An organic solar cell based on amino acid-modified MXene as an electron transport layer and a preparation method thereof

Abstract

The present invention discloses an organic solar cell based on amino acid-modified MXene as an electron transport layer and a preparation method thereof. The structure of the solar cell includes a cathode layer, an electron transport layer, an active layer, a hole transport layer, and an anode layer from bottom to top; the electron transport layer is amino acid-modified MXenes. The solar cell of the present invention uses amino acid-modified MXene as the electron transport layer to replace the traditional ZnO, overcoming the disadvantages of low conductivity of ZnO and the need for high-temperature annealing treatment. The present invention uses amino acid-modified MXene to prepare an electron transport layer film that is flat and dense. At the same time, after amino acid modification, the amino acid can effectively passivate the defect vacancies of the MXene film, thereby improving its conductivity. In addition, the amino acid will form a dipole on the surface of the MXene film, thereby causing a decrease in its work function, making its energy level more matched with that of the active layer and improving the conversion efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and in particular relates to an organic solar cell based on amino acid-modified MXene as an electron transport layer and a preparation method thereof. Background Art

[0002] Ti3C2T x As a typical representative of the MXenes family, it has attracted the attention of researchers in various fields due to its ultra-high electrical conductivity, excellent mechanical properties and hydrophilicity. x The WF of -O-rich Ti3C2T x With extremely high WF (6.5 eV), Ti3C2T x It has a very low WF (1.8 eV). However, Ti3C2T x During the preparation process, its surface functional groups are difficult to regulate, which greatly restricts the development of Ti3C2T x Application in electronic devices. Currently, MXenes are mainly treated with oxygen plasma to improve their work function, and then applied to the transport layer of solar cells. However, this method is also prone to oxidation of MXenes and is not easy to achieve large-scale preparation (Surface-ModifiedMetallic Ti3C2T x MXene as Electron Transport Layer for Planar Heterojunction Perovskite Solar Cells). In addition, although Ti3C2T x With up to 5000S cm -1 The conductivity of Ti3C2T is much higher than that of Ti3C2T in practical applications. x A large number of crystal defects are generated, resulting in a decrease in conductivity. Therefore, it is necessary to x The WF and crystal defects of the transistor are optimized to improve its electrical performance.

[0003] Amino acids have attracted widespread attention due to their environmentally friendly, non-toxic, abundant earth resources, and good biocompatibility. Currently, various amino acids have been used in the field of electronic devices, including photovoltaic devices, and have been proven to significantly improve electrical properties. Summary of the invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an organic solar cell based on amino acid-modified MXene as the electron transport layer and a preparation method thereof, and to provide a low-temperature liquid-phase exfoliation method with simple process and easy regulation for preparing an organic solar cell based on amino acid-modified MXene as the electron transport layer and a preparation method thereof.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] An organic solar cell based on amino acid-modified MXenes as the electron transport layer, the structure includes a cathode layer, an electron transport layer, an active layer, a hole transport layer, and an anode layer from bottom to top; the electron transport layer is amino acid-modified MXenes.

[0007] Preferably, the cathode is indium tin oxide (ITO), the active layer is PM6:BTP-eC9, the hole transport layer is MoO3, and the anode layer is silver (Ag).

[0008] More preferably, the mass ratio of PM6 to BTP-eC9 in PM6:BTP-eC9 is 1:1 to 1.2.

[0009] Preferably, the MXenes are at least one of Ti3C2Tx, Ti2CT x , Nb2CT x , V2CT x and Mo2CT x ; the amino acid is at least one of glycine, D-alanine, L-cysteine, L-lysine, and L-arginine.

[0010] Preferably, the thickness of the electron transport layer is 5-10 nm, the thickness of the active layer is 100-110 nm, the thickness of the hole transport layer is 1-3 nm, and the thickness of the anode layer is 90-100 nm.

