PbO / CuI double-interlayer-based lead iodine-based perovskite solar cell structure and preparation method thereof

Abstract

The invention discloses a lead iodine-based perovskite solar cell structure based on PbO / CuI double intermediate layers and a preparation method thereof, and belongs to the technical field of solar cells. Comprising a substrate, a transparent electrode, an electron transport layer, a PbO intermediate layer, a perovskite active layer, a CuI intermediate layer, a hole transport layer and a metal electrode which are stacked in sequence. Aiming at the ion characteristics of lead iodine-based perovskite, the PbO intermediate layer is arranged between the electron transport layer and the perovskite active layer, and the CuI intermediate layer is arranged between the hole transport layer and the perovskite active layer. The migration of ions is effectively inhibited, the defect density at an interface is reduced, and the transition potential barrier of a current carrier is reduced. And the PbO intermediate layer and the CuI intermediate layer can form good interface contact with the perovskite layer, the electron transport layer and the hole transport layer, so that the capture probability of current carriers at the interface is reduced, more effective extraction and transmission of charges are promoted, and the charge collection efficiency and the photoelectric conversion efficiency of the cell are improved.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and particularly relates to a lead iodide-based perovskite solar cell structure with a PbO / CuI double intermediate layer and a preparation method thereof. Background Art

[0002] Lead iodide-based perovskite is a semiconductor material with strong visible light absorption, high carrier mobility, strong defect tolerance, convenient preparation process, and high photoelectric conversion efficiency when used as the active layer in solar cells. For example, in August 2023, research groups from Northwestern University in the United States and the University of Toronto in Canada fabricated a reverse perovskite solar cell device with an efficiency of 26.1%, which has an open-circuit voltage of 1.174 V, a short-circuit current of 26.31 mA / cm2, and a fill factor of 85.2%.

[0003] However, the inherent stability problem of perovskite materials limits the wide application of devices. First, the migration and oxidation reaction of iodide ions will cause a large number of iodine vacancies in the bulk and at the interfaces (especially at the interface between perovskite and the hole transport layer). These vacancies may not only act as carrier trapping centers to reduce the current density but also provide carrier transition barriers to reduce the open-circuit voltage. Second, the organic cations (including methylammonium ions and formamidinium ions) in the A-site cations have poor thermal stability and a polarization effect, which may cause a certain degree of hysteresis. Third, positively charged defects may appear at the interface between perovskite and the electron transport layer, which will also act as electron trapping centers and increase the transition barrier. Summary of the Invention

[0004] The purpose of the present application is to provide a lead iodide-based perovskite solar cell structure with a PbO / CuI double intermediate layer and a preparation method thereof, which is used to solve the problem of poor stability of perovskite solar cells in the prior art.

[0005] To solve the above technical problems, the present application is implemented by adopting the following technical solutions:

[0006] On the one hand, the present application provides a lead iodide-based perovskite solar cell structure with a PbO / CuI double intermediate layer and a preparation method thereof, including: a lead iodide-based perovskite solar cell structure with a PbO / CuI double intermediate layer, including a substrate, a transparent electrode, an electron transport layer, a PbO intermediate layer, a perovskite active layer, a CuI intermediate layer, a hole transport layer, and a metal electrode stacked in sequence.

[0007] Optionally, the perovskite chemical formula includes one of the following: CsPbI 3 , MAPbI 3 , FAPbI 3 , CsPbBrx I 3-x 、 MAPbBr x I 3-x 、 FAPbBr x I 3-x 。

[0008] Optionally, the PbO intermediate layer is a PbO thin film with a thickness of 2 nm - 50 nm;

[0009] Optionally, the CuI intermediate layer is a CuI thin film with a thickness of 2 nm - 50 nm.

[0010] Optionally, the transparent electrode is FTO or ITO. FTO (fluorine-doped tin oxide) and ITO (indium-doped tin oxide) are both transparent conductive oxide (TCO) materials, having high light transmittance and good electrical conductivity. They can allow sunlight to penetrate to reach the perovskite active layer, while collecting the photo-generated current generated by the perovskite layer. FTO and ITO serve as the bottom electrode in the perovskite solar cell, providing a path for the extraction of electrons.

