Photovoltaic conversion layer and its preparation method, photovoltaic devices and applications

Abstract

This application relates to the field of photovoltaic technology, providing a photoelectric conversion layer and its fabrication method, photovoltaic devices, and applications. The photoelectric conversion layer includes at least one Janus MXY two-dimensional material layer, where M includes Mo or W, X includes S, Se, or Te, and Y includes S, Se, or Te, and X and Y are of different elements. This application utilizes the vertical polarization characteristics of the Janus MXY two-dimensional material layer to exhibit extremely strong self-emissive current, enabling the photovoltaic device to possess ultra-high photosensitivity and ultra-fast photosensitivity speed.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and in particular to a photoelectric conversion layer and its preparation method, photovoltaic devices and applications. Background Technology

[0002] In traditional technologies, photovoltaic materials such as monocrystalline silicon, polycrystalline silicon, and gallium arsenide (GaAs), which have three-dimensional crystal structures, are used. To improve photoelectric conversion efficiency, it is usually necessary to increase the thickness and area of ​​the photovoltaic material layer. This not only increases the size of the device but also limits its application in integrated and miniaturized devices. In addition, traditional technologies use two-dimensional materials such as transition metal chalcogenides to form heterojunctions for photodetectors. Although this can achieve device miniaturization, it still suffers from problems such as low output power. Summary of the Invention

[0003] Based on this, one embodiment of this application provides a photoelectric conversion layer with small size and high photoelectric conversion efficiency, a method for preparing the same, a photovoltaic device, and an application thereof.

[0004] In a first aspect, this application provides a photoelectric conversion layer comprising at least one JanusMXY two-dimensional material layer, wherein M comprises Mo or W, X comprises S, Se or Te, Y comprises S, Se or Te, and the elements of X and Y are different.

[0005] In some embodiments, the photoelectric conversion layer includes at least two stacked Janus MXY two-dimensional material layers, wherein the elements on the contact interface of adjacent Janus MXY two-dimensional material layers are different.

[0006] Optionally, the included angle between two adjacent Janus MXY two-dimensional material layers is 0° to 360°.

[0007] In some embodiments, the thickness of the photoelectric conversion layer is 0.67 nm to 100 nm.

[0008] Secondly, this application provides a method for preparing a photoelectric conversion layer, the method comprising:

[0009] Provide a substrate with an MX2 two-dimensional material layer on its surface;

[0010] Using a metal compound containing Y as the Y source, the X element on the side of the MX2 two-dimensional material layer away from the substrate is replaced with Y element by vapor deposition to prepare a photoelectric conversion layer including a Janus MXY two-dimensional material layer.

[0011] Where M includes Mo or W, X includes S, Se or Te, Y includes S, Se or Te, and the elements of X and Y are different.

[0012] In some embodiments, the substrate is coupled to the MX2 two-dimensional material layer; optionally, the substrate comprises aluminum oxide with a <11-20> crystal orientation.

[0013] In some embodiments, the reaction temperature of the vapor deposition method is greater than or equal to the temperature at which the metal compound containing element Y releases element Y, and the difference between the reaction temperature of the vapor deposition method and the temperature at which the metal compound containing element Y releases element Y is ≤50°C.

[0014] In some embodiments, the Janus MXY two-dimensional material layer is a Janus MoSSe two-dimensional material layer.

[0015] Optionally, the MX2 two-dimensional material layer is MoS2, and the metal compound containing Y element includes ZnSe.

[0016] Optionally, the MX2 two-dimensional material layer is MoSe2, and the metal compound containing Y element includes ZnS.

[0017] Optionally, the temperature of the vapor deposition method is 800℃~900℃, the pressure is ≤2 torr, and the time is 30min~60min; the atmosphere of the vapor deposition method includes hydrogen and argon, the flow rate of hydrogen is 2sccm~30sccm, and the flow rate of argon is 100sccm~300sccm.

