better than Comparative Example 2.

[0018] 3. Significantly reduced interface resistance: The introduction of a MoO3 interface modification layer (work function 6.9 eV matching the P3HT energy level) reduced the interface contact resistance from 100-120 Ω·cm² to ≤20 Ω·cm² (reaching 18 Ω·cm² in Example 1); the fill factor increased from 0.55-0.65 to 0.65-0.75, with Example 1 showing a 20.7% improvement over the unmodified sample.

[0019] 4. Breakthrough in long-term stability: The dual encapsulation of "UV curable adhesive + aluminum-plastic composite film" maintains an efficiency of ≥80% (83% in Example 1) for 1000 hours in an 85℃ / 85%RH environment, far exceeding the traditional single encapsulation (55%-70%); the efficiency decay is ≤5% after 1 year of storage at room temperature, while the decay of traditional encapsulation reaches 15%-20%.

[0020] 5. Significant advantages in cost and mass production: The "solution spin coating + physical deposition" process reduces equipment investment by 40% compared to silicon-based materials and reduces the cost of quantum dot materials by 60% compared to CIGS; the mass production yield reaches 95%, and the overall manufacturing cost is reduced to 0.28 yuan / W, which is 38%-44% lower than that of monocrystalline silicon (0.45-0.5 yuan / W) and 26%-33% lower than that of CIGS (0.38-0.42 yuan / W). Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the quantum dot photovoltaic cell of the present invention. Detailed Implementation

[0022] A method for manufacturing quantum dot photovoltaic cells includes the following steps: S1: Quantum dot preparation and surface modification; S2: Pretreatment of transparent conductive substrate; S3: Gradient film formation of quantum dot active layer; S4: Plasma modification of the active layer; S5: Hole transport layer and electrode fabrication; S6: Interface optimization and encapsulation; S7: Finished product inspection and screening.

[0023] In step S1, core-shell quantum dots are prepared using metal halides (CdCl2, InCl3) and chalcogenides (Se powder, S powder, ZnS) with a purity ≥99.9% as raw materials, under nitrogen protection with a purity ≥99.999%, via a hot-injection method. The core layer is CdSe or InP, and the shell layer is ZnS or ZnSe. The particle size of the core layer is precisely controlled by the reaction time (at 220℃, the particle size increases by approximately 0.5 nm for every 1 min increase in reaction time). The prepared quantum dots are then filtered through a 0.22 μm organic filter membrane and dispersed in a nitrogen atmosphere with a purity ≥99.999%. Prepare a 50 mg / mL dispersion in 0.5% anhydrous n-hexane, add a composite ligand consisting of ≥98% mercaptoacetic acid and ≥99% oleic acid (molar ratio 1:3-1:5, ligand to quantum dot mass ratio 1:10-1:20), and magnetically stir at 300-500 rpm for 2-4 hours in an oil bath at 60-80℃. After modification, centrifuge for 10-15 minutes using a high-speed refrigerated centrifuge (10000-12000 rpm, 4℃), discard the supernatant, and redissolve twice with n-hexane to obtain a final surface defect density ≤5×10¹. 5 Modified quantum dots of cm⁻³.

[0024] In step S2, FTO or ITO transparent conductive glass with a sheet resistance ≤10Ω / sq and a transmittance ≥85% is selected as the substrate and cut into 2cm×2cm or 4cm×4cm sizes. It is then ultrasonically cleaned for 15-20 minutes each in an ultrasonic cleaner (power 100-150W) using analytical grade acetone, anhydrous ethanol, and deionized water (resistivity ≥18.2MΩ·cm) to remove surface oil and impurities. After drying with nitrogen gas (pressure 0.3-0.5MPa) at a 45° angle, it is placed in a plasma cleaner using argon gas (flow rate 20-30sccm) as the carrier gas at a power of 100-150W. After processing for 5-8 minutes, the water contact angle on the substrate surface decreased from ≥60° to ≤20°, significantly improving hydrophilicity. Subsequently, a dense TiO2 layer with a thickness of 30-50 nm was deposited on the substrate surface using radio frequency magnetron sputtering. The sputtering target was a TiO2 ceramic target (purity ≥99.9%), the sputtering pressure was 0.5-1 Pa, the sputtering power was 80-120 W, and the deposition rate was 0.5-1 nm / s. After deposition, the substrate was placed in a muffle furnace and heated to 300-350°C at a heating rate of 5-10°C / min, held at that temperature for 1-2 hours, and then naturally cooled to room temperature to form a dense layer with good water vapor permeability (≤1×10⁻⁻⁻⁻⁶). 6 Electron transport layer substrate (g / (m²·d)).