[0011] The preparation method of the above-mentioned organic solar cell based on amino acid-modified MXenes as the electron transport layer includes the following steps:

[0012] (1) Perform plasma treatment on the surface of the cathode layer for 10-15 minutes;

[0013] (2) Spin-coat the MXene precursor solution on the surface of the cathode layer at 1000-3000 rpm, and perform annealing treatment at 80-100 °C in a protective atmosphere for 5-10 minutes;

[0014] (3) Spin-coat the amino acid solution onto the MXenes film, and then anneal it at 80-100 °C for 5-10 minutes in a protective atmosphere;

[0015] (4) Spin-coat the active layer solution onto the electron transport layer of amino acid-modified MXenes, and after drying, anneal it at 80-100 °C for 7-10 minutes;

[0016] (5) Evaporate and deposit the hole transport layer material on the active layer to form a hole transport layer;

[0017] (7) Evaporate and deposit the anode layer material on the hole transport layer to form an anode layer.

[0018] Preferably, the preparation method of the MXenes precursor solution in step (2) is: Add LiF to the hydrochloric acid solution, dissolve it, add Ti2AlC2 ceramic powder, react at 30-35 °C for 24 h under stirring conditions, and centrifuge and wash; Redisperse the product in deionized water, ultrasonically disperse it, and then centrifuge at 3000-3500 rpm for 30-60 min. The black supernatant is few-layer Ti3C2T x , that is, the MXenes precursor solution.

[0019] Further preferably, the concentration of the hydrochloric acid solution is 8-10 M; the mass-volume ratio of LiF to the hydrochloric acid solution is 1:(15-25) g / mL; the mass ratio of LiF to Ti2AlC2 ceramic powder is (1-1.2):1; the stirring is magnetic stirring; the centrifugal washing is multiple centrifugal cleanings until the pH value is 6-7; the time of ultrasonic dispersion is 0.5-1 h.

[0020] Preferably, the concentration of the MXenes precursor solution in step (2) is 1-3 mg / mL.

[0021] Further preferably, the concentration of the MXenes precursor solution in step (2) is 2-3 mg / mL.

[0022] Preferably, the spin-coating time in step (2) is 30-40 s;

[0023] Preferably, the concentration of the amino acid solution in step (3) is 0.02-0.2 mg / mL; the dosage of the amino acid solution is 20-30 microliters per square centimeter;

[0024] Preferably, the spin-coating speed in step (3) is 2000-4000 rpm, and the time is 30-40 s.

[0025] Preferably, the protective atmosphere in steps (2) and (3) is nitrogen.

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

[0027] (1) The solar cell of the present invention uses amino acid-modified MXene as the electron transport layer to replace the traditional ZnO, overcoming the disadvantages of low conductivity of ZnO and the need for high-temperature annealing treatment.

[0028] (2) The present invention prepares the electron transport layer by using amino acid to modify MXene, which has the characteristics of simple process and easy regulation. The prepared amino acid-modified MXene film is flat and dense. At the same time, after amino acid modification, the amino acid can effectively passivate the defect vacancies of the MXene film, thereby improving its conductivity. In addition, the amino acid will form dipoles on the surface of the MXene film, which will cause the work function to decrease, making its energy level more matched with that of the active layer and improving the conversion efficiency. Description of the Drawings

[0029] Figure 1 For unmodified Ti3C2T x film and amino acid-modified Ti3C2T x Raman spectra (a), electron paramagnetic resonance (EPR) spectra (b) and passivation schematic diagram (c) of the film.

[0030] Figure 2 For unmodified Ti3C2T x film and amino acid-modified Ti3C2T x Schematic diagrams of the charge transport process (a and b) and conductivity curve (c) of the film.

[0031] Figure 3 For unmodified Ti3C2T x film and amino acid-modified Ti3C2T x Optoelectron spectra of the film.

[0032] Figure 4 Graph of the relationship between current density and voltage of the solar devices of Comparative Examples 1-2 and Examples 1-5. Detailed Embodiments

[0033] The present invention will be further described below in conjunction with embodiments. This description is only for better explaining the present invention rather than limiting it. The present invention is not limited to the specific examples and implementation schemes described here. For those of ordinary skill in the art, other different forms of changes or modifications can be made on this basis. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention. For example, the active layer material is not only limited to the PM6:BTP-eC9 system, but also can include other types of active layer materials; the types of MXenes are not only limited to Ti3C2Tx, but also include other members of other MXenes families, including Ti2CTx , Nb2CT x , V2CT x , Mo2CT x etc.; The types of amino acids are not only limited to the glycine, D-alanine, L-cysteine, L-lysine, and L-arginine used in the examples, but also include other types of amino acids.

