Light conversion film based on quantum dots and application of light conversion film in solar cell

Abstract

The invention discloses a light conversion film based on quantum dots and application of the light conversion film in a solar cell, and belongs to the technical field of photovoltaic materials. The light conversion film comprises a transparent polymer matrix, core-shell structure quantum dots dispersed in the polymer matrix, a modification layer coating the surfaces of the core-shell structure quantum dots, and an anti-reflection micro-nano structure layer arranged on at least one side of the surface of the polymer matrix. By optimizing the film layer structure and performing surface modification on the quantum dots, the technical problems that the quantum dots are easy to agglomerate, poor in stability and high in interface reflection are solved, the obtained light conversion film is applied to a crystalline silicon solar cell or a perovskite solar cell, and the photoelectric conversion efficiency and the environmental stability of the cell can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic materials and devices technology, specifically relating to an optical light conversion film that utilizes quantum dots to achieve down-conversion and / or up-conversion functions, and the application of this light conversion film in crystalline silicon solar cells or perovskite solar cells. Background Technology

[0002] Crystalline silicon solar cells and perovskite solar cells are currently the mainstream photovoltaic technologies. However, both suffer from limited spectral response ranges: crystalline silicon cells have weak responses to ultraviolet light with wavelengths less than 400 nm and are prone to aging of encapsulation materials due to ultraviolet radiation; while perovskite cells, although exhibiting excellent absorption in the visible light region, have insufficient utilization of near-infrared light (>800 nm). Furthermore, approximately 30% of the solar spectrum's energy lies in the ultraviolet and near-infrared regions; failure to effectively utilize this energy will limit further improvements in cell efficiency.

[0003] Light conversion technology can transform the spectrum insensitive to a solar cell into a sensitive wavelength band, which is an effective way to improve the efficiency of solar cells. Traditional light conversion materials are mainly phosphors, but they suffer from problems such as low quantum yield, wide emission peak, and poor dispersibility, which limit their application. Quantum dots (QDs), as a novel fluorescent material, have advantages such as narrow emission peak, high quantum yield, and emission wavelength that can be tuned by particle size, which makes it possible to optimize light conversion films: by designing quantum dots with specific compositions (such as CdSe, PbS, CsPbBr3, etc.) and sizes, it is possible to convert high-energy ultraviolet light into visible light (downconversion) or low-energy near-infrared light into visible / near-infrared light (upconversion), thereby matching the optimal response wavelength of the solar cell. However, successfully integrating quantum dots into photovoltaic modules still faces multiple technical challenges: First, the dispersion stability of quantum dots in polymer matrices is insufficient, easily leading to aggregation and fluorescence quenching; second, high-concentration regions in traditional quantum dot light-conversion films are prone to concentration quenching effects; third, interfacial reflection loss between the light-conversion film and the cell surface is not effectively suppressed, typically exceeding 8%; furthermore, existing light-conversion films lack customized designs for different cell spectral characteristics, making it difficult to simultaneously meet the differentiated needs of crystalline silicon and perovskite cells. Moreover, current light-conversion film technologies mostly focus on improving single performance indicators, failing to systematically address the synergistic optimization problem between quantum dot stability, optical coupling efficiency, and spectral matching accuracy. Particularly in terms of long-term weather resistance, conventional quantum dot light-conversion films exhibit significant performance degradation under high temperature and humidity environments, limiting their practical application value. Therefore, developing a quantum dot light-conversion film that combines high light-conversion efficiency, excellent environmental stability, and good spectral adaptability is of great significance for promoting the development of photovoltaic technology. Summary of the Invention

[0004] In response to the technical problems of quantum dot light conversion films in existing solar cell applications, such as easy aggregation of quantum dots, poor stability, high reflection loss at the interface with the cell, and insufficient spectral matching and versatility, this invention provides an optical light conversion film that utilizes quantum dots to achieve down-conversion and / or up-conversion functions. This film can effectively solve the above problems, and its application in crystalline silicon solar cells or perovskite solar cells can significantly improve the photoelectric conversion efficiency of the cells and the utilization rate of the solar spectrum.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A quantum dot-based optical conversion film, comprising at least the following components: (1) A transparent polymer matrix; (2) Core-shell structured quantum dots uniformly dispersed in the polymer matrix; (3) A modification layer covering the outer surface of the core-shell quantum dot; (4) An anti-reflection micro / nano structure layer is provided on at least one side of the surface of the polymer matrix.

