CN114538412A

CN114538412A - Preparation and application of perovskite solar cell stannic oxide electron transport layer passivation material

Info

Publication number: CN114538412A
Application number: CN202210082007.7A
Authority: CN
Inventors: 陶劲松; 薛启帆; 房东君; 牛天启; 刘浩
Original assignee: Anhui Yuezhi Huiyuan Biotechnology Co ltd; South China University of Technology SCUT
Current assignee: Anhui Yuezhi Huiyuan Biotechnology Co ltd; South China University of Technology SCUT
Priority date: 2022-01-24
Filing date: 2022-01-24
Publication date: 2022-05-27

Abstract

The invention belongs to the field of perovskite solar cells, and discloses preparation and application of a tin dioxide electronic transmission layer passivation material of a perovskite solar cell. The invention uses biomass, especially lignin, as raw material, via H₂O₂And carrying out a hydrothermal reaction with ammonia water after pre-oxidation to prepare the carbon dots with the surfaces rich in C ═ O bonds. Doping the carbon dots into a tin dioxide electron transport layer SnO of the perovskite solar cell₂In, SnO can be effectively passivated₂Electron transport layer defects, lowering energy barrier and increasing electron mobility of the ETL, thereby increasingThe photovoltaic performance of the perovskite solar cell and the electron mobility of an electron transport layer of a device are improved by 3.5 times, the defect state density is reduced by 11.8%, and the maximum PCE can reach 20.91%.

Description

Preparation and application of perovskite solar cell stannic oxide electron transport layer passivation material

Technical Field

The invention belongs to the field of Perovskite Solar Cells (PSC), and particularly relates to a preparation method and application of a Perovskite solar cell stannic oxide electronic transmission layer passivation material.

Background

The perovskite solar cell has important significance for sustainable development on efficient utilization of solar energy. Perovskite Solar Cells (PSC) are considered as a promising new type of solar cells due to their excellent carrier mobility, high absorption coefficient, long electron and hole diffusion length, etc. In current research, the Photoelectric Conversion Efficiency (PCE) of PSCs has exceeded 20%. Traditionally, PSCs can be classified into mesoporous structures and planar heterojunction structures. The planar heterojunction-type PSC can be prepared by a solution at a low temperature, has a simple process and low cost, and has certain advantages compared with the mesoporous PSC, so that the planar heterojunction-type PSC is gradually paid extensive attention by researchers. In the planar heterojunction PSC, an Electron Transport Layer (ETL) is an important structure, which functions to extract electrons from a functional layer and block holes. It was studied that the PSC device lacking ETL may have a reduction in photoelectric conversion efficiency by 2.7% and no stable power output. The ETL is very important in terms of efficiency and stability of the PSC device. The material most commonly used for preparing ETL is TiO₂，ZnO，SnO₂And the like. Of all these materials, SnO₂Has the advantages of wider band gap, high light transmittance in the visible light range, high electron mobility, low conduction band offset and the like, and is therefore more suitable for use as an ETL. However, SnO₂The crystal itself mainly has oxygen vacancy defects (O)^2-The absence of oxygen anions), which typically occur naturally during processing, are key factors affecting the electrical properties of the film. From a device perspective, these unavoidable defects can create charge traps and induceCharge accumulation is at the bulk and interface of the ETL and perovskite layers, resulting in non-radiative recombination and reduced charge extraction efficiency. In addition, severe device hysteresis may occur due to charge accumulation caused by interface contact failures and interface defects. Thus, the defects are passivated by a suitable method to further increase SnO₂The charge extraction efficiency of the electron transport layer is extremely important to improve PSC device performance.

In the current study, for SnO₂The passivation of defects is mainly divided into two types of methods: doping elements and using passivating agents. The doping element is mainly to dope a metal element into SnO₂In the bulk to passivate SnO₂Defects, to some extent regulated SnO₂Energy level, thereby making SnO₂Better matching of adjacent electrodes or perovskite layers, elements such as Ru, Sb, Y, Zr, etc. have been reported for doping into SnO₂To passivate the defects. However, most of the reported element doping options are largely empirical, the effectiveness of which is judged mainly by the PCE value, and these metal elements are expensive and mostly have some toxicity. In another aspect, passivating SnO with a passivating agent₂The oxygen vacancy defect of (2) is a novel idea. The addition of passivating agents can significantly affect SnO₂Charge extraction efficiency of (1). Currently, the commonly used passivating agents include ionic compounds, organic acids, high molecular polymers, carbon materials and the like. Among them, carbon materials are attracting attention because of their advantages such as controllable fermi level, low cost, abundant raw materials, highly adjustable structures with various extraordinary characteristics, good electrical and thermal conductivity, chemical stability and high charge carrier mobility. Although reported to be SnO₂The ETL is prepared by mixing to improve the electron transmission performance, but the CNT or fullerene is not easy to prepare, and the preparation process of the ETL of the battery device is in an organic system and is not easy to be mixed with SnO dispersed in water₂And (4) compounding the nano particles. Carbon dots are an emerging carbon material that can be used for SnO because of excellent electronic properties, such as photoinduced electron transfer and electron storage properties₂Passivation of the electron transport layer. For example, the preparation of carbon dots by using glucose and cystine as raw materials has been used for SnO₂Passivation of the electron transport layer, but the PCE of the battery device is increased to a lesser extent. In summary, the above studies have some disadvantages, heavy metal elements with high price and toxicity are mostly used in the method of doping elements, and materials such as carbon nanotubes or fullerenes are not easy to prepare and not easy to disperse SnO in water₂Mixed, and the carbon dots are SnO₂The conventional raw materials are used for preparing carbon dots in the current reports, and the PCE of the battery device is improved to a lower degree.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention mainly aims to provide a preparation method of a tin dioxide electron transport layer passivation material of a perovskite solar cell.