[0034] Comparative Example 1

[0035] In this comparative example, an organic solar cell structure based on Ti3C2T x as the electron transport layer, the device structure includes a cathode layer, an electron transport layer, an active layer, a hole transport layer, and an anode layer from bottom to top. The specific preparation method is as follows:

[0036] 1. Cleaning of the cathode substrate ITO: Ultrasonic clean with dishwashing liquid, deionized water, acetone, absolute ethanol, and isopropanol in an ultrasonic cleaner for 15 minutes in sequence, and then dry in a vacuum drying oven at 70 - 80 °C to obtain a clean substrate surface required for the experiment.

[0037] 2. Preparation of Ti3C2T x as the electron transport layer: Perform plasma treatment on the cleaned and dried ITO for 10 minutes. Spin-coat the Ti3C2T x solution (prepared in the same way as in Example 1) on the surface of ITO at a rotation speed of 2000 rpm for 40 seconds. Finally, anneal Ti3C2T x at 80 °C for 10 min in a glove box filled with nitrogen to form an electron transport layer based on Ti3C2T x with a thickness of 5 nm.

[0038] 3. Preparation of the active layer: Dissolve PM6 and BTP-eC9 in a chlorobenzene solution at a mass ratio of 1:1.2 to prepare a solution with a concentration of 9 mg / mL. Then add 0.5% (v / v) DIO as an additive. Spin-coat the PM6:BTP-eC9 solution into a film at 3000 rpm for 60 s. After the film is completely dried, anneal it at 100 °C for 10 minutes to obtain the active layer with a thickness of 100 nm.

[0039] 4. Preparation of the hole transport layer: Evaporate MoO3 onto the active layer using a vacuum evaporation instrument to form a 2-nm-thick hole transport layer.

[0040] 5. Preparation of the anode layer: Evaporate metal Ag onto the hole transport layer using a vacuum evaporation instrument to form a 100-nm-thick anode layer.

[0041] Comparative Example 2

[0042] In this comparative example, the structure of the organic solar cell based on ZnO as the electron transport layer. The device structure includes a cathode layer, an electron transport layer, an active layer, a hole transport layer, and an anode layer from bottom to top. The specific preparation method is as follows:

[0043] 1. Cleaning of the cathode substrate ITO: Ultrasonic clean with dishwashing liquid, deionized water, acetone, absolute ethanol, and isopropanol in an ultrasonic cleaner for 15 minutes in sequence, and then dry in a vacuum drying oven at 70 - 80 °C to obtain a clean substrate surface required for the experiment.

[0044] 2. Preparation of the ZnO-based electron transport layer: Perform plasma treatment on the cleaned and dried ITO for 10 minutes. Spin-coat the ZnO solution on the surface of the ITO at a rotation speed of 4500 rpm for 40 seconds. Then anneal at 200 °C for 60 minutes to form the ZnO-based electron transport layer with a thickness of 30 nm.

[0045] 3. Preparation of the active layer: Dissolve PM6 and BTP-eC9 in a chlorobenzene solution at a mass ratio of 1:1.2 to prepare a solution with a concentration of 9 mg / mL. Then add 0.5% (v / v) DIO as an additive. Spin-coat the PM6:BTP-eC9 solution at 3000 rpm to form a film, and the spinning time is 60 s. After the film is completely dried, anneal at 100 °C for 10 minutes to obtain the active layer with a thickness of 100 nm.

[0046] 4. Preparation of the hole transport layer: Evaporate MoO3 onto the active layer using a vacuum evaporator to form a 2-nm-thick hole transport layer.

[0047] 5. Preparation of the anode layer: Evaporate metal Ag onto the hole transport layer using a vacuum evaporator to form a 100-nm-thick anode layer.