[0006] Furthermore, the polymer matrix is ​​one or more of polyacrylic resins, polyolefin elastomers (POE), ethylene-vinyl acetate copolymers (EVA), polydimethylsiloxane (PDMS), or epoxy resins.

[0007] Furthermore, the core-shell structured quantum dot is a downconversion quantum dot and / or an upconversion quantum dot.

[0008] Furthermore, the downconversion quantum dots are selected from CdSe / ZnS, InP / ZnS, or CsPbBr3 perovskite quantum dots, which can convert 300-450 nm ultraviolet light into 500-700 nm visible light.

[0009] Furthermore, the upconversion quantum dot is selected from NaYF4:Yb 3+ Er 3+ Or PbS / CdS quantum dots, which are used to convert near-infrared light (900-1600 nm) into photons of 600-900 nm.

[0010] Furthermore, the mass percentage of core-shell quantum dots in the light-converting film is 0.1-5 wt%.

[0011] Preferably, when the mass percentage of quantum dots is 0.1-1 wt%, the thickness of the light-converting film is 50-100 μm; when the mass percentage of quantum dots is 1-5 wt%, the thickness of the light-converting film is 100-200 μm.

[0012] Furthermore, the modification layer is composed of a silane coupling agent and / or a mercapto-containing compound, used to improve the dispersibility and environmental stability of quantum dots in the polymer matrix.

[0013] Furthermore, the silane coupling agent may be 3-mercaptopropyltrimethoxysilane (MPTMS), etc.

[0014] Furthermore, the compound containing polythiol groups may be trimethylolpropane tris(3-mercaptopropionate) (TMPMP), etc.

[0015] Furthermore, the anti-reflection micro / nanostructure layer has a subwavelength structure. This micro / nanostructure suppresses Fresnel reflection by constructing a refractive index gradient region, thereby reducing the interface reflectivity. Its parameters need to be optimized in conjunction with the refractive index of the light conversion film and the target enhanced spectral band to achieve efficient light capture over a wide spectrum and wide angle.

[0016] Furthermore, the subwavelength structure is conical, parabolic (such as a moth-eye structure), or square pyramidal in shape, with a structural period of 200-400 nm and a structural height of 150-300 nm.

[0017] The method for preparing the light-converting film includes the following steps: 1) Surface modification: Silane coupling agents and / or compounds containing polythiol groups are used as modifiers to modify the surface of core-shell quantum dots in order to improve the compatibility between quantum dots and polymer matrix and reduce agglomeration.

[0018] 2) Mixing and dispersing: The modified quantum dots are mixed with the polymer matrix, dispersant and additives at high temperature and high speed to ensure that each component is uniformly dispersed to obtain a mixed dispersion; 3) Film formation process: The obtained mixed dispersion is prepared into a film by solution coating, hot pressing or extrusion casting process, and then an anti-reflective micro-nano structure layer is made on it by nanoimprinting and other technologies.

[0019] The dispersant is zinc stearate or polycarboxylate. The additives include antioxidants and UV stabilizers.

[0020] Furthermore, a SiO2 or TiO2 coating can be added to the surface of the light-converting film as an additional anti-reflection layer to further improve light transmittance.

[0021] The light conversion film obtained above can be used in solar cells.

