Electron transport material, preparation method thereof, solar cell and photovoltaic module

Abstract

The invention discloses an electron transport material and a preparation method thereof, a solar cell and a photovoltaic module, the electron transport material for the perovskite solar cell comprises TiO2 and a doping material, and the doping material comprises noble metal nanoparticles and carbon quantum dots loaded on the surface of TiO2, and nickel and cobalt co-doped in crystal lattices of TiO2. Through the combined action of the precious metal nanoparticles, the carbon quantum dots and the nickel-cobalt co-doped TiO2, photon-generated carrier separation is promoted, the electron mobility is improved, meanwhile, light utilization and absorption of perovskite are promoted, and the effect of further improving the energy conversion efficiency of the solar cell is remarkable.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solar cells, in particular to an electron transport material, a preparation method thereof, a solar cell and a photovoltaic module. BACKGROUND

[0002] In a solar cell, an electron transport layer serves as a bridge between a perovskite layer and an electrode, blocks the transmission of holes to the electrode while extracting electrons, and requires the material itself to have good morphology, high mobility, and a high matching energy band structure with the perovskite. TiO2 is a commonly used electron transport material, but the energy band structure matching between TiO2 and the perovskite is poor, the electron mobility is low, and hysteresis is prone to occur, which limits the further improvement of the energy conversion efficiency of the solar cell. SUMMARY

[0003] Embodiments of the present application disclose an electron transport material, a preparation method thereof, a solar cell and a photovoltaic module, which can promote the separation of photo-generated carriers, improve the electron mobility, promote the utilization and absorption of light by the perovskite, and solve the problems of poor energy band structure matching between TiO2 and the perovskite, low electron mobility, and hysteresis.

[0004] In a first aspect, the embodiments of the present application provide an electron transport material for a perovskite solar cell.

[0005] The electron transport material comprises TiO2 and a doping material, the doping material comprises noble metal nanoparticles loaded on the surface of the TiO2, carbon quantum dots, and nickel and cobalt co-doped in the crystal lattice of the TiO2.

[0006] As an optional implementation, in the embodiments of the present application, the size of the carbon quantum dots is between 1 nm and 10 nm; and / or, the size of the noble metal nanoparticles is between 5 nm and 20 nm.

[0007] As an optional implementation, in the embodiments of the present application, the doping mass fraction of the nickel is 0.3% to 1%; and / or, the doping mass fraction of the cobalt is 0.3% to 1%.

[0008] As an optional implementation, in the embodiments of the present application, the noble metal comprises one or more of Pt, Ag, Au and Pd; and / or, the crystal phase of the TiO2 is any one of an anatase crystal phase, a rutile crystal phase or an anatase and rutile mixed crystal phase.

[0009] In a second aspect, the embodiments of the present application provide a preparation method of an electron transport material.

[0010] The electronic transport material co-dopes the nickel and the cobalt in the crystal lattice of the TiO2 first, and then loads the carbon quantum dots and the noble metal nanoparticles on the surface of the TiO2 co-doped with the nickel and the cobalt.

[0011] As an optional embodiment, in the embodiment of the present application, after the nickel and the cobalt are co-doped in the crystal lattice of the TiO2, the loading treatment of the carbon quantum dots is performed first, and then the loading treatment of the noble metal nanoparticles is performed.

[0012] As an optional embodiment, in the embodiment of the present application, the preparation method of co-doping the nickel and the cobalt in the TiO2 crystal lattice is as follows: titanium source, nickel salt and cobalt salt are placed in a solution state for hydrolysis to form a precipitate, and the precipitate is dried and calcined to obtain nickel-cobalt co-doped TiO2.

[0013] When the nickel-cobalt co-doped TiO2 surface is loaded with the carbon quantum dots first and then loaded with the noble metal nanoparticles, the preparation method of the electronic transport material includes the following steps:

[0014] Loading the carbon quantum dots: mixing carbon quantum dot solution with the nickel-cobalt co-doped TiO2, and then performing stirring or ultrasonic treatment, followed by washing and drying to load the carbon quantum dots on the surface of the nickel-cobalt co-doped TiO2;

[0015] Loading the noble metal nanoparticles: mixing noble metal precursor solution with the nickel-cobalt co-doped TiO2 loaded with the carbon quantum dots, reducing the noble metal precursor solution to the noble metal nanoparticles by a photoreduction reaction, and loading the noble metal nanoparticles on the nickel-cobalt co-doped TiO2 loaded with the carbon quantum dots;

[0016] When the TiO2 surface is loaded with the noble metal nanoparticles first and then loaded with the carbon quantum dots, the preparation method of the electronic transport material includes the following steps:

[0017] Loading the noble metal nanoparticles: mixing noble metal precursor solution with the nickel-cobalt co-doped TiO2, reducing the noble metal precursor solution to the noble metal nanoparticles by a photoreduction reaction, and loading the noble metal nanoparticles on the nickel-cobalt co-doped TiO2;

[0018] Loading the carbon quantum dots: mixing carbon quantum dot solution with the nickel-cobalt co-doped TiO2 loaded with the noble metal nanoparticles, and then performing stirring or ultrasonic treatment, followed by washing and drying to load the carbon quantum dots on the surface of the nickel-cobalt co-doped TiO2 loaded with the noble metal nanoparticles.

[0019] As an optional implementation, in the embodiment of the present application, in the step of doping the nickel and the cobalt in the TiO2 lattice, the calcination temperature is 550-750℃, and the time is 1-4h; and / or, in the step of loading the carbon quantum dots, the stirring temperature is 10-30℃, and the time is 1-2h; and / or, in the step of loading the noble metal nanoparticles, the photoreduction reaction is performed under ultraviolet light irradiation for 30-100min.

[0020] As an optional implementation, in the embodiment of the present application, the titanium source includes one or both of tetrabutyl titanate and isopropyl titanate; and / or, the nickel salt includes one or both of nickel nitrate and nickel acetate; and / or, the cobalt salt includes one or both of cobalt nitrate and cobalt acetate.

[0021] As an optional implementation, in the embodiment of the present application, the carbon quantum dot solution is prepared by heating a carbon source in a solvent to pyrolysis, and the mass ratio of the carbon source to the solvent is 1:280-330.

[0022] When the carbon quantum dots are loaded first and the noble metal nanoparticles are loaded later, the input ratio of the carbon quantum dot solution to the nickel-cobalt co-doped TiO2 is 100μL:0.1g-0.2g, the input ratio of the noble metal precursor solution to the nickel-cobalt co-doped TiO2 loaded with the carbon quantum dots is 50-100μL:0.1g-0.2g, and the concentration of the noble metal precursor solution is 5-10mmol / L.