[0018] Thirdly, this application provides a photovoltaic device, which includes a first conductive layer, a photoelectric conversion layer, and a second conductive layer. The photoelectric conversion layer has a light-facing surface and a backlight surface disposed opposite to each other along its thickness direction. The first conductive layer is disposed on the light-facing surface, and the second conductive layer is disposed on the backlight surface. The projections of the first conductive layer and the second conductive layer on the photoelectric conversion layer at least partially overlap.

[0019] The photoelectric conversion layer includes the photoelectric conversion layer as described in the first aspect or the photoelectric conversion layer prepared by the preparation method of the photoelectric conversion layer as described in the second aspect.

[0020] In some embodiments, the material of the first conductive layer includes at least one of graphene and a transparent conductive material.

[0021] In some embodiments, the material of the second conductive layer includes at least one of graphene, a metallic conductive material, and a transparent conductive glass.

[0022] In some embodiments, the thickness of the first conductive layer is 0.34 nm to 10 nm.

[0023] In some embodiments, the thickness of the second conductive layer is 0.34 nm to 1 μm.

[0024] In some embodiments, the transmittance of the first conductive layer is ≥10%.

[0025] In some embodiments, the photovoltaic device further includes a first encapsulation layer and a second encapsulation layer, wherein the first encapsulation layer is disposed on the side of the first conductive layer away from the photoelectric conversion layer; and the second encapsulation layer is disposed on the side of the second conductive layer away from the photoelectric conversion layer.

[0026] Optionally, the material of the first encapsulation layer includes boron nitride.

[0027] Optionally, the material of the second encapsulation layer includes at least one of boron nitride and silicon oxide.

[0028] Optionally, the thickness of the first encapsulation layer is 1nm to 100nm.

[0029] Optionally, the thickness of the second encapsulation layer is 1 nm to 1 μm.

[0030] Fourthly, this application provides an application of the photovoltaic device as described in the third aspect, wherein the photovoltaic device is used to fabricate solar cells, photodetectors, or photoelectric chips.

[0031] Compared with traditional technologies, this application has at least the following beneficial effects:

[0032] In this application, the Janus MXY two-dimensional material layer is flanked by X and Y elements, which are arranged in an orderly manner on both sides of the M element. This gives the Janus MXY two-dimensional material layer vertical polarization characteristics, exhibiting a very strong self-luminous current phenomenon. Compared with traditional transition metal chalcogenide (e.g., MoS2 or MoSe2) two-dimensional materials, the photoelectric conversion layer of this application not only enables a single-layer Janus MXY two-dimensional material layer to output a high photocurrent, but also eliminates the need for interlayer rotation control and heterojunction formation in its multilayer structure.

[0033] In this application, the photoelectric conversion layer spontaneously polarizes, leading to the accumulation of surface charge. Free electrons in the conductive layer shield these surface charges, forming dipoles with the same orientation, thus generating a potential at the interface between the conductive and photoelectric conversion layers. Since the induced charge cannot completely compensate for the charge in the Janus MXY two-dimensional material layer, the resulting depolarization field drives the separation of electron-hole pairs. Ultimately, these electron-hole pairs can be collected by electrodes through interface charge transfer, thereby forming a photocurrent. The photovoltaic device of this application exhibits ultra-high photosensitivity and ultra-fast photosensitivity speed. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of a photovoltaic device provided in one embodiment of this application; wherein, 100-photovoltaic conversion layer; 200-first conductive layer; 300-second conductive layer; 400-first encapsulation layer; 500-second encapsulation layer; 600-substrate.

[0035] Figure 2 This is a perspective view of the photovoltaic device prepared in Example 1 of this application.

[0036] Figure 3 This is the photocurrent response diagram of the photovoltaic device prepared in Example 1 of this application.

[0037] Figure 4 This is an ultrafast photocurrent response diagram of the photovoltaic device prepared in Example 1 of this application. Detailed Implementation

[0038] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application; therefore, it is not limited to the specific embodiments disclosed below.