[0011] Optionally, the electron transport layer is TiO 2 or SnO 2 。 TiO 2 (titanium dioxide) and SnO 2 (tin dioxide) are both commonly used n-type semiconductor materials, having excellent electron transport performance and chemical stability. They can effectively extract electrons from the perovskite active layer and transport them to the transparent electrode, thus completing the process of generation and collection of photo-generated current. TiO 2 and SnO 2 can also serve as a blocking layer to inhibit the reverse transport of holes to the electron transport layer and reduce the recombination loss of carriers.

[0012] Optionally, the hole transport layer includes one of the following: P3HT, PEDOT:PSS, doped PTAA, doped Spiro-OMeTAD.

[0013] In the perovskite solar cell, the hole transport layer plays a crucial role. It is responsible for receiving the photo-generated holes from the perovskite absorption layer and transporting them to the anode to generate current.

[0014] P3HT (poly(3-hexylthiophene)) is an organic polymer material, having good hole transport performance and stability. In the carbon-based perovskite solar cell, P3HT as the hole transport layer can significantly improve the photoelectric conversion efficiency of the device. For example, some studies have shown that for the carbon-based perovskite solar cell with P3HT introduced as the hole transport layer, its photoelectric conversion efficiency is increased from 11.16% to 13.37%.

[0015] PEDOT:PSS (Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate)) is a kind of polymer conductive polymer, which has good conductivity, high light transmittance and stability. In organic solar cells, PEDOT:PSS is often used as the hole transport layer, which can effectively transport the photo-generated holes from the active layer to the electrode, thus improving the photoelectric conversion efficiency of the solar cell. Its high light transmittance ensures that sunlight can fully penetrate into the active layer, while good conductivity ensures the efficient transport of holes.

[0016] PTAA (Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) is a new type of organic polymer material, which has high hole mobility and good optical properties. Its conductivity and interaction with the perovskite layer can be further improved by doping. In inverted perovskite solar cells, doped PTAA as the hole transport layer can significantly improve the performance and stability of the device. For example, some studies have achieved the improvement of the efficiency of perovskite solar cells by doping PTAA with nanographene.

[0017] Spiro-OMeTAD (2,2',7,7'-tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene) is an organic small molecule material, which has good charge transport performance and stability. It is usually used in combination with dopants (such as lithium salts and monotoluenesulfonates, etc.) to improve its conductivity and optoelectronic properties. In perovskite solar cells, doped Spiro-OMeTAD is one of the most commonly used hole transport materials. By optimizing the dopant and doping process, the performance and stability of the device can be further improved. For example, some studies have achieved a significant improvement in the working stability of perovskite solar cells by doping Spiro-OMeTAD with alkyl thiol derivatives.

[0018] Optionally, the metal electrode is Au or Ag, and the thickness of the metal electrode is 60 nm - 100 nm.

[0019] On the other hand, the present application also provides a preparation method of a lead iodide-based perovskite solar cell structure with a PbO / CuI double intermediate layer, which is characterized by including the following steps:

[0020] Deposit a layer of FTO or ITO on the substrate to obtain a transparent electrode;

[0021] Spin-coat and calcine a layer of TiO 2 or SnO 2 to obtain an electron transport layer;

[0022] Prepare a layer of PbO film on the electron transport layer by spin-coating and calcining or chemical vapor deposition or doctor blade coating method;

[0023] A perovskite active layer is prepared on the PbO film by a one-step spin coating method, a two-step spin coating method or a spin coating impregnation method;

[0024] A CuI film is prepared on the electron transport layer by spin coating calcination, chemical vapor deposition or doctor blade coating;

[0025] A layer of P3HT, PEDOT:PSS, doped PTAA or doped Spiro-OMeTAD is prepared on the CuI film by spin coating to obtain a hole transport layer, wherein the spin coating calcination temperature is lower than the perovskite decomposition temperature;

[0026] A layer of metal is prepared on the hole transport layer by evaporation to obtain a metal electrode.