The invention also aims to provide the perovskite solar cell tin dioxide electron transport layer passivation material prepared by the method.

The invention further aims to provide application of the tin dioxide electron transport layer passivation material for the perovskite solar cell in PSC.

The purpose of the invention is realized by the following scheme:

a preparation method of a perovskite solar cell stannic oxide electron transport layer passivation material comprises the following steps:

(1) dispersing lignin in water, and then adding hydrogen peroxide for reaction;

(2) and (2) adding a nitrogen dopant into the reaction solution after the reaction in the step (1) is finished, transferring the obtained mixed solution into a Teflon-lined high-pressure kettle for reaction, and obtaining nitrogen-doped carbon dots prepared by taking lignin as a carbon source after the reaction is finished, namely the perovskite solar cell tin dioxide electronic transmission layer passivation material.

The lignin in step (1) contains a large number of aromatic ring structures, ether bonds and unsaturated bonds, which pass through H₂O₂After the pre-oxidation and hydrothermal reaction, carbon dots containing a large number of C ═ O double bonds can be obtained.

The hydrogen peroxide in the step (1) can be pure H₂O₂May also be H₂O₂An aqueous solution of (a); adding H in the step (1)₂O₂Lignin, water and H in the mixture formed₂O₂The dosage of the composition satisfies the following requirements: 10-50mL of water and 1-10mL of H are used per 1g of lignin₂O₂In which H₂O₂The amount of (A) is pure H₂O₂When different concentrations of H are used₂O₂In the case of an aqueous solution, the concentration of H in water may be determined by the concentration of H in water₂O₂The amount of the aqueous solution is converted correspondingly.

The reaction in the step (1) is carried out at 18-25 ℃ for 10-20h under the condition of keeping out of the light, and preferably the reaction is carried out for 12h under the condition of stirring at 25 ℃ in the environment of keeping out of the light.

The nitrogen dopant in the step (2) can dope nitrogen to the carbon material and adjust the surface activity of the carbon material; the nitrogen doping agent is preferably ammonia water, the dosage of the ammonia water is 5-15mL for every 1g of lignin, and the concentration of the ammonia water is 20-30%.

The reaction in the step (2) is carried out at the temperature of 150 ℃ and 200 ℃ for 10-20h, and preferably carbonization at the temperature of 180 ℃ for 12 h.

The method also comprises the following specific steps after the reaction in the step (2) is finished: after the reaction is finished, the solution is cooled to room temperature, and is centrifuged at 12000rpm for 20 minutes to remove insoluble large particles and collect light brown supernatant, the solution is filtered by a 0.22 mu m nylon membrane syringe filter, and then is frozen and dried into powder, and carbon dots prepared by taking lignin as a carbon source, namely the perovskite solar cell tin dioxide electron transport layer passivation material, are obtained.

The perovskite solar cell tin dioxide electron transport layer passivation material prepared by the method is a CD1 passivator.

The perovskite solar cell tin dioxide electron transport layer passivation material (namely the CD1 passivation agent) is applied to the manufacture of a PSC device, and particularly applied to the manufacture of an ETL material in the PSC device.

A PSC device containing a CD1 passivating agent is prepared from the tin dioxide electron transport layer passivation material of the perovskite solar cell, and specifically comprises the following steps:

(1) ultrasonically cleaning the ITO glass, and then drying for later use;

(2) mixing nano SnO₂Mixing with CD1 aqueous solution, spin-coating the mixed dispersion on ITO glass substrate, and annealing to prepare SnO₂a/CD 1 electron transport layer;

(3) uniformly and spirally coating the prepared perovskite precursor liquid on SnO₂Annealing on the/CD 1 electron transport layer to prepare a perovskite light absorption layer;

(4) coating the prepared Spiro-OMeTAD solution on the perovskite light absorption layer in a spinning mode to prepare a Spiro-OMeTAD hole transport layer;

(5) evaporating MoO on a Spiro-OMeTAD hole transport layer₃Buffer layer and Ag electrode layer to obtain the PSC device containing the CD1 passivator.

SnO in the dispersion liquid in the step (2)₂And CD1 in an amount such that CD1 is SnO₂0-10% by volume and not 0; the SnO₂The thickness of the electron transport layer of the/CD 1 is 20-40nm, preferably 30 nm.

When the volume of CD1 in step (2) is SnO₂At 0% by volume, SnO was prepared without doping with a passivating agent of CD1₂The electron transport layer, and the PSC device prepared therefrom were used as comparative examples (other steps were the same as those for PSC device preparation containing the passivating agent CD 1).