[0039] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0041] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0042] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0043] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] Traditional technologies integrate monocrystalline silicon, polycrystalline silicon, and gallium arsenide (GaAs) photovoltaic materials with photovoltaic modules, improving photoelectric conversion efficiency and driving the large-scale application of solar power generation. However, due to the physical properties of the materials, traditional photovoltaic devices typically suffer from large size and weight. Furthermore, the manufacturing process of traditional photovoltaic devices is complex and energy-intensive, resulting in high manufacturing costs. In contrast, two-dimensional van der Waals materials (such as MoS2 or MoSe2) possess unique atomic-level thickness, dangling-bond-free surfaces, and high optical nonlinear effects, demonstrating excellent performance potential in the field of micro-nano integration. They can be combined with various optical microcavities to achieve even higher photoelectric conversion efficiencies. However, current optoelectronic devices based on two-dimensional materials still face technical challenges such as large thickness, complex structure, and low photoelectric conversion efficiency, hindering their large-scale practical application.

[0046] Based on this, the first aspect of this application provides a photoelectric conversion layer, which includes at least one Janus MXY two-dimensional material layer, where M includes Mo or W, X includes S, Se or Te, Y includes S, Se or Te, and the elements of X and Y are different.

[0047] In this application, the Janus MXY two-dimensional material layer is flanked by X and Y elements, which are arranged in an orderly manner on both sides of the M element. This gives the Janus MXY two-dimensional material layer vertical polarization characteristics, exhibiting a very strong self-luminous current phenomenon. Compared with traditional transition metal chalcogenide (e.g., MoS2 or MoSe2) two-dimensional materials, the photoelectric conversion layer of this application not only enables a single-layer Janus MXY two-dimensional material layer to output a high photocurrent, but also eliminates the need for interlayer rotation control and heterojunction formation in its multilayer structure.

[0048] It should be noted that Janus MXY two-dimensional materials refer to those formed by breaking the out-of-plane symmetry of the structure of traditional two-dimensional transition metal chalcogenides. In other words, in the Janus MXY two-dimensional material of this application, the M element is located at the center, all X elements are on the same side of the M element, and all Y elements are on the side of the M element opposite to the X element, forming an XMY sandwich structure. Taking MoS2 as an example, which has an S-Mo-S symmetrical structure, Janus-type MoSSe is formed by replacing all S atoms in one layer of the MoS2 two-dimensional material with Se atoms, thus forming an S-Mo-Se sandwich structure.

[0049] In some embodiments, the photoelectric conversion layer comprises at least two Janus MXY two-dimensional material layers stacked together, wherein the elements at the contact interface of adjacent Janus MXY two-dimensional material layers are different. That is, the multiple Janus MXY two-dimensional material layers are stacked in an XMY or YMX pattern along the stacking direction. For example, the photoelectric conversion layer comprises a first Janus MXY two-dimensional material layer and a second Janus MXY two-dimensional material layer stacked sequentially. If the side of the first Janus MXY two-dimensional material layer closer to the second Janus MXY two-dimensional material layer is an X element, then the side of the second Janus MXY two-dimensional material layer closer to the first Janus MXY two-dimensional material layer is a Y element.

[0050] This application employs a stacking method of multiple Janus MXY two-dimensional material layers as described above, ensuring that the surface charge polarity of the Janus MXY two-dimensional material layers is the same during the spontaneous photovoltaic effect, effectively enhancing the spontaneous photovoltaic effect. If the elements at the contact interface of two adjacent Janus MXY two-dimensional material layers are the same, the charges induced by spontaneous polarization may cancel each other out at the contact interface, preventing the generation of photocurrent.

[0051] Optionally, the angle between two adjacent Janus MXY two-dimensional material layers is 0° to 360°. In this application, the Janus MXY two-dimensional material layers do not require adjustment of the stacking angle, and efficient photocurrent output can be achieved at any angle.