[0048] Example 1

[0049] In this example, the organic solar cell structure based on glycine-modified Ti3C2T x as the electron transport layer. The device structure includes a cathode layer, an electron transport layer, an active layer, a hole transport layer, and an anode layer from bottom to top. The specific preparation method is as follows:

[0050] 1. Cleaning of the cathode substrate ITO: Ultrasonic clean with dishwashing liquid, deionized water, acetone, absolute ethanol, and isopropanol in an ultrasonic cleaner for 15 minutes in sequence, and then dry in a vacuum drying oven at 70 - 80 °C to obtain a clean substrate surface required for the experiment.

[0051] 2. Glycine-modified Ti3C2T xFor the preparation of the electron transport layer: The cleaned and dried ITO was subjected to plasma treatment for 10 minutes. The Ti3C2T x solution was spin-coated on the surface of ITO at a rotation speed of 2000 rpm for 40 seconds. Finally, the Ti3C2T x was annealed at 80 °C for 10 min, and its thickness was 5 nm. Then, 50 μL (concentration of 0.02 mg / mL) of glycine aqueous solution was spin-coated onto the Ti3C2T x film (spin-coating area was 2.25 square centimeters) for 30 s, and annealed at 80 °C for 10 min in a glove box filled with nitrogen to form a glycine-modified Ti3C2T x electron transport layer.

[0052] Among them, the preparation method of the Ti3C2T x solution was as follows: 2 g of LiF was added to a polytetrafluoroethylene cup containing 40 mL of hydrochloric acid solution (concentration of 9 M), and sealed for magnetic stirring until LiF was completely dissolved. Subsequently, 2 g of Ti2AlC2 ceramic powder was added to the cup, the reaction temperature was adjusted to 35 °C, and magnetic stirring was carried out for 24 h. After the reaction, the product was centrifuged and washed several times until the pH value reached 6. The product was redispersed in deionized water, then ultrasonically dispersed for 1 h, and then centrifuged at 3500 rpm for 30 min. The black supernatant was the few-layer Ti3C2T x . Take a portion of the Ti3C2T x dispersion for filtration and drying and weighing to obtain a dispersion concentration of 2 mg / mL.

[0053] 3. Preparation of the active layer: PM6 and BTP-eC9 were dissolved in chlorobenzene solution at a mass ratio of 1:1.2 to prepare a solution with a concentration of 9 mg / mL. Then, 0.5% (v / v) of DIO as an additive was added to it. The PM6:BTP-eC9 solution was spin-coated into a film at 3000 rpm for 60 s. After the film was completely dried, it was annealed at 100 °C for 10 minutes to obtain the active layer with a thickness of 100 nm.

[0054] 4. Preparation of the hole transport layer: MoO3 was evaporated onto the active layer by a vacuum evaporator to form a 2-nm-thick hole transport layer.

[0055] 5. Preparation of the anode layer: Metal Ag was evaporated onto the hole transport layer by a vacuum evaporator to form a 100-nm-thick anode layer.

[0056] Example 2

[0057] Device preparation was based on Example 1, on the amino acid-modified Ti3C2T xWhen preparing the electron transport layer, glycine was replaced with alanine.

[0058] Example 3

[0059] Based on Example 1 for device preparation, during the preparation of the electron transport layer, glycine was replaced with cystine in the amino acid-modified Ti3C2T x When preparing the electron transport layer, glycine was replaced with cystine.

[0060] Example 4

[0061] Based on Example 1 for device preparation, during the preparation of the electron transport layer, glycine was replaced with lysine in the amino acid-modified Ti3C2T x When preparing the electron transport layer, glycine was replaced with lysine.

[0062] Example 5

[0063] Based on Example 1 for device preparation, during the preparation of the electron transport layer, glycine was replaced with arginine in the amino acid-modified Ti3C2T x When preparing the electron transport layer, glycine was replaced with arginine.