[0025] In step S3, the modified quantum dots are dispersed in a chlorobenzene-n-octanol mixed solvent (chlorobenzene purity ≥99.5%, n-octanol purity ≥99%), and then dispersed magnetically (400 rpm) for 30 min, followed by ultrasonic dispersion (80 W) for 10 min to prepare a quantum dot slurry with a concentration of 20-50 mg / mL. The volume ratio of chlorobenzene to n-octanol is 4:1-6:1, which can be used to adjust the slurry viscosity (10-20 mPa·s) to suit the spin coating process. The slurry is coated onto the electron transport layer substrate surface using a programmable gradient spin coater. The first stage involves a spin speed of 500-800 rpm for 5-10 s to ensure uniform spreading and coverage of the substrate. The second stage involves a spin speed of 2000-3000 rpm for 5-10 s. The spin coating process is carried out in a clean glove box (humidity ≤10%, oxygen content ≤1ppm) to avoid the influence of ambient moisture on the film quality. Immediately after spin coating, the film is annealed in an inert gas (nitrogen or argon, purity ≥99.999%) furnace using a stepped annealing process: first, it is held at 80-100℃ for 10-15min to remove residual solvent from the film, and then the temperature is increased to 150-180℃ at a rate of 5℃ / min and held for 20-30min to promote dense quantum dot stacking. Finally, a quantum dot active layer with a thickness of 100-200nm and uniform particle dispersion (aggregate particle size ≤20nm) is formed, and the surface roughness is ≤5nm as measured by atomic force microscopy (AFM).

[0026] In step S4, the active layer substrate after film formation is transferred to a plasma treatment instrument for surface modification in an O2 / Ar = 1:4 (volume ratio) mixed atmosphere: treatment power 80-100W, pressure 0.3-0.5Pa, treatment time 30-60s. This process generates hydroxyl (-OH) groups through plasma bombardment, increasing the hydroxyl content on the surface of the active layer by 30%-40%, reducing the water contact angle from 65° to below 35°, and significantly enhancing the interfacial bonding force with the hole transport layer (peel strength increased from 0.8N / cm to 1.5N / cm). At the same time, residual organic impurities on the surface are removed. X-ray photoelectron spectroscopy (XPS) test shows that the surface carbon content is reduced from 8.5% to 3.2%, reducing charge transport traps.

[0027] In step S5, poly(3-hexylthiophene) (P3HT, number average molecular weight 50,000-100,000) is dissolved in anhydrous chloroform (purity ≥99.8%), magnetically stirred (300 rpm) for 2 hours, and then filtered through a 0.22 μm organic filter membrane to prepare a solution with a concentration of 5-10 mg / mL. This solution is then spin-coated onto the surface of the quantum dot active layer in a clean glove box at 1500-2000 rpm for 20 seconds. Immediately after spin-coating, the layer is placed on a hot plate and annealed at 120-140℃ for 10-15 minutes to remove the solvent and promote the orientation of P3HT molecules, forming a hole transport layer with a thickness of 20-40 nm. The transmittance is measured to be ≥90% (wavelength 400-800 nm) using a UV-Vis spectrophotometer. A metal electrode is then deposited on the surface of the hole transport layer using an electron beam evaporation system with a vacuum degree ≤5×10⁻⁻⁻⁶. 4 First, an Au or Ag electrode with a thickness of 80-120 nm (metal purity ≥99.99%) is evaporated at a rate of 0.1-0.5 nm / s. The electrode pattern is controlled using a stainless steel mask with an effective area of ​​0.25-1 cm². The parallelism error between the mask and the substrate is ≤0.1 mm to ensure the uniformity of the electrode thickness. To improve the conductivity of the electrode, after evaporation, a thermoforming process (pressure 0.2-0.3 MPa, temperature 80℃, time 30 s) is used to weld the lead wires.

