EDTA-2Na modified indium tin oxide and application thereof in perovskite solar cell

Abstract

The invention discloses an EDTA-2Na (Ethylene Diamine Tetraacetic Acid-2Na) modified indium tin oxide and an application of the EDTA-2Na modified indium tin oxide in a perovskite solar cell. The EDTA-2Na in the EDTA-2Na modified indium tin oxide can play a role in inhibiting the acid etching reaction between the perovskite and the ITO (indium tin oxide) and preventing indium ions from migrating and entering the perovskite. The ITO substrate is modified and protected by adopting EDTA-2Na capable of being combined with uncoordinated indium ions on the ITO and utilizing the chelating capability of the EDTA-2Na on free indium ions, and the indium ions in the ITO are prevented from being migrated to perovskite. The operation stability of a perovskite solar cell device adopting the modified indium tin oxide is improved, degradation of a perovskite lower interface after operation is inhibited, and the efficiency of the device is improved to a certain extent.

Description

Technical Field

[0001] The present invention relates to indium tin oxide modified with EDTA-2Na and its application in perovskite solar cells, belonging to the technical fields of optoelectronic devices and solar cells. Background Art

[0002] Perovskite solar cells are a type of promising new optoelectronic device. Compared with silicon solar cells, their manufacturing process is simpler, the raw material cost is lower, and they are suitable for flexible devices, thus receiving extensive attention from academia and industry. In recent years, the efficiency of perovskite solar cells has continuously achieved breakthroughs. The current record highest efficiency reaches 26.1%, which is very close to the 26.81% efficiency of silicon heterojunction cells. However, the stability issue has always been a major obstacle to the industrialization of perovskite solar cells, including the intrinsic stability of perovskite materials and the stability of the overall device. When subjected to external influences such as light, oxidation, high temperature, and high humidity environments, perovskite materials will undergo varying degrees of degradation and ion migration phenomena, resulting in severe degradation of their photovoltaic properties, which is the intrinsic stability problem of perovskite materials. On the other hand, there are also unstable factors in the overall device, mainly that different functional layers, including the perovskite layer, charge carrier transport layer, and electrodes, will interact with each other, thus interfering with the normal working state of the device. Therefore, it is necessary to improve the stability of perovskite solar cell devices. Summary of the Invention

[0003] The purpose of the present invention is to provide indium tin oxide modified with EDTA-2Na, that is, to modify the ITO electrode with a chelating material (EDTA-2Na) that can bind to the uncoordinated indium ions and free indium ions on ITO (indium tin oxide), which can effectively bind to ITO and block the acid etching reaction between perovskite and ITO, thereby improving the stability of perovskite solar cell devices.

[0004] After modifying ITO with EDTA-2Na, EDTA-2Na forms coordination bonds with indium ions on the ITO surface, enhancing the stability of the ITO surface, acting as a protective layer, and blocking the migration of decomposition products of perovskite to ITO for acid etching reaction. After introducing EDTA-2Na to modify ITO, the reaction between perovskite and ITO is successfully inhibited, greatly improving the degradation effect of the lower interface of perovskite, and reducing the holes and lead iodide generated by the decomposition reaction at the lower interface of perovskite. At the same time, due to the strong chelating ability of EDTA-2Na, which can form chelation products with most divalent and trivalent metal ions, EDTA-2Na can effectively block the migration of indium ions from ITO to perovskite. By modifying with EDTA-2Na, free indium ions will be chelated and blocked by EDTA-2Na, avoiding the carrier transport barrier formed due to the doping effect of indium ions on perovskite, and further ensuring the efficiency of the device during operation.

[0005] The present invention provides a method for modifying ITO with EDTA-2Na, comprising the following steps:

[0006] Spin-coat an aqueous solution of EDTA-2Na on ITO, and anneal to form an EDTA-2Na protective layer, thus obtaining the ITO substrate.

[0007] In the above preparation method, in the aqueous solution, the concentration of EDTA-2Na is 0 to 1 mg / mL, preferably 0.5 to 1 mg / mL, more preferably 0.5 to 0.75 mg / mL.

[0008] In the above preparation method, the rotation speed of the spin-coating is 3000 to 5000 rpm, and the acceleration is to reach the set rotation speed within 0.5 to 1.5 s.

[0009] In the above preparation method, the annealing temperature is 100 to 150 °C, and the time is 10 to 15 minutes.