[0023] When the noble metal nanoparticles are loaded first and the carbon quantum dots are loaded later, the input ratio of the noble metal precursor solution to the nickel-cobalt co-doped TiO2 is 50-100μL:0.1g-0.2g, the concentration of the noble metal precursor solution is 5-10mmol / L, and the input ratio of the carbon quantum dot solution to the nickel-cobalt co-doped TiO2 loaded with the noble metal nanoparticles is 100μL:0.1g-0.2g.

[0024] In a third aspect, the embodiments of the present application provide a solar cell.

[0025] The solar cell includes an electron transport layer, and the material of the electron transport layer includes the electron transport material as mentioned in the first aspect or the electron transport material prepared by the preparation method as mentioned in the second aspect.

[0026] As an optional implementation, in the embodiment of the present application, the solar cell is a perovskite tandem solar cell, which comprises a bottom cell and a first transparent conductive layer, a first transport layer, a perovskite layer, a second transport layer, a second transparent conductive layer and a first electrode arranged in sequence on the bottom cell, one of the first transport layer and the second transport layer is the electron transport layer, and the other is the hole transport layer.

[0027] As an optional implementation, in the embodiment of the present application, the solar cell is a perovskite single-junction solar cell, which comprises a first electrode, a transparent conductive substrate, a first transport layer, a perovskite layer, a second transport layer, a transparent conductive layer and a second electrode arranged in sequence, one of the first transport layer and the second transport layer is the electron transport layer, and the other is the hole transport layer.

[0028] In a fourth aspect, the present application provides a photovoltaic module.

[0029] A photovoltaic module comprises the solar cell mentioned in the third aspect.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] Nickel and cobalt are co-doped in the crystal lattice of TiO2, and at the same time, noble metal nanoparticles and carbon quantum dots are loaded on the surface of TiO2. These four materials show a better synergistic effect in TiO2, and the obtained electron transport material not only has an excellent matching effect with perovskite, but also can significantly reduce the recombination rate of photo-generated electrons and holes, and improve the electron mobility of the electron transport material. Specifically, the radius of nickel and cobalt elements is relatively small compared with the radius of titanium ions, and can partially replace the Ti 3+ defect state on the surface of titanium dioxide, passivate the defect state of TiO2, and load carbon quantum dots on the surface of TiO2, which can provide an effective charge transport channel and accelerate the extraction of carriers. The Schottky junction formed between the noble metal and TiO2 helps to separate the photo-generated carriers, so the noble metal cooperates with the carbon quantum dots and nickel-cobalt ions to synergistically passivate the defects of TiO2, further improve the electron mobility, reduce the probability of carrier and defect state recombination at the interface, and realize the significant improvement of the electron mobility of TiO2.

[0032] And more importantly, the co-doping of nickel and cobalt elements can change the electronic structure and energy level distribution inside TiO2, thereby reducing the band gap width of TiO2 and increasing the absorption of photons by perovskite; the conduction band and valence band of carbon quantum dots are located between TiO2 and perovskite, which helps to reduce the energy level barrier of TiO2 and perovskite layer, avoiding additional energy loss of photo-generated electrons in the transmission process; in addition to scattering photons, the electronic dipole oscillation effect of noble metals can trigger the absorption of electromagnetic energy, increase the local light field, and help to improve the utilization rate of light by perovskite. Through the synergistic effect of the three, the absorption and utilization of light by perovskite can be fully improved, and the energy conversion efficiency of the solar cell can be improved.

[0033] In summary, through the combined effect of noble metal nanoparticles, carbon quantum dots and nickel-cobalt co-doped TiO2, the separation of photo-generated carriers is promoted, the electron mobility is improved, and the utilization and absorption of light by perovskite are also promoted, which has a significant effect on improving the energy conversion efficiency of the solar cell. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0035] Figure 1 is a structural schematic diagram of a perovskite laminated solar cell disclosed by the embodiments of the present application.

[0036] Figure legend: 1, bottom cell; 11, second electrode; 2, first transparent conductive layer; 3, hole transport layer; 4, perovskite layer; 5, passivation layer; 6, electron transport layer; 7, buffer layer; 8, second transparent conductive layer; 81, first electrode; 9, anti-reflection layer. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0038] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "transverse", "longitudinal", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not intended to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0039] In addition, in addition to being used to indicate the orientation or positional relationship, the above-mentioned partial terms can also be used to indicate other meanings, for example, the term "upper" can also be used to indicate a certain dependent relationship or connection relationship in some cases. For those skilled in the art, the specific meaning of these terms in the present application can be understood according to the specific circumstances.

[0040] In addition, the terms "mount", "set", "provided with", "connected", "connected" should be broadly understood. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or internal communication between two devices, elements or components. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0041] In addition, the terms "first", "second", and the like are mainly used to distinguish different devices, elements or components (the specific type and structure can be the same or different), and are not intended to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise stated, the meaning of "multiple" is two or more.

[0042] The technical solutions of the present application will be further described below in conjunction with the embodiments.

[0043] In a first aspect, the embodiments of the present application provide an electron transport material for a perovskite solar cell.

[0044] The electron transport material includes TiO2 and a doping material, the doping material includes noble metal nanoparticles loaded on the surface of TiO2, carbon quantum dots, and nickel and cobalt co-doped in the lattice of TiO2.

[0045] The inventors found that co-doping nickel and cobalt in the lattice of TiO2, and at the same time loading noble metal nanoparticles and carbon quantum dots on the surface of TiO2, the four materials used in TiO2 show a better synergistic effect, the obtained electron transport material not only has excellent matching effect with perovskite, but also can significantly reduce the recombination rate of photo-generated electrons and holes, and improve the electron mobility of the electron transport material.

[0046] Specifically, the radius of nickel-cobalt element is relatively close to the radius of titanium ion, which can partially replace the electron-rich defect state Ti 3+ , passivate the defect state of TiO2, and carbon quantum dots loaded on the surface of TiO2 can provide an effective charge transport channel and accelerate the extraction of carriers. The Schottky junction formed between the noble metal and TiO2 helps to separate the photo-generated carriers, so the noble metal, carbon quantum dots, and nickel-cobalt ions work together to passivate the defects of TiO2, further improve the electron mobility, reduce the probability of carrier and defect state recombination at the interface, and significantly improve the electron mobility of TiO2.

[0047] Moreover, and more importantly, the co-doping of nickel and cobalt elements can change the electronic structure and energy level distribution inside TiO2, thereby reducing the band gap width of TiO2 and increasing the absorption of photons by perovskite; the conduction band and valence band of carbon quantum dots are located between TiO2 and perovskite, which helps to reduce the energy level barrier between TiO2 and perovskite layer, avoiding additional energy loss of photo-generated electrons during transmission; in addition to scattering photons, the electronic dipole oscillation effect of noble metal can trigger the absorption of electromagnetic energy, increase the local light field, and help to improve the utilization rate of light by perovskite. Through the synergistic effect of the three, the absorption and utilization of light by perovskite can be fully improved, and the energy conversion efficiency of solar cells can be improved.

