Composite Metal Carbonate Interface Layer, Preparation Method and Perovskite Solar Cell

Abstract

The present application provides a composite metal carbonate interfacial layer, a preparation method, and a perovskite solar cell. The composite metal carbonate interfacial layer is disposed between the perovskite active layer and the electron transport layer of the perovskite solar cell, and is composed of two different alkali metal carbonate layers, namely a first alkali metal carbonate layer and a second alkali metal carbonate layer; the first alkali metal carbonate layer is formed on the side close to the perovskite active layer and is selected from cesium carbonate, potassium carbonate, or sodium carbonate; the second alkali metal carbonate layer is formed on the side close to the electron transport layer and is selected from rubidium carbonate, potassium carbonate, or sodium carbonate. The double-layer structure of the present application can not only synergistically improve the open-circuit voltage and fill factor of the device, but also break through the design constraint that the thickness of the existing interfacial layer is usually limited within 2 nm, enabling the total interfacial thickness to stably reach 1 nm - 5 nm, and still maintaining excellent charge transport performance and interfacial function integration ability within this thickness range.

Description

Technical Field

[0001] The present application relates to the technical field of perovskite solar cells, and particularly to a composite metal carbonate interface layer, a preparation method thereof, and a perovskite solar cell. Background Art

[0002] In perovskite solar cells, the regulation of the interface layer is widely used to improve energy level matching, passivate defects, increase the open-circuit voltage, and enhance device stability. Common interface layer materials include organic molecules, metal oxides, alkali metal salts, etc. Among these materials, metal carbonates, especially cesium carbonate, have been partially studied for modifying the electron transport layer of perovskite cells because they can form a dipole moment at the interface, effectively reduce the work function, and have good thermal stability and chemical inertness.

[0003] In perovskite solar cell devices, the thickness of the interface layer has an important influence on the carrier transport characteristics. Relevant research and technical literature generally believe that when the thickness of the interface layer exceeds about 2 nm, an insulating effect may be caused, resulting in a decrease in the electron injection or extraction efficiency, and further having an adverse effect on the short-circuit current density (J SC ) and fill factor (FF) of the device. Therefore, the thickness of the interface regulation layer is usually limited within 2 nm. Therefore, the prior art mostly adopts the strategy of an ultrathin interface layer. Summary of the Invention

[0004] The inventors of the present application have found that the strategy of the ultrathin interface layer in the prior art has been difficult to meet the comprehensive performance requirements in some actual application scenarios, such as perovskite-silicon heterojunction tandem solar cells with a complex multilayer stack structure, flexible packaging devices or large-area modular devices, and in cases where there are many lattice defects and strong ion migration tendency in the perovskite film body. In these scenarios, the device has higher requirements for the comprehensive performance of the interface layer, such as thermal stability, chemical inertness, interface passivation ability, ion migration inhibition ability, and stress adaptability. However, the ultrathin interface layer in the prior art has obvious limitations when considering the performance in the above-mentioned multiple dimensions.

[0005] In view of this, according to the first aspect of the present application, a composite metal carbonate interface layer is provided. The composite metal carbonate interface layer is disposed between the perovskite active layer and the electron transport layer of a perovskite solar cell and is composed of two different alkali metal carbonate layers, namely a first alkali metal carbonate layer and a second alkali metal carbonate layer;

[0006] The first alkali metal carbonate layer is formed on the side close to the perovskite active layer and is selected from cesium carbonate, potassium carbonate, or sodium carbonate;

[0007] The second alkali metal carbonate layer is formed on the side close to the electron transport layer and is selected from rubidium carbonate, potassium carbonate, or sodium carbonate.

[0008] Optionally, the total thickness of the composite metal carbonate interface layer is 1 nm - 5 nm;

[0009] The thickness of the first alkali metal carbonate layer is 0.5 nm - 3 nm.

[0010] Optionally, the thickness ratio of the first alkali metal carbonate layer to the second alkali metal carbonate layer is 1:1 - 5:1.

[0011] Optionally, a gradually changing interfacial dipole structure is formed between the first alkali metal carbonate layer and the second alkali metal carbonate layer.

[0012] Optionally, the composite metal carbonate interface layer includes a transition region located between the first alkali metal carbonate layer and the second alkali metal carbonate layer, and the material components of both the first alkali metal carbonate layer and the second alkali metal carbonate layer coexist in the transition region;

[0013] The thickness of the transition region is 5% - 30% of the total thickness of the composite metal carbonate interface layer.

[0014] According to the second aspect of the present application, there is also provided a method for preparing the composite metal carbonate interface layer as described above, including the following steps:

[0015] Depositing a first alkali metal carbonate layer on the surface of the perovskite active layer of the perovskite solar cell by using a vacuum thermal evaporation method;

[0016] During or after the deposition of the first alkali metal carbonate layer, gradually reduce the evaporation rate of the first alkali metal carbonate material and gradually increase the evaporation rate of the second alkali metal carbonate material, so as to form a transition region containing two carbonate components;

[0017] Deposit the second alkali metal carbonate layer on the transition region to obtain the composite metal carbonate interface layer.

[0018] Optionally, during or after the deposition of the first alkali metal carbonate layer, gradually reduce the evaporation rate of the first alkali metal carbonate material and gradually increase the evaporation rate of the second alkali metal carbonate material, so as to form a transition region containing two carbonate components, including the following steps:

[0019] During or after the deposition of the first alkali metal carbonate layer, within a first preset time, gradually reduce the evaporation rate of the first alkali metal carbonate material from a first evaporation rate to a second evaporation rate;

[0020] Within a second preset time, reduce the second evaporation rate to zero;

[0021] Within a third preset time, gradually increase the evaporation rate of the second alkali metal carbonate material from zero to a third evaporation rate;

[0022] Within a fourth preset time, gradually increase the third evaporation rate to a fourth evaporation rate, thereby forming a transition region containing two carbonate components.