[0022] Furthermore, the light-converting film is used as a front-panel encapsulation layer or an independent optical functional layer on the light-receiving surface of a crystalline silicon solar cell or a perovskite solar cell. Specifically, the light-converting film is covered onto the light-receiving surface of the crystalline silicon solar cell or perovskite solar cell and fixed with a transparent adhesive layer, thus serving as a front-panel encapsulation layer or an independent optical functional layer.

[0023] Furthermore, when used in crystalline silicon solar cells, the core-shell quantum dots used in the light-converting film emit at a wavelength of 500-700 nm.

[0024] Furthermore, when used in perovskite solar cells, the core-shell quantum dots used in the light-converting film emit at wavelengths of 600-900 nm.

[0025] This invention, by selecting different quantum dots (downconversion for crystalline silicon and upconversion for perovskite / stacked layers), enables the same technology platform to be adapted to two current mainstream and cutting-edge technologies, demonstrating strong application flexibility—a significant application innovation. Meanwhile, existing quantum dot light conversion films often use a single stabilizing agent in their modification layers, resulting in insufficient dispersion stability and efficiency degradation exceeding 30% after 1000 hours under high temperature and humidity. Furthermore, existing light conversion films, lacking anti-reflection functionality, still exhibit interface reflectivity exceeding 5%. This invention, however, integrates an "anti-reflection micro / nanostructure layer" as a component of the light conversion film (rather than a separately added component), reducing reflectivity to below 2%, thereby significantly improving light coupling efficiency and ultimately enhancing photoelectric conversion efficiency. Additionally, since the anti-reflection micro / nanostructure is formed directly on the light conversion film body, it avoids interface and reliability issues caused by additional bonding. Moreover, its structural parameters (such as period and height) can be synergistically optimized with the refractive index, thickness, and target spectral range of the light conversion film to achieve optimal results.

[0026] The beneficial effects of this invention are as follows: (1) High light conversion efficiency and spectral matching: The present invention uses core-shell structure quantum dots combined with surface modification technology, which can achieve a quantum yield of over 80%. Its narrow emission peak (half width at half maximum < 50 nm) can accurately match the sensitive spectrum of the battery, effectively improving light absorption.

[0027] (2) Excellent dispersibility and stability: Through the synergistic effect of the surface modification layer and the dispersant, this invention can effectively prevent quantum dot aggregation and ensure the uniformity of light transmission of the film. After adding antioxidants and UV stabilizers, the efficiency retention rate of the light conversion film is ≥90% after aging at 85℃ / 85%RH for 5000 hours.

[0028] (3) Enhanced optical coupling efficiency: This invention optimizes the parameters (period, height, shape) of the integrated anti-reflection micro-nano structure based on the optical properties (refractive index, target conversion band) of the light conversion film, which can significantly reduce interface light loss.

[0029] (4) Wide compatibility and application flexibility: By selecting quantum dots with different emission wavelengths, this invention can be adapted to crystalline silicon cells (500-700nm) and perovskite cells (650-850nm), and even tandem cells, and achieve an efficiency improvement of 3-8%.

[0030] (5) Good process feasibility: The preparation process of this invention (such as solution coating, extrusion casting) is mature and easy to scale up production. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the light-converting film prepared in Example 1.

[0032] Figure 2 This is a schematic diagram of the structure in Example 1 where the prepared light-converting film is applied to the assembly of a solar cell. Detailed Implementation

[0033] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0034] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0035] Example 1: CdS / ZnS quantum dot light conversion film for crystalline silicon solar cells 1) Quantum dot selection: Conventional CdS / ZnS core-shell quantum dots are used, with an emission wavelength of 440nm, a full width at half maximum (FWHM) of less than 25nm, and a quantum yield of greater than 85%.

[0036] 2) Surface modification: 5g of CdS / ZnS core-shell quantum dots were dispersed in 100mL of toluene, and 1g of a mixture of MPTMS and TMPMP (molar ratio 1:1) was added. The mixture was stirred at 70℃ for 4h, centrifuged and dried to obtain the modified quantum dots.