[0010] In the above preparation method, before spin-coating, the ITO is cleaned and the surface wettability is modified;

[0011] The cleaning steps are as follows: Scrub the ITO with a glass cleaning agent in sequence, and then ultrasonically clean it in an aqueous solution of the glass cleaning agent, deionized water, acetone, and isopropanol for 45 minutes each;

[0012] The steps for surface wettability modification are as follows: Place the cleaned ITO in air plasma for surface treatment, which is beneficial to the subsequent spin-coating of EDTA-2Na.

[0013] After modifying ITO with EDTA-2Na, the transport layer can be directly prepared thereon, such as the electron transport layer of tin oxide and titanium oxide, and the hole transport layer of PTAA, etc. There is no need to use ozone or plasma to change the wettability, and the aqueous or organic solutions of other materials will not damage the EDTA-2Na protective layer.

[0014] The ITO modified with EDTA-2Na provided by the present invention can not only improve the efficiency and stability of perovskite solar cells, but also improve the stability of the bottom interface of perovskite after the device operates.

[0015] Based on the ITO modified with EDTA-2Na, the present invention also provides a perovskite solar cell device including the substrate.

[0016] The principle of the present invention is as follows: Blocking the acid etching reaction process between perovskite and ITO is the key to improving the stability of perovskite solar cell devices. By reasonably selecting the material for modifying ITO as the barrier protective layer, it is possible to cut off the paths of perovskite decomposition products and indium ion migration, and delay the efficiency degradation during device operation. The process of the present invention based on EDTA-2Na modified ITO can effectively block the acid etching reaction between perovskite and ITO, and has great value and significance for the wide application of ITO and the promotion of the commercialization of perovskite solar cells.

[0017] The present invention is based on the existing technology of cleaning ITO, and then introduces a layer of EDTA-2Na protective layer to modify the surface of ITO. By using the fact that EDTA-2Na can interact with the uncoordinated indium ions on ITO and the chelating effect of EDTA-2Na on free indium ions, the problem that the acid etching reaction between perovskite and ITO affects the overall device stability is specifically solved. Compared with the existing process flow, the advantages of the present invention are mainly reflected in the following aspects:

[0018] 1. Modifying directly on the surface of ITO to better protect ITO: There is a significant ion migration phenomenon in perovskite solar cell devices. The decomposition products of perovskite are in the form of ions, such as FA + , H + and I - etc., which can penetrate the transport layer to reach the interface of ITO, thus causing an acid etching reaction, which not only damages ITO but also triggers the continuous decomposition of perovskite. The introduced EDTA-2Na in the present invention can form a coordination effect with ITO to protect ITO from corrosion by acidic substances, breaking the positive feedback cycle effect of the continuous decomposition and corrosion of perovskite on ITO.

[0019] 2. Block the migration of indium ions and improve the operational stability of perovskite solar cells: Research shows that during the operation of perovskite solar cells, due to the effects of light and built-in electric fields, free indium ions will enter the perovskite and gradually migrate to the upper surface of the perovskite, producing an n-type doping effect on the perovskite surface, thereby changing the energy level structure of the perovskite. In positive (n-i-p) devices, this indium ion doping effect will form a barrier to carrier transport, affecting the operational stability of the device. The EDTA-2Na material has a strong chelating ability for free indium ions, blocking the migration of indium ions and avoiding the doping of perovskite by indium ions.

[0020] 3. Reduce the degradation and deterioration of the perovskite lower interface: The generation of holes and decomposition at the perovskite lower interface is a phenomenon that has been widely studied and reported. Among them, the reaction between perovskite and ITO will also cause the degradation of the perovskite lower interface. The lead iodide and holes generated by the degradation will affect the device efficiency and are not conducive to the long-term operational stability of perovskite solar cells. The ITO modified by EDTA-2Na in the present invention will not undergo a harmful etching reaction with perovskite. After the long-term operation of the device, the lower interface of the perovskite still maintains a good morphology, and the migration phenomenon of iodine ions is also inhibited, indicating that the degree of degradation and deterioration of the perovskite lower interface is significantly reduced after inhibiting the etching reaction. Brief Description of the Drawings

[0021] Figure 1 It is the characterization of the indium ion migration phenomenon and its influence on the device in the overall device of the perovskite solar cell; among them, Figure a is the TOF-SIMS characterization of the indium ion distribution before the operation of the overall device, Figure b is the TOF-SIMS characterization of the indium ion distribution after the operation of the overall device, Figure c is the cross-sectional KPFM characterization before the operation of the overall device, and Figure d is the cross-sectional KPFM characterization after the operation of the overall device.

[0022] Figure 2 It is the characterization of the interaction between the material EDTA-2Na introduced in the present invention, free indium ions, and ITO; among them, Figure a is the nuclear magnetic resonance hydrogen spectrum before and after the combination of EDTA-2Na and free indium ions, and Figure b is the XPS spectrum of indium elements on the surface of ITO before and after the modification of EDTA-2Na.

[0023] Figure 3 It is the elemental analysis characterization inside the perovskite in the overall device of the perovskite solar cell before and after applying the ITO substrate modified by EDTA-2Na in the present invention; among them, Figure a is the TEM-EDS spectrum inside the perovskite of the overall device with ITO as the substrate, and Figure b is the TEM-EDS spectrum inside the perovskite of the overall device with the ITO modified by EDTA-2Na as the substrate.

[0024] Figure 4SEM characterization of the perovskite lower interface after the operation of the perovskite solar cell device before and after applying the ITO substrate modified by EDTA-2Na of the present invention; among them, Figure a is the SEM image of the perovskite lower interface of the device with ITO as the substrate, and Figure b is the SEM image of the perovskite lower interface of the device with ITO modified by EDTA-2Na as the substrate.

[0025] Figure 5 Comparison chart of I-V scanning curves of perovskite solar cell devices under a standard sunlight before and after applying the ITO substrate modified by EDTA-2Na of the present invention; among them, the red curve is the device after modifying ITO with EDTA-2Na, and the blue curve is the device with ordinary ITO as the substrate. The champion efficiency devices after optimization are selected.

[0026] Figure 6 Stability test chart of the perovskite solar cell prepared in Example 1 of the present invention; among them, Figure a is the maximum power point tracking test of the unencapsulated device under the external environment and continuous light illumination, and Figure b is the stability test under the nitrogen environment and a standard sunlight; among them, the red curve is the device after modifying ITO with EDTA-2Na, and the blue curve is the device with ordinary ITO as the substrate.

[0027] Figure 7 For the perovskite solar devices prepared in the same batch, different concentrations of EDTA-2Na are used to modify ITO, and the optimal devices with different concentrations are selected. The I-V scanning curves of these devices are shown in the figure. Detailed implementation method

[0028] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0029] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained from commercial channels.

[0030] Example 1: Modify the ITO bottom electrode with EDTA-2Na

[0031] 1. Pretreatment of indium tin oxide substrate: Using the traditional cleaning process, first scrub the ITO substrate (ITO thickness is about 200 nanometers) with a glass cleaner, and then ultrasonically clean it in an aqueous solution of the glass cleaner, deionized water, acetone and isopropanol for about 45 minutes. Place the cleaned ITO substrate under air plasma for about 2 minutes, and the beam power is about 90 watts.

[0032] 2. Preparation of EDTA-2Na solution: Dissolve 1 mg of EDTA-2Na powder in 2 mL of deionized water, stir evenly until completely dissolved, and then filter the solution.

[0033] 3. Preparation of the EDTA-2Na layer on ITO: Dissolve approximately 100 μL of EDTA-2Na in deionized water and drop it onto the ITO substrate. Spin-coat it at a rate of 4000 rpm with an acceleration of 4000 rpm / s for 30 s. Subsequently, transfer the substrate to a hot plate and anneal it at 120 °C for 10 minutes.

[0034] The perovskite solar cell device was fabricated using the ITO substrate modified with EDTA-2Na obtained in this example, and the perovskite solar device was characterized.

[0035] The preparation method of the perovskite solar cell device is as follows:

[0036] 1) Preparation of the electron transport layer: Spin-coat a tin oxide colloidal solution (a commercially purchased 15% tin oxide solution diluted with 3 volumes of deionized water) on the ITO substrate modified with EDTA-2Na at 3000 rmp for 30 s. Subsequently, anneal it on a hot plate at 150 °C for 30 minutes.

[0037] 2) Preparation of the perovskite layer: Transfer the ITO substrate with the prepared tin oxide to a glove box filled with nitrogen. Spin-coat a lead iodide solution (1.5 mol / L, with a solvent of a mixed solvent of dimethylformamide:dimethyl sulfoxide = 9:1 by volume) at 1500 rmp for 30 s. Subsequently, anneal it on a hot plate at 70 °C for 1 minute. Then, spin-coat an organic salt solution (90 mg formamidinium hydroiodide, 6.4 mg methylammonium hydroiodide, 9 mg methylammonium hydrochloride dissolved in 1 mL isopropanol) on the lead iodide at 2000 rmp for 30 s. Subsequently, transfer the perovskite to the air and anneal it on a hot plate at 150 °C for 15 minutes.

[0038] 3) Preparation of the passivation layer and the hole transport layer: Transfer the prepared perovskite to the glove box. Spin-coat an octylammonium iodide solution (7 mg / mL dissolved in isopropanol) as the passivation layer at 5000 rmp for 30 s and anneal it at 100 °C for 5 minutes. Subsequently, spin-coat a Spiro-OMeTAD solution as the hole transport layer (72.3 mg Spiro-OMeTAD dissolved in 1 ml chlorobenzene, adding 28.8 μL of tetra-tert-butylpyridine and 17.5 μL of Li-TFSI solution, and the Li-TFSI solution is 520 mg / mL dissolved in acetonitrile) at 4000 rmp for 30 s.

[0039] 4) Preparation of the gold electrode: Deposit 60 nm of gold as the electrode on the perovskite thin film with the prepared hole transport layer using thermal evaporation.

[0040] A perovskite solar cell device was fabricated using the ITO before modification with EDTA-2Na as a comparison.

[0041] Figure 1For the characterization of indium ion migration phenomenon and its impact on the perovskite solar cell device, the indium ions mainly come from the acid etching reaction between perovskite and ITO. Among them, Figure a is the TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) characterization of indium ion distribution in the whole device before operation, and Figure b is the TOF-SIMS characterization of indium ion distribution in the whole device after operation. It can be seen that indium ions accumulate on the upper surface of perovskite after the device operates. Figure c is the cross-sectional KPFM (Kelvin Probe Force Microscopy) characterization of the whole device before operation, and Figure d is the cross-sectional KPFM characterization of the whole device after operation. It can be seen that the work function of the upper surface of perovskite is smaller after the device operates. The main reason is the n-doping effect caused by indium ions, which will form a potential barrier in the p-type device and is not conducive to the transport of carriers.

[0042] In this embodiment, the measuring instrument for TOF-SIMS is TOF-SIMS 5 (IONTOF), and the area covered by the gold electrode is selected for testing before and after the device operates. The measuring instrument for AFM-KPFM is Dimension Icon (Bruker), and the cross-section of the device before and after operation is measured. The bias voltage is applied at the tip, so the larger the CPD value in the figure, the smaller the work function of the area.

[0043] Figure 2 It is the characterization of the material EDTA-2Na introduced in the present invention interacting with free indium ions and ITO. Among them: Figure a is the nuclear magnetic resonance hydrogen spectrum of EDTA-2Na before and after binding with free indium ions; Figure b is the XPS (X-ray photoelectron spectroscopy) spectrum of indium element on the ITO surface before and after EDTA-2Na modification.

[0044] It can be seen from the nuclear magnetic resonance hydrogen spectrum that after indium iodide is added to the solution, the two original peaks of EDTA-2Na at about 3.82 and 3.59 ppm split into four peaks (at 3.46, 3.41, 3.31, and 3.27 ppm respectively) that form an AB system (AB pattern) and a single peak at 2.94, indicating that EDTA-2Na has undergone a chelation reaction with metal indium ions in the solution.

[0045] It can be seen from the XPS spectrum that after a layer of EDTA-2Na is modified on the ITO surface, the XPS peak position of indium ions moves towards a lower binding energy direction, indicating that the electron concentration around indium ions increases, showing that EDTA-2Na can form a coordination bond with indium ions, thereby changing the electron concentration around it.

[0046] Figure 3 Before and after applying the ITO substrate modified by EDTA-2Na of the present invention, in the overall device of the perovskite solar cell, elemental analysis and characterization inside the perovskite are as follows: Figure a is the TEM-EDS (Transmission electron microscope-energy dispersive spectra) spectrum inside the perovskite of the overall device with ITO as the substrate, and Figure b is the TEM-EDS spectrum inside the perovskite of the overall device with ITO modified by EDTA-2Na as the substrate. It can be seen that when using ITO as the substrate, indium ions can migrate into the perovskite layer, while when using ITO modified by EDTA-2Na as the substrate, the migration of indium ions can be effectively blocked.

[0047] In this embodiment, the test instrument for TEM is Talos F200X (Thermo Scientific), equipped with a STEM / HAADF resolution of 0.16 nm, and the electron energy is 200 kV; the measuring instrument for EDS elemental characterization is the Super-XEDS system, equipped with a symmetric SDD energy spectrum probe.

[0048] Figure 4 Before and after applying the ITO substrate modified by EDTA-2Na of the present invention, after the perovskite solar cell device operates, SEM (Scanning electron microscope) characterization of the perovskite lower interface is as follows: Figure a is the SEM image of the perovskite lower interface of the device with ITO as the substrate, and Figure b is the SEM image of the perovskite lower interface of the device with ITO modified by EDTA-2Na as the substrate. It can be seen that modifying ITO with EDTA-2Na can block the acid etching reaction between the perovskite and ITO, thereby reducing the degradation of the perovskite lower interface.

[0049] In this embodiment, the measuring instrument for SEM is Apero 2S (Thermo Scientific), the vacuum degree of the chamber is 0.68 Torr, and the applied voltage is 10 kV. After preparing the perovskite solar cell device and operating it for a period of time, the perovskite lower interface is exposed by peeling for SEM characterization.

[0050] Figure 5 It is a comparison chart of the I-V scanning curves of the perovskite solar cell device before and after applying EDTA-2Na modified ITO under a standard sunlight. Among them, the red curve is the device after modifying ITO with EDTA-2Na, and the blue curve is the device with ordinary ITO as the substrate. It can be seen from the IV curve that the efficiency of the perovskite solar cell device after modifying ITO with EDTA-2Na is improved compared to the original, indicating that the modification of EDTA-2Na can reduce the defects at the perovskite lower interface and improve the quality of the thin film.

[0051] In this embodiment, the IV curve was measured with an Agilent B2900 precision source meter in the external environment. The scanning rate was 50 mV / s (voltage interval 10 mV, delay 200 ms), and it was scanned backward from 1.21 V to 0.01 V. The light source used was a Xeon solar simulator (Solar IV-150A, Zolix), and the experiment was carried out under the irradiation condition of AM 1.5G (100 mW / cm 2 ), and this light source was calibrated with a Newport-certified silicon wafer.

[0052] Figure 6 It is a stability test diagram of a perovskite solar cell. Among them: Figure a is the maximum power point tracking (MPP tracking) test of the unencapsulated device in the external environment and continuous light illumination conditions, and Figure b is the stability test in a nitrogen environment and under one standard sunlight. Among them, the red curve is the device after ITO is modified with EDTA-2Na, and the blue curve is the device with ordinary ITO as the substrate. It can be seen that the device modified with EDTA-2Na has better stability, verifying the protective effect of EDTA-2Na on the substrate.

[0053] According to the method of Example 1, ITO bottom electrodes were modified with 0.5 mg / mL and 0.75 mg / mL of EDTA-2Na respectively, and then perovskite solar cell devices were prepared. Figure 7 They are the I-V scanning curves of the optimal devices of the same batch with different concentrations of EDTA-2Na used to modify ITO. When the concentration is 0.5 and 0.75 mg / mL, the efficiency of the device reaches the highest. When the concentration is 1 mg / mL, the efficiency of the device begins to decline, but it is higher than that of the unmodified control group device. It shows that the modification of ITO with EDTA-2Na helps to reduce the defects of perovskite and plays a role in improving the device efficiency, but too high a concentration will affect the carrier transport. Therefore, the optimal concentration of EDTA-2Na should be in the range of 0.5-1 mg / mL.

Claims

1. An ITO substrate is obtained by modifying ITO with EDTA-2Na.

2. The ITO substrate according to claim 1, characterized in that: The ITO and the EDTA-2Na are combined through a coordination bond formed by the EDTA-2Na and indium ions on the surface of the ITO.

3. The preparation method of the ITO substrate according to claim 1 or 2, comprising the following steps: Spin-coat an aqueous solution of EDTA-2Na on the ITO and anneal to form an EDTA-2Na protective layer, thereby obtaining the ITO substrate.

4. The preparation method according to claim 3, characterized in that: In the aqueous solution, the concentration of the EDTA-2Na is 0 to 1 mg / mL, but not zero.

5. The preparation method according to claim 3 or 4, characterized in that: The rotation speed of the spin-coating is 3000 to 5000 rpm, and the acceleration is to reach the set rotation speed within 0.5 to 1.5 s.

6. The preparation method according to any one of claims 3-5, characterized in that: The annealing temperature is 100 to 150 °C, and the time is 10 to 15 minutes.

7. The preparation method according to any one of claims 3-6, characterized in that: Before spin-coating, the ITO is cleaned and the surface wettability is modified.

8. The application of the ITO substrate according to claim 1 or 2 in the preparation of perovskite solar cell devices.

9. The application according to claim 8, characterized in that: The ITO substrate improves the efficiency and stability of the perovskite solar cell device and the stability of the bottom interface of the perovskite after operation.

10. A perovskite solar cell device, which comprises the ITO substrate according to claim 1 or 2.

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