[0023] Optionally, the first evaporation rate is 0.05 Å / s - 0.15 Å / s, the second evaporation rate is 0.02 Å / s - 0.04 Å / s, the third evaporation rate is 0.06 Å / s - 0.08 Å / s, and the fourth evaporation rate is 0.05 Å / s - 0.15 Å / s;

[0024] The first preset time, the second preset time, the third preset time, and the fourth preset time are all 5 s - 30 s.

[0025] Optionally, in the preparation method, the substrate provided with the perovskite active layer is kept rotating at a constant speed of 10 rpm - 30 rpm, and the substrate is maintained at 30°C - 60°C during the deposition process.

[0026] According to the third aspect of the present application, a perovskite solar cell is further provided, including a composite metal carbonate interface layer prepared by using the preparation method as described above.

[0027] According to the solution of the embodiment of the present application, the composite metal carbonate interface layer forms an interface regulation region with a functional hierarchical structure by setting two different types of alkali metal carbonate materials between the perovskite active layer and the electron transport layer. Among them, the first alkali metal carbonate layer close to the perovskite active layer has a larger ionic radius and stronger interface dipole formation ability, which can effectively adjust the work function of the perovskite surface, passivate lattice defects, and improve interface chemical stability. The second alkali metal carbonate layer close to the electron transport layer is used to further regulate the energy level matching relationship between the perovskite layer and the electron transport layer, and enhance the carrier extraction efficiency. This double-layer structure can not only synergistically improve the open-circuit voltage and fill factor of the device, but also break through the design constraint that the thickness of the existing interface layer is usually limited within 2 nm, enabling the total interface thickness to stably reach 1 nm - 5 nm, and still maintaining excellent charge transport performance and interface function integration ability within this thickness range, which is particularly suitable for the application requirements of perovskite-silicon tandem devices, flexible solar devices, and large-area modular batteries with higher requirements for interface performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic structural diagram showing a partial battery structure according to an embodiment of the present invention;

[0029] Figure 2Shows a schematic flow chart of a method for preparing a composite metal carbonate interface layer according to an embodiment of the present invention;

[0030] Figure 3 Shows a schematic flow chart of the formation of a transition region according to an embodiment of the present invention;

[0031] Figure 4 Shows an X-ray photoelectron spectroscopy depth profiling spectrum of a composite metal carbonate interface layer according to an embodiment of the present invention;

[0032] Figure 5 Shows a schematic structural diagram of a battery structure according to Embodiment 1 of the present invention;

[0033] Figure 6 Shows the J-V curve of a perovskite solar cell device obtained according to Embodiment 1 of the present invention and Comparative Example 1 and the corresponding optoelectronic performance parameter diagram;

[0034] In the figure: 101 - perovskite active layer, 102 - composite metal carbonate interface layer, 103 - electron transport layer, 104 - conductive substrate, 105 - hole transport layer, 106 - buffer layer, 107 - top electrode. Detailed embodiments

[0035] To make the above objects, features, and advantages of the present application more apparent and understandable, the following will describe in detail the specific embodiments of the present application with reference to the accompanying drawings. It can be understood that the specific embodiments described herein are only used to explain the present application, rather than limiting the present application. Additionally, it should be noted that for the sake of convenience of description, only parts related to the present application are shown in the drawings, rather than all the structures. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0036] In addition, for a better illustration of the present invention, numerous specific details are given in the following detailed embodiments. Those skilled in the art should understand that the present invention can still be implemented without some specific details. In some instances, methods, means, elements, and circuits well-known to those skilled in the art are not described in detail to highlight the gist of the present disclosure.

[0037] In the embodiments of the present invention, "a plurality of" means two or more. The first, second, etc. descriptions in the embodiments of the present invention are only for schematic and differentiating the described objects, without an order, nor indicating a special limitation on the number in the embodiments of the present invention, and cannot constitute any limitation to the embodiments of the present invention.

[0038] An embodiment of the present invention provides a composite metal carbonate interfacial layer. This composite metal carbonate interfacial layer is applicable to various types of perovskite photovoltaic device structures, including all-perovskite tandem solar cells, planar perovskite solar cells, perovskite-silicon heterojunction tandem solar cells, flexible perovskite devices, and large-area modular solar modules, for improving the energy level matching stability, interfacial passivation ability, and overall operating life of the devices. The typical structure of this perovskite solar cell includes a transparent conductive glass (such as ITO or FTO), a hole transport layer, a perovskite active layer, a composite metal carbonate interfacial layer, an electron transport layer, and a metal back electrode. Among them, the composite metal carbonate interfacial layer concerned in the embodiment of the present invention is disposed between the perovskite active layer and the electron transport layer.

[0039] Figure 1 Figure 4 shows a schematic structural diagram of a partial cell structure according to an embodiment of the present invention. As Figure 1 shown, the composite metal carbonate interfacial layer 102 is composed of two different alkali metal carbonate layers, namely the first alkali metal carbonate layer and the second alkali metal carbonate layer. The first alkali metal carbonate layer is formed on the side close to the perovskite active layer 101 and is selected from cesium carbonate, potassium carbonate, or sodium carbonate. The second alkali metal carbonate layer is formed on the side close to the electron transport layer 103 and is selected from rubidium carbonate, potassium carbonate, or sodium carbonate.