A PSC device containing a passivating agent of CD1, comprising:

(1) ultrasonically cleaning an ITO glass substrate (1.5cm multiplied by 1.5cm) with ethanol and ultrapure water for 30 minutes, and then drying in an oven for 10-15 minutes (70 ℃);

(2) mixing nano SnO₂Mixing with CD1 aqueous solution, spin-coating the mixed dispersion on cleaned ITO glass substrate at 3000rpm for 30 seconds, and annealing at 150 deg.C for 20min to prepare SnO₂a/CD 1 electron transport layer with a thickness of 30 nm;

(3) uniformly and spirally coating the prepared perovskite precursor liquid on SnO₂Carrying out annealing on a substrate (the spin coating process is divided into two stages, namely 1000rpm and 10 seconds, then 4000rpm and 40 seconds), at 110 ℃ for 30 minutes, and preparing a perovskite light absorption layer with the thickness of 700 nm;

(4) cooling to room temperature, and then spin-coating the prepared Spiro-OMeTAD solution on the perovskite light absorption layer at 5000rpm for 30s to prepare a Spiro-OMeTAD hole transport layer with the thickness of 150 nm;

(5) evaporation of MoO in evaporation chambers using thermal evaporation₃A buffer layer (12nm) and an Ag electrode (80 nm).

The mechanism of the invention is as follows:

SnO₂oxygen vacancy defects themselves create traps that trap electrons, causing carrier recombination, reducing charge extraction efficiency, and reducing performance of the PSC device. The invention selects lignin as raw material to prepare carbon dots as SnO₂The passivating agent of (1). Pass through H₂O₂The carbon dots containing a large amount of oxygen-containing groups (C ═ O, COOH, etc.) are prepared by pre-oxidation and hydrothermal reaction, and when the number of oxygen-containing groups (including carbonyl, carboxyl, etc.) on the surface of the carbon dots is large, the carrier recombination rate on the surface of the carbon dots is low. We have used lignin containing a large number of aromatic ring structures, ether bonds and unsaturated bonds, via H₂O₂Preoxidation and hydrothermal reaction produce carbon sites containing a large number of C ═ O double bonds. When using small amount of H₂O₂Upon reaction with lignin, a large number of ether bonds in the lignin macromolecules are broken and partially unsaturated groups are oxidized to C ═ O or COOH. Carbon point to SnO₂The mechanism of defect passivation is due to the fact that the carbon dot surface contains a large number of oxygen-containing functional groups, and C ═ O double bonds with certain negative charges in the functional groups can passivate oxygen vacancy defects with positive charges. The carbon dot surface containing a large number of hydroxyl groups has a smaller electric field (or lower upward band bending), which promotes the recombination of carriers on the surface and thus reduces the charge extraction efficiency, while the carbon dot containing a large number of C ═ O double bonds has a larger electric field (or higher upward band bending), which promotes the separation of electron/hole pairs, reduces the recombination rate and promotes the extraction of charges. Thereby reducing the recombination rate and promoting the transmission of holes to the surface, and being beneficial to SnO₂The extraction of electrons in the perovskite layer effectively improves the electron mobility, so that the photovoltaic performance of the PSC device is improved.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) the raw material lignin of the invention is abundant on the earth;

(2) the preparation process of the carbon dot CD1 is simple;

(3) the carbon dot CD1 prepared by the method has low surface carrier recombination rate, and is beneficial to extraction of electrons and improvement of electron mobility. Carbon dot CD1 capable of passivating SnO₂Defects, reduction of defect state density, reduction of carrier recombination, improvement of electron mobility and improvement of PCE. SnO of PSC device added with CD1₂The electron mobility of the electron transport layer is improved by 3.5 times, the defect state density is reduced by 11.8%, and the maximum PCE of the device can reach 20.91%.

Drawings

FIG. 1 shows the preparation of carbon point CD1 from natural wood by extracting lignin and using CD1 as passivator to modify SnO₂Thereby, a schematic flow chart of a process for preparing a PSC device containing a passivating agent of CD 1.

FIG. 2 shows the carbon dots CD1 and nano SnO prepared in example 1₂Performance detection maps of; (a) is an SEM image of CD 1; (b) and (c) is an AFM image of CD 1; (d) is a statistical plot of the particle size distribution of CD 1; (e) is the XRD pattern of CD 1; (f) is an ultraviolet absorption spectrum, a fluorescence excitation spectrum and a fluorescence emission spectrum of CD1 at 200-600 nm; (g) is nano SnO₂SEM image of (a); (h) is XRD pattern of electron transport layer corresponding to CD1 doping amount of 0%, 1.5%, 3%, 5%, 10%, respectively.

FIG. 3 is a structural representation of carbon dot CD1 prepared in example 1; wherein (a) is an infrared spectrum of CD 1; (b) XPS spectra of CD1, and (C), (d), (e), and (f) fine spectra of C1S, O1S, N1S, and S2p of CD1, respectively.

FIG. 4 shows nano SnO₂And prepared CD1, SnO₂XPS spectrum of/CD 1 electron transport layer; wherein (a) is nano SnO₂And SnO₂Sn3d XPS spectrum of/CD 1 electron transport layer; (b) are CD1 and SnO₂C1s XPS spectrum of/CD 1 electron transport layer; (c) is SnO₂And SnO₂O1s XPS spectrum of/CD 1 electron transport layer.