[0048] In summary, through the combined action of noble metal nanoparticles, carbon quantum dots, and nickel-cobalt co-doped TiO2, the utilization and absorption of light by perovskite are promoted while the separation of photo-generated carriers and the improvement of electron mobility are achieved, which has a significant effect on improving the energy conversion efficiency of solar cells.

[0049] In some embodiments, the size of the carbon quantum dots is between 1 nm and 10 nm; and / or, the size of the noble metal nanoparticles is between 5 nm and 20 nm.

[0050] By further limiting the size of carbon quantum dots and noble metal nanoparticles, the light transmission and electrical conductivity of the composite material can be further improved. Moreover, the size of the noble metal nanoparticles described above is very low, which can increase the specific surface area of the composite material, improve the interface contact performance of the composite material with perovskite, and improve the carrier mobility.

[0051] For example, the size of the carbon quantum dots can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, and 10 nm, etc. The size of the noble metal nanoparticles can be 5 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, and 20 nm, etc.

[0052] In some embodiments, the nickel doping mass fraction is 0.3% to 1%; and / or, the cobalt doping mass fraction is 0.3% to 1%.

[0053] When the nickel or cobalt doping concentration is within the aforementioned doping mass fraction range, TiO2 exhibits better passivation of internal defects and significantly reduces electron recombination. However, excessively high nickel or cobalt doping concentrations can actually increase recombination centers within TiO2, leading to a higher likelihood of electron-hole recombination.

[0054] For example, the mass fraction of nickel doping can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%, etc. The mass fraction of cobalt doping can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%, etc.

[0055] In some embodiments, the noble metal includes one or more of Pt, Ag, Au and Pd; and / or, the crystal phase of TiO2 is any one of anatase, rutile, or a mixed anatase and rutile phase.

[0056] Preferably, the crystal phase of TiO2 is a mixed crystal structure of anatase and rutile. Since the interface between anatase and rutile can form a heterojunction, the positive charge of anatase will move to the valence band of rutile under the drive of the interfacial electric field, which has a passivating effect on deep-level oxygen vacancy defects. Meanwhile, the electrons of anatase remain in the conduction band due to the presence of the potential barrier. Therefore, the above-mentioned TiO2 with the mixed crystal structure of anatase and rutile can promote the separation of photogenerated carriers and greatly reduce its bulk recombination.

[0057] Secondly, embodiments of this application provide a method for preparing an electronic transport material.

[0058] The preparation method of the electron transport material includes the following steps: first, nickel and cobalt are co-doped in the TiO2 lattice, and then carbon quantum dots and noble metal nanoparticles are loaded onto the nickel and cobalt co-doped TiO2 surface.

[0059] By co-doping TiO2 with nickel and cobalt, nickel and cobalt enter the TiO2 lattice in an ionic state, replacing titanium ions or occupying oxygen vacancies, thereby forming new chemical bonds and altering the material's band structure, thus changing its properties. Therefore, pre-doping with nickel and cobalt can avoid interference from subsequent carbon quantum dots and noble metal nanoparticles loaded on the TiO2 surface.

[0060] Carbon quantum dots and noble metal nanoparticles are loaded onto the TiO2 surface. In the preparation of electron transport materials, the loading order of carbon quantum dots and noble metal nanoparticles can be changed.

[0061] In some embodiments, nickel and cobalt are co-doped into the TiO2 lattice, followed by carbon quantum dot loading treatment and then noble metal nanoparticle loading treatment.

[0062] The above preparation method can further improve the performance of electron transport materials because: by first loading carbon quantum dots, the carbon quantum dots can better bind to TiO2 via adsorption using hydroxyl groups and other groups on the TiO2 surface, thereby increasing the carbon quantum dot loading on the TiO2 surface and thus improving the electron transport performance of the electron transport material. However, by first loading noble metal nanoparticles, the chemical environment on the TiO2 surface changes, leading to a decrease in the loading effect of carbon quantum dots and a decline in the electron transport performance of the material.

[0063] In some embodiments, the preparation method of nickel and cobalt doping in TiO2 lattice is as follows: a titanium source, nickel salt and cobalt salt are placed in a solution for hydrolysis to form a precipitate, and the precipitate is dried and calcined to obtain nickel-cobalt co-doped TiO2;

[0064] When carbon quantum dots are first loaded onto the surface of nickel-cobalt co-doped TiO2, followed by noble metal nanoparticles, the preparation method of the electron transport material includes the following steps:

[0065] Loading carbon quantum dots: The carbon quantum dot solution is mixed with nickel-cobalt co-doped TiO2, and then the mixture is stirred or sonicated, followed by washing and drying to load the carbon quantum dots onto the surface of nickel-cobalt co-doped TiO2.

[0066] Loading noble metal nanoparticles: The noble metal precursor solution is mixed with nickel-cobalt co-doped TiO2 loaded with carbon quantum dots, and the noble metal precursor solution is reduced to noble metal nanoparticles through photoreduction reaction, and the noble metal nanoparticles are loaded onto nickel-cobalt co-doped TiO2 loaded with carbon quantum dots.

[0067] The preparation method of electron transport material when noble metal nanoparticles are first loaded onto the TiO2 surface and then carbon quantum dots are loaded includes the following steps:

[0068] Loading noble metal nanoparticles: The noble metal precursor solution is mixed with nickel-cobalt co-doped TiO2, and the noble metal precursor solution is reduced to noble metal nanoparticles through photoreduction reaction, and the noble metal nanoparticles are loaded onto nickel-cobalt co-doped TiO2.

[0069] Loading carbon quantum dots: A carbon quantum dot solution is mixed with nickel-cobalt co-doped TiO2 loaded with noble metal nanoparticles. The mixture is then stirred or sonicated, followed by washing and drying to load carbon quantum dots onto the surface of the nickel-cobalt co-doped TiO2 loaded with noble metal nanoparticles.

[0070] In some embodiments, in the step of doping nickel and cobalt into the TiO2 lattice, the calcination temperature is 550℃~750℃ and the time is 1h~4h; and / or, in the step of loading carbon quantum dots, the stirring temperature is 10℃~30℃ and the time is 1h~2h; and / or, in the step of loading noble metal nanoparticles, the photoreduction reaction is carried out under ultraviolet light irradiation for 30min~100min.