[0027] The preparation method of the lead iodide-based perovskite solar cell structure based on the PbO / CuI double intermediate layer according to claim 9, characterized in that the perovskite active layer is prepared by spin coating and calcining a DMF / DMSO solution of PbI 2 and MAI with a molar ratio of 1:1.

[0028] Compared with the prior art, the beneficial effects achieved by the present application are as follows: In view of the ionic characteristics of lead iodide-based perovskite, a PbO intermediate layer is arranged between the electron transport layer and the perovskite active layer, and a CuI intermediate layer is arranged between the hole transport layer and the perovskite active layer. Among them, PbO can inhibit the ion migration in the perovskite layer, while CuI can form good chemical compatibility with the perovskite layer, reducing the chemical reaction at the interface. Thereby effectively inhibiting the ion migration, reducing the defect density at the interface, and lowering the carrier transition barrier. Moreover, the PbO intermediate layer and the CuI intermediate layer can form good interfacial contact with the perovskite layer, the electron transport layer and the hole transport layer, reducing the capture probability of carriers at the interface, promoting more effective extraction and transport of charges, thereby improving the charge collection efficiency and the photoelectric conversion efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 are schematic structural diagrams of some embodiments provided by the present application.

[0031] Description of the reference numerals:

[0032] 1 - Substrate; 2 - Transparent electrode; 3 - Electron transport layer; 4 - PbO intermediate layer; 5 - Perovskite active layer; 6 - CuI intermediate layer; 7 - Hole transport layer; 8 - Metal electrode. Detailed implementation mode

[0033] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present disclosure / the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present application and its application or use.

[0034] To solve the inherent stability problem of perovskite materials, researchers usually use a passivation layer to reduce the defect density between the perovskite and the electron transport layer and the hole transport layer, and reduce the transition barrier. Among them, organic ions with a long carbon chain structure are the most commonly used passivation layer materials. They can not only increase the open-circuit voltage and short-circuit current, but also greatly enhance the environmental stability and working stability of perovskite solar cell devices. At the same time, inorganic compounds or inorganic ions have also been proven to be applicable to the passivation layer.

[0035] In view of the ionic characteristics of lead iodide-based perovskites, the present invention uses inorganic materials as intermediate layers between the electron transport layer and the perovskite active layer, and between the hole transport layer and the perovskite active layer, respectively, to inhibit the migration of ions, reduce the defect density at the interface, lower the carrier transition barrier, and thereby increase the efficiency of perovskite solar cells and improve the environmental stability and working stability of perovskite solar cell devices. This is a problem that needs to be solved in the art. The present invention will be further described in detail below with reference to embodiments.

[0036] Example 1

[0037] This example introduces a lead iodide-based perovskite solar cell structure device based on a PbO / CuI double intermediate layer. Referring to Figure 1 , the lead iodide-based perovskite solar cell structure in this example includes a substrate 1, a transparent electrode 2, an electron transport layer 3, a PbO intermediate layer 4, a perovskite active layer 5, a CuI intermediate layer 6, a hole transport layer 7, and a metal electrode 8 that are sequentially stacked. Among them, the perovskite chemical formula includes one of the following: CsPbI 3 (cesium lead triiodide), MAPbI 3 (methylammonium lead iodide), FAPbI 3 (formamidinium lead iodide), CsPbBr x I 3-x (cesium lead bromide iodide mixture), MAPbBr x I 3-x (methylammonium lead bromide iodide mixture), FAPbBrx I 3-x (formamidinium lead bromide iodide mixture).

[0038] Regarding problems such as ion migration, interface defects, and carrier transition barriers in lead-iodide perovskite solar cells, in this example, PbO (lead oxide) and CuI (cuprous iodide) are used as intermediate layers, playing multiple roles between the electron transport layer 3 and the perovskite active layer 5, and between the hole transport layer 7 and the perovskite active layer 5.