[0028] In step S6, a MoO3 interface modification layer with a thickness of 2-5 nm (MoO3 purity ≥ 99.9%) is deposited between the hole transport layer and the metal electrode using electron beam evaporation at an evaporation rate of 0.05-0.1 nm / s. This layer can form an energy level gradient (MoO3 work function is approximately 6.9 eV, matching the energy level of the highest occupied molecular orbital of P3HT), reducing the interfacial contact resistance. The encapsulation adopts a dual protection scheme of "UV-curable adhesive + aluminum-plastic composite film". First, a UV-curable encapsulating adhesive is applied to the front (transparent substrate side) and side of the device using a dispensing machine (needle diameter 0.5 mm, dispensing rate 0.1 mL / s). (Viscosity 500-1000 mPa·s, transmittance ≥90%), encapsulating adhesive thickness 50-100 μm, avoid generating air bubbles during coating (can be treated with a vacuum degassing machine for 10 min); then cure in a UV curing machine (wavelength 365 nm, power 100-150 mW / cm²) for 5-10 min, and after curing, test the bond strength with a tensile testing machine to ≥5 MPa; finally, use a heat bonding machine (temperature 120℃, pressure 0.4 MPa, time 20 s) to bond an aluminum-plastic composite film with a thickness of 20-30 μm (aluminum layer thickness 5-10 μm, barrier properties ≤1×10⁻) to the back of the device. 5 g / (m²·d)) to complete the encapsulation; after encapsulation, a sealing tester was used to test the airtightness. The airtightness was tested under a pressure of 0.1MPa for 30s, and there was no air leakage.

[0029] In step S7, according to the IEC60904-9 standard, an AM1.5G solar simulator (light intensity 100mW / cm², standard silicon cell calibration) is used to conduct preliminary photovoltaic performance tests on the packaged cells. Qualified samples with an energy conversion efficiency ≥18%, open-circuit voltage ≥0.85V, and short-circuit current density ≥25mA / cm² are selected. 10% of the qualified samples are then sampled and subjected to a 100-hour accelerated aging test at 85℃ / 85%RH. A pass rate is ≤5% efficiency degradation. For the flexible version, an additional bending test is conducted according to the IEC61646 standard (bending radius 5mm, 100 cycles). A pass rate is ≥95% efficiency retention. The final product yield is improved from 92% to 95%. The main defects are poor interface contact (3%) and encapsulation leakage (2%), which can be further improved by optimizing plasma treatment time and encapsulation pressure.

[0030] The quantum dot photovoltaic cell has the following structure from bottom to top: transparent conductive substrate → TiO2 dense layer → quantum dot active layer → P3HT hole transport layer → MoO3 interface modification layer → metal electrode → encapsulation layer; the energy conversion efficiency of this cell is ≥18%, and the efficiency retention rate is ≥80% after aging at 85℃ and 85%RH for 1000h; the thickness of the quantum dot active layer is 100-200nm, and the surface roughness is ≤5nm; the thickness of the MoO3 interface modification layer is 2-5nm, and the thickness of the metal electrode is 80-120nm.