[0040] According to the solution of the embodiment of the present application, the composite metal carbonate interfacial layer forms an interfacial regulation region with a functional layered structure by setting two different types of alkali metal carbonate materials between the perovskite active layer and the electron transport layer. Among them, the first alkali metal carbonate layer close to the perovskite active layer has a larger ionic radius and a stronger ability to form interfacial dipoles, which can effectively adjust the work function of the perovskite surface, passivate lattice defects, and improve interfacial chemical stability. The second alkali metal carbonate layer close to the electron transport layer is used to further regulate the energy level matching relationship between the perovskite layer and the electron transport layer and enhance the carrier extraction efficiency. This double-layer structure can not only synergistically improve the open-circuit voltage and fill factor of the device, but also break through the design constraint that the thickness of the existing interfacial layer is usually limited within 2 nm, enabling the total interfacial thickness to stably reach 1 nm - 5 nm, and still maintaining excellent charge transport performance and interfacial function integration ability within this thickness range, which is particularly suitable for the application requirements of perovskite-silicon tandem devices, flexible solar devices, and large-area modular batteries with higher interfacial performance requirements.

[0041] It should be noted that before it was discovered that by introducing a composite interface layer composed of two different alkali metal carbonates in a perovskite solar cell and approaching the perovskite active layer and the electron transport layer respectively through a functional stratification method, comprehensive optimization of key properties such as the interface energy level structure, ion migration, and defect passivation can be achieved, the inventors had conducted a large number of explorations and attempts, trying to improve the device efficiency and stability by optimizing the interface modification method of a single carbonate material.

[0042] For example, the inventors initially tried to use a single carbonate material such as cesium carbonate or rubidium carbonate as the interface layer to adjust the work function and construct an interface dipole, so as to improve the electron injection efficiency and energy level matching. Although a slight increase in the open-circuit voltage (V OC oc) was achieved in some thin-film devices, when the thickness of the interface layer increased to more than 2 nm, the phenomenon of blocked carrier injection and decreased short-circuit current density (J SC sc) generally occurred, showing an obvious insulating effect, and it was difficult to balance stability and transport efficiency.

[0043] To break through this bottleneck, the inventors also tried to prepare a more uniform ultra-thin interface layer by adjusting the evaporation conditions, or introduce a third component such as metal oxide doping or anion blending in the carbonate material to optimize its electrical properties and interface affinity. However, these solutions have problems such as poor reproducibility, poor interface compatibility, or a narrow process window in the actual device preparation, and it is difficult to meet the stability requirements of large-area devices or heterojunction stack structures. Further, the inventors also tried to induce interface component diffusion by means of post-annealing reconstruction, but experiments showed that this process has a high degree of uncontrollability and often leads to the reformation of interface defects, instead reducing the long-term stability of the device.

[0044] After repeated experiments failed, the inventors realized that continuing to rely on local modification of single-layer interface materials or the doping optimization idea of traditional material systems was difficult to achieve systematic regulation of interface functions. It was not until a comparative experiment that the inventors observed that after constructing a hierarchical structure with two different alkali metal carbonate materials on the perovskite side and the electron transport layer side of the device respectively, the work function distribution of the device was more reasonable, the interface state density was significantly reduced, and the open-circuit voltage, fill factor, and stability were all improved.

[0045] After systematic analysis and verification, the inventor finally established the technical solution of the embodiment of the present invention, that is, a composite interface layer composed of a first alkali metal carbonate layer and a second alkali metal carbonate layer is deposited between the perovskite active layer and the electron transport layer. Among them, the first carbonate layer preferably uses materials with a large ionic radius and a high polarizability to adjust the surface work function of the perovskite and passivate defects, and the second carbonate layer preferably uses materials with a strong dipole response to optimize the energy level coupling with the electron transport layer. This solution breaks the traditional modification idea that relies on ultra-thin single-layer materials or post-treatment doping, and realizes the collaborative optimization of interface electrical properties, chemical stability and device reliability without sacrificing the carrier transport ability.

[0046] In one embodiment, the total thickness of the composite metal carbonate interface layer is 1 nm to 5 nm, such as 1 nm, 2 nm, 3 nm, 4 nm or 5 nm. The composite metal carbonate interface layer can balance the carrier transport efficiency and interface stability within this thickness range. Among them, the thickness of the first alkali metal carbonate layer is preferably set to 0.5 nm to 3 nm, such as 0.5 nm, 1 nm, 2 nm or 3 nm. The first alkali metal carbonate layer within this thickness range not only ensures its effective dipole regulation and defect passivation on the perovskite surface, but also avoids charge accumulation or blocking effects caused by excessive thickness.

[0047] In one embodiment, the thickness ratio between the first alkali metal carbonate layer and the second alkali metal carbonate layer is preferably 1:1 to 5:1, such as 1:1, 2:1, 3:1, 4:1 or 5:1. The setting of this thickness ratio helps to enhance the functional dominance of the first alkali metal carbonate layer in regulating the surface work function of the perovskite active layer and inhibiting interface ion migration, and at the same time ensures that the optimization effect of the second alkali metal carbonate layer on the energy level matching between the perovskite active layer and the electron transport layer can be effectively exerted, so that the composite metal carbonate interface layer realizes collaborative optimization in multiple performance dimensions such as interface energy level regulation, carrier extraction efficiency and defect passivation, and improves the overall optoelectronic performance and operation stability of the device.