FIG. 5 is a detection spectrum of the electron transport layer prepared in example 2; (a) the electron transport layer is pure SnO₂The dark state I-V curve graph of the single-electron device; (b) the electron transport layer is SnO added with 3 vol% of CD1₂The dark state I-V curve graph of the single-electron device; (c) is the steady state fluorescence spectrum (SSPL) of the perovskite layer deposited on the electron transport layer at 650-900nm when the addition amounts of CD1 in the electron transport layer are respectively 0%, 1.5%, 3%, 5% and 10%; (d) is the time-resolved fluorescence spectrum (TRPL) of the perovskite layer deposited on the electron transport layer when the doping amount of CD1 in the electron transport layer is respectively 0%, 1.5%, 3%, 5% and 10%; (e) the doping amount of CD1 is 0 percent respectively (the electron transport layer is pure SnO₂) And 3 vol% of electrochemical impedance spectrum and fitted curve equivalent circuit diagram of the corresponding PSC device; (f) the doping amount of CD1 is 0 (the electron transport layer is pure SnO)₂) And 3 vol% corresponding to the normalized transient photovoltage decay curve of the PSC device.

FIG. 6 is a graph of PSC device performance with the passivating agent CD 1; (a) is a schematic diagram of a structure of a PSC device; (b) is a schematic diagram of the structure of lignin; (c) is SnO with different doping amounts₂Drawing of a mixed dispersion with CD1 in water (SnO first from left)₂The second from the left is a dark brown CD1 dispersion, and the third from the left to the sixth are CD1 added with SnO₂1.5%, 3%, 5%, 10% by volume of dispersion); (d) is a current density graph of PSC devices with 0% and 3% by volume doping of CD1, respectively; (e) is an EQE diagram of the PSC device at 300-900nm corresponding to the doping amounts of CD1 being 0% and 3 vol%, respectively; (f) is a dark state I-V diagram of the PSC device in a high bias region corresponding to the doping amount of CD1 being 0% and 3 vol%, respectively; (g) is a current density graph of PSC devices with CD1 doping levels of 1.5%, 3%, 5%, 10%, respectively; (h) the PCE of the PSC device corresponding to the CD1 doping amount of 0%, 1.5%, 3%, 5% and 10% respectively is a statistical graph; (i) is a graph comparing the stability of PSC devices with 0% and 3% by volume doping of CD1, respectively.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are not indicated by manufacturers and are commercially available.

Alkaline lignin (analytically pure) source phyllo biol ltd; ammonia (25% by mass), Guangzhou chemical reagent factory; h₂O₂(30% by mass), Guangzhou chemical reagent factory; dialysis bag (7000Da), Shanghai-derived Phyllobiology, Inc.; PbI₂(99.9985%), Tokyo Chemical Industry (TCI); formamidine iodide (99.95%); methyl amine iodide (99.5%); PbCl₂(99.99%); 4-tert-butylpyridine (tBP) (96%); Spiro-OMeTAD (99.5%); SnO₂An aqueous dispersion (15%) was prepared by Alfa Aesar (particle size: 100 nm).

The CD1 solution was characterized in this example using scanning electron microscopy (SEM, Zeiss, EVO 18, Germany) and atomic force microscopy (AFM, Bruker, Multimode, Germany). The crystal structure of CD1 was studied by D8 advanced X-ray diffractometer (Bruker, germany). The functionality of CD1 was characterized by infrared spectroscopy (Bruker, Tensor27/Hyperion, Germany). And analyzing the element components and the element valence states of the CD1 by using an x-ray photoelectron spectrometer. The fluorescence properties of the CD1 solutions were measured by fluorescence spectroscopy (FluoroMax-4, Horiba, American). The UV absorption of the CD1 solution was measured in the range of 200-900nm using a UV-visible-IR spectrophotometer (Lambda 950, PerkinElmer, American). The electron extraction capacity of the ETL layer was characterized with a Time-resolved fluorescence spectrometer (Fluo Time 300, germany, PicoQuant). The photovoltaic performance of the PSC devices was characterized with a Solar simulator system (Solar S150, zhulihan, beijing). Defect state density and electron mobility were characterized using a digital source table (eithley2400, gishy, usa).

The reagents used in the examples are commercially available without specific reference.

Example 1 preparation of CD1 and PSC devices

(1) Preparation of CD1

1g of lignin was dissolved in 40mL of deionized water and 6mL of H was added₂O₂Stirring in a light-tight environmentStirring for 12 hours (25 ℃). 10mL of aqueous ammonia was added to the solution and the mixed solution was transferred to a Teflon-lined autoclave and carbonized at 180 ℃ for 12 hours. After completion of the reaction, it was cooled to room temperature, and the obtained solution was centrifuged at 12000rpm for 20 minutes to remove large insoluble particles and collect a light brown supernatant, and the solution was filtered with a 0.22 μm nylon membrane syringe filter. The filtrate was freeze-dried to a powder form to obtain carbon dots prepared using lignin as a carbon source, and the sample was named CD1 and prepared into an aqueous solution of appropriate concentration.