[0052] In some embodiments, the thickness of the photoelectric conversion layer is 0.67 nm to 100 nm. The thickness of the photoelectric conversion layer selected above in this application effectively increases the photoelectric current. However, since the intensity of the depolarization field that generates the photovoltaic effect is inversely proportional to the thickness of the photoelectric conversion layer, a relatively large thickness of the photoelectric conversion layer may lead to a decrease in the intensity of the depolarization field, as well as problems such as insufficient light penetration depth and an increase in defects in the photoelectric conversion layer.

[0053] A second aspect of this application provides a method for preparing a photoelectric conversion layer, the method comprising:

[0054] Provide a substrate with an MX2 two-dimensional material layer on its surface;

[0055] Using a metal compound containing Y as the Y source, the X element on the side of the MX2 two-dimensional material layer away from the substrate is replaced with Y element by vapor deposition to prepare a photoelectric conversion layer including a Janus MXY two-dimensional material layer.

[0056] Where M includes Mo or W, X includes S, Se or Te, Y includes S, Se or Te, and the elements of X and Y are different.

[0057] This application uses a metal compound containing Y as the Y source, which features good release uniformity and high activity. This allows for the complete replacement of the X element on the side of the MX2 two-dimensional material layer away from the substrate, effectively avoiding the problem of uneven replacement. The resulting Janus MXY two-dimensional material layer has few impurities and defects. In the Janus MXY two-dimensional material layer prepared in this application, the M element is flanked by X and Y elements, respectively. The orderly arrangement of X and Y elements on both sides of the M element gives the Janus MXY two-dimensional material layer vertical polarization characteristics, exhibiting a very strong self-luminous current phenomenon. Compared with traditional transition metal chalcogenide (e.g., MoS2 or MoSe2) two-dimensional materials, the photoelectric conversion layer of this application not only enables a single-layer Janus MXY two-dimensional material layer to output a high photocurrent, but also eliminates the need for interlayer rotation control and heterojunction formation in the multilayer structure.

[0058] It is understandable that the photoelectric conversion layer may include multiple Janus MXY two-dimensional material layers, which can be stacked by transfer.

[0059] In some embodiments, the substrate is coupled to the MX2 two-dimensional material layer. It is understood that coupling between the substrate and the MX2 two-dimensional material layer means that the substrate and the MX2 two-dimensional material layer are tightly bonded, making it difficult for the Y element to replace the X element on the side of the MX2 two-dimensional material layer closest to the substrate during fabrication.

[0060] Optionally, the substrate comprises aluminum oxide with a <11-20> crystal orientation.

[0061] The substrate selected in this application has a strong coupling and tight bond with the MX2 material. Therefore, during the vapor deposition substitution process, it is easy to substitute the X element on the side of the MX2 material away from the substrate, but not easy to substitute the X element on the side closer to the substrate. This further improves the purity and uniformity of the prepared Janus MXY two-dimensional material layer and reduces material defects.

[0062] In some embodiments, the reaction temperature of the vapor deposition method is greater than or equal to the temperature at which the Y-containing metal compound releases Y, and the difference between the reaction temperature of the vapor deposition method and the temperature at which the Y-containing metal compound releases Y is ≤50°C. The Y source selected in this application releases Y at a temperature close to the reaction temperature, further improving dispersion uniformity and reducing defects in the Janus MXY two-dimensional material layer.

[0063] In some embodiments, the Janus MXY two-dimensional material layer is a Janus MoSSe two-dimensional material layer.

[0064] Optionally, the MX2 two-dimensional material layer is MoS2, and the Y-containing metal compound includes ZnSe. The release temperature of Se in ZnSe is 750℃~880℃.

[0065] Optionally, the temperature of the vapor deposition method is 800℃~900℃, for example, it can be 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃ or 900℃.

[0066] Optionally, the pressure of the vapor deposition method is ≤2 torr.

[0067] Optionally, the vapor deposition time is 30 min to 60 min.