[0071] In some embodiments, the titanium source includes one or both of tetrabutyl titanate and isopropyl titanate; and / or, the nickel salt includes one or both of nickel nitrate and nickel acetate; and / or, the cobalt salt includes one or both of cobalt nitrate and cobalt acetate.

[0072] In some embodiments, the carbon quantum dot solution is prepared as follows: a carbon source is placed in a solvent and heated until pyrolysis is achieved to obtain a carbon quantum dot solution, wherein the mass ratio of the carbon source to the solvent is 1:280-330;

[0073] When carbon quantum dots are loaded first and then noble metal nanoparticles are loaded, the ratio of the amount of carbon quantum dot solution to nickel-cobalt co-doped TiO2 is 100 μL: 0.1 g to 0.2 g, the ratio of the amount of noble metal precursor solution to nickel-cobalt co-doped TiO2 loaded with carbon quantum dots is 50 μL to 100 μL: 0.1 g to 0.2 g, and the concentration of the noble metal precursor solution is 5 mmol / L to 10 mmol / L.

[0074] When noble metal nanoparticles are loaded first, followed by carbon quantum dots, the ratio of the amount of noble metal precursor solution to nickel-cobalt co-doped TiO2 is 50 μL–100 μL: 0.1 g–0.2 g, the concentration of the noble metal precursor solution is 5 mmol / L–10 mmol / L, and the ratio of the amount of carbon quantum dot solution to nickel-cobalt co-doped TiO2 loaded with noble metal nanoparticles is 100 μL: 0.1 g–0.2 g.

[0075] In the preparation of carbon quantum dot solutions, a mixture of water and ethanol can be used as the solvent. The carbon source can be ascorbic acid, glucose, fructose, citric acid, or corn stalks, etc.

[0076] Furthermore, the dispersant can be placed together with the carbon source in the aforementioned solvent. The addition of the dispersant can improve the dispersion stability and uniformity of the carbon source in the solvent, which is more conducive to the conversion of the carbon source into carbon quantum dot materials. The dispersant can be one or more of hexadecyltrimethylammonium bromide, lauryl alcohol, stearic acid, and sodium dodecylbenzene sulfonate.

[0077] The ratio of carbon source to dispersant is 1:0.01 to 0.05. For example, the mass ratio of ascorbic acid, hexadecyltrimethylammonium bromide, and lauryl alcohol is 1:0.01:0.01.

[0078] A noble metal precursor solution is a solution containing noble metal ions. For example, when the noble metal nanoparticles are Pt, the noble metal precursor solution can be an H2PtCl6 solution.

[0079] Thirdly, embodiments of this application provide a solar cell.

[0080] Reference Figure 1 The solar cell includes an electron transport layer 6, the material of which includes the electron transport material mentioned in the first aspect or the electron transport material prepared by the preparation method mentioned in the second aspect.

[0081] In some embodiments, the solar cell is a perovskite tandem solar cell, which includes a base cell 1 and a first transparent conductive layer 2, a first transport layer, a perovskite layer 4, a second transport layer, a second transparent conductive layer 8 and a first electrode 81 sequentially disposed on the base cell 1. One of the first transport layer and the second transport layer is an electron transport layer 6 and the other is a hole transport layer 3.

[0082] It should be noted that the bottom cell 1 has a second electrode 11 corresponding to the first electrode 81. The first electrode 81 and the second electrode 11 are made of metal materials with good conductivity, such as gold, silver or copper, which can collect electrons or holes, ensuring that the charge can be smoothly discharged from the inside of the solar cell and promoting the efficient operation of the solar cell.

[0083] Furthermore, the bottom cell 1 can be a heterojunction bottom cell or other crystalline silicon bottom cells; the first transparent conductive layer 2 and the second transparent conductive layer 8 can be fluorine-doped tin oxide or indium-doped tin oxide. The thickness of the first transparent conductive layer 2 can be 15nm to 30nm, and the thickness of the second transparent conductive layer 8 can be 80nm to 110nm; the hole transport layer 3 can be made of nickel oxide with a thickness of 10nm to 30nm; and the electron transport layer 6 has a thickness of 15nm to 30nm.

[0084] Furthermore, a passivation layer 5 is disposed between the perovskite layer 4 and the electron transport layer 6. The material of the passivation layer 5 can be LiF, and the thickness is 1nm to 3nm. A buffer layer 7 is disposed between the electron transport layer 6 and the second transparent conductive layer 8. The material of the buffer layer 7 can be SnO2, and the thickness is 20nm to 35nm. An antireflection layer 9 is disposed on the side of the second transparent conductive layer 8 away from the bottom cell 1. The material of the antireflection layer 9 can be LiF or MgF2, and the thickness is 200nm to 300nm.

[0085] In some embodiments, the solar cell is a perovskite single-junction solar cell. The perovskite single-junction solar cell includes a first electrode, a transparent conductive substrate, a first transport layer, a perovskite layer, a second transport layer, a transparent conductive layer, and a second electrode stacked sequentially. One of the first transport layer and the second transport layer is an electron transport layer, and the other is a hole transport layer.

[0086] Transparent conductive substrates, as substrate materials for perovskite single-junction solar cells, possess both excellent conductivity and optical transmittance. For example, the material of the transparent conductive substrate can be fluorine-doped tin oxide or indium-doped tin oxide. For example, the transparent conductive substrate can be indium-doped tin oxide transparent conductive glass.

[0087] Fourthly, this application provides a photovoltaic module.

[0088] A photovoltaic module, comprising solar cells as mentioned in the third aspect.

[0089] The technical solution of the present invention will be further described below with reference to more specific preparation examples, embodiments and accompanying drawings.

[0090] Preparation Example 1

[0091] This application provides an electron transport material comprising TiO2 and doped materials. The TiO2 has a mixed anatase and rutile crystal structure. The doped materials are Pt nanoparticles, carbon quantum dots, and nickel and cobalt co-doped in the TiO2 lattice, all loaded on the surface of TiO2. The carbon quantum dots have a size between 1 nm and 10 nm, the Pt nanoparticles have a size between 5 nm and 20 nm, the nickel doping mass fraction is 0.5%, and the cobalt doping mass fraction is 0.5%.

[0092] The electron transport material is prepared by first loading carbon quantum dots onto the TiO2 surface after preparing nickel-cobalt co-doped TiO2, and then loading Pt nanoparticles. The preparation method of this electron transport material is as follows:

[0093] Preparation of nickel-cobalt co-doped TiO2: 5 mL of tetrabutyl titanate was dissolved in 25 mL of anhydrous ethanol to obtain the first solution. 78 mg of cobalt nitrate, 78 mg of nickel nitrate, 20 g of 2% polyvinylpyrrolidone aqueous solution and 25 mL of anhydrous ethanol were mixed to obtain the second solution. The first solution was added dropwise to the second solution at a speed of 0.5 drops / second using a dropping funnel at a speed of 400 r / min to form a precipitate. The mixture was stirred for 36 h. The precipitate was washed with deionized water and anhydrous ethanol in a volume ratio of 1:1, dried in a 55 °C drying oven, and then calcined in a muffle furnace at 650 °C for 3 h to obtain nickel-cobalt co-doped TiO2.

[0094] Loaded carbon quantum dots:

[0095] Preparation of carbon quantum dot solution: 1g ascorbic acid, 0.05g hexadecyltrimethylammonium bromide and 1g lauryl alcohol were added to 200g anhydrous ethanol, then 100g distilled water was added, and the mixture was stirred evenly. The mixture was then hydrothermally reacted at 180℃ for 5h and cooled to room temperature to obtain carbon quantum dot solution.

[0096] Loading: Take 100 μL of the above carbon quantum dot solution and mix it with 0.15 g of nickel-cobalt co-doped TiO2. Stir at 25 °C for 1 h, then wash with distilled water and dry in a drying oven at 55 °C to obtain a sample with carbon quantum dots loaded on the surface of nickel-cobalt co-doped TiO2.

[0097] Loaded Pt nanoparticles:

[0098] 0.15 g of nickel-cobalt co-doped TiO2 loaded with carbon quantum dots was ultrasonically dispersed in 10 mL of a mixed solvent of water and ethanol to obtain a third solution. The ratio of water to ethanol in the mixed solvent was 1:1. Then, 80 μL of 10 mmol / L H2PtCl6 solution was added dropwise to the third solution, while N2 was introduced. The mixture was stirred for 0.5 h to remove dissolved oxygen. The mixture was then irradiated under a UV lamp for 1 h while stirring. The suspended matter gradually turned blackish-brown. After centrifugation and filtration, the product on the sieve was washed and dried in a 55 °C drying oven to obtain the target sample.

[0099] Preparation Example 2

[0100] This application provides an electron transport material, which differs from Preparation Example 1 only in that: after preparing nickel-cobalt co-doped TiO2, Pt nanoparticles are first loaded onto the TiO2 surface, and then carbon quantum dots are loaded. The preparation method of this electron transport material is as follows:

[0101] Preparation of nickel-cobalt co-doped TiO2: 5 mL of tetrabutyl titanate was dissolved in 25 mL of anhydrous ethanol to obtain the first solution. 78 mg of cobalt nitrate, 78 mg of nickel nitrate, 20 g of 2% polyvinylpyrrolidone aqueous solution and 25 mL of anhydrous ethanol were mixed to obtain the second solution. The first solution was added dropwise to the second solution at a speed of 0.5 drops / second using a dropping funnel at a speed of 400 r / min to form a precipitate. The mixture was stirred for 36 h. The precipitate was washed with deionized water and anhydrous ethanol in a volume ratio of 1:1, dried in a 55 °C drying oven, and then calcined in a muffle furnace at 650 °C for 3 h to obtain nickel-cobalt co-doped TiO2.

[0102] Loaded Pt nanoparticles:

[0103] 0.15 g of nickel-cobalt co-doped TiO2 was ultrasonically dispersed in 10 mL of a mixed solvent of water and ethanol to obtain a third solution. The ratio of water to ethanol in the mixed solvent was 1:1. Then, 80 μL of 10 mmol / L H2PtCl6 solution was added dropwise to the third solution while N2 was introduced. The mixture was stirred for 0.5 h to remove dissolved oxygen. The mixture was then irradiated under a UV lamp for 1 h while stirring. The suspension gradually turned dark brown. The suspension was centrifuged, filtered, and the product on the sieve was washed and dried in a 55 °C drying oven to obtain a sample of nickel-cobalt co-doped TiO2 loaded with Pt nanoparticles.

[0104] Loaded carbon quantum dots:

[0105] Preparation of carbon quantum dot solution: 1g ascorbic acid, 0.05g hexadecyltrimethylammonium bromide and 1g lauryl alcohol were added to 200g anhydrous ethanol, then 100g distilled water was added, and the mixture was stirred evenly. The mixture was then hydrothermally reacted at 180℃ for 5h and cooled to room temperature to obtain carbon quantum dot solution.

[0106] Loading: Take 100 μL of the above carbon quantum dot solution and mix it with 0.15 g of nickel-cobalt co-doped TiO2 loaded with Pt nanoparticles. Stir at 25 °C for 1 h, then wash with distilled water and dry in a drying oven at 55 °C to obtain the target sample.

[0107] Preparation Example 3

[0108] This application provides an electron transport material prepared in the example, which differs from the first preparation example only in that the mass fraction of nickel doping is 0.3% and the mass fraction of cobalt doping is 1%. Accordingly, in the step of preparing nickel-cobalt co-doped TiO2, the amount of nickel nitrate added is 47 mg and the amount of cobalt nitrate added is 156 mg.

[0109] Preparation Example 4

[0110] This application provides an electron transport material prepared in the example, which differs from the first preparation example only in that the mass fraction of nickel doping is 1% and the mass fraction of cobalt doping is 0.3%. Accordingly, in the step of preparing nickel-cobalt co-doped TiO2, the amount of nickel nitrate added is 156 mg and the amount of cobalt nitrate added is 47 mg.

[0111] Preparation of Comparative Example 1

[0112] This application provides an electron transport material in a comparative example, which differs from the preparation example 1 only in that: in this electron transport material, the surface of TiO2 is only loaded with carbon quantum dots and not with Pt nanoparticles.

[0113] The preparation method of this electron transport material includes the following steps:

[0114] Preparation of nickel-cobalt co-doped TiO2: 5 mL of tetrabutyl titanate was dissolved in 25 mL of anhydrous ethanol to obtain the first solution. 78 mg of cobalt nitrate, 78 mg of nickel nitrate, 20 g of 2% polyvinylpyrrolidone aqueous solution and 25 mL of anhydrous ethanol were mixed to obtain the second solution. The first solution was added dropwise to the second solution at a speed of 0.5 drops / second using a dropping funnel at a speed of 400 r / min to form a precipitate. The mixture was stirred for 36 h. The precipitate was washed with deionized water and anhydrous ethanol in a volume ratio of 1:1, dried in a 55 °C drying oven, and then calcined in a muffle furnace at 650 °C for 3 h to obtain nickel-cobalt co-doped TiO2.

[0115] Loaded carbon quantum dots:

[0116] Preparation of carbon quantum dot solution: 1g ascorbic acid, 0.05g hexadecyltrimethylammonium bromide and 1g lauryl alcohol were added to 200g anhydrous ethanol, then 100g distilled water was added, and the mixture was stirred evenly. The mixture was then hydrothermally reacted at 180℃ for 5h and cooled to room temperature to obtain carbon quantum dot solution.