[0031] The application of the quantum dot photovoltaic cell manufacturing method, using the steps and methods described in claim 1, ① can prepare flexible quantum dot photovoltaic cells (using a 125μm thick flexible ITO / PET substrate). Mechanical performance tests show that the bending radius can reach 5mm, and the efficiency retention rate is ≥90% after repeated bending 1000 times (90.5% for the flexible version in Example 2); low-light power generation performance tests: under 500lux indoor natural light, the output power density reaches 5mW / cm², providing a charging current of 15mA (the standby charging current of a smartphone is about 10mA); under 1000lux fluorescent lamp, the output power density reaches... 10mW / cm², charging current increased to 30mA; in outdoor cloudy environment (light intensity 30mW / cm²), it can achieve 0.5C fast charging (charging current 1A) for smartphones, which is 150% higher than silicon-based flexible batteries (0.2C fast charging); integrated into the surface of outdoor flashlights (area 10cm²), it can output 1W power under strong light to meet the continuous lighting needs of flashlights; ② Colorization and transparency can be achieved by adjusting the particle size of quantum dots: blue with a particle size of 3nm and a light transmittance of 50%; green with a particle size of 5nm and a light transmittance of 40%; red with a particle size of 7nm and a light transmittance of 30%, which meets the requirements of architectural decoration. It is manufactured into a 1m×1m photovoltaic curtain wall module with a light transmittance of 45% (green version) and a power output of 150W. In Shanghai (with an average annual sunshine of 1400h), a 100㎡ photovoltaic curtain wall can generate 12000kWh of electricity annually, meeting 30%-40% of the electricity needs of an average household (based on an annual household electricity consumption of 3000-4000kWh). Thermal performance tests show that the heat transfer coefficient of this curtain wall is 2.8W / (m²·K), which is better than that of traditional double-glazed curtain walls (3.0-3.5W / (m²·K)). It can reduce air conditioning load by 15% in summer and reduce heat loss by 10% in winter. Weather resistance tests (1 year of outdoor exposure) show that the light transmittance decreases by ≤3% and the power generation efficiency decreases by ≤4%.

[0032] Example 1: Manufacturing of photovoltaic cells based on CdSe / ZnS quantum dots 1. Quantum Dot Preparation and Modification: 0.5 mmol CdO and 2 mmol stearic acid were added to a three-necked flask and heated to 200 °C under nitrogen protection (purity ≥99.999%) to dissolve and form a Cd precursor. 1 mmol Se powder was dissolved in 5 mL of trioctylphosphine (TOP) to prepare a Se precursor. The Se precursor was rapidly injected into the Cd precursor, and the mixture was reacted at 220 °C for 5 min to prepare CdSe core quantum dots (particle size 5 nm). Subsequently, a TOP mixed precursor of 2 mmol Zn(Ac)2 and 2 mmol S powder was injected, and the mixture was reacted at 200 °C for 30 min to form CdSe / ZnS core-shell quantum dots (shell thickness 1 nm). The quantum dots were dispersed in 10 mL of n-hexane, and 0.1 g mercaptoacetic acid and 0.3 g oleic acid (molar ratio 1:3) were added. The mixture was stirred at 70 °C for 3 h, and centrifuged to obtain modified quantum dots with a surface defect density of 3.2 × 10¹. 5 cm⁻³, quantum yield 88%.

[0033] 2. Substrate Pretreatment: 1.1mm thick FTO glass (sheet resistance 8Ω / sq, transmittance 86%) was selected and ultrasonically treated sequentially with analytical grade acetone, anhydrous ethanol, and deionized water with resistivity ≥18.2MΩ·cm for 18 min each. The glass was then dried by blowing with a 0.4MPa nitrogen gun at a 45° angle. A plasma cleaning machine (argon flow rate 25sccm, 120W) was used for 6 min, reducing the surface water contact angle from 65° to 18°. A 40nm TiO2 dense layer was deposited by RF magnetron sputtering (target purity 99.9%, sputtering pressure 0.8Pa, power 100W, deposition rate 0.8nm / s), annealed at 320℃ for 1.5h, achieving a water vapor permeability of 0.8×10⁻⁻⁻⁻⁶. 6 g / (m²·d).

[0034] 3. Formation of active layer: The modified quantum dots were dissolved in 8 mL of chlorobenzene and 2 mL of n-octanol (volume ratio 4:1), stirred at 400 rpm for 30 min, and then sonicated at 80 W for 10 min to prepare a 30 mg / mL slurry; the slurry was spin-coated with a controlled gradient (600 rpm / 8 s, 2500 rpm / 25 s), and then stepped annealed under 99.999% nitrogen protection (90℃ / 12 min, 160℃ / 25 min) to form a 150 nm thick active layer. The surface roughness (5 μm × 5 μm) was 3.5 nm according to AFM testing, and the agglomerate particle size was ≤15 nm.

[0035] 4. Plasma modification of active layer: Transfer to plasma treatment instrument, O2 / Ar=1:4 (volume ratio), power 100W, pressure 0.4Pa, treatment for 45s; XPS test showed that the surface carbon content was 3.0%, the water contact angle was 32°, and the interfacial peel strength with P3HT was 1.6N / cm.