Example 2 preparation of PSC device

The ITO glass (1.5cm is multiplied by 1.5cm) is cleaned by ethanol and ultrapure water for 30 minutes in an ultrasonic mode, and then dried in an oven for 10-15 minutes (70 ℃). SnO₂The aqueous dispersion was mixed with an appropriate amount of an aqueous solution of CD1, and the volumes of CD1 added to the mixed dispersion were SnO, respectively₂0%, 1.5%, 3%, 5%, 10% by volume, the mixed dispersion was spin-coated on a cleaned ITO glass substrate at 3000rpm for 30 seconds, and then annealed at 150 ℃ for 20min to prepare an electron transport layer having a thickness of 30 nm. Preparing perovskite precursor solution (PbI)₂、CH₃NH₃I, the molar ratio is 1:1) is evenly coated on SnO in a spinning way₂The perovskite light absorbing layer was prepared to a thickness of 700nm on a substrate (the spin coating process was divided into two stages, first 1000rpm, 10s, then 4000rpm, 40s) and then annealed at 110 c for 30 minutes. After cooling to room temperature, the prepared Spiro-OMeTAD solution was spin-coated on the perovskite light-absorbing layer at 5000rpm for 30 seconds to prepare a hole transport layer having a thickness of 150 nm. Evaporation of MoO in evaporation chambers using thermal evaporation₃A buffer layer (12nm) and an Ag electrode (80 nm).

FIG. 1 is a diagram of the preparation of carbon-point CD1 from raw materials and the use of CD1 as a passivating agent to modify SnO₂Thereby, a schematic flow chart of a process for preparing a PSC device containing a passivating agent of CD 1. The raw material of the carbon dots is lignin (b) derived from natural wood (a). Compared with the traditional carbon source, lignin is a byproduct in the pulping and papermaking industry, contains a large number of groups such as benzene rings, ether bonds, unsaturated bonds and the like in the structure, and is an ideal material for preparing carbon dots. H for lignin₂O₂After pre-oxidation, adding ammonia water for increasingAnd (4) carbonizing at a warm temperature to obtain a carbon point aqueous solution (c). The carbon dots prepared in this way were designated as CD 1. The carbon dot surface prepared by the method has a large number of oxygen-containing groups (such as carbonyl, carboxyl and the like) and has excellent water solubility. Mixing the carbon dot aqueous solution with nano SnO₂The aqueous dispersion was blended to make a composite ETL. CD1 can be passivated SnO₂The defects on the surface reduce the energy barrier and improve the electron mobility of the ETL, thereby improving the photovoltaic performance of the perovskite solar cell.

Example 3: performance testing

(1) Characterization of carbon dots CD1

Morphology, size, structure and basic Properties of CD1 prepared in example 1 and Nano SnO₂The topography of (a) is shown in fig. 2. The SEM image (FIG. 2 (a)) and AFM image (FIG. 2 (b), (c)) of CD1 show that the size is relatively uniform, the dispersibility is good, and no serious agglomeration occurs. The size distribution plot of CD1 (FIG. 2 (d)) shows that the carbon dot diameter distribution we prepared is in the range of 18-26 nm. The XRD pattern of CD1 ((e) in fig. 2) shows a broad low-intensity diffraction peak at 23.3 ° 2 θ, which corresponds to the (002) crystal plane of carbon, suggesting an amorphous carbon structure of CD 1. The interlayer spacing was calculated by the Bragg equation to be 0.387nm, greater than that of natural graphite (0.335nm), due to the presence of a large number of oxygen-containing functional groups on the surface of CD 1. The ultraviolet absorption performance and the fluorescence performance are basic properties of the carbon dot, and in fig. 2 (f), it can be seen that the carbon dot CD1 has the absorption performance in the ultraviolet band of 200-300nm, the fluorescence excitation spectrum can see that the optimal excitation wavelength of the fluorescence is 370nm, and the fluorescence emission spectrum (excitation wavelength 370nm) can see that the fluorescence emission of the CD1 is strongest at 450 nm. In FIG. 2, (g) shows nano SnO₂The SEM image shows that the nano SnO is₂The size of (A) is about 100 nm. FIG. 2 (h) shows the doping amount of CD1 (i.e., the volume of CD1 in SnO₂Volume percent) of the electron transport layer is respectively 0% (V/V), 1.5% (V/V), 3% (V/V), 5% (V/V) and 10% (V/V), and peaks of the XRD patterns are identical to those of SnO₂Correspondingly, it can be seen that the addition of CD1 is to SnO₂The crystal structure of (a) has no influence.

(2) Characterization of the constituent elements and structures of the carbon dots CD1

Infrared spectroscopic analysis of CD1 prepared in example 1 As shown in (a) of FIG. 3, it can be seen that CD1 was at 3423cm^-1Has a strong characteristic absorption peak due to the stretching vibration of the free hydroxyl (O-H). At 3236cm^-1The weak absorption peak is the stretching vibration of amino (N-H). 1620cm^-1The absorption peak at (b) is a characteristic peak of the conjugated carbonyl group, and presumably contains a carboxyl group (COOH) due to its shift to a low wavenumber. 1600cm^-1，1507cm^-1，1417cm^-1The three absorption peaks are the vibration of the aromatic ring skeleton, which is because the structural unit of the lignin for preparing CD1 contains a benzene ring structure. 1041cm^-1，1120cm^-1，1170cm^-1The absorption peaks at three positions are all ether bonds (C-O) in the lignin structural unit, wherein 1170cm^-1The absorption peak is the stretching vibration of ether bond connected with p-hydroxyphenyl structural unit (H-type lignin structural unit), and is 1041cm^-1And 1120cm^-1The absorption peak at (A) is aliphatic ether on the side chain. 600cm^-1To 900cm^-1The absorption peaks in the range are all C-H substituents on the benzene ring. From the infrared spectrum, it can be seen that CD1 prepared from lignin as a raw material has a structure similar to that of lignin structural units, such as ether bonds, aromatic rings, etc.