[0037] 3) Mixing and dispersing: Add 80g EVA, 5g modified quantum dots, 3g zinc stearate, 0.5g hindered phenolic antioxidant, and 0.5g benzotriazole UV stabilizer to a high-speed mixer and mix at 100℃ for 2 hours.

[0038] 4) Film formation: The film is prepared by extrusion casting process with a thickness of 50 μm; and a moth-eye anti-reflective structure layer with a period of 350 nm and a height of 250 nm is formed on the film surface by nanoimprinting technology.

[0039] 5) Component assembly: The obtained light conversion film is bonded to the light-receiving surface of the monocrystalline silicon solar cell using transparent silicone.

[0040] 6) Performance test: The photoelectric conversion efficiency of this component is 23.5%, which is 5.2% higher than that of the cell without the light conversion film; after aging at 85℃ / 85%RH for 5000h, the conversion efficiency is maintained at 90%.

[0041] Example 2: InP / ZnSe / ZnS quantum dot light conversion film for perovskite solar cells 1) Quantum dot selection: Conventional InP / ZnSe / ZnS core-shell quantum dots are used, with an emission wavelength of 800nm, a full width at half maximum (FWHM) of less than 50nm, and a quantum yield of 85%.

[0042] 2) Surface modification: 8g of InP / ZnSe / ZnS core-shell quantum dots were dispersed in 100mL of chloroform, and 1g of a mixture of MPTMS and TMPMP (molar ratio 1:1) was added. The mixture was stirred at 60℃ for 3h, centrifuged and dried to obtain the modified quantum dots.

[0043] 3) Mixing and dispersing: Add 80g of POE plastic particles, 8g of modified quantum dots, 4g of tristearate, 0.8g of hindered phenolic antioxidant, and 0.7g of benzotriazole UV stabilizer to a high-speed mixer and stir at 90°C for 1.5h.

[0044] 4) Film formation: The film is prepared by blending granulation and hot pressing molding process, with a film thickness of 100 μm; and a moth-eye anti-reflection structure layer with a period of 300 nm and a height of 200 nm is formed on the film surface by nanoimprinting technology.

[0045] 5) Component assembly: The obtained light conversion film is bonded to the light-receiving surface of the perovskite solar cell using hot melt adhesive.

[0046] 6) Performance testing: The photoelectric conversion efficiency of the obtained component is 25.3%, which is 6.8% higher than that of the cell without the light conversion film; after aging at 85℃ / 85%RH for 3000 hours, the conversion efficiency retention rate is 91%. At the same time, spectral reflectance testing revealed that its average reflectance in the 600-900nm wavelength range is less than 2%.

[0047] Example 3: Dual quantum dot system light conversion film used in solar cells 1) Quantum dot selection: Conventional CdSe / ZnS quantum dots (emission wavelength 470nm) and conventional PbS / ZnS quantum dots (emission wavelength 850nm) are mixed at a mass ratio of 1:1.

[0048] 2) Surface modification: 12g of mixed quantum dots were dispersed in 100mL of toluene, and 6g of a mixture of MPTMS and TMPMP (molar ratio 1:1) were added. The mixture was stirred at 70℃ for 4h, centrifuged and dried to obtain the modified double quantum dots.

[0049] 3) Mixing and dispersing: Add 100g PVDF, 12g modified double quantum dots, 3.5g polycarboxylate dispersant, 0.6g hindered phenolic antioxidant, 0.4g benzotriazole UV stabilizer and 0.8g N-methylpyrrolidone to a high-speed mixer and mix at 110℃ for 2.5h.

[0050] 4) Film formation: A film with a thickness of 150 μm was prepared by solution coating. A moth-eye anti-reflection structure layer with a period of 350 nm and a height of 250 nm was formed on the film surface by nanoimprinting technology. Then, a 30 nm TiO2 anti-reflection layer was deposited on its surface.

[0051] 5) Component assembly: The obtained light conversion film is bonded to the light-receiving surface of the perovskite-silicon type tandem solar cell using transparent silicone.

[0052] 6) Performance test: The battery conversion efficiency reached 30.1%, which is 7.5% higher than that of the uncoated light conversion film.

[0053] Example 4: Dual quantum dot system light conversion film for solar cells 1) Quantum dot selection: Conventional CdSe / ZnS quantum dots (emission wavelength 550nm) and conventional NaYF4:Yb³⁺,Er³⁺ quantum dots (emission wavelength 680nm) are mixed at a mass ratio of 1:1.

[0054] 2) Surface modification: 12g of mixed quantum dots were dispersed in 100mL of toluene, and 6g of a mixture of MPTMS and TMPMP (molar ratio 1:1) were added. The mixture was stirred at 70℃ for 4h, centrifuged and dried to obtain the modified double quantum dots.

[0055] 3) Polymer matrix: Mix EVA and POE at a mass ratio of 3:1.

[0056] 4) Mixing and dispersing: Add 100g of polymer matrix, 12g of modified double quantum dots, 3.5g of polycarboxylate dispersant, 0.6g of hindered phenolic antioxidant, 0.4g of benzotriazole UV stabilizer and 0.8g of N-methylpyrrolidone to a high-speed mixer and mix at 110℃ for 2.5h.

[0057] 5) Film formation: A film with a thickness of 150 μm was prepared by solution coating. A moth-eye anti-reflection structure layer with a period of 350 nm and a height of 250 nm was formed on the film surface by nanoimprinting technology. Then, a 30 nm TiO2 anti-reflection layer was deposited on its surface.

[0058] 6) Component assembly: The obtained light conversion film is bonded to the light-receiving surface of the crystalline silicon solar cell using transparent silicone.

[0059] 7) Performance test: The battery conversion efficiency reached 29%, which is 7.5% higher than that without the light conversion film, and the interface reflectivity was 2.8%.

[0060] In this embodiment, considering the wide spectral response of the battery, a TiO2 coating is selected as the anti-reflection layer. This coating has excellent anti-reflection effect in a wide spectral range from ultraviolet to near infrared, and its deposition process is well compatible with the solution coating process of this embodiment, demonstrating the optimized selection of anti-reflection solutions in different application scenarios of this invention.

[0061] Comparative Example 1 Pure CdS core quantum dots (emission wavelength of about 440 nm, quantum yield of about 65%) were used to replace CdS / ZnS core-shell quantum dots, and other operations were the same as in Example 1.

[0062] Performance testing: The initial photoelectric conversion efficiency of the obtained module was 22.1%, which was only 2.8% higher than that of the cell without the light conversion film. After aging at 85℃ / 85%RH for 1000 hours, the conversion efficiency decreased to 78% of the initial value, indicating that the use of core-shell quantum dots can enable the obtained solar cell to have higher luminous efficiency and stability.

[0063] Comparative Example 2 Step 2 is omitted, i.e., InP / ZnSe / ZnS core-shell quantum dots are directly mixed with POE plastic particles, etc., and other specific operations are the same as in Example 2.

[0064] Performance testing: The obtained light conversion film showed visible cloud-like defects due to localized agglomeration of quantum dots. The initial photoelectric conversion efficiency of the obtained module was 24.0%, an improvement of only 5.5% compared to the cell without the light conversion film. After aging at 85℃ / 85%RH for 3000 hours, the conversion efficiency retention rate was only 85%, indicating that surface modification can effectively improve the dispersion of quantum dots, thereby affecting the optical uniformity and long-term stability of the obtained solar cell.

[0065] Comparative Example 3 Step 4) After the film is prepared, a 100nm ordinary planar SiO2 coating is directly deposited on the film surface. Other specific operations are the same as in Example 2.

[0066] Performance testing: The initial photoelectric conversion efficiency of the obtained component was 24.8%, which is 5.3% higher than that of the cell without the light conversion film. Spectral reflectance testing revealed that the average reflectance in the 600-900nm wavelength range increased to 4.5%, indicating that the specific micro-nano structure used in this invention enables the obtained solar cell to have a better broadband anti-reflection effect.

[0067] Comparative Example 4 In step 2), only 1g of MPTMS was used for modification, and the other operations were the same as in Example 1.

[0068] Performance testing: The initial photoelectric conversion efficiency of the obtained module was 22.8%, which was only 1.5% higher than that of the cell without the light conversion film. After aging at 85℃ / 85%RH for 1000 hours, the conversion efficiency decreased to 82% of the initial value, indicating that the synergistic advantage of using composite materials to modify the module was more significant in improving the stability of the obtained solar cell.

[0069] Comparative Example 5 The moth-eye anti-reflective structure layer with a period of 500 nm and a height of 200 nm, which was fabricated in step 4), was operated in the same manner as in Example 2.

[0070] Performance testing: The photoelectric conversion efficiency of the obtained component was 18.7%, which is only 0.2% higher than that of the cell without the light conversion film, indicating a negligible improvement in conversion efficiency. Meanwhile, spectral reflectance testing revealed an average reflectance of 5.8% in the 600-900nm wavelength range.

[0071] A comparison of the data from the above embodiments and comparative examples shows that: 1. Compared to non-core-shell structures, quantum dots with core-shell structures have significant advantages in both initial luminous efficacy and long-term stability.

[0072] 2. Compared with unmodified quantum dots, surface modification of quantum dots can effectively improve quantum dot dispersion, resulting in solar cells with better and more stable photoelectric performance.

[0073] 3. Compared to using ordinary planar anti-reflective coatings, the use of anti-reflective micro / nano structure layers can further reduce interface light loss, resulting in additional efficiency improvements.

[0074] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A quantum dot-based optical conversion film, characterized in that, The light conversion film comprises at least the following components: (1) A transparent polymer matrix; (2) Core-shell structured quantum dots uniformly dispersed in the polymer matrix; (3) A modification layer covering the outer surface of the core-shell quantum dot, wherein the modification layer is composed of a silane coupling agent and / or a compound containing multiple thiol groups, for improving the dispersibility and stability of the quantum dots in the polymer matrix; (4) An anti-reflection micro / nano structure layer is provided on at least one side of the surface of the polymer matrix.

2. The light-converting film according to claim 1, characterized in that, The polymer matrix is ​​one or more of polyacrylic resins, POE, EVA, PDMS, or epoxy resin.

3. The light-converting film according to claim 1, characterized in that, The core-shell structured quantum dots are downconversion quantum dots and / or upconversion quantum dots.

4. The light-converting film according to claim 3, characterized in that, The downconversion quantum dots are selected from CdSe / ZnS, InP / ZnS, or CsPbBr3 perovskite quantum dots.

5. The light-converting film according to claim 3, characterized in that, The upconversion quantum dots are selected from NaYF4:Yb 3+ Er 3 + Or PbS / CdS quantum dots.

6. The light-converting film according to claim 1, characterized in that, The mass percentage of core-shell quantum dots in the light-converting film is 0.1-5 wt%.

7. The light-converting film according to claim 1, characterized in that, The subwavelength structure is conical, parabolic, or square pyramidal in shape, with a structural period of 200-400 nm and a structural height of 150-300 nm.

8. The light-converting film according to claim 1, characterized in that, The thickness of the light-converting film is 50-200 μm.

9. The application of the light conversion film as described in any one of claims 1-8 in a solar cell, characterized in that, The light-converting film is used as a front-panel encapsulation layer or an independent optical functional layer, and is disposed on the light-incident surface of a crystalline silicon solar cell or a perovskite solar cell.

10. The application according to claim 9, characterized in that, When used in crystalline silicon solar cells, the core-shell quantum dots used in the light-conversion film emit at a wavelength of 500-700 nm; when used in perovskite solar cells, the core-shell quantum dots used in the light-conversion film emit at a wavelength of 600-900 nm.

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