[0117] Loading: 100 μL of the above carbon quantum dot solution was mixed with 0.15 g of nickel-cobalt co-doped TiO2, stirred at 25 °C for 1 h, then washed with distilled water and dried in a drying oven at 55 °C to obtain a sample of carbon quantum dots loaded on the surface of nickel-cobalt co-doped TiO2. This sample was used as the target sample for preparing Comparative Example 1.

[0118] Preparation of Comparative Example 2

[0119] This application provides an electron transport material in a comparative example, which differs from the preparation example 1 only in that: in this electron transport material, the surface of TiO2 is only loaded with Pt nanoparticles and not with carbon quantum dots.

[0120] The preparation method of this electron transport material includes the following steps:

[0121] Preparation of nickel-cobalt co-doped TiO2: 5 mL of tetrabutyl titanate was dissolved in 25 mL of anhydrous ethanol to obtain the first solution. 78 mg of cobalt nitrate, 78 mg of nickel nitrate, 20 g of 2% polyvinylpyrrolidone aqueous solution and 25 mL of anhydrous ethanol were mixed to obtain the second solution. The first solution was added dropwise to the second solution at a speed of 0.5 drops / second using a dropping funnel at a speed of 400 r / min to form a precipitate. The mixture was stirred for 36 h. The precipitate was washed with deionized water and anhydrous ethanol in a volume ratio of 1:1, dried in a 55 °C drying oven, and then calcined in a muffle furnace at 650 °C for 3 h to obtain nickel-cobalt co-doped TiO2.

[0122] Loading Pt nanoparticles: 0.15 g of nickel-cobalt co-doped TiO2 was ultrasonically dispersed in a 10 mL mixture of water and ethanol to obtain a third solution. The ratio of water to ethanol in the mixed solvent was 1:1. Then, 80 μL of 10 mmol / L H2PtCl6 solution was added dropwise to the third solution, while N2 was introduced and stirred for 0.5 h to remove dissolved oxygen. The mixture was then irradiated under a UV lamp for 1 h with stirring. The suspension gradually turned dark brown. After centrifugation and filtration, the product on the sieve was washed and dried in a 55 °C drying oven to obtain a sample of nickel-cobalt co-doped TiO2 loaded with Pt nanoparticles. This sample was used as the target sample for preparing Comparative Example 1.

[0123] Preparation of Comparative Example 3

[0124] This application provides an electron transport material in a comparative example, which differs from the preparation example 1 only in that the TiO2 lattice in this electron transport material is doped with only nickel.

[0125] The preparation method of this electron transport material includes the following steps:

[0126] Preparation of nickel-doped TiO2: 5 mL of tetrabutyl titanate was dissolved in 25 mL of anhydrous ethanol to obtain the first solution. 78 mg of nickel nitrate, 20 g of 2% polyvinylpyrrolidone aqueous solution and 25 mL of anhydrous ethanol were mixed to obtain the second solution. The first solution was added dropwise to the second solution at a rate of 0.5 drops / second using a dropping funnel at a speed of 400 r / min to form a precipitate. The mixture was stirred for 36 h. The precipitate was washed with deionized water and anhydrous ethanol in a volume ratio of 1:1, dried in a drying oven at 55 °C, and then calcined in a muffle furnace at 650 °C for 3 h to obtain nickel-doped TiO2.

[0127] Loaded carbon quantum dots:

[0128] Preparation of carbon quantum dot solution: 1g ascorbic acid, 0.05g hexadecyltrimethylammonium bromide and 1g lauryl alcohol were added to 200g anhydrous ethanol, then 100g distilled water was added, and the mixture was stirred evenly. The mixture was then hydrothermally reacted at 180℃ for 5h and cooled to room temperature to obtain carbon quantum dot solution.

[0129] Loading: 100 μL of the above carbon quantum dot solution was mixed with 0.15 g of nickel-doped TiO2, stirred at 25 °C for 1 h, then washed with distilled water, and dried in a drying oven at 55 °C to obtain a sample of carbon quantum dots loaded on the surface of nickel-doped TiO2.

[0130] Loading Pt nanoparticles: 0.15 g of nickel-doped TiO2 loaded with carbon quantum dots was ultrasonically dispersed in 10 mL of a mixed solvent of water and ethanol to obtain a third solution. The ratio of water to ethanol in the mixed solvent was 1:1. Then, 80 μL of 10 mmol / L H2PtCl6 solution was added dropwise to the third solution, while N2 was introduced and stirred for 0.5 h to remove dissolved oxygen. The mixture was then irradiated under a UV lamp for 1 h with stirring. The suspension gradually turned blackish-brown. After centrifugation and filtration, the product on the sieve was washed and dried in a 55 °C drying oven to obtain the target sample.

[0131] Preparation of Comparative Example 4

[0132] This application provides an electron transport material in a comparative example, which differs from the preparation example 1 only in that the TiO2 lattice in this electron transport material is doped with only cobalt.

[0133] The electron transport material is prepared as follows:

[0134] Preparation of cobalt-doped TiO2: 5 mL of tetrabutyl titanate was dissolved in 25 mL of anhydrous ethanol to obtain the first solution. 78 mg of cobalt nitrate, 20 g of 2% polyvinylpyrrolidone aqueous solution and 25 mL of anhydrous ethanol were mixed to obtain the second solution. The first solution was added dropwise to the second solution at a speed of 0.5 drops / second using a dropping funnel at a speed of 400 r / min to form a precipitate. The mixture was stirred for 36 h. The precipitate was washed with deionized water and anhydrous ethanol in a volume ratio of 1:1, dried in a drying oven at 55 °C, and then calcined in a muffle furnace at 650 °C for 3 h to obtain cobalt-doped TiO2.

[0135] Loaded carbon quantum dots:

[0136] Preparation of carbon quantum dot solution: 1g ascorbic acid, 0.05g hexadecyltrimethylammonium bromide and 1g lauryl alcohol were added to 200g anhydrous ethanol, then 100g distilled water was added, and the mixture was stirred evenly. The mixture was then hydrothermally reacted at 180℃ for 5h and cooled to room temperature to obtain carbon quantum dot solution.

[0137] Loading: 100 μL of the above carbon quantum dot solution was mixed with 0.15 g of cobalt-doped TiO2, stirred at 25 °C for 1 h, then washed with distilled water, and dried in a drying oven at 55 °C to obtain a sample of carbon quantum dots loaded on the surface of cobalt-doped TiO2.