[0039] Specifically, ion migration in lead-iodide perovskite materials is one of the key factors leading to the degradation of battery performance. In this embodiment, PbO and CuI are used as intermediate layers. Among them, PbO can inhibit ion migration in the perovskite layer, while CuI can form good chemical compatibility with the perovskite layer, reducing chemical reactions at the interface. Thus, it can effectively block or slow down the migration of ions (such as iodide ions) in the perovskite layer under the action of an electric field. This inhibitory effect not only reduces the performance degradation caused by ion migration but also maintains the stability of the perovskite structure and extends the service life of the battery.

[0040] In addition, defects at the interface are the main sites of carrier recombination in perovskite solar cells, which will reduce the open-circuit voltage and short-circuit current of the battery, thus affecting the overall efficiency. However, PbO and CuI have good chemical compatibility and physical contact with the perovskite layer and the adjacent transport layer, and can effectively fill the tiny voids at the interface, reducing defect sites. And they can respectively form good interface contacts with the perovskite layer, the electron transport layer 3, and the hole transport layer 7. This "smooth contact" effect reduces the capture probability of carriers at the interface, promotes more effective extraction and transport of charges, and thus improves the charge collection efficiency and the photoelectric conversion efficiency of the battery.

[0041] In this embodiment, the PbO intermediate layer 4 is a PbO thin film with a thickness of 2 nm - 50 nm. The CuI intermediate layer 6 is a CuI thin film with a thickness of 2 nm - 50 nm. By adjusting the thicknesses of PbO and CuI, the charge distribution in the perovskite solar cell can be further optimized, and the charge collection efficiency and photoelectric conversion efficiency can be improved.

[0042] In this embodiment, the transparent electrode 2 is FTO (fluorine-doped tin oxide) or ITO (indium tin oxide), and the electron transport layer 3 is TiO 2 or SnO 2 . Both FTO and ITO are transparent conductive oxide (TCO) materials, with high light transmittance and good conductivity. They can allow sunlight to penetrate to reach the perovskite active layer 5, while collecting the photocurrent generated by the perovskite layer. FTO and ITO act as the bottom electrodes in the perovskite solar cell, providing a path for the export of electrons. And TiO 2 and SnO 2They are all commonly used n-type semiconductor materials, having excellent electron transport performance and chemical stability. They can effectively extract electrons from the perovskite active layer 5 and transport them to the transparent electrode 2, thus completing the process of generating and collecting photocurrent. TiO 2 and SnO 2 can also act as a blocking layer to inhibit the reverse transport of holes to the electron transport layer 3 and reduce the recombination loss of carriers.

[0043] In this embodiment, the hole transport layer 7 includes one of the following: P3HT, PEDOT:PSS, doped PTAA, doped Spiro-OMeTAD. Among them, P3HT is an organic polymer material with good hole transport performance and stability. In carbon-based perovskite solar cells, P3HT as the hole transport layer 7 can significantly improve the photoelectric conversion efficiency of the device. For example, some studies have shown that the photoelectric conversion efficiency of carbon-based perovskite solar cells with P3HT introduced as the hole transport layer 7 has increased from 11.16% to 13.37%.

[0044] PEDOT:PSS is a polymer conductive polymer with good conductivity, high light transmittance and stability. In organic solar cells, PEDOT:PSS is often used as the hole transport layer 7, which can effectively transport photo-generated holes from the active layer to the electrode, thus improving the photoelectric conversion efficiency of the solar cell. Its high light transmittance ensures that sunlight can fully penetrate into the active layer, while good conductivity ensures the efficient transport of holes.

[0045] PTAA is a new type of organic polymer material with high hole mobility and good optical properties. Its conductivity and interaction with the perovskite layer can be further improved by doping. In inverted perovskite solar cells, doped PTAA as the hole transport layer 7 can significantly improve the performance and stability of the device. For example, some studies have achieved an improvement in the efficiency of perovskite solar cells by doping PTAA with nano-graphene.