[0048] In some embodiments, a gradually varying interfacial dipole structure is formed between the first alkali metal carbonate layer and the second alkali metal carbonate layer. This "interfacial dipole structure" refers to a local electric dipole arrangement formed in the direction perpendicular to the device structure through the polarization property differences of different materials in the interfacial layer, thereby guiding the formation of a built-in electric field structure beneficial to carrier separation between the perovskite active layer and the electron transport layer. The formation of this interfacial dipole structure can be gradient or a stepped arrangement composed of multiple layers stacked. This interfacial dipole structure is based on the differences in dipole strength, surface energy, and deposition behavior between the two alkali metal carbonate materials, and realizes an orderly transition of the component distribution through process means such as gradually changing the evaporation rate, thereby forming a gradient region with a change from high dipole strength to low dipole strength or from low polarizability to high polarizability between the layers. This dipole gradient structure can guide the formation of a directional built-in electric field in the interfacial region, which is beneficial to promoting the accelerated migration of electrons and carrier separation, further reducing the probability of interfacial non-radiative recombination, and improving the charge extraction efficiency and overall optoelectronic performance of the device.

[0049] To achieve the gradient construction of this interfacial dipole structure, a transition region is introduced between the first alkali metal carbonate layer and the second alkali metal carbonate layer. This transition region contains both the first alkali metal carbonate component and the second alkali metal carbonate component, and the components vary continuously along the film thickness direction, thereby realizing a smooth transition of the material composition from the first alkali metal carbonate component to the second alkali metal carbonate component in terms of structure and avoiding the formation of interface mutations or carrier transport obstacles. Since this transition region is not a simple superposition interface, but through the cross-gradient control of the evaporation rates of the first alkali metal carbonate component and the second alkali metal carbonate component, the two components form a continuously varying compositional distribution in the transition region. Therefore, the transition region realizes a continuous transition of the interfacial chemical composition in terms of structure, and forms a spatial gradient distribution of dipole strength electrically, thereby macroscopically constructing a gradually varying interfacial dipole structure. Therefore, the transition region not only realizes an orderly transition of the interfacial material composition in terms of structure, but also undertakes the extension and support functions of the interfacial dipole structure in terms of electrical function, and is the key spatial region for constructing a gradually varying interfacial dipole structure, which is beneficial to realizing the synergistic enhancement of interfacial regulation performance.

[0050] In some embodiments, the thickness of the transition region accounts for 5% to 30% of the total thickness of the composite metal carbonate interfacial layer, and can be, for example, 5%, 10%, 20%, or 30%. This thickness range can ensure the effective construction of the dipole gradient while maintaining the continuity of electron transport and the smooth transition of interfacial energy levels, thereby enhancing the overall electrical performance synergy of the interface and further improving the stability and optoelectronic conversion performance of the perovskite solar cell.

[0051] It should be noted that after the composite metal carbonate interfacial layer is disposed between the perovskite active layer and the electron transport layer of the perovskite solar cell, the inventors have attempted to construct the interfacial layer structure by sequential deposition, such as sequentially depositing different combinations of alkali metal carbonates such as cesium carbonate and rubidium carbonate, potassium carbonate and rubidium carbonate. However, through further device performance testing and interfacial potential analysis, it is found that in such sequential deposition structures, there are generally obvious physical boundaries between different material layers, and energy level mutations or potential discontinuity regions are likely to form at the interfaces during the carrier transport process, thereby triggering local energy level mismatches and barrier effects, resulting in a decrease in the charge extraction efficiency and it is difficult to guarantee the overall performance and operation stability of the device.

[0052] To address the above problems, the inventors have systematically analyzed the interfacial dipole construction mechanism and the influence mechanism of dipole distribution on electron transport behavior, and finally proposed to introduce a transition region with continuously varying composition between two different alkali metal carbonate material layers, such that the interfacial dipole strength, material polarizability, and local potential distribution exhibit a gradient-like smooth transition along the film thickness direction. Through the setting of this transition region, interfacial mutations can be eliminated at the structural level, and an interfacial dipole gradient can be constructed at the electrical level, thereby effectively avoiding the formation of electron barriers and enhancing the interfacial electric field coordination and carrier extraction efficiency.

[0053] Figure 2 FIG. shows a schematic flow chart of a method for preparing a composite metal carbonate interfacial layer according to an embodiment of the present invention. As Figure 2 shown, the preparation method includes:

[0054] Step S100, depositing a first alkali metal carbonate layer on the surface of the perovskite active layer of the perovskite solar cell by using a vacuum thermal evaporation method;

[0055] Step S200, during or after the deposition of the first alkali metal carbonate layer, gradually decreasing the evaporation rate of the first alkali metal carbonate material and gradually increasing the evaporation rate of the second alkali metal carbonate material, thereby forming a transition region containing two carbonate components;

[0056] Step S300, depositing a second alkali metal carbonate layer on the transition region, thereby obtaining a composite metal carbonate interfacial layer.

[0057] According to the solution of the embodiment of the present invention, by sequentially depositing a first alkali metal carbonate layer, a transition region, and a second alkali metal carbonate layer between the perovskite active layer and the electron transport layer of the perovskite solar cell, a composite interface structure with functional differentiation and gradient transition characteristics is constructed, which can achieve multi-dimensional cooperative regulation in terms of structure and electrical properties. In this method, the first alkali metal carbonate layer is formed on the side close to the perovskite active layer, and has excellent work function regulation ability and interface passivation effect, which helps to reduce the interface trap state density and inhibit ion migration. The second alkali metal carbonate layer is arranged on the side close to the electron transport layer, which helps to improve the energy level matching and enhance the electron extraction efficiency. On this basis, by dynamically regulating the evaporation rates of the two materials, a transition region with continuously changing components is formed in the middle, so as to realize the gradient distribution of material composition and dipole response intensity in the thickness direction of the interface layer, and further construct a gradually changing interface dipole structure. This structure not only improves the carrier separation efficiency and reduces the probability of non-radiative recombination, but also has a certain stress buffering ability, and is especially suitable for perovskite photovoltaic device structures with complex multi-layer stacking, high electrical stability and mechanical compatibility requirements. The method of the present invention directly realizes continuous component transition during the deposition process, has high interface construction accuracy and process controllability, can significantly improve the open circuit voltage and short circuit current density of the device, and has long-term operation stability.