[0064] Performance parameter description

[0065] As can be seen from a) in the Raman spectrum ( Figure 1 ), the peak at 154 cm -1 position is the A x Raman peak of Ti3C2T 1g , which reflects the defect concentration status of Ti3C2T x . It can be found that after the modification with amino acids, the A x Raman peak of the Ti3C2T 1g thin film becomes sharper and stronger, indicating a decrease in the defect concentration of the Ti3C2T x thin film. After the modification with amino acids, the A 1g peak shifts towards lower wavenumbers, which also indicates that the Ti3C2T x thin film after the modification with amino acids has a lower defect concentration. In addition, in the electron paramagnetic resonance (EPR) spectrum ( Figure 1 b)), Ti3C2T x has an obvious EPR signal (g = 2.0), which indicates that there are a large number of Ti and C vacancy defects in Ti3C2T x . After the modification with amino acids, their EPR signals are significantly reduced compared to Ti3C2T x , further confirming that they have a lower density of Ti and C vacancies. Therefore, the results of Raman and EPR both show that amino acids can effectively passivate the Ti and C vacancy defects of Ti3C2T x . For a better understanding of the amino acid passivation of Ti3C2T xFor the mechanism of Ti and C vacancy defects, we take glycine-passivated Ti3C2T as an example. x As shown Figure 1 in c of x , the positively charged -NH2 of the amino acid will passivate the negatively charged Ti vacancies of Ti3C2T, x while the negatively charged -COOH of the amino acid passivates the positively charged C vacancies of Ti3C2T. x The lone electron pairs of -NH2 and -COOH on the amino acid respectively form a coordination relationship with the C atoms and Ti atoms with insufficient surface coordination of Ti3C2T, x thus passivating the Ti and C vacancies of Ti3C2T respectively.

[0066] Figure 2 a in x is the charge transport process of the Ti3C2T thin film. Its large number of vacancies itself become trap states that capture carriers and cause non-radiative recombination, reducing the carrier lifetime and thus the charge extraction efficiency. In addition, these vacancies also act as recombination centers at the interface, forming a shunt leakage current path and hindering the transport of charge carriers. In contrast, after modification and passivation with amino acids ( Figure 2 b in x ), the density of Ti and C vacancies in Ti3C2T Figure 2 is significantly reduced, so the recombination sites of charge carriers are reduced. Therefore, as can be seen from the conductivity of the thin film in x c, the conductivity of the Ti3C2T thin film is 6.87 μS / cm.

[0067] After modification with amino acids, the conductivities of the Ti3C2T x / Gly, Ti3C2T x / D-Ala, Ti3C2T x / L-Cys, Ti3C2T x / L-Lys and Ti3C2T x / L-Arg thin films are 15.44, 14.61, 14.70, 15.35 and 16.17 μS / cm respectively.

[0068] The increase in conductivity after modification and passivation with amino acids is due to the significant reduction in the density of Ti and C vacancies in Ti3C2T x , resulting in a reduction in non-radiative carrier recombination.

[0069] As can be seen from Figure 3 the X-ray photoelectron spectroscopy, after modification with amino acids, the work function of the Ti3C2T x thin film decreases from 4.75 eV to 4.32, 4.32, 4.37, 4.22 and 4.41 eV. After amino acid modification, Ti3C2Tx The decrease in WF will make its energy level more matched with that of the active layer, thereby reducing the barrier height of electrons. At the same time, the lower WF will enhance the built-in electric field of the device, and then reduce the losses of the open-circuit voltage and short-circuit current. Figure 4 Figure 1 shows the current density-voltage relationship diagrams of the solar devices of the comparative examples and the examples, and the corresponding performance parameters are listed in Table 1. It can be seen that based on Ti3C2T x The PCE of the device is 7.26%, and J sc is 20.64 mA / cm 2 , V oc is 0.65 V, and the FF is 54.13%. After the modification and passivation of amino acids, based on Ti3C2T x / Gly, Ti3C2T x / D-Ala, Ti3C2T x / L-Cys, Ti3C2T x / L-Lys, Ti3C2T x / L-Arg devices have significantly improved J sc , V oc and FF, and achieve PCEs of 17.09%, 17.07%, 17.03%, 17.16% and 17.00% respectively, which are comparable to 17.18% of the ZnO-based device (J sc =26.41 mA / cm 2 , V oc =0.84 V, FF=77.42%). In summary, it shows that applying amino acid-modified Ti3C2T x to the electron transport layer of organic solar cells has great development prospects.