[0036] 5. Hole transport layer and electrode: A 7 mg / m³ P3HT (number average molecular weight 80,000) chloroform solution was prepared, stirred at 300 rpm for 2 h, and then filtered through a 0.22 μm filter. The solution was then spin-coated at 1800 rpm for 20 s and annealed at 130 °C for 12 min to form a 30 nm hole transport layer. UV-Vis spectrophotometry showed a transmittance of 92% in the 400-800 nm range. Electron beam evaporation system (vacuum degree 3 × 10⁻⁻⁻⁻⁴) was used. 4 First, evaporate 3nm MoO3 (rate 0.08nm / s), then evaporate 100nm Au electrode (rate 0.3nm / s). The effective area of ​​the stainless steel mask is controlled at 0.5cm², and the parallelism error is 0.08mm. The lead wire is welded by hot pressing at 0.25MPa and 80℃ for 30s.

[0037] 7. Encapsulation: In a nitrogen glove box (oxygen content 5ppm, water content 5ppm), apply 80μm of UV-curable encapsulating adhesive (viscosity 800mPa·s, light transmittance 91%) using a 0.5mm needle dispensing machine (dispensing rate 0.1mL / s), followed by vacuum degassing for 10min; cure for 8min using a 365nm UV curing machine (120mW / cm²), and test the bond strength using a tensile testing machine to achieve 5.8MPa; then bond a 25μm aluminum-plastic composite film (aluminum layer thickness 8μm, barrier 0.6×10⁻) at 120℃ and 0.4MPa for 20s. 5 g / (m²·d)); 0.1MPa pressure holding for 30s sealing test showed no air leakage.

[0038] 8. Finished Product Testing and Screening: AM1.5G solar simulator test (standard silicon cell calibration), open circuit voltage 0.92V, short circuit current density 32mA / cm², fill factor 0.72, conversion efficiency 21.5%; sampled for aging at 85℃ / 85%RH for 100h, efficiency decay 3.2%, judged as qualified.

[0039] Performance Testing: The photovoltaic performance of the cells was tested using a solar simulator (AM1.5G standard spectrum, light intensity 100mW / cm², conforming to IEC60904-9 standard). The open-circuit voltage was 0.92V, the short-circuit current density was 32mA / cm², the fill factor was 0.72, and the energy conversion efficiency was 21.5%. Standard silicon cells were used for calibration before testing. Stability testing was conducted in a high and low temperature humidity test chamber, with a set temperature of 85℃ and relative humidity of 85%. Accelerated aging tests were performed according to IEC61215 standard. After 1000 hours, the cells were removed, cooled to room temperature, and the photovoltaic performance was tested again, with an efficiency retention rate of 83%. The interfacial contact resistance was tested using an electrochemical workstation, and the results showed that the interfacial resistance decreased to 18Ω·cm² after MoO3 modification. The surface roughness of the active layer was measured to be 3.5nm using atomic force microscopy (AFM, scanning range 5μm×5μm), and scanning electron microscopy (SEM) showed that the quantum dot particles were uniformly dispersed without obvious agglomeration.

[0040] Example 2: Manufacturing of photovoltaic cells based on InP / ZnSe quantum dots The difference from Example 1 is as follows: the quantum dot core layer is InP (6 nm in diameter) and the shell layer is ZnSe (1.2 nm thick); the composite ligand is 0.1 g of mercaptoacetic acid and 0.4 g of oleic acid in a molar ratio of 1:4; the gradient spin coating parameters are 700 rpm / 10 s and 2800 rpm / 30 s; the annealing process is 80 °C / 15 min and 170 °C / 20 min; and the electrode material is Ag (90 nm thick).

[0041] Performance testing: Tested using an AM1.5G standard solar simulator, with an open-circuit voltage of 0.98V, a short-circuit current density of 28mA / cm², a fill factor of 0.70, and an energy conversion efficiency of 19.2%; the interface contact resistance measured by the electrochemical workstation was 22Ω·cm²; the surface roughness of the active layer was measured to be 4.2nm (5μm×5μm scanning range) by AFM; stability testing: after aging at 85℃ and 85%RH for 1000h, the efficiency retention rate was 81%; after one year of storage at room temperature, the efficiency decreased by 4.8%; bending performance testing (flexible ITO / PET substrate, bending radius of 5mm, repeated bending 1000 times) showed an efficiency retention rate of 90.5%.