[0058] In this step S100, the vacuum thermal evaporation process is carried out in a vacuum chamber, and the chamber pressure is controlled between 5×10 -4 Pa and 1×10 -3 Pa, so as to effectively inhibit the thermal decomposition reaction of the carbonate material and reduce the interference of residual gases (including water vapor and oxygen) on the deposition process. The heating source is a resistively heated tungsten boat or quartz boat, and its heating temperature is adjusted according to the material properties and controlled between 270°C and 380°C to ensure the stable evaporation of the carbonate material without chemical decomposition. When the first alkali metal carbonate layer is cesium carbonate, the temperature is controlled between 350°C and 380°C. When the first alkali metal carbonate layer is potassium carbonate, the temperature is controlled between 320°C and 340°C. When the first alkali metal carbonate layer is sodium carbonate, the temperature is controlled between 270°C and 310°C. It should be noted that if the heating temperature is lower than the starting evaporation temperature of the first alkali metal carbonate material, it may lead to insufficient evaporation rate, resulting in uneven film thickness or deposition failure; on the contrary, if the heating temperature exceeds its thermal stability upper limit, it may cause adverse effects such as material decomposition, non-uniform crystallization, and interface instability. Therefore, the above temperature control range is the preferred parameter range obtained through experimental verification on the premise of considering evaporation efficiency, film uniformity, and material chemical stability.

[0059] During the evaporation process, it is preferable to monitor the deposition rate in real time through a quartz crystal monitor. The initial evaporation rate of the first alkali metal carbonate can be set to 0.05 Å / s to 0.15 Å / s and maintained within a stable range, so that the deposited first alkali metal carbonate layer achieves better results in terms of thickness uniformity, surface coverage, and structural density. Preferably, the target thickness of the first alkali metal carbonate layer is controlled between 0.5 nm and 3.0 nm. During the deposition process, the substrate where the perovskite active layer is located can be placed on a rotating sample holder and rotated at a constant speed of 10 rpm to 30 rpm, thereby improving the deposition uniformity of the thin film on a large-area substrate and avoiding local thickness deviation at the interface. In addition, the substrate is preferably heated to between 30 °C and 60 °C to maintain an appropriate surface temperature, enhance the interfacial bonding force at the initial stage of deposition, and inhibit the formation of agglomerates of the first alkali metal carbonate particles on the surface. After this step is completed, it is possible to directly proceed to step S200.

[0060] Step S200 adopts a dual-source evaporation rate cross-control strategy, specifically by adjusting the evaporation rates of the two evaporation sources to form a transition region containing the first alkali metal carbonate component and the second alkali metal carbonate component. Figure 3 The schematic flowchart of the formation of the transition region according to an embodiment of the present invention is shown. As Figure 3 shown, the formation method of the transition region includes:

[0061] Step S210, during or after the deposition of the first alkali metal carbonate layer, within the first preset time, gradually reduce the evaporation rate of the first alkali metal carbonate material from the first evaporation rate to the second evaporation rate;

[0062] Step S220, within the second preset time, reduce the second evaporation rate to zero;

[0063] Step S230, within the third preset time, gradually increase the evaporation rate of the second alkali metal carbonate material from zero to the third evaporation rate;

[0064] Step S240, within the fourth preset time, gradually increase the third evaporation rate to the fourth evaporation rate, thereby forming a transition region containing two carbonate components.

[0065] Through the sequential regulation of the evaporation rate by the above four time windows, the concentration distribution of the first alkali metal carbonate component and the second alkali metal carbonate component in the interface layer is dynamically staggered and gradually adjusted during the deposition process, so as to form a transition region with a continuously changing composition between the two materials. There is no obvious physical boundary in the structure of this transition region, showing good compositional smoothness. The above compositional gradual change characteristics further lead to a gradient distribution of the interfacial dipole strength along the film thickness direction, which helps to construct an interface structure with a gradually changing energy level between the perovskite active layer and the electron transport layer, thereby improving the continuity of interfacial carrier transport, reducing the charge extraction barrier, and optimizing the energy level matching and interface stability of the overall device.

[0066] In this step S210, the first evaporation rate is 0.05 Å / s - 0.15 Å / s, for example, it can be 0.05 Å / s, 0.1 Å / s or 0.15 Å / s. The second evaporation rate is 0.02 Å / s - 0.04 Å / s, for example, it can be 0.02 Å / s, 0.03 Å / s or 0.04 Å / s. The first preset time is 5 s - 30 s, for example, it can be 5 s, 10 s, 15 s, 20 s or 30 s. In step S220, the second preset time is 5 s - 30 s, for example, it can be 5 s, 10 s, 15 s, 20 s or 30 s. In step S230, the third preset time is 5 s - 30 s, for example, it can be 5 s, 10 s, 15 s, 20 s or 30 s. The third evaporation rate is 0.06 Å / s - 0.08 Å / s, for example, it can be 0.06 Å / s, 0.07 Å / s or 0.08 Å / s. In step S240, the fourth preset time is 5 s - 30 s, for example, it can be 5 s, 10 s, 15 s, 20 s or 30 s. The fourth evaporation rate is 0.05 Å / s - 0.15 Å / s, for example, it can be 0.05 Å / s, 0.1 Å / s or 0.15 Å / s.