[0070] Table 1

[0071]

[0072] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. An organic solar cell based on amino acid-modified MXenes as an electron transport layer, characterized in that, The structure includes a cathode layer, an electron transport layer, an active layer, a hole transport layer, and an anode layer from bottom to top. The active layer is PM6:BTP-eC9; the electron transport layer is amino acid-modified MXenes, the MXenes is Ti3C2Tx, and the amino acid is at least one of glycine, alanine, cystine, lysine, and arginine; The preparation method of the electron transport layer is as follows: Spin-coat the MXene precursor solution on the surface of the cathode layer at 1000-3000 rpm, and anneal it at 80-100 °C for 5-10 minutes in a protective atmosphere; Spin-coat the amino acid solution onto the MXenes film, and then anneal it at 80-100 °C for 5-10 minutes in a protective atmosphere.

2. The organic solar cell based on amino acid-modified MXenes as the electron transport layer according to claim 1, wherein The cathode layer is indium tin oxide, the hole transport layer is MoO3, and the anode layer is silver.

3. The organic solar cell based on amino acid-modified MXenes as the electron transport layer according to claim 1, wherein The thickness of the electron transport layer is 5-10 nm, the thickness of the active layer is 100-110 nm, the thickness of the hole transport layer is 1-3 nm, and the thickness of the anode layer is 90-100 nm.

4. The preparation method of the organic solar cell based on amino acid-modified MXenes as the electron transport layer according to any one of claims 1-3, characterized in that, It includes the following steps: (1) Perform plasma treatment on the surface of the cathode layer for 10-15 minutes; (2) Spin-coat the MXene precursor solution on the surface of the cathode layer at 1000-3000 rpm, and anneal it at 80-100 °C for 5-10 minutes in a protective atmosphere; (3) Spin-coat the amino acid solution onto the MXenes film, and then anneal it at 80-100 °C for 5-10 minutes in a protective atmosphere; (4) Spin-coat the active layer solution on the electron transport layer of amino acid-modified MXenes, and anneal it at 80-100 °C for 7-10 minutes after drying; (5) Evaporate the hole transport layer material on the active layer to form a hole transport layer; (6) Evaporate the anode layer material on the hole transport layer to form an anode layer.

5. The preparation method according to claim 4, characterized in that, The preparation method of the MXenes precursor solution described in step (2) is as follows: Add LiF to the hydrochloric acid solution. After dissolution, add Ti2AlC2 ceramic powder, and react at 30-35 °C for 24-36 h under stirring conditions, followed by centrifugal washing; redisperse the product in deionized water, perform ultrasonic dispersion, and then centrifuge at 3000-3500 rpm for 30-60 min. The black supernatant is few-layer Ti3C2T x , that is, the MXenes precursor solution.

6. The preparation method according to claim 5, characterized in that The concentration of the hydrochloric acid solution is 8-10 M; the mass-volume ratio of LiF to the hydrochloric acid solution is 1:(15-25) g / mL; the mass ratio of LiF to Ti2AlC2 ceramic powder is (1-1.2):1; the stirring is magnetic stirring; the centrifugal washing is multiple centrifugal cleanings until the pH value is 6-7; the time of ultrasonic dispersion is 0.5-1 h.

7. The preparation method according to claim 4, wherein In step (2), the concentration of the MXene precursor solution is 1-3 mg / mL; the spin-coating time in step (2) is 30-40 s.

8. The preparation method according to claim 4, characterized in that, In step (3), the concentration of the amino acid solution is 0.02-0.2 mg / mL; the dosage of the amino acid solution is 20-30 microliters per square centimeter; the spin-coating speed in step (3) is 2000-4000 rpm, and the time is 30-40 s.

9. The preparation method according to claim 4, characterized in that The protective atmosphere in steps (2) and (3) is nitrogen.

Images