[0138] Loading Pt nanoparticles: 0.15 g of cobalt-doped TiO2 loaded with carbon quantum dots was ultrasonically dispersed in a 10 mL mixture of water and ethanol to obtain a third solution. The ratio of water to ethanol in the mixed solvent was 1:1. Then, 80 μL of 10 mmol / L H2PtCl6 solution was added dropwise to the third solution, while N2 was introduced and stirred for 0.5 h to remove dissolved oxygen. The mixture was then irradiated under a UV lamp for 1 h with stirring. The suspension gradually turned dark brown. After centrifugation and filtration, the product on the sieve was washed and dried in a 55 °C drying oven to obtain the target sample.

[0139] Example 1

[0140] This application provides a method for fabricating a perovskite tandem solar cell, including:

[0141] Provide heterojunction base cells;

[0142] A first transparent conductive layer was fabricated on the front side of the heterojunction bottom cell by magnetron sputtering. The material of the first transparent conductive layer is indium tin oxide and the thickness is 25 nm.

[0143] A hole transport layer was prepared by physical vapor deposition on the side of the first transparent conductive layer away from the heterojunction bottom cell. The hole transport layer was made of nickel oxide and had a thickness of 15 nm.

[0144] A lead iodide framework layer with a thickness of 300 nm was first prepared on the side of the first transparent conductive layer away from the heterojunction bottom cell. Then, a cationic solution was spin-coated and annealed at 150 °C for 20 min to obtain a perovskite layer with a thickness of 450 nm.

[0145] A passivation layer made of LiF with a thickness of 1 nm was prepared by vapor deposition on the side of the perovskite layer away from the heterojunction bottom cell.

[0146] An electron transport layer was prepared by chemical vapor deposition on the side of the passivation layer away from the heterojunction bottom cell. The electron transport layer was made of the same electron transport material as in Preparation Example 1, and had a thickness of 25 nm.

[0147] A buffer layer was prepared by atomic layer deposition on the side of the electron transport layer away from the heterojunction bottom cell. The material of the buffer layer was SnO2 and the thickness was 25 nm.

[0148] A second transparent conductive layer was prepared by magnetron sputtering on the side of the buffer layer away from the heterojunction bottom cell. The material of the second transparent conductive layer was indium tin oxide and the thickness was 100 nm.

[0149] A first electrode is prepared by vapor deposition on the side of the heterojunction bottom cell away from the first transparent conductive layer. The first electrode forms an ohmic contact with the heterojunction bottom cell. A second electrode is prepared by vapor deposition on the side of the second transparent conductive layer away from the heterojunction bottom cell. The second electrode and the second transparent conductive layer form an ohmic contact. Both the first electrode and the second electrode are silver electrodes with a thickness of 275 nm.

[0150] An antireflection layer was prepared by vapor deposition on the side of the second transparent conductive layer away from the heterojunction bottom cell. The antireflection layer was made of MgF2 and had a thickness of 250 nm.

[0151] Example 2

[0152] This application provides a method for preparing a perovskite tandem solar cell, which differs from Example 1 in that the electron transport material is the same as that used in Example 2.

[0153] Example 3

[0154] This application provides a method for preparing a perovskite tandem solar cell, which differs from Example 1 in that the electron transport material is the same as that used in Example 3.

[0155] Example 4

[0156] This application provides a method for preparing a perovskite tandem solar cell. The difference from Example 1 is that the electron transport material is the same as that used in Example 4.

[0157] Comparative Example 1

[0158] This application provides a comparative example of a method for preparing a perovskite tandem solar cell. The difference between this method and Example 1 is that the electron transport material used in Example 1 is the same as the electron transport material used in Example 1.

[0159] Comparative Example 2

[0160] This application provides a comparative example of a method for preparing a perovskite tandem solar cell. The difference between this method and Example 1 is that the electron transport material used in Comparative Example 2 is the same electron transport material used in this method.

[0161] Comparative Example 3

[0162] This application provides a comparative example of a method for preparing a perovskite tandem solar cell. The difference between this method and Example 1 is that the electron transport material used in Comparative Example 3 is the same electron transport material used in this method.

[0163] Comparative Example 4

[0164] This application provides a comparative example of a method for preparing a perovskite tandem solar cell. The difference between this method and Example 1 is that the electron transport material used in Comparative Example 4 is the same electron transport material used in Comparative Example 4.

[0165] Experiment 1

[0166] Electron mobility test

[0167] The electron transport materials prepared in the above preparation examples and comparative examples were used as titanium dioxide samples for testing. The electron mobility was measured using the Hall effect method, as follows:

[0168] A constant magnetic field is applied to a titanium dioxide sample, and the magnetic field strength can produce a significant Hall effect. A constant current is applied to the titanium dioxide sample in a direction perpendicular to the magnetic field. By measuring the Hall voltage generated in the direction perpendicular to the current and magnetic field, the electron mobility of titanium dioxide can be calculated according to the principle and formula of the Hall effect.

[0169] Energy barrier test

[0170] The electron transport materials prepared in the above preparation examples and comparative examples were used as titanium dioxide samples for testing. The energy barrier was tested using the voltammetric characteristic method, and the test method is as follows:

[0171] By measuring the current response of titanium dioxide at different voltages, the rate at which the current increases with voltage at a specific point on the IV curve slows down significantly. The voltage corresponding to this point is the energy barrier value.

[0172] Experiment 2

[0173] Solar cell performance testing

[0174] The performance of solar cells was tested using the Wavelabs solar simulator under the following conditions: AM1.5, 1000 W / m. 2 The test environment temperature was 25℃. Before testing, the light source was calibrated to simulate sunlight intensity using a standard silicon cell. Performance tests included energy conversion efficiency, open-circuit voltage, short-circuit current, and fill factor.

[0175] The test results of the above embodiments and comparative examples are detailed in Table 1.

[0176] Table 1

[0177]

[0178]

[0179] As can be seen from the comparison of the data of Example 1 with Comparative Examples 1, 2, 3, and 4 in Table 1, the electron mobility, energy conversion efficiency, open-circuit voltage, and fill factor of Example 1 are all higher than those of Comparative Examples 1, 2, 3, and 4, and the energy barrier value is lower than that of Comparative Examples 1, 2, 3, and 4. This proves that by simultaneously doping TiO2 with nickel and cobalt, and simultaneously loading carbon quantum dots and Pt nanoparticles on the TiO2 surface, the synergistic effect of nickel, cobalt, carbon quantum dots, and Pt nanoparticles in passivating the defects of TiO2 and reducing the energy barrier between TiO2 and the perovskite layer is excellent. The electron transport capability of TiO2 is significantly improved, thereby significantly improving the energy conversion efficiency of the above-mentioned perovskite tandem solar cell.