[0042] In summary, the manufacturing method and application of this quantum dot photovoltaic cell, through the above steps, solves the problems of high carrier recombination rate, poor film quality, poor interface contact, and insufficient stability in existing quantum dot photovoltaic cells.

Claims

1. A method for manufacturing quantum dot photovoltaic cells, characterized in that, Includes the following steps: S1: Quantum dot preparation and surface modification; S2: Pretreatment of transparent conductive substrate; S3: Gradient film formation of quantum dot active layer; S4: Plasma modification of the active layer; S5: Hole transport layer and electrode fabrication; S6: Interface optimization and encapsulation; S7: Finished product inspection and screening.

2. The method for manufacturing quantum dot photovoltaic cells according to claim 1, characterized in that: In step S1, metal halides (CdCl2, InCl3) and chalcogenides (Se powder, S powder, ZnS) with a purity ≥99.9% are used as raw materials. Core-shell structured quantum dots are prepared by hot injection under nitrogen protection with a purity ≥99.999%. The core layer is CdSe or InP, and the shell layer is ZnS or ZnSe. The particle size of the core layer is precisely controlled by the reaction time (at 220℃, the particle size increases by approximately 0.5 nm for every 1 min increase in reaction time). The prepared quantum dots are filtered through a 0.22 μm organic filter membrane and then dispersed in a nitrogen atmosphere with a purity ≥99.999%. A 50 mg / mL dispersion was prepared in 9.5% anhydrous n-hexane. A composite ligand consisting of ≥98% mercaptoacetic acid and ≥99% oleic acid (molar ratio 1:3-1:5, ligand to quantum dot mass ratio 1:10-1:20) was added and magnetically stirred at 300-500 rpm for 2-4 hours in an oil bath at 60-80℃. After modification, the mixture was centrifuged for 10-15 minutes using a high-speed refrigerated centrifuge (10000-12000 rpm, 4℃). The supernatant was discarded, and the mixture was redissolved twice in n-hexane to obtain a final surface defect density ≤5×10¹. 5 Modified quantum dots of cm⁻³.

3. The method for manufacturing quantum dot photovoltaic cells according to claim 1, characterized in that: In step S2, an FTO or ITO substrate with a sheet resistance ≤10Ω / sq and a transmittance ≥85% is selected. The substrate is then ultrasonically treated with analytical grade acetone, anhydrous ethanol, and deionized water with a resistivity ≥18.2MΩ·cm for 15-20 minutes each, dried with nitrogen at 0.3-0.5MPa, and subjected to argon atmosphere plasma treatment for 5-8 minutes. A 30-50nm dense TiO2 layer (target purity ≥99.9%) is deposited by radio frequency magnetron sputtering, followed by annealing at 300-350℃ for 1-2 hours to achieve a water vapor transmission rate ≤1×10⁻⁻⁻⁶. 6 Electron transport layer substrate with g / (m²·d).

4. The method for manufacturing quantum dot photovoltaic cells according to claim 1, characterized in that: In step S3, the modified quantum dots are dispersed in a chlorobenzene-n-octanol mixed solvent (volume ratio 4:1-6:1) to prepare a 20-50 mg / mL slurry, which is then ultrasonically dispersed. The slurry is then spin-coated in a clean glove box (500-800 rpm / 5-10 s, 2000-3000 rpm / 20-30 s) and annealed in a stepwise manner under inert gas protection (80-100℃ / 10-15 min, 150-180℃ / 20-30 min) to form an active layer with a thickness of 100-200 nm and a surface roughness of ≤5 nm.

5. The method for manufacturing quantum dot photovoltaic cells according to claim 1, characterized in that: In step S4, the active layer substrate is placed in a plasma treatment instrument with O2 / Ar=1:4 (volume ratio) and treated for 30-60s at 80-100W power and 0.3-0.5Pa pressure to make the surface carbon content ≤3.5% and the water contact angle ≤35°.