[0067] The first evaporation rate is selected between 0.05Å / s and 0.15Å / s, which can not only ensure the effective evaporation of the first alkali carbonate layer under a lower risk of thermal decomposition, but also control the deposition rate within an appropriate range to avoid excessive particle size or rough film. The second evaporation rate is set to 0.02Å / s to 0.04Å / s, which is the attenuation rate of the first component in the transition stage to the transition zone. It is between the main deposition rate and the termination state, ensuring that the film layer gradually weakens rather than terminates suddenly, which is conducive to the formation of a physically continuous intermediate transition zone. The third evaporation rate is set to 0.06Å / s to 0.08Å / s, corresponding to the initial stage of evaporation of the second component. The slower rate increase method facilitates the establishment of a cooperative deposition zone with the previous component in the transition zone, reduces the risk of composition mutation at the interface, and improves the dipole gradient control capability. The fourth evaporation rate is selected to be 0.05Å / s to 0.15Å / s, corresponding to the final rate of the main deposition stage of the second alkali carbonate layer, and maintaining a rate range consistent with the first evaporation rate, which is conducive to obtaining a double-layer structure with equal film thickness control ability and maintaining the structural controllability of the overall film thickness within the range of 1nm-5nm. Each preset time is set to 5 seconds to 30 seconds. This time range is determined based on the consideration of the equipment temperature rise response, the evaporation source response lag, the film thickness control accuracy and the component diffusion behavior. The above-mentioned coordinated regulation of evaporation rate and time causes the first alkali carbonate component to gradually decay and the second alkali carbonate component to gradually increase, thereby forming a stable component continuous gradient distribution area in the film thickness direction, avoiding potential barriers or electron transport blocking problems caused by component interface mutations. This strategy not only improves the stability of the interface structure, film uniformity and dipole strength synergy, but also provides excellent charge extraction channels and interface energy level matching transitions for perovskite solar cell devices, effectively reducing the probability of interface recombination and improving device performance and stability.

[0068] In step S300, after the transition zone is gradually constructed, the second alkali carbonate material is heated to maintain its evaporation state, and a second alkali carbonate layer is deposited above the transition zone at a set evaporation rate, thereby completing the construction of the entire composite metal carbonate interface layer. The evaporation rate of the second alkali carbonate material is preferably controlled to be a fourth evaporation rate, i.e., 0.05Å / s to 0.15Å / s, for example, 0.05Å / s, 0.10Å / s or 0.15Å / s. The evaporation duration can be precisely adjusted according to the target film thickness requirements to form a second metal carbonate layer with a complete structure and a uniform interface.

[0069] The vacuum thermal evaporation environment of step S300 is consistent with that of the aforementioned step S100 and step S200, that is, it is preferably performed in a vacuum chamber, and the chamber pressure is maintained at 5×10 -4 Pa to 1×10 -3Within the range of Pa to prevent hydrolysis or pyrolysis reactions of carbonate materials. The substrate where the perovskite active layer is located remains within the temperature control range of 30°C to 60°C in this step and rotates at a constant speed of 10 rpm to 30 rpm to ensure the spatial uniformity of film deposition and the consistency of interface morphology during evaporation.

[0070] The second alkali metal carbonate layer deposited and formed in this step is on the side close to the electron transport layer. It plays the following key roles in the device structure: First, by regulating the energy level alignment relationship between the perovskite active layer and the electron transport layer, the difference in interface work function between the two is reduced, thereby optimizing the electron injection and extraction paths and improving the electron transport efficiency; Second, this layer has excellent interface defect passivation ability and ion migration barrier characteristics, which can effectively inhibit ion migration and interface recombination phenomena in the perovskite layer; Third, the second alkali metal carbonate layer and the aforementioned transition region together constitute an interfacial dipole structure with a continuous component gradient, thereby establishing a spatial potential gradient and an electron transport potential gradient inside the device, which is beneficial to the directional transport of carriers and the interface electric field-assisted separation effect, thereby improving the overall J SC 、V O and other key performance parameters such as FF.

[0071] To verify that a structure feature with continuous component transition is indeed formed in the composite metal carbonate interface layer constructed in this embodiment, the inventor used XPS depth profiling to characterize the interface layer. As Figure 4 shown, the characterization results show that different metal carbonate components (such as Cs + and Rb + ) show a concentration distribution curve that gradually changes along the film thickness direction in the interface layer, and no obvious element mutation boundary is observed.

[0072] The embodiment of the present invention also provides a perovskite solar cell, including a composite metal carbonate interface layer prepared by using the aforementioned preparation method.

[0073] The following further elaborates on the performance improvement effects achieved by the composite metal carbonate interface layer constructed according to the embodiment of the present invention in perovskite solar cell devices in combination with specific embodiments.

[0074] Example 1:

[0075] This embodiment provides a broadband-gap perovskite solar cell structure including a composite metal carbonate interface layer and its preparation method. This interface layer is composed of a double-layer composite structure formed by cesium carbonate and rubidium carbonate, where cesium carbonate is close to the perovskite active layer, rubidium carbonate is close to the electron transport layer, and a transition region with gradually changing components is introduced between the two.

[0076] Figure 5Shows a schematic structural diagram of the battery structure according to Embodiment 1 of the present invention. The preparation steps of the battery structure are as follows:

[0077] Step 1: Substrate preparation

[0078] The patterned ITO conductive glass is ultrasonically cleaned successively with acetone, isopropyl alcohol, and ethanol, and the treatment time for each solvent is 10 min; after cleaning, it is dried with a nitrogen gun to obtain a clean and flat conductive substrate 104.

[0079] Step 2: Deposition of the hole transport layer

[0080] A self-assembled small molecule hole transport layer is prepared on the surface of the conductive substrate 104 by spin coating. The spin coating rate is 4000 rpm, the spin coating time is 30 s, and then it is annealed at 100 °C for 10 min to complete film formation, obtaining the hole transport layer 105.

[0081] Step 3: Preparation of the perovskite active layer

[0082] A wide-bandgap perovskite active layer 101 is spin-coated on the hole transport layer 105, and its composition is Cs 0.05 MA 0.15 FA 0.8 PbI 2.25 Br 0.75 , with a bandgap of about 1.68 eV. The concentration of the precursor solution is 1.4 M, using DMF:DMSO = 4:1 as the solvent system, and the anti-solvent is added dropwise step by step during spin coating, and then annealed at 100 °C for 30 min.

[0083] Step 4: Deposition of the composite metal carbonate interface layer

[0084] First, cesium carbonate is evaporated on the perovskite active layer 101. The initial evaporation rate is set to 0.1 Å / s and gradually reduced to 0.04 Å / s within 15 s to form a first metal carbonate layer with a thickness of about 1 nm.

[0085] Continue to further reduce the evaporation rate of cesium carbonate from 0.04 Å / s to 0 and complete this stage within 10 s to end the feeding of the first evaporation source.

[0086] Start the rubidium carbonate evaporation source and increase its evaporation rate from 0 to 0.06 Å / s within 10 s to start constructing the composition-mixed transition zone.

[0087] Further increase the evaporation rate of rubidium carbonate to the target evaporation rate of 0.08 Å / s and complete the stable establishment of this rate within 15 s, and then deposit and form a second alkali metal carbonate layer with a thickness of about 1.0 nm - 1.5 nm, thereby obtaining the composite metal carbonate interface layer 102.

[0088] Step Five: Deposition of Electron Transport Layer and Buffer Layer

[0089] Deposit C on the composite metal carbonate interface layer 102 by thermal evaporation 60 Electron transport layer 103 with a thickness of 20 nm, evaporation temperature of 450 °C, and rate of 0.5 Å / s; Subsequently, deposit the SnO2 buffer layer 106 on the electron transport layer 103 by atomic layer deposition, with a thickness of 20 nm and deposition temperature of 100 °C.

[0090] Step Six: Preparation of Top Electrode

[0091] Deposit a silver electrode layer on the SnO2 buffer layer 106 using a thermal evaporation process. The silver electrode layer serves as the top electrode 107 with a thickness of 100 nm and an evaporation rate of 1 Å / s. After preparation, encapsulate the device in an inert atmosphere.

[0092] Comparative Example One:

[0093] The only difference between Comparative Example One and Example One is that Comparative Example One does not include Step Four in Example One during the preparation process, that is, a composite metal carbonate interface layer is not set between the perovskite active layer and the electron transport layer. Except for this difference, the remaining process steps, material systems, and operating parameters are the same as those in Example One. This control setting is used to comparatively analyze the specific impact of the introduction of the composite metal carbonate interface layer on the optoelectronic performance of the device.

[0094] Comparative Example Two:

[0095] The only difference between Comparative Example One and Example One is that the composite metal carbonate interface layer formed in Comparative Example One does not have a transition region that includes a continuous transition between the first alkali metal carbonate component and the second alkali metal carbonate component, that is, the two carbonate materials in the interface layer are deposited sequentially, and there is an obvious material boundary between the interfaces. Except for the above differences, Comparative Example One is the same as Example One in terms of the remaining process flow, material selection, and process parameter settings. This control setting is used to verify the specific impact of the transition region structure on the optoelectronic performance of the device and its effect in interface regulation.

[0096] The deposition steps of the composite metal carbonate interface layer in Step Four of Comparative Example Two are as follows: First, deposit cesium carbonate on the surface of the perovskite active layer by vacuum thermal evaporation, with a constant evaporation rate set at 0.1 Å / s and continuous evaporation for 20 s to form a first alkali metal carbonate layer with a thickness of approximately 1.5 nm; Subsequently, terminate the feeding of the first evaporation source, turn on the evaporation source of rubidium carbonate, directly set the evaporation rate at 0.08 Å / s, and continuously evaporate for 20 s to form a second alkali metal carbonate layer with a thickness of approximately 1.5 nm.

[0097] In this process, the deposition of the first alkali metal carbonate material and the second alkali metal carbonate material is carried out continuously in segments, without setting a step for gradually regulating the evaporation rate between the two, and no transition region with a continuous distribution of the two components is formed. Therefore, there is a clear physical boundary between the two material layers in the obtained interface structure.

[0098] Figure 6 The J-V curves of the perovskite solar cell devices obtained in Example 1 and Comparative Example 1 of the present invention and the corresponding optoelectronic performance parameter diagrams are shown. As Figure 6 shown, compared with Comparative Example 1 without a composite metal carbonate interface layer, Example 1 of the present invention significantly improves the overall performance of the device by introducing an interface regulation layer with a composite structure. Among them, the power conversion efficiency (PCE) of the device is increased from 20.13% in Comparative Example 1 to 21.98%, achieving an increase of nearly two percentage points, indicating that the interface structure optimization plays a significant role in improving the energy conversion efficiency of the device.