[0180] The electron transport materials and their preparation methods, solar cells, and photovoltaic modules disclosed in the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the electron transport materials and their preparation methods, solar cells, photovoltaic modules, and their core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An electron transport material for perovskite solar cells, characterized in that, It includes TiO2 and doped materials, the doped materials including noble metal nanoparticles and carbon quantum dots loaded on the surface of the TiO2, and nickel and cobalt co-doped in the lattice of the TiO2.

2. The electron transport material according to claim 1, characterized in that, The size of the carbon quantum dots is between 1 nm and 10 nm; and / or the size of the noble metal nanoparticles is between 5 nm and 20 nm.

3. The electron transport material according to claim 1, characterized in that, The nickel doping mass fraction is 0.3% to 1%; and / or, the cobalt doping mass fraction is 0.3% to 1%.

4. The electron transport material according to any one of claims 1-3, characterized in that, The precious metal includes one or more of Pt, Ag, Au and Pd; and / or, the crystal phase of the TiO2 is any one of anatase, rutile, or a mixed anatase and rutile phase.

5. A method for preparing an electron transport material, characterized in that, The method for preparing the electron transport material according to any one of claims 1-4 includes the following steps: first, co-doping the nickel and the cobalt in the lattice of the TiO2, and then loading the carbon quantum dots and the noble metal nanoparticles onto the surface of the nickel and cobalt co-doped TiO2.

6. The method for preparing the electron transport material according to claim 5, characterized in that, After co-doping the nickel and cobalt into the TiO2 lattice, the carbon quantum dots are loaded first, followed by the loading of the noble metal nanoparticles.

7. The method for preparing the electron transport material according to claim 5, characterized in that, The preparation method of doping the nickel and cobalt in the TiO2 lattice is as follows: placing the titanium source, nickel salt and cobalt salt in a solution for hydrolysis to form a precipitate, taking the precipitate, drying and calcining it to obtain nickel-cobalt co-doped TiO2; When the nickel-cobalt co-doped TiO2 surface is first loaded with carbon quantum dots and then with noble metal nanoparticles, the preparation method of the electron transport material includes the following steps: Loading the carbon quantum dots: The carbon quantum dot solution is mixed with the nickel-cobalt co-doped TiO2, and then the mixture is stirred or sonicated, followed by washing and drying to load the carbon quantum dots onto the surface of the nickel-cobalt co-doped TiO2. Loading the noble metal nanoparticles: Mix the noble metal precursor solution with the nickel-cobalt co-doped TiO2 loaded with the carbon quantum dots, reduce the noble metal precursor solution to the noble metal nanoparticles through a photoreduction reaction, and load the noble metal nanoparticles onto the nickel-cobalt co-doped TiO2 loaded with the carbon quantum dots. When the noble metal nanoparticles are first loaded onto the surface of the nickel-cobalt co-doped TiO2, and then the carbon quantum dots are loaded, the preparation method of the electron transport material includes the following steps: Loading the noble metal nanoparticles: The noble metal precursor solution is mixed with the nickel-cobalt co-doped TiO2, and the noble metal precursor solution is reduced to the noble metal nanoparticles through a photoreduction reaction, and the noble metal nanoparticles are loaded onto the nickel-cobalt co-doped TiO2. Loading the carbon quantum dots: The carbon quantum dot solution is mixed with the nickel-cobalt co-doped TiO2 loaded with the noble metal nanoparticles, and then the mixture is stirred or sonicated, followed by washing and drying to load the carbon quantum dots onto the surface of the nickel-cobalt co-doped TiO2 loaded with the noble metal nanoparticles.

8. The method for preparing the electron transport material according to claim 7, characterized in that, In the step of doping the TiO2 lattice with nickel and cobalt, the calcination temperature is 550℃~750℃ and the time is 1h~4h; and / or, in the step of loading the carbon quantum dots, the stirring temperature is 10℃~30℃ and the time is 1h~2h; and / or, in the step of loading the noble metal nanoparticles, the photoreduction reaction is carried out under ultraviolet light irradiation for 30min~100min.

9. The method for preparing the electron transport material according to claim 7, characterized in that, The titanium source includes one or both of tetrabutyl titanate and isopropyl titanate; and / or, the nickel salt includes one or both of nickel nitrate and nickel acetate; and / or, the cobalt salt includes one or both of cobalt nitrate and cobalt acetate.

10. The method for preparing the electron transport material according to any one of claims 7, characterized in that, The carbon quantum dot solution is prepared as follows: a carbon source is placed in a solvent and heated until pyrolysis is achieved to obtain the carbon quantum dot solution, wherein the mass ratio of the carbon source to the solvent is 1:280-330. When the carbon quantum dots are loaded first, followed by the noble metal nanoparticles, the ratio of the amount of carbon quantum dot solution to the amount of nickel-cobalt co-doped TiO2 is 100 μL: 0.1 g to 0.2 g, the ratio of the amount of noble metal precursor solution to the amount of nickel-cobalt co-doped TiO2 loaded with the carbon quantum dots is 50 μL to 100 μL: 0.1 g to 0.2 g, and the concentration of the noble metal precursor solution is 5 mmol / L to 10 mmol / L. When the noble metal nanoparticles are loaded first, followed by the carbon quantum dots, the ratio of the noble metal precursor solution to the nickel-cobalt co-doped TiO2 is 50 μL–100 μL: 0.1 g–0.2 g, the concentration of the noble metal precursor solution is 5 mmol / L–10 mmol / L, and the ratio of the carbon quantum dot solution to the nickel-cobalt co-doped TiO2 loaded with the noble metal nanoparticles is 100 μL: 0.1 g–0.2 g.

11. A solar cell, characterized in that, It includes an electron transport layer, the material of which includes the electron transport material as described in any one of claims 1-4 or the electron transport material prepared by the preparation method as described in any one of claims 5-10.

12. The solar cell according to claim 11, characterized in that, The solar cell is a perovskite tandem solar cell, which includes a base cell and a first transparent conductive layer, a first transport layer, a perovskite layer, a second transport layer, a second transparent conductive layer, and a first electrode stacked sequentially on the base cell. One of the first transport layer and the second transport layer is the electron transport layer, and the other is the hole transport layer.

13. The solar cell according to claim 11, characterized in that, The solar cell is a perovskite single-junction solar cell, which includes a first electrode, a transparent conductive substrate, a first transport layer, a perovskite layer, a second transport layer, a transparent conductive layer, and a second electrode stacked sequentially. One of the first transport layer and the second transport layer is the electron transport layer, and the other is the hole transport layer.

14. A photovoltaic module, characterized in that, Including the solar cell as described in any one of claims 11-13.

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