Preparation method and application of composite photoanode doped with upconversion nanoparticles

Abstract

The present invention discloses a preparation method of a composite photoanode doped with upconversion nanoparticles, which can broaden the light absorption range of the photoanode and improve the light utilization rate, so as to achieve the purpose of improving the photoelectric conversion efficiency. The novel composite photoanode prepared by the method of the present invention is of great help to the performance improvement of dye-sensitized solar cells. On the one hand, the added upconversion nanoparticles can broaden the light absorption range to the near-infrared light region. On the other hand, the prepared TiO2 hollow spheres can improve the light scattering performance and accelerate the rapid electron transport, thereby improving the light utilization rate. Finally, by introducing gold nanoparticles, the surface plasmon resonance effect is generated to further promote light absorption. The present invention provides a new idea for the preparation of composite photoanodes in dye-sensitized solar cells. Not only is the preparation method simple, but the photoelectric conversion efficiency of the prepared composite photoanode material can reach up to 13.65%, which has certain application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of dye-sensitized solar cells, and particularly relates to a preparation method and application of a composite photoanode doped with upconversion nanoparticles. Background Art

[0002] Dye-sensitized solar cells (DSSCs) have become a good sunlight collection device due to their low production cost, simple manufacturing process, and relatively high photoelectric conversion efficiency, and have broad application prospects in many fields. Although DSSCs have achieved rapid development in the past three decades, their highest photoelectric conversion efficiency is still less than 15%. The main reason for this result is that the absorption spectrum of the photosensitizer, which is one of the main components of DSSCs, does not match the solar radiation spectrum. In particular, the response of the photosensitizer to near-infrared light is very limited, while near-infrared light almost accounts for half of the sunlight transmitted to the Earth's surface, severely restricting the further improvement of the photoelectric conversion efficiency of DSSCs devices. A feasible method to solve the above problems is to introduce upconversion nanoparticles (UCNPs) into the photoanode of DSSCs devices.

[0003] Common photoanode materials are usually wide-bandgap semiconductors, such as TiO2, ZnO, SnO2, etc. Among them, TiO2 has attracted much attention due to its non-toxic, abundant source, and low cost. However, traditional TiO2 nanoparticles have disadvantages such as small specific surface area, poor electron transport performance, narrow spectral response range (only able to absorb about 5% of the ultraviolet light band in the solar spectrum), and easy recombination of photo-generated electron-hole pairs, which greatly limit its wide application. To address these deficiencies, preparing composite photoanode materials is an effective strategy to improve the photoelectric performance of DSSCs, including but not limited to: (1) preparing TiO2 nanomaterials with different morphologies (such as nanospheres, nanosheets, nanotubes, etc.), whose larger specific surface area is beneficial to increasing the loading amount of dye molecules and improving the light scattering ability; (2) introducing rare-earth-doped UCNPs into the photoanode to broaden the light absorption range of dyes such as N719, thereby increasing the photocurrent density of DSSCs; (3) introducing nanoparticles such as gold and silver to further promote light absorption through surface plasmon resonance effect, thereby improving the photoelectric conversion efficiency of DSSCs.

[0004] It should be noted that many researchers only use one or two of the above strategies to change the structure of the photoanode, and the prepared DSSCS devices still have problems such as poor photoelectric performance. Therefore, it is very necessary to prepare multifunctional composite photoanode materials to synergistically improve the photoelectric performance of dye-sensitized solar cells. Summary of the Invention

[0005] In view of this, in order to solve the technical problem of how to significantly improve the photoelectric conversion efficiency of dye-sensitized solar cells, the present invention provides a preparation method and application of a composite photoanode doped with upconversion nanoparticles.

[0006] The primary object of the present invention is to provide a composite photoanode doped with upconversion nanoparticles. This composite photoanode is also referred to as a composite photoanode comprising a P25 layer, a TiO2-HSs / UCNPs layer, and an AuNPs layer.

[0007] Another object of the present invention is to provide a preparation method of a composite photoanode doped with upconversion nanoparticles. The preparation method of this composite photoanode is also referred to as the preparation method of a composite photoanode comprising a P25 layer, a TiO2-HSs / UCNPs layer, and an AuNPs layer. The composite photoanode prepared by this method can greatly improve the photoelectric conversion efficiency of dye-sensitized solar cells.