To further determine the elemental composition and chemical bonds in CD1, we also performed X-ray photoelectron spectroscopy (XPS) analysis on the samples. The XPS spectrum of CD1 is shown in fig. 3 (b), in which C1S peak, O1S peak, N1S peak and S1S and S2p peak can be clearly observed, indicating that CD1 prepared by us mainly contains C, O, N, S, 4 elements, i.e. N element is successfully doped into CD 1. The C1s spectrum of fig. 3 (C) shows 4 peaks, 284.8eV (C ═ C), 285.4eV (C — N), 286.8eV (C-O) and 288.2eV (C ═ O), respectively. Similarly, the O1S spectrum of fig. 3 (d) shows 3 peaks, 532.1eV (C ═ O), 532.9eV (C — O) and 536.8eV (S ═ O), respectively. The presence of C-O, C ═ O suggests that we prepared CD1 contains oxygen-containing polar groups such as hydroxyl, carbonyl, carboxyl, etc. To ascertain the presence of N, S in the carbon dots, a fine XPS spectrum of N, S was also studied. The N1s spectrum of FIG. 3 (e) shows 3 peaks, 399.6eV (amide) and 400.4eV (pyrazine) respectivelyPyrrole) and 401.8eV (N-H). The S2p spectrum of FIG. 3 (f) shows 4 peaks, each at 169.3eV (C-SO)₂)、170.1eV(C-SO₃) 171.8eV (SO4), 168.4eV (S ═ O). The N element is mainly present in CD1 in the form of amide, free amino and heterocyclic compounds. The S element is mainly introduced into the carbon dots in the form of sulfonate. The XPS test showed that the surface composition of the carbon dots was substantially consistent with the ir spectroscopy data.

(3) CD1 doped SnO₂XPS analysis of the/CD 1 Electron transport layer

SnO prepared in example 1₂a/CD 1 electron transport layer (CD1 doping amount is 3 percent), CD1 and raw material nano SnO₂XPS analysis of (A) As shown in FIG. 4, to investigate CD1 and SnO₂Whether or not there is an interaction between them. As can be seen from (a), (b) and (c) in FIG. 4, SnO was observed after addition of CD1₂The Sn3d peak of (a) was shifted towards higher binding energies, while the O1s peak position did not change significantly. The peak of C1s of carbon point CD1 is in the same state with SnO₂After mixing, it also shifts slightly towards high binding energy. SnO₂The high shift in the binding energy of Sn3d with C1s of CD1 may be due to the shift of the electrons of the Sn and C atoms to the nuclei of the other. The above XPS spectrum suggests that CD1 may react with SnO through Sn atoms₂A chemical bond is formed.

(4) Carbon point CD1 vs SnO₂Influence of defect state density and Electron extraction efficiency of

We evaluated the SnO of PSC devices prepared in example 2 in doped (1.5%, 3%, 5%, 10% doped respectively) and undoped (0%) CD1 using the SCLC method₂Defect state density of the layer. The defect state density measurement needs to prepare ITO/SnO₂the/Perovskite/PCBM/Ag structure is a single-electron device with only an electron transport layer (i.e. does not contain a hole transport layer). The defect state density (Nt) can be calculated by the following formula:

in the formula V_TFLIs a trap fill threshold voltage, and q is an electron charge amount (q is 1.6 × 10)^-19C) L is the thickness, ε_rAnd ε₀Respectively, relative dielectric constant (SnO)₂Of_r11.5) and vacuum dielectric constant. FIG. 5 (a) and (b) are I-V curves of dark states of a single-electron device having only an electron transport layer, wherein the electron transport layer in FIG. 5 (a) is pure SnO with a CD1 doping amount of 0%₂The electron transport layer in FIG. 5 (b) is SnO with 3 vol% of CD1 added₂. When the bias voltage is applied to the turning point V_TFLWhile the applied electric field causes the defects to be completely filled with injected carriers, V in FIG. 5 (a)_TFLIs 0.09, V of (b) in FIG. 5_TFLWas 0.08. Pure SnO is obtained by calculation₂And SnO with 3 vol% of CD1₂Respectively, the defect densities of (A) are 1.27X 10¹⁵cm^-3And 1.12X 10¹⁵cm^-3The defect state density was reduced by 11.8%. This shows that the addition of the carbon point CD1 can effectively reduce SnO₂Reducing non-radiative recombination losses of carriers. Steady-state fluorescence spectroscopy (SSPL) and time-resolved fluorescence spectroscopy (TRPL) can characterize the extraction of perovskite layer electrons by the ETL from fluorescence intensity and fluorescence lifetime, respectively. FIG. 5 (c) shows deposition of SnO at different CD1 doping levels₂Steady state fluorescence spectra of the perovskite layer on the electron transport layer. When the doping amount of CD1 is less than 5%, SnO is accompanied by SnO, compared with a sample without CD1₂The doping amount of the medium carbon dot CD1 is gradually increased, the fluorescence intensity of the perovskite layer is gradually reduced, and particularly when the doping amount is 3%, the fluorescence intensity is weakest, namely fluorescence quenching occurs. Fluorescence quenching indicated that SnO after addition of CD1₂The carrier recombination rate in the process is reduced, namely the extraction of electrons and the barrier property to holes are improved. FIG. 5 (d) shows deposition of SnO at different CD1 doping levels₂Time-resolved fluorescence spectroscopy of the perovskite layer on the electron transport layer. Fluorescence intensity decay curve I (t) ═ I₀+A₁exp(-t/τ₁)+A₂exp(-t/τ₂) Fitting of the double exponential decay equation of where τ₁And τ₂Respectively representing the fast and slow decay time constants, I being the fluorescence intensity, t being the time, I₀、A₁、A₂The coefficients of the terms in the formula. Average time constant (. tau.)_ave) Using τ_ave＝(A₁τ₁ ²+A₂τ₂ ²)/(A₁τ₁+A₂τ₂) The relationship of (2). The results of the calculations for each parameter are listed in table 1.

TABLE 1 comparison of fluorescence intensity decay curves of perovskite layers corresponding to different CD1 doping amounts

It can be seen that when the doping amount of CD1 is 1.5% and 3%, tau₁、τ₂And τ_aveThere is a significant decrease in both, indicating a shortened fluorescence lifetime and an accelerated decay, i.e., a reduced rate of carrier recombination, and more efficient extraction of electrons from the perovskite layer. Fig. 5 (f) is a normalized transient light voltage attenuation curve of the PSC device with doping amounts of 0% and 3 vol% CD1, respectively, which can be characterized by the light voltage attenuation degree in the case of no external circuit conduction for the recombination of photogenerated carriers. It can be seen that the degree of photovoltage attenuation is reduced after the addition of 3 vol% CD1, indicating SnO₂The recombination rate of the carriers of the layer is reduced, also due to CD1 for SnO₂Passivation of defects (c). Fig. 5 (e) is an equivalent circuit diagram of electrochemical impedance spectroscopy and fitted curves of the PSC device with doping levels of 0% and 3 vol% CD1, respectively. PSC can be equivalent to the circuit shown in the figure, the smaller the series resistance Rs of a theoretically ideal photovoltaic device, the smaller the parallel resistance R_recThe larger the resistance value of the whole in the operating state, the more advantageous the transfer and extraction of electric charges. Rs, R calculated by electrochemical impedance spectroscopy fitting_recThe values are listed in table 2 (Control means CD1 doping amount is 0).

TABLE 2 Rs, R calculated by electrochemical impedance Spectroscopy fitting_recValue of

It can be seen that Rs decreased from 11.7 Ω to 8 with the addition of CD1.7Ω，R_recAs the addition of CD1 increased from 598.9 Ω to 1078.8 Ω, this suggests that the passivation effect of CD1 may effectively reduce the carrier recombination of the device, enhancing the charge extraction capability. The above data all show SnO₂Is effectively passivated and electrons are more effectively extracted from the perovskite layer to SnO₂Layers, i.e. SnO₂The enhanced electron extraction capability of the layer can be attributed to the fact that the CD1 prepared by us helps to slow down SnO₂The surface current carrier is compounded, and the electron extraction capability is improved.

(5) Carbon dot CD1 passivated SnO₂Impact on PSC device performance

Example 1 the obtained lignin (the structure of the lignin is schematically shown in (b) in FIG. 6) is used as a raw material and is subjected to H₂O₂The oxidized carbon dot CD1 surface has a stronger electric field (or higher upward bending band) due to the presence of more C ═ O double bonds, which is beneficial for separating electron-hole pairs. By adding CD1 into SnO₂The layer can reduce defect state density and improve SnO₂The electron extraction capability of the layer reduces the recombination rate and facilitates the transport of holes to the surface. Thus CD1 can act as a passivating agent for the PSC, doped into the Electron Transport Layer (ETL) of the PSC to enhance electron mobility. We attempted to add CD1 to SnO₂To improve device performance. A schematic diagram of the structure of the PSC device is shown in fig. 6 (a). As can be seen in FIG. 6 (c), nano SnO₂Dispersed in an aqueous solution, and is easier to mix with carbon dots that are also readily soluble in water.

Table 3 photovoltaic performance data comparison

From the comparison of the photovoltaic properties shown in (d) of FIG. 6 and Table 3, SnO₂After the layer is doped with CD1, the photovoltaic performance is improved, the FF (filling factor) is improved by 5.6%, and the PCE is improved by 2.16%. We explored the effect of the doping level of CD1 on PSC performance. FIG. 6 (g) and Table 3 show that the photovoltaic performance parameter V of PSC increases with the doping amount of CD1_OC(open circuit Voltage) J_SC(short-circuit current),FF and PCE have a tendency to rise first and then fall. The PSC has the best performance when the doping amount of CD1 reaches 3 vol%, and the performance of the PSC is reduced even when the doping amount of CD1 is increased, namely the PSC is lower than that of the PSC without CD 1. This shows that the amount of CD1 needs to be strictly controlled, and although CD1 can play a role in passivating ETL defects, an excessive amount of CD1 may cause carbon dots to aggregate to form new defect centers, thereby reducing the performance of the PSC device, as is also apparent from the statistical graph of PCEs of PSC devices corresponding to different amounts of CD1 in fig. 6 (h), when the amount of CD1 reaches 3 vol%, the PCE distribution of the device is in a higher interval of 19-20.5%, and when the amount of CD1 reaches 10 vol%, the PCE distribution is in a lower interval of 16.5-18.5%. FIG. 6(e) shows that the EQE of the PSC doped with CD1 is improved in the range of 300-450nm and around 700nm due to the interface modification of CD1 resulting in improved electron extraction capability and carrier mobility. In order to further explore the influence of carbon dot doping ETL on the carrier mobility, the carrier mobility of ETL is measured by using an SCLC method. Measurement of carrier mobility requires preparation of ITO/SnO₂The single-electron device of the/Perovskite/PCBM/Ag structure only has an electron transmission layer. FIG. 6 (f) is a diagram of dark states I-V in a high bias region of the device based on the above structure. According to the Mott-Gurney formula:

the carrier mobility of the ETL can be calculated by fitting the curve to this segment. Where μ is the carrier mobility, J_DIs the dark current density (J)_DI/S, S is the device area), V is the applied bias, L is the thickness, J_D/V²Is the slope k, epsilon of the fitted straight line_rAnd ε₀Relative and vacuum dielectric constants, SnO₂Has a relative dielectric constant of 11.5. The above equation can thus be simplified: mu-8L³×k/S×9×ε_rε₀. According to this formula, it can be calculated that the electron mobility of ETL with the amount of doping and the amount of undoped ETL with doping of 3 vol% are 1.16X 10, respectively^-3cm²V^-1s^-1And 4.08X 10^-3cm²V^-1s^-1The electron mobility is improved by 3.5 times. The calculation result shows that the doping amount is 3 vol% of ETL, and the carrier mobility is obviously improved. This indicates that the doping of the carbon dots has a positive effect on the electron mobility enhancement of the ETL. The significant improvement in electron mobility can effectively promote electron transfer in the PSC, reduce charge accumulation at the ETL/perovskite interface, increase the conductivity of ETL and reduce the recombination of defect centers on carriers, thereby improving the efficiency of PSC devices. In addition, the addition of carbon dots also provides some improvement in the stability of the PSC device. In FIG. 6, (i) is SnO₂Comparison of device stability for CD1 with 0% and 3 vol% for medium doping levels, respectively. After 300h of continuous irradiation, the PSC with 3 vol% CD1 added still remained over 79% of the initial PCE, while the PSC without CD1 remained only 55% of the initial PCE. The carbon point's improvement in PSC stability is attributed to its SnO₂Passivation of the defects can reduce ion migration, thereby slowing decomposition of the perovskite layer.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a perovskite solar cell tin dioxide electron transport layer passivation material is characterized by comprising the following steps:

(1) dispersing lignin in water, and then adding hydrogen peroxide for reaction;

(2) and (2) adding a nitrogen dopant into the reaction solution after the reaction in the step (1), transferring the obtained mixed solution into a reaction kettle lined with Teflon for reaction, and obtaining nitrogen-doped carbon dots prepared by taking lignin as a carbon source, namely the perovskite solar cell tin dioxide electronic transport layer passivation material after the reaction is finished.

2. The preparation method of the perovskite solar cell tin dioxide electron transport layer passivation material as claimed in claim 1, wherein the preparation method comprises the following steps:

the hydrogen peroxide in the step (1) is pure H₂O₂Or H₂O₂An aqueous solution of (a); adding hydrogen peroxide in the step (1) to form mixed liquor containing lignin, water and H₂O₂The dosage of the composition satisfies the following requirements: 10-50mL of water and 1-10mL of H are used per 1g of lignin₂O₂In which H is₂O₂The amount of (A) is pure H₂O₂When different concentrations of H are used₂O₂In the case of an aqueous solution, water and H are added according to their concentrations₂O₂The amount of the aqueous solution is converted correspondingly.

3. The preparation method of the perovskite solar cell tin dioxide electron transport layer passivation material as claimed in claim 1, wherein the preparation method comprises the following steps:

the reaction in the step (1) is carried out at 18-25 ℃ for 10-20h, preferably at 25 ℃ for 12h under stirring in a dark environment.

4. The preparation method of the perovskite solar cell tin dioxide electron transport layer passivation material as claimed in claim 1, wherein the preparation method comprises the following steps:

the nitrogen doping agent in the step (2) is ammonia water, the dosage of the ammonia water meets the requirement that 5-15mL of ammonia water is used for every 1g of lignin, and the concentration of the ammonia water is 20-30%.

5. The preparation method of the perovskite solar cell tin dioxide electron transport layer passivation material as claimed in claim 1, wherein the preparation method comprises the following steps:

6. The preparation method of the perovskite solar cell tin dioxide electron transport layer passivation material as claimed in claim 1, wherein the preparation method comprises the following steps:

7. The perovskite solar cell tin dioxide electron transport layer passivation material prepared by the method of any one of claims 1 to 6, namely a CD1 passivating agent.

8. Use of the perovskite solar cell tin dioxide electron transport layer passivation material according to claim 7 in the preparation of perovskite solar cell devices, in particular in the preparation of electron transport layer materials in perovskite solar cell devices.

9. The perovskite solar cell tin dioxide electron transport layer passivation material as claimed in claim 8, wherein the perovskite solar cell device is prepared by the following steps:

(1) ultrasonically cleaning the ITO glass, and then drying for later use;

(5) MoO is evaporated on the spiral-OMeTAD hole transport layer₃And a buffer layer and an Ag electrode layer to obtain the perovskite solar cell device containing the CD1 passivator.

10. The perovskite solar cell tin dioxide electron transport layer passivation material as claimed in claim 9, wherein the perovskite solar cell device comprises:

SnO in the dispersion liquid in the step (2)₂And CD1 in an amount such that CD1 is SnO₂0-10% by volume and not 0.