[0099] Further analyzing the main performance parameters, V in Example 1 OC is increased to 1.242V, and J SC is increased to 21.13 mA / cm 2 , and the FF reaches 83.75%. The above performance improvement shows that the composite metal carbonate interface layer can effectively regulate the interface energy level matching relationship between the perovskite active layer and the electron transport layer, reduce the interface recombination loss, and optimize the electron extraction path, thereby playing a synergistic enhancement role in improving the device output voltage, current density, and energy utilization efficiency.

[0100] Table 1 below lists the comparison of the optoelectronic performance parameters of the perovskite solar cells in Example 1 and Comparative Example 2 of the present invention.

[0101]

[0102] As can be seen from Table 1 above, compared with Comparative Example 2 without a composition gradient transition region, the composition continuously changing transition structure introduced in the composite metal carbonate interface layer constructed in Example 1 of the present invention has a positive effect on significantly improving the optoelectronic performance of the device. Specifically, V in Example 1 OC is increased by about 29 mV compared with Comparative Example 2, indicating that this interface design plays a better role in regulating the interface energy level and reducing non-radiative recombination. J SC is increased from 20.48 mA / cm² to 21.13 mA / cm², reflecting an enhanced carrier extraction efficiency. The FF is increased from 80.91% to 83.75%, further indicating a reduction in the carrier transport resistance and a decrease in the recombination loss.

[0103] Finally, the power conversion efficiency (PCE) increased from 20.06% in Comparative Example 2 to 21.98% in this Example, with an increase of nearly two percentage points. This result indicates that constructing a transition region with a composition gradient feature in the interface layer can achieve the spatial synergy effect of dipole regulation while maintaining the electrical stability of the interface, thereby comprehensively optimizing the performance at both the electron transport and energy conversion levels.

[0104] The above are only some specific implementation manners of this application. Any improvements made on the premise of the concept of this application are regarded as the protection scope of this application.

Claims

1. A composite metal carbonate interface layer, characterized in that: The composite metal carbonate interface layer is disposed between the perovskite active layer and the electron transport layer of the perovskite solar cell, and is composed of two different alkali metal carbonate layers, namely a first alkali metal carbonate layer and a second alkali metal carbonate layer; The first alkali metal carbonate layer is formed on a side close to the perovskite active layer and is selected from cesium carbonate, potassium carbonate or sodium carbonate; The second alkali metal carbonate layer is formed on a side close to the electron transport layer and is selected from rubidium carbonate, potassium carbonate or sodium carbonate; A step-by-step interface dipole structure is formed between the first alkali metal carbonate layer and the second alkali metal carbonate layer.

2. The composite metal carbonate interface layer according to claim 1, characterized in that: The total thickness of the composite metal carbonate interface layer is 1nm-5nm; The thickness of the first alkali metal carbonate layer is 0.5 nm-3 nm.

3. The composite metal carbonate interface layer according to claim 2, characterized in that: The thickness ratio of the first alkali metal carbonate layer to the second alkali metal carbonate layer is 1:1-5:

1.

4. The composite metal carbonate interface layer according to claim 3, characterized in that: The composite metal carbonate interface layer includes a transition zone between the first alkali metal carbonate layer and the second alkali metal carbonate layer, wherein the material components of the first alkali metal carbonate layer and the second alkali metal carbonate layer coexist in the transition zone; The thickness of the transition zone is 5%-30% of the total thickness of the composite metal carbonate interface layer.

5. A method for preparing a composite metal carbonate interface layer according to any one of claims 1 to 4, characterized in that: The steps include: Depositing a first alkali metal carbonate layer on the surface of a perovskite active layer of a perovskite solar cell using a vacuum thermal evaporation method; During or after the deposition of the first alkali carbonate layer, gradually reducing the evaporation rate of the first alkali carbonate material and gradually increasing the evaporation rate of the second alkali carbonate material, thereby forming a transition zone comprising two carbonate components; The second alkali metal carbonate layer is deposited on the transition zone to obtain the composite metal carbonate interface layer.

6. The preparation method according to claim 5, characterized in that: During or after the deposition of the first alkali carbonate layer, the evaporation rate of the first alkali carbonate material is gradually reduced, and the evaporation rate of the second alkali carbonate material is gradually increased, thereby forming a transition zone containing two carbonate components, comprising the following steps: During or after the deposition of the first alkali carbonate layer, gradually reducing the evaporation rate of the first alkali carbonate material from a first evaporation rate to a second evaporation rate within a first preset time; Within a second preset time, reducing the second evaporation rate to zero; Within a third preset time, gradually increasing the evaporation rate of the second alkali metal carbonate material from zero to a third evaporation rate; Within a fourth preset time, the third evaporation rate is gradually increased to a fourth evaporation rate, thereby forming a transition zone containing two carbonate components.

7. The preparation method according to claim 6, characterized in that: The first evaporation rate is 0.05Å / s-0.15Å / s, the second evaporation rate is 0.02Å / s-0.04Å / s, the third evaporation rate is 0.06Å / s-0.08Å / s, and the fourth evaporation rate is 0.05Å / s-0.15Å / s; The first preset time, the second preset time, the third preset time and the fourth preset time are all 5s-30s.

8. The preparation method according to any one of claims 6-7, characterized in that: In the preparation method, the substrate provided with the perovskite active layer is rotated at a constant speed of 10 rpm to 30 rpm, and the substrate is maintained at 30° C. to 60° C. during the deposition process.

9. A perovskite solar cell, characterized in that It comprises a composite metal carbonate interface layer prepared by the preparation method described in any one of claims 5 to 8.

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