6. The method for manufacturing quantum dot photovoltaic cells according to claim 1, characterized in that: In step S5, P3HT with a number average molecular weight of 50,000-100,000 is dissolved in anhydrous chloroform to prepare a 5-10 mg / mL solution, which is then filtered. After spin coating, the solution is annealed at 120-140°C to form a 20-40 nm hole transport layer. After evaporating 2-5 nm of MoO3 with an electron beam, an 80-120 nm Au or Ag electrode is then evaporated, and the lead wire is welded by thermocompression welding.

7. The method for manufacturing quantum dot photovoltaic cells according to claim 1, characterized in that: In step S6, a 50-100μm UV-curable encapsulating adhesive is coated and cured in a nitrogen glove box (oxygen content ≤10ppm, water content ≤10ppm), with an adhesion strength ≥5MPa; a 20-30μm aluminum-plastic composite film is heat-bonded, and a 0.1MPa pressure holding test for 30s shows no air leakage.

8. The method for manufacturing quantum dot photovoltaic cells according to claim 1, characterized in that: In step S7, samples with an initial screening efficiency of ≥18% using the AM1.5G solar simulator are sampled and aged at 85℃ / 85%RH for 100h. A decrease in efficiency of ≤5% is considered acceptable.

9. A quantum dot photovoltaic cell, characterized in that, According to the manufacturing method of quantum dot photovoltaic cell as described in claim 1, the structure from bottom to top is as follows: transparent conductive substrate → TiO2 dense layer → quantum dot active layer → P3HT hole transport layer → MoO3 interface modification layer → metal electrode → encapsulation layer; the energy conversion efficiency of the cell is ≥18%, and the efficiency retention rate is ≥80% after aging at 85℃ and 85%RH for 1000h; the thickness of the quantum dot active layer is 100-200nm, and the surface roughness is ≤5nm; the thickness of the MoO3 interface modification layer is 2-5nm, and the thickness of the metal electrode is 80-120nm.

10. The application of a quantum dot photovoltaic cell manufacturing method, using the steps and methods described in claim 1, characterized in that, ① Flexible quantum dot photovoltaic cells can be fabricated (using a 125μm thick flexible ITO / PET substrate). Mechanical performance tests show that the bending radius can reach 5mm, and the efficiency retention rate is ≥90% after 1000 repeated bending cycles (90.5% for the flexible version in Example 2). Low-light power generation performance tests: Under 500 lux indoor natural light, the output power density reaches 5mW / cm², providing a charging current of 15mA (the standby charging current of a smartphone is about 10mA); under 1000 lux fluorescent lamp, the output power density reaches 10mW / cm², and the charging current increases to... 30mA; Under outdoor cloudy conditions (light intensity 30mW / cm²), it can achieve 0.5C fast charging for smartphones (charging current 1A), which is 150% higher than that of silicon-based flexible batteries (0.2C fast charging); Integrated into the surface of an outdoor flashlight (area 10cm²), it can output 1W of power under strong light to meet the continuous lighting needs of the flashlight; ② Colorization and transparency can be achieved by adjusting the particle size of quantum dots: blue with a particle size of 3nm and a light transmittance of 50%; green with a particle size of 5nm and a light transmittance of 40%; red with a particle size of 7nm and a light transmittance of 30%, which meets the requirements of architectural decoration. It is manufactured into a 1m×1m photovoltaic curtain wall module with a light transmittance of 45% (green version) and a power output of 150W. In Shanghai (with an average annual sunshine of 1400h), a 100㎡ photovoltaic curtain wall can generate 12000kWh of electricity annually, meeting 30%-40% of the electricity needs of an average household (based on an annual household electricity consumption of 3000-4000kWh). Thermal performance tests show that the heat transfer coefficient of this curtain wall is 2.8W / (m²·K), which is better than that of traditional double-glazed curtain walls (3.0-3.5W / (m²·K)). It can reduce air conditioning load by 15% in summer and reduce heat loss by 10% in winter. Weather resistance tests (1 year of outdoor exposure) show that the light transmittance decreases by ≤3% and the power generation efficiency decreases by ≤4%.

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