[0068] Optionally, the atmosphere of the vapor deposition method includes hydrogen and argon, wherein the flow rate of hydrogen is 2 sccm to 30 sccm and the flow rate of argon is 100 sccm to 300 sccm.

[0069] Optionally, the MX2 two-dimensional material layer is MoSe2, and the metal compound containing Y element includes ZnS.

[0070] It is understandable that different Y sources can be selected based on different MX2 two-dimensional material layers to make the temperature at which the Y source releases Y elements close to the reaction temperature, thereby improving the dispersion uniformity of Y elements during the reaction process and reducing defects in the Janus MXY two-dimensional material layer.

[0071] Exemplarily, a method for preparing the above-mentioned photoelectric conversion layer is provided, comprising the following steps:

[0072] Provide a substrate with an MX2 two-dimensional material layer on its surface;

[0073] Using a metal compound containing Y as the Y source, the X element on the side of the MX2 two-dimensional material layer away from the substrate is replaced with Y element by vapor deposition to prepare a photoelectric conversion layer including a Janus MXY two-dimensional material layer.

[0074] Furthermore, multiple Janus MXY two-dimensional material layers are prepared and transferred and stacked to form a photoelectric conversion layer composed of multiple Janus MXY two-dimensional material layers.

[0075] A third aspect of this application provides a photovoltaic device, the photovoltaic device comprising a first conductive layer, a photoelectric conversion layer, and a second conductive layer, the photoelectric conversion layer having a light-facing surface and a back-light surface disposed opposite to each other along the thickness direction; the first conductive layer is disposed on the light-facing surface, the second conductive layer is disposed on the back-light surface, and the projections of the first conductive layer and the second conductive layer on the photoelectric conversion layer at least partially overlap.

[0076] The photoelectric conversion layer includes the photoelectric conversion layer as described in the first aspect or the photoelectric conversion layer prepared by the preparation method of the photoelectric conversion layer as described in the second aspect.

[0077] In this application, the photoelectric conversion layer spontaneously polarizes, leading to the accumulation of surface charge. Free electrons in the conductive layer shield these surface charges, forming dipoles with the same orientation, thus generating a potential at the interface between the conductive and photoelectric conversion layers. Since the induced charge cannot completely compensate for the charge in the Janus MXY two-dimensional material layer, the resulting depolarization field drives the separation of electron-hole pairs. Ultimately, these electron-hole pairs can be collected by electrodes through interface charge transfer, thereby forming a photocurrent. The photovoltaic device of this application exhibits ultra-high photosensitivity and ultra-fast photosensitivity speed.

[0078] In some embodiments, the projections of the first conductive layer and the second conductive layer onto the photoelectric conversion layer completely overlap. This application's research found that the photoelectric effect in the non-overlapping portions of the projections of the first and second conductive layers is very weak and negligible compared to the photoelectric effect in the overlapping portions.

[0079] It is understood that the function of the first conductive layer and the second conductive layer in this application is to conduct the current formed in the photoelectric conversion layer.

[0080] In some embodiments, the material of the first conductive layer includes graphene and a transparent conductive material. The transparent conductive material may be transparent conductive glass, etc.

[0081] In some embodiments, the material of the second conductive layer includes at least one of graphene, a metallic conductive material, and a transparent conductive material.

[0082] It is understood that the first and second conductive layers need only cover the photoelectric conversion layer and be able to conduct current. In some embodiments, the thickness of the first conductive layer is 0.34 nm to 100 nm. In some embodiments, the thickness of the second conductive layer is 0.34 nm to 1 μm.

[0083] In some embodiments, the transmittance of the first conductive layer is ≥10%.

[0084] In some embodiments, the photovoltaic device further includes a first encapsulation layer and a second encapsulation layer, wherein the first encapsulation layer is disposed on the side of the first conductive layer away from the photoelectric conversion layer; and the second encapsulation layer is disposed on the side of the second conductive layer away from the photoelectric conversion layer.