[0008] Another object of the present invention is to provide an application of a composite photoanode doped with upconversion nanoparticles. This application is also referred to as the application of a composite photoanode comprising a P25 layer, a TiO2-HSs / UCNPs layer, and an AuNPs layer.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] The composite photoanode of the present invention includes a P25 layer, a TiO2-HSs / UCNPs layer, and an AuNPs layer; for the composite photoanode, TiO2-HSs and UCNPs are first prepared, and then P25 slurry and TiO2-HSs / UCNPs slurry are respectively prepared. Specifically, a preparation method of a composite photoanode doped with upconversion nanoparticles is to layer-print TiO2 slurry (P25 slurry) and TiO2-HSs / UCNPs slurry on a conductive substrate, dry to obtain a photoanode film, and then calcine at 475 - 500 °C for 15 - 45 min, and in-situ grow gold nanoparticles AuNPs on the calcined photoanode film to obtain the product.

[0011] The effective area of the photoanode film is about 0.36 cm 2 . The conductive substrate is FTO conductive glass.

[0012] Specifically, TiO2 can be added to a mixed solution containing α-terpineol, ethyl cellulose, and absolute ethanol, followed by ultrasonic treatment and continuous stirring in a water bath until the ethanol completely evaporates to obtain a TiO2 slurry; TiO2-HSs and UCNPs are added to a mixed solution containing α-terpineol, ethyl cellulose, and absolute ethanol, and stirred at room temperature for 36 - 60 h to obtain a TiO2-HSs / UCNPs slurry; the mass ratio of absolute ethanol, α-terpineol, and ethyl cellulose is (1.0 - 1.2):(1.57 - 1.58):(0.09 - 1.00).

[0013] Further, the TiO2-HSs are titanium dioxide hollow spheres; the TiO2-HSs are prepared through the following steps: 0.50 - 0.70 g of oxalic acid is added to a mixed solution composed of 25 - 40 ml of isopropanol and 0.3 - 0.5 ml of tetrabutyl titanate and stirred evenly, then hydrothermally reacted at 170 - 190 °C for 4 - 8 h, and the obtained product is centrifuged, washed, and dried to obtain TiO2-HSs.

[0014] Further, the UCNPs are NaYF4:Yb,Er@NaLuF4:Eu@SiO2; the preparation steps of the UCNPs are as follows:

[0015] S1. Add the rare earth ion source 1 to a mixed solution of oleic acid and 1-octadecene, heat and stir to form a homogeneous solution A; mix NH4F and NaOH in methanol to form a colorless transparent solution B; add solution B to solution A, stand and react at 110 - 130 °C for 20 - 40 min, then heat to 290 - 310 °C under an argon atmosphere and stand and react for 50 - 70 min. The obtained product is centrifuged, separated, washed, and then dispersed in cyclohexane to obtain a solution C with a concentration of 0.05 - 0.15 mmol / ml;

[0016] S2. Add the rare earth ion source 2 to a mixed solution of oleic acid and 1-octadecene, heat and stir to form a homogeneous solution D (with a concentration of 0.05 - 0.15 mmol / ml); add the solution C prepared in step S1 to solution D (the volume addition ratio of solution C to solution D is 5:18 - 24), stand and react at 110 - 130 °C for 20 - 40 min, then heat to 290 - 310 °C under an argon atmosphere and stand and react for 80 - 100 min. The obtained product is centrifuged, separated, washed, and then dispersed in cyclohexane to obtain solution E;

[0017] S3. Mix cyclohexane, isopropanol, and polyvinylpyrrolidone in a single-neck flask, then add solution E, deionized water, tetraethyl orthosilicate (tetraethoxysilane), and ammonia water (mass percentage concentration 20 - 30%), and continuously stir for 20 - 40 min; the obtained product is washed with absolute ethanol, centrifuged, and dried to obtain UCNPs powder.

[0018] In the above preparation method, in step S1, the rare earth ion source 1 is composed of a mixture of Y(CH3COO)3·4H2O, Yb(CH3COO)3·4H2O, and Er(CH3COO)3·4H2O with a molar ratio of 0.7 - 0.9:0.10 - 0.30:0.01 - 0.03; the dosage ratio of NH4F, NaOH, and methanol is 0.1 - 0.2 g:0.1 - 0.3 g:8 - 12 mL; in steps S1 and S2, the volume ratio of oleic acid to 1-octadecene is 5 - 7:12 - 18.

[0019] In the above preparation method, in step S2, the rare earth ion source 2 is composed of a mixture of Lu(CH3COO)3·4H2O and Eu(CH3COO)3·4H2O with a molar ratio of 3 - 5:1; in step S3, the dosage ratio of solution E, cyclohexane, isopropanol, and polyvinylpyrrolidone is 8 - 12 mL:8 - 12 mL:15 - 25 mL:0.01 - 0.03 g, and the volume ratio of deionized water, tetraethyl orthosilicate, and ammonia water is 3 - 5:0.05 - 0.07:0.4 - 0.6; the mass percentage concentration of solution E is 15 - 25%.

[0020] Further, the in-situ growth of gold nanoparticles AuNPs on the calcined photoanode film is as follows:

[0021] Mix deionized water, trisodium citrate, and a HAuCl4 solution with a concentration of 4 - 7 mM and stir to form solution G; put the calcined photoanode film into solution G and irradiate it under ultraviolet light, then wash and dry it, and then immerse the photoanode film in an aqueous TiCl4 solution and keep it at 60 - 80 °C for 20 - 40 min, then take it out and calcine it to obtain.

[0022] Further, the dosage ratio of deionized water, trisodium citrate, and the HAuCl4 solution is 40 - 60 mL:0.04 - 0.06 g:480 - 550 µL, the ultraviolet light irradiation time is 110 - 130 min, the calcination temperature is 475 - 500 °C, and the calcination time is 20 - 40 min.

[0023] The present invention provides a composite photoanode doped with upconversion nanoparticles prepared by the above method.

[0024] The present invention also provides the application of the composite photoanode doped with the above upconversion nanoparticles in dye-sensitized solar cells.

[0025] The novel composite photoanode material prepared by the method of the present invention greatly improves the performance of dye-sensitized solar cells. The added upconversion nanoparticles can enhance the response of dye-sensitized solar cells to infrared light and expand the light absorption range of the photoanode. The added layered multifunctional photoanode material can accelerate electron transport and reduce charge recombination. The preparation method of the novel composite photoanode material provided by the present invention provides a new idea for the preparation of dye-sensitized solar cells. Not only is the preparation method simple, but the prepared dye-sensitized solar cells have very good performance and have certain application value.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) The composite photoanode in the present invention is a composite photoanode comprising a P25 layer, a TiO2-HSs / UCNPs layer and an AuNPs layer. The preparation method is simple, and the photoelectric conversion efficiency of the prepared dye-sensitized solar cells is extremely high. TiO2-HSs has a large specific surface area, which is beneficial to adsorb more dye molecules, thus improving the performance of dye-sensitized solar cells. In addition, dye-sensitized solar cells are very suitable for large-scale mass production, which has important practical significance for meeting the electricity needs of urban residents and the vast rural areas, especially for the electricity demand of the population in remote areas of our country;

[0028] 2) In the present invention, the rare-earth-doped upconversion nanoparticle NaYF4:Yb,Er@NaLuF4:Eu@SiO2 is a material that can perform upconversion. It has high fluorescence intensity and can also convert the infrared light that accounts for most of the light wave into visible light that can be absorbed by the dye, and the light trapping efficiency will be greatly improved, thereby effectively improving the photoelectric conversion efficiency;

[0029] 3) In the present invention, AuNPs are grown on the surface of the photoanode film containing TiO2-HSs / UCNPs. By utilizing the surface plasmon resonance effect of AuNPs, the light absorption of dye molecules is further promoted, and the photoelectric conversion efficiency is further improved. Description of the Drawings

[0030] Figure 1 is the TEM spectrum of rare-earth-doped upconversion nanoparticles; the left figure is the transmission electron micrograph of NaYF4:Yb,Er nanoparticles, and the right figure is the transmission electron micrograph of NaYF4:Yb,Er@NaLuF4:Eu nanoparticles;

[0031] Figure 2 is the electron micrograph of TiO2-HSs; the left figure is the TEM image, and the right figure is the SEM image;

[0032] Figure 3 XRD patterns of TiO2 / FTO and Au / TiO2 / FTO show that Au nanoparticles are successfully coated on the surface of TiO2 thin film;

[0033] Figure 4 I-V test results of dye-sensitized solar cells show that by doping TiO2-HSs and UCNPs and growing Au nanoparticles on the surface of the photoanode thin film, high-efficiency photocurrent is finally achieved and the performance of the dye-sensitized cells is improved. Specific Embodiments

[0034] To make the above objects, features and advantages of the present invention more obvious and understandable, the following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0035] In the following embodiments, the raw materials used are all ordinary commercially available products that can be directly purchased. For example, TiO2 is a commonly available product with a particle size of 25 nm. Room temperature refers to 25 ± 5 °C.

[0036] Example 1

[0037] NaYF4:Yb,Er upconversion nanoparticles were prepared by the solvothermal method as follows:

[0038] (1) Weigh 0.78 mmol Y(CH3COO)3·4H2O, 0.2 mmol Yb(CH3COO)3·4H2O, 0.02 mmol Er(CH3COO)3·4H2O, 6 mL oleic acid and 15 mL 1-octadecene and pour them into a 100 mL three-necked round-bottom flask;

[0039] (2) Under an argon atmosphere, heat and magnetically stir the mixture obtained in step (1) to 156 °C and keep it for 10 min to form a homogeneous solution A;

[0040] (3) Mix 0.1 g NH4F, 0.148 g NaOH and 10 mL methanol to form a colorless transparent solution B;

[0041] (4) Slowly drop the solution B obtained in step (3) into the solution A in step (2) to form a milky precursor solution;

[0042] (5) Let the solution obtained in step (4) stand for reaction at 120 °C for 10 min, and then stand for reaction at 120 °C in vacuum (about -0.1 MPa, the same below) for 20 min;

[0043] (6) Keeping an argon atmosphere, heat the solution obtained in step (5) to 300 °C and let it stand for reaction for 60 min to form a pale yellow solution;

[0044] (7) Cool to room temperature, separate the nanoparticles from the product of step (6) by centrifugation (conditions: rotation speed 8000 rpm; time 5 min), then wash with ethanol and disperse in cyclohexane to obtain solution C with a concentration of 0.1 mmol / ml.

[0045] Detect the crystal morphology of the nanoparticles obtained in step (7) by TEM (see Figure 1 on the left). It can be seen from the figure that the nanoparticles are 20 - 30 nm in size, with uniform size and high crystallinity. The NaYF4:Yb,Er upconversion nanoparticles can convert near-infrared light into ultraviolet and visible light. The TiO2 layer doped with upconversion nanoparticles can act as a reflective layer, expanding the light absorption range of the photoanode film, improving the utilization rate of sunlight, facilitating the excitation of more photogenerated electrons, and improving the battery performance.

[0046] Example 2

[0047] First, the rare earth ions are Lu(CH3COO)3·4H2O and Eu(CH3COO)3·4H2O, and the upconversion nanoparticles NaYF4:Yb,Er@NaLuF4:Eu are prepared by the solvothermal method as follows:

[0048] (1) Weigh 0.8 mmol of Lu(CH3COO)3·4H2O, 0.2 mmol of Eu(CH3COO)3·4H2O, 6 mL of oleic acid and 15 mL of 1-octadecene and pour them into a 100 mL three-necked round-bottom flask.

[0049] (2) Under an argon atmosphere, heat the mixture obtained in (1) with magnetic stirring to 156 °C and keep it for 10 min to form a homogeneous solution D;

[0050] (3) Slowly drop 5 ml of solution C with a concentration of 0.1 mmol / ml prepared in Example 1 into solution D in step (2) to form a white precursor solution;

[0051] (4) Let the solution obtained in step (3) stand for reaction at 120 °C for 10 min, and then stand for reaction at 120 °C in vacuum for 20 min;

[0052] (5) Maintain an argon atmosphere, heat the solution obtained in step (4) to 300 °C, and let it stand for reaction for 90 min to form a pale yellow solution;

[0053] (6) Cool to room temperature (at this time it becomes a yellow turbid liquid), separate the nanoparticles from the product of step (5) by centrifugation (conditions: rotation speed 8000 rpm; time 5 min), then wash with ethanol and disperse in cyclohexane to obtain solution E (mass concentration 20%).

[0054] Detect the crystal morphology of the core-shell nanoparticles NaYF4:Yb,Er@NaLuF4:Eu prepared in step (6) by TEM (see Figure 1 right). It can be seen from the figure that the nanoparticles are 35 - 40 nm in size, with uniform size and high crystallinity. The upconversion nanoparticles can convert near-infrared light into ultraviolet and visible light. The TiO2 layer doped with upconversion nanoparticles can be used as a reflective layer to expand the light absorption range of the photoanode film, improve the utilization rate of sunlight, facilitate the excitation of more photogenerated electrons, and improve the battery performance.

[0055] Secondly, using tetraethyl orthosilicate as the silicon source, coat SiO2 on the surface of the upconversion core-shell nanoparticles NaYF4:Yb,Er@NaLuF4:Eu to prepare UCNPs (NaYF4:Yb,Er@NaLuF4:Eu@SiO2), which specifically includes the following steps:

[0056] (1) Weigh 10 mL of cyclohexane, 20 mL of isopropanol, and 0.02 g of polyvinylpyrrolidone and pour them into a 100 mL single-neck flask. Add 10 mL of NaYF4:Yb,Er@NaLuF4:Eu (20%) nanoparticle solution (i.e., solution E) and keep stirring;

[0057] (2) Drop 4 mL of deionized water and 0.06 mL of tetraethyl orthosilicate into the product of step (1), and then gradually add 0.5 mL of ammonia water (mass percentage concentration 25%), and keep stirring for 30 min;

[0058] (3) Wash the product of step (2) with absolute ethanol, collect by centrifugation, and dry (conditions: drying temperature 70 °C; time 12 h) to obtain UCNPs powder.

[0059] Example 3

[0060] The preparation method of the TiO2-HSs (i.e., TiO2 hollow spheres) is as follows:

[0061] (1) Weigh 0.58 g of oxalic acid, 30 mL of isopropanol, and 0.4 mL of tetrabutyl titanate and pour them into a single-neck flask, and stir for 40 min to mix evenly;

[0062] (2) Place it in a Teflon-lined autoclave and carry out hydrothermal reaction at 180 °C for 6 h.

[0063] (3) After the reaction is completed, centrifuge and collect the product of step (2) (conditions: rotation speed 8000 rpm; time 10 min), wash it three times with distilled water and absolute ethanol respectively, and dry it (conditions: temperature 70 °C; time 6 h) to obtain the product TiO2-HSs.

[0064] The morphology of TiO2-HSs was obtained by TEM and SEM (see Figure 2 ). The TEM image on the left reveals that these spheres are hierarchical hollow structures. The gradual contrast from the edge to the center of the sphere indicates that the whole sphere is a hollow structure with a shell thickness of about 80 nm. It can be seen from the SEM image on the right that the surface is composed of a hierarchical structure.

[0065] The preparation process of the TiO2 slurry is as follows:

[0066] Take 0.34 g of TiO2 (P25) and place it in a 100 mL single-necked flask. Then add 1 g of absolute ethanol, 1.58 g of α-terpineol, and 0.09 g of ethyl cellulose in sequence, and then place it in a stirrer and stir at room temperature for 48 h.

[0067] The preparation process of the TiO2-HSs / UCNPs slurry is as follows:

[0068] Take 0.306 g of TiO2-HSs and 0.034 g of UCNPs powder in a single-necked flask. Then add 1 g of absolute ethanol, 1.58 g of α-terpineol, and 0.09 g of ethyl cellulose in sequence, and then place it in a stirrer and stir at room temperature for 48 h.

[0069] Example 4

[0070] A preparation method of an upconversion nanoparticle-doped composite photoanode, which is to layer-print the TiO2 slurry and the TiO2-HSs / UCNPs slurry on a conductive substrate FTO conductive glass (each layer has a thickness of about 4 microns, the TiO2 slurry is printed continuously for 5 layers, and then the TiO2-HSs / UCNPs slurry is printed continuously for 2 layers). After drying (first at room temperature for 5 min, then at 120 °C for 5 min), a photoanode film is obtained. Then it is calcined at 475 °C for 15 min and at 500 °C for 15 min. Then gold nanoparticles AuNPs are in-situ grown on the calcined photoanode film to obtain the composite photoanode, denoted as Au / TiO2-120min+UCNPs. The effective area of the photoanode film is about 0.36 cm 2 .

[0071] The in-situ growth of gold nanoparticles AuNPs on the calcined photoanode film is as follows:

[0072] (1) Take 50 mL of deionized water, 0.050 g of trisodium citrate, and 500 μL of 5 mM HAuCl4 solution in a beaker, and stir evenly to form solution G;

[0073] (2) Place the calcined photoanode film into solution G with the conductive side facing up, maintain the temperature at 60 °C, and place it under an ultraviolet lamp for irradiation for 120 min. The solution turns red, and at the same time, the photoanode film turns purple-red;

[0074] (3) Dropwise add deionized water and ethanol to clean the film obtained in step (2) respectively, and then dry it at 60 °C for 10 min;

[0075] (4) Immerse the photoanode film obtained in step (3) into an aqueous solution of TiCl4 (20 mM), keep it at a temperature of 70 °C for 30 min, and take it out (a thin layer of TiO2 nanoparticles is formed);

[0076] (5) Calcinate the film obtained in step (4) (conditions: temperature programming to 475 °C, hold for 15 min; 500 °C, hold for 15 min) to obtain the product.

[0077] Comparative example

[0078] A preparation method of an upconversion nanoparticle-doped photoanode, which layer-by-layer prints TiO2 slurry on a conductive substrate FTO conductive glass (each layer has a thickness of about 4 microns, and the TiO2 slurry is continuously printed in 5 layers). After drying (first at room temperature for 5 min, then at 120 °C for 5 min), a photoanode film is obtained. Then, it is calcined at 475 °C for 15 min and at 500 °C for 15 min to obtain the photoanode, denoted as TiO2 / FTO. The effective area of the photoanode film is about 0.36 cm 2 .

[0079] A preparation method of an upconversion nanoparticle-doped photoanode, which layer-by-layer prints TiO2 slurry on a conductive substrate FTO conductive glass (each layer has a thickness of about 4 microns, and the TiO2 slurry is continuously printed in 5 layers). After drying (first at room temperature for 5 min, then at 120 °C for 5 min), a photoanode film is obtained. Then, it is calcined at 475 °C for 15 min and at 500 °C for 15 min, and then gold nanoparticles AuNPs are in-situ grown on the calcined photoanode film to obtain the photoanode, denoted as Au / TiO2 / FTO. The effective area of the photoanode film is about 0.36 cm 2 .

[0080] The in-situ growth of gold nanoparticles AuNPs on the calcined photoanode film is as follows:

[0081] (1) Take 50 mL of deionized water, 0.050 g of trisodium citrate, and 500 μL of 5 mM HAuCl4 solution in a beaker, and stir evenly to form solution G;

[0082] (2) Place the calcined photoanode film into solution G with the conductive side facing up, keep the temperature at 60 °C, and place it under an ultraviolet lamp for irradiation for 120 min. The solution turns red, and at the same time, the photoanode film turns purple-red;

[0083] (3) Dropwise add deionized water and ethanol to clean the film obtained in step (2) respectively, and then dry it at 60 °C for 10 min;

[0084] (4) Immerse the photoanode film obtained in step (3) into an aqueous solution of TiCl4 (20 mM), keep it at 70 °C for 30 min, and take it out (a thin layer of TiO2 nanoparticles is formed);

[0085] (5) Calcinate the film obtained in step (4) (conditions: programmed heating to 475 °C, hold for 15 min; 500 °C, hold for 15 min), and then it is obtained.

[0086] Figure 3 The XRD patterns of the photoanodes TiO2 / FTO and Au / TiO2 / FTO are given. Figure 3 It can be seen from [here] that Au nanoparticles are successfully coated on the surface of the TiO2 film.

[0087] In addition, this application investigated the performance of dye-sensitized solar cells assembled with photoanodes prepared by irradiating under an ultraviolet lamp for different times (60 min, 120 min, 180 min) (denoted as: Au / TiO2-60min, Au / TiO2-120min, Au / TiO2-180min) respectively. The specific battery assembly is as follows:

[0088] Place the prepared photoanode into 0.5 mmol / L N719 dye and keep it at room temperature for 24 h. After the dyeing is completed, rinse the surface with anhydrous ethanol. Seal the platinum electrode and the photoanode with a 25-μm-thick hot melt adhesive, dropwise add the electrolyte (Dalian Qise Guang Solar Technology Co., Ltd., DHS-ET23), and seal the hole with a 5-mm round glass sheet.

[0089] The battery performance results are shown in Figure 4 . Figure 4 It can be seen from [here] that when irradiated under an ultraviolet lamp for 120 min, the battery efficiency is the best.

[0090] On this basis, it was selected to irradiate for 120 min under ultraviolet light, and at the same time, UCNPs were assisted to prepare a composite photoanode (i.e., Au / TiO2-120min+UCNPs in Example 4).

[0091] The current density-voltage relationship of the dye-sensitized solar cell assembled with the composite photoanode obtained in Example 4 is as Figure 4 shown, Figure 4 It can be seen from 2 that the highest photoelectric conversion efficiency of the prepared dye-sensitized solar cell can reach 13.65%, the corresponding short-circuit current density is 26.42 mA / cm

[0092] The preparation method of the composite photoanode doped with upconversion nanoparticles of the present invention can broaden the light absorption range of the photoanode and improve the light utilization rate, so as to achieve the purpose of improving the photoelectric conversion efficiency. The novel composite photoanode prepared by the method of the present invention is of great help to the performance improvement of dye-sensitized solar cells. On the one hand, the added upconversion nanoparticles can broaden the light absorption range to the near-infrared light region. On the other hand, the prepared TiO2 hollow spheres can improve the light scattering performance and accelerate the rapid electron transport, thereby improving the light utilization rate. Finally, by introducing gold nanoparticles, the surface plasmon resonance effect is generated to further promote light absorption. The present invention provides a new idea for the preparation of composite photoanodes in dye-sensitized solar cells. Not only is the preparation method simple, but the photoelectric conversion efficiency of the prepared composite photoanode material can reach up to 13.65%, which has certain application value.

[0093] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, several improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of an upconversion nanoparticle-doped composite photoanode, characterized in that, The TiO2 slurry and the TiO2-HSs / UCNPs slurry are printed layer by layer on a conductive substrate, and after drying, a photoanode film is obtained. Then, it is calcined at 475 - 500 °C for 15 - 45 min, and gold nanoparticles AuNPs are grown in-situ on the calcined photoanode film to obtain the product; The TiO2-HSs are titanium dioxide hollow spheres; The UCNPs are NaYF4:Yb,Er@NaLuF4:Eu@SiO2; the preparation steps of the UCNPs are as follows: S1. Add the rare earth ion source 1 into the mixed solution of oleic acid and 1-octadecene, heat and stir to form a homogeneous solution A; mix NH4F and NaOH into methanol to form a colorless and transparent solution B; add solution B to solution A, stand and react at 110 - 130 °C for 20 - 40 min, then heat up to 290 - 310 °C under an argon atmosphere and stand and react for 50 - 70 min. The obtained product is centrifuged, washed, and then dispersed in cyclohexane to obtain solution C; S2. Add the rare earth ion source 2 into the mixed solution of oleic acid and 1-octadecene, heat and stir to form a homogeneous solution D; add the solution C prepared in step S1 to solution D, stand and react at 110 - 130 °C for 20 - 40 min, then heat up to 290 - 310 °C under an argon atmosphere and stand and react for 80 - 100 min. The obtained product is centrifuged, washed, and then dispersed in cyclohexane to obtain solution E; S3. Mix cyclohexane, isopropanol and polyvinylpyrrolidone, then add solution E, deionized water, tetraethyl orthosilicate and ammonia water, and continuously stir for 20 - 40 min; the obtained product is centrifuged and dried to obtain UCNPs powder; In step S1, the rare earth ion source 1 is composed of a mixture of Y(CH3COO)3·4H2O, Yb(CH3COO)3·4H2O and Er(CH3COO)3·4H2O with a molar ratio of 0.7 - 0.9:0.10 - 0.30:0.01 - 0.03; the dosage ratio of NH4F, NaOH and methanol is 0.1 - 0.2 g:0.1 - 0.3 g:8 - 12 mL; in steps S1 and S2, the volume ratio of oleic acid and 1-octadecene is 5 - 7:12 - 18; In step S2, the rare earth ion source 2 is composed of a mixture of Lu(CH3COO)3·4H2O and Eu(CH3COO)3·4H2O with a molar ratio of 3 - 5:1; in step S3, the dosage ratio of solution E, cyclohexane, isopropanol and polyvinylpyrrolidone is 8 - 12 mL:8 - 12 mL:15 - 25 mL:0.01 - 0.03 g, and the volume ratio of deionized water, tetraethyl orthosilicate and ammonia water is 3 - 5: 0.05 - 0.07:0.4 - 0.6; the mass percentage concentration of solution E is 15 - 25%.

2. The preparation method of the composite photoanode doped with upconversion nanoparticles according to claim 1, characterized in that, TiO2 was added to a mixed solution containing α-terpineol, ethyl cellulose, and absolute ethanol, followed by ultrasonic treatment and continuous stirring in a water bath until the ethanol completely evaporated to obtain a TiO2 slurry; TiO2-HSs and UCNPs were added to a mixed solution containing α-terpineol, ethyl cellulose, and absolute ethanol, stirred at room temperature for 36 - 60 h, followed by ultrasonic treatment and continuous stirring in a water bath until the ethanol completely evaporated to obtain a TiO2-HSs / UCNPs slurry; the mass ratio of absolute ethanol, α-terpineol, and ethyl cellulose was (1.0~1.2):(1.57~1.58):(0.09~1.00).

3. The preparation method of the composite photoanode doped with upconversion nanoparticles according to claim 1, wherein, The TiO2-HSs were prepared through the following steps: 0.50 - 0.70 g of oxalic acid was added to a mixed solution composed of 25 - 40 ml of isopropanol and 0.3 - 0.5 ml of tetrabutyl titanate and stirred evenly, then hydrothermally reacted at 170 - 190 °C for 4 - 8 h. The obtained product was centrifuged, washed, and dried to obtain TiO2-HSs.

4. The preparation method of the composite photoanode doped with upconversion nanoparticles according to claim 1, characterized in that, The in-situ growth of AuNPs on the calcined photoanode film was specifically as follows: Deionized water, trisodium citrate, and a HAuCl4 solution with a concentration of 4 - 7 mM were mixed and stirred to form solution G; the calcined photoanode film was placed in solution G and irradiated under ultraviolet light, then washed and dried. Then the photoanode film was immersed in an aqueous TiCl4 solution and maintained at 60 - 80 °C for 20 - 40 min, then taken out and calcined to obtain the product.

5. The preparation method of the composite photoanode doped with upconversion nanoparticles according to claim 4, characterized in that, The dosage ratio of deionized water, trisodium citrate, and the HAuCl4 solution was 40 - 60 mL: 0.04~0.06 g: 480~550 µL, the ultraviolet light irradiation time was 110 - 130 min, the calcination temperature was 475 - 500 °C, and the calcination time was 20 - 40 min.

6. A composite photoanode doped with upconversion nanoparticles prepared by the method according to any one of claims 1 to 5.

7. Use of the composite photoanode doped with upconversion nanoparticles according to claim 6 in a dye-sensitized solar cell.

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