[0046] Spiro-OMeTAD is an organic small molecule material with good charge transport performance and stability. It is usually used in combination with dopants (such as lithium salts and monomethylbenzenesulfonates, etc.) to improve its conductivity and optoelectronic properties. In perovskite solar cells, doped Spiro-OMeTAD is one of the most commonly used hole transport materials. By optimizing the dopant and doping process, the performance and stability of the device can be further improved. For example, some studies have achieved a significant improvement in the working stability of perovskite solar cells by doping Spiro-OMeTAD with alkyl thiol derivatives.

[0047] In this embodiment, the metal electrode 8 is Au or Ag.

[0048] In summary, the present invention not only optimizes the internal structure of the perovskite solar cell, effectively inhibits ion migration, reduces interface defects, and lowers the carrier transition barrier, but also significantly improves its photoelectric conversion efficiency and extends the service life of the solar cell.

[0049] Example Two:

[0050] This example provides a preparation method for a lead iodide-based perovskite solar cell structure with a PbO / CuI double intermediate layer, including the following steps:

[0051] First step, deposit a layer of FTO or ITO on the substrate 1 to form FTO conductive glass or ITO conductive glass, or FTO conductive glass or ITO conductive glass can also be obtained by purchase. Use detergent to remove the grease and dirt on the surface of the FTO conductive glass or ITO conductive glass, and then further remove the grease and organic impurities through acetone. Remove the residual acetone and other organic substances through isopropyl alcohol. Wash off all solvents and impurities through deionized water. Finally, clean with ethanol to ensure the surface is clean. After cleaning, blow dry the glass with dry gas (such as nitrogen) to obtain clean conductive glass. In this example, the FTO conductive glass or ITO conductive glass is successively soaked in detergent, acetone, isopropyl alcohol, deionized water, and ethanol and ultrasonically treated for 30 minutes.

[0052] Second step, drop an appropriate amount of SnO 2 precursor aqueous solution on the clean conductive glass to ensure an appropriate concentration. Then spin-coat the SnO 2 precursor aqueous solution on the conductive glass so that the SnO 2 layer evenly covers the conductive glass. Then anneal the spin-coated sample to form a stable SnO 2 layer. This step ensures good contact between the electron transport layer 3 and the transparent electrode 2 and provides an effective electron transport channel. In related examples, the SnO 2 precursor aqueous solution can also be replaced with a TiO 2 precursor aqueous solution.

[0053] Third step, soak the product obtained in the previous step in an alkaline solution containing a lead salt to allow the lead salt to fully react on the glass surface to obtain a PbO layer. After soaking for a sufficient time, take it out and rinse it clean with deionized water and ethanol to remove the unreacted lead salt and impurities. In related examples, the PbO layer can also be prepared by spin-coating and calcination, chemical vapor deposition (CVD), or doctor blade coating method.

[0054] Fourth step, drop a DMF / DMSO (dimethylformamide / dimethyl sulfoxide) solution containing PbI 2 (lead iodide) and MAI (methylammonium iodide) on the PbO layer. Among them, PbI2 The molar ratio with MAI is 1:1. Then, spin coating is carried out at an appropriate spin coating rate and time to make the perovskite precursor evenly distributed on the PbO layer. After spin coating is completed, the spin coated sample is annealed to form a perovskite layer. It should be noted that the perovskite active layer 5 can be prepared by a one-step spin coating method, a two-step spin coating method or a spin coating impregnation method. The perovskite active layer 5 is the core part of the solar cell, responsible for light absorption and charge generation.

[0055] In the fifth step, an isopropanol solution of CuI with an appropriate concentration is dropped on the perovskite layer. Then, spin coating is carried out at an appropriate spin coating rate and time to make the CuI layer evenly cover the perovskite layer. After spin coating is completed, the spin coated sample is annealed to form a stable CuI intermediate layer 6. In related embodiments, the CuI layer can also be prepared by spin coating calcination, chemical vapor deposition or doctor blade coating.

[0056] In the sixth step, a chlorobenzene solution of P3HT (poly(3-hexylthiophene)) with an appropriate concentration is dropped on the CuI intermediate layer 6. And spin coating is carried out to make the P3HT layer evenly cover the CuI layer. After spin coating is completed, the spin coated sample is annealed to form a hole transport layer 7. In related embodiments, the hole transport layer 7 can also be prepared from P3HT, PEDOT:PSS, doped PTAA or doped Spiro-OMeTAD. The hole transport layer 7 is responsible for transporting the holes generated in the perovskite layer to the metal electrode 8. It should be noted that the spin coating calcination temperature in this step needs to be lower than the perovskite decomposition temperature to avoid damaging the perovskite layer.

[0057] In the seventh step, a 100-nm-thick gold layer is evaporated on the P3HT hole transport layer 7 as the electrode of the solar cell.

[0058] It should be noted that the FTO conductive glass or ITO conductive glass, SnO 2 precursor aqueous solution, lead salt, alkali solution, PbI 2 powder, MAI powder, DMF, DMSO, CuI powder, isopropanol, P3HT conductive polymer, chlorobenzene, copper, can all be obtained by purchase. And in each step, parameters such as the spin coating rate, time, temperature and concentration can be optimized according to specific experimental conditions and target performance.

[0059] The above are only the preferred embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the technical principles of the present disclosure / the present application, several improvements and deformations can still be made, and these improvements and deformations should also be regarded as the protection scope of the present disclosure / the present application.

Claims

1. A lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer, comprising a substrate, a transparent electrode, an electron transport layer, a PbO intermediate layer, a perovskite active layer, a CuI intermediate layer, a hole transport layer and a metal electrode stacked in sequence.

2. The lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to claim 1, characterized in that: The perovskite chemical formula includes one of the following: CsPbI3, MAPbI3, FAPbI3, CsPbBr x I 3-x MAPbBr x I 3-x , FAPbBr x I 3-x .

3. The lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to claim 1, characterized in that: The PbO intermediate layer is a PbO film with a thickness of 2nm-50nm.

4. The lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to claim 1, characterized in that: The CuI intermediate layer is a CuI thin film with a thickness of 2nm-50nm.

5. The lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to claim 1, characterized in that: The transparent electrode is FTO or ITO.

6. The lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to claim 1, characterized in that: The electron transport layer is TiO2 or SnO2.

7. The lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to claim 1, characterized in that: The hole transport layer includes one of the following: P3HT, PEDOT:PSS, doped PTAA, and doped Spiro-OMeTAD.

8. The lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to claim 1, characterized in that: The metal electrode is Au or Ag, and the thickness of the metal electrode is 60 nm-100 nm.

9. A method for preparing a lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1 deposits a layer of FTO or ITO on the substrate to obtain a transparent electrode; S2 spin-coating and calcining a layer of TiO2 or SnO2 on the transparent electrode to obtain an electron transport layer; S3 prepares a PbO thin film on the electron transport layer by spin coating calcination or chemical vapor deposition or doctor blade coating; S4 prepares a perovskite active layer on the PbO film by a one-step spin coating method, a two-step spin coating method, or a spin coating and dipping method; S5: preparing a CuI thin film on the electron transport layer by spin coating calcination or chemical vapor deposition or doctor blade coating; S6: preparing a layer of P3HT or PEDOT:PSS or doped PTAA or doped Spiro-OMeTAD on the CuI film by spin coating to obtain a hole transport layer, wherein the spin coating calcination temperature is lower than the decomposition temperature of perovskite; S7: preparing a layer of metal on the hole transport layer by evaporation to obtain a metal electrode.

10. The method for preparing a lead-iodine-based perovskite solar cell structure based on a PbO / CuI double intermediate layer according to claim 9, characterized in that: The perovskite active layer is prepared by spin coating and calcining a DMF / DMSO solution of PbI2 and MAI in a molar ratio of 1:1.

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