[0085] Optionally, the material of the first encapsulation layer includes boron nitride.

[0086] Optionally, the material of the second encapsulation layer includes at least one of boron nitride and silicon oxide.

[0087] Optionally, the thickness of the first encapsulation layer is 1nm to 100nm.

[0088] Optionally, the thickness of the second encapsulation layer is 1 nm to 1 μm.

[0089] In some embodiments, the photovoltaic device further includes a first electrode and a second electrode, the first electrode being connected to a first conductive layer and the second electrode being connected to a second conductive layer, the first electrode and the second electrode being used to enable electronic conduction of the photovoltaic device.

[0090] In some embodiments, the photovoltaic device further includes a substrate disposed on the side of the second encapsulation layer away from the photoelectric conversion layer, for providing support for the photovoltaic device.

[0091] like Figure 1 As shown, the photovoltaic device includes a substrate 600, a second encapsulation layer 500, a second conductive layer 300, a photoelectric conversion layer 100, a first conductive layer 200, and a first encapsulation layer 400 stacked sequentially.

[0092] It is understandable that the first encapsulation layer, the first conductive layer, the photoelectric conversion layer, the second conductive layer, and the second encapsulation layer can be stacked and assembled in sequence by means of transfer.

[0093] The fourth aspect of this application provides an application of the photovoltaic device as described in the third aspect, the photovoltaic device being used to fabricate solar cells, photodetectors, or photoelectric chips.

[0094] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0095] Example 1

[0096] (1) Preparation of Janus MoSSe two-dimensional material layer

[0097] A substrate with MoS2 on its surface is provided, wherein the substrate is aluminum oxide with crystal orientation <11-20>;

[0098] Using ZnSe as the Se source, 120 sccm of argon and 5 sccm of hydrogen were introduced at a pressure of 1 torr, and the material was grown at 870℃ for 30 min to Se-modify MoS2, replacing the S element on the side of MoS2 away from the substrate, thus preparing a Janus MoSSe two-dimensional material layer with a thickness of 0.67 nm.

[0099] (2) Assembling photovoltaic devices

[0100] Using PPC (polymethyl methacrylate) and PMMA (polymethyl methacrylate), the layers are transferred and stacked in the following order: first encapsulation layer, first conductive layer, photoelectric conversion layer, second conductive layer, and second encapsulation layer. The projections of the first and second conductive layers onto the photoelectric conversion layer completely overlap. The photoelectric conversion layer is a Janus MoSSe two-dimensional material layer prepared in step (1) above; the first and second encapsulation layers are 10 nm thick boron nitride; and the first and second conductive layers are 1 nm thick graphene. Gold electrodes are then deposited on the first and second conductive layers respectively to assemble the photovoltaic device.

[0101] Example 2

[0102] The Janus MoSSe two-dimensional material layer and photovoltaic device were prepared according to the method of Example 1, the difference being that the photoelectric conversion layer includes two stacked Janus MoSSe two-dimensional material layers. The Janus MoSSe two-dimensional material layers are placed in the order S-Mo-Se along the stacking direction.

[0103] Example 3

[0104] The Janus MoSSe two-dimensional material layer and photovoltaic device were prepared according to the method of Example 1, except that the second conductive layer was replaced with ITO with a thickness of 50 nm.

[0105] Comparative Example 1

[0106] The Janus MoSSe two-dimensional material layer and photovoltaic device were prepared according to the method of Example 1, the difference being that the projections of the first conductive layer and the second conductive layer on the photoelectric conversion layer do not overlap, only the first conductive layer or the second conductive layer overlaps with the photoelectric conversion layer.

[0107] Comparative Example 2

[0108] The photovoltaic device is assembled according to the method of Example 1, except that the photoelectric conversion layer is replaced with a first MoS2 two-dimensional material layer and a second MoS2 two-dimensional material layer stacked in sequence. The interlayer rotation angle between the first MoS2 two-dimensional material layer and the second MoS2 two-dimensional material layer is 60 degrees, which refers to the rotation angle between the two MoS2 crystal phases.

[0109] Comparative Example 3

[0110] The photovoltaic device was assembled according to the method of Example 2, except that a layer of graphene with a thickness of 1 nm was added between the two Janus MoSSe two-dimensional material layers to form a photoelectric conversion layer.

[0111] The photovoltaic device prepared above was subjected to performance testing. The testing method included testing the photocurrent intensity of the photovoltaic device under zero bias voltage under illumination (633nm, 100 microwatts). The test results are shown in Table 1.

[0112] Table 1

[0113]

[0114] As can be seen from the table above:

[0115] (1) Compared with Example 3, Example 1 shows that in this application, graphene and ITO are used only as conductive layers, that is, the conductive layer only needs to have a conductive effect. Compared with ITO, graphene has an atomically flat surface and fewer surface defects, thus having a better photovoltaic effect.

[0116] (2) Through Example 1 and Comparative Examples 1-2, and in combination with Figure 3 It can be seen that under illumination (633nm), the photovoltaic device of this application exhibits a significant self-emissive current, while the MoS2 device does not show a similar phenomenon. By scanning the photocurrent, it was found that the spontaneous photovoltaic effect only occurs in the stacked region of the first conductive layer, the photoelectric conversion layer, and the second conductive layer. The photocurrent in the stacked region with only the photoelectric conversion layer and the first conductive layer, and in the region with only the photoelectric conversion layer and the second conductive layer, is negligible, thus eliminating the influence of thermal effects or pn junction effects caused by laser radiation. Moreover, compared with Example 2, the spontaneous photovoltaic effect of the photoelectric conversion layer of this application is significantly enhanced with the increase of the number of layers.

[0117] Furthermore, such as Figure 4As shown, this application employs ultrafast time-resolved photocurrent autocorrelation spectroscopy. By applying a 0.5mW continuous laser pulse with a time delay, it was found that the photocurrent reaches its minimum when two pulses overlap, reflecting the saturation effect under high power; while when the time delay is not zero, the photocurrent gradually increases. The rising portion of the photocurrent curve reveals the photovoltaic device's ability to resolve continuous pulses. Exponential fitting of the rising curve shows that the typical response time of the photovoltaic device in Example 1 is approximately 50 ps, ​​with a bandwidth of 11 GHz, and is unaffected by pump power.

[0118] Therefore, in the Janus MXY two-dimensional material layer of this application, the M element is flanked by X and Y elements, which are arranged in an orderly manner on both sides of the M element. This gives the Janus MXY two-dimensional material layer vertical polarization characteristics, exhibiting a very strong self-luminous current phenomenon. Compared with traditional transition metal chalcogenide (e.g., MoS2 or MoSe2) two-dimensional materials, the photoelectric conversion layer of this application not only enables a single-layer Janus MXY two-dimensional material layer to output a high photocurrent, but also eliminates the need for interlayer rotation control and heterojunction formation in the multilayer structure.

[0119] (3) Compared with Comparative Example 3, in Example 2, graphene was inserted into the photoelectric conversion layer. Although a heterojunction structure was formed between the Janus MXY two-dimensional material layer and the graphene, the presence of graphene enhanced the spontaneous polarization shielding effect of the photoelectric conversion layer and weakened the depolarization field. At the same time, graphene also produced additional light absorption, which affected the photoelectric conversion effect.

[0120] Therefore, the spontaneous polarization of the photoelectric conversion layer in this application induces the accumulation of surface charge in the optoelectronic device. Free electrons in the conductive layer form dipoles with the same orientation by shielding these surface charges, thereby generating a potential at the interface between the conductive layer and the photoelectric conversion layer. Since the induced charge cannot completely compensate for the charge in the Janus MXY two-dimensional material layer, the resulting depolarization field drives the separation of electron-hole pairs. Ultimately, the electron-hole pairs can be collected by the electrodes through interface charge transfer, thereby forming a photocurrent. The photovoltaic device of this application exhibits ultra-high photosensitivity and ultra-fast photosensitivity speed.

[0121] In summary, this application integrates a photoelectric conversion layer containing a Janus MXY two-dimensional material layer with a photovoltaic device. By utilizing the unique asymmetric lattice structure and inherent vertical polarization of Janus MXY two-dimensional material, and by adjusting its atomic composition and thickness to optimize photoelectric performance, the conversion efficiency of spontaneous photovoltaic effect is greatly improved.

[0122] The structure of the photoelectric conversion layer in this application has significant advantages in photocurrent generation, enabling efficient photoelectric conversion and electron-hole pair separation, thus achieving more precise photovoltaic performance optimization. Compared with traditional photovoltaic materials, the photoelectric conversion layer in this application not only improves conversion efficiency but also achieves high-efficiency self-emitting current output, providing a new direction for the design of miniaturized, high-efficiency photovoltaic devices.

[0123] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0124] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A photovoltaic device, characterized by, The photovoltaic device includes a first conductive layer, a photoelectric conversion layer, and a second conductive layer stacked together. The photoelectric conversion layer has a light-facing surface and a back-light surface disposed opposite each other along its thickness direction. The first conductive layer is disposed on the light-facing surface, and the second conductive layer is disposed on the back-light surface. The projections of the first conductive layer and the second conductive layer on the photoelectric conversion layer at least partially overlap. The photoelectric conversion layer is composed of at least one Janus MXY two-dimensional material layer; when the photoelectric conversion layer is composed of at least two Janus MXY two-dimensional material layers, there is no need to adjust the interlayer rotation angle or form a heterojunction between the Janus MXY two-dimensional material layers. The method for preparing the photoelectric conversion layer includes: A substrate having an MX2 two-dimensional material layer on its surface is provided, the substrate being coupled to the MX2 two-dimensional material layer; Using a metal compound containing Y as the Y source, the X element on the side of the MX2 two-dimensional material layer away from the substrate is replaced with Y element by vapor deposition to prepare a photoelectric conversion layer including a Janus MXY two-dimensional material layer. Wherein, M includes Mo or W, X includes S, Se or Te, Y includes S, Se or Te, and X and Y are not the same element; the reaction temperature of the vapor deposition method is greater than or equal to the temperature at which the metal compound containing element Y releases element Y, and the difference between the reaction temperature of the vapor deposition method and the temperature at which the metal compound containing element Y releases element Y is ≤50℃.

2. The photovoltaic device as described in claim 1, characterized in that, The substrate comprises aluminum oxide with a <11-20> crystal orientation.

3. The photovoltaic device as described in claim 1 or 2, characterized in that, The Janus MXY two-dimensional material layer is a JanusMoSSe two-dimensional material layer, and the preparation method satisfies at least one of the following conditions: (1) The MX2 two-dimensional material layer is MoS2, and the metal compound containing Y element includes ZnSe; (2) The MX2 two-dimensional material layer is MoSe2, and the metal compound containing Y element includes ZnS; (3) The temperature of the vapor deposition method is 800℃~900℃, the pressure is ≤2torr, and the time is 30min~60min; the atmosphere of the vapor deposition method includes hydrogen and argon, the flow rate of hydrogen is 2sccm~30sccm, and the flow rate of argon is 100sccm~300sccm.

4. The photovoltaic device as described in claim 1, characterized in that, The photoelectric conversion layer includes at least two stacked Janus MXY two-dimensional material layers, and the elements on the contact interface of adjacent Janus MXY two-dimensional material layers are different.

5. The photovoltaic device as described in claim 4, characterized in that, The included angle between two adjacent Janus MXY two-dimensional material layers is 0° to 360°.

6. The photovoltaic device as described in any one of claims 1, 4, or 5, characterized in that, The thickness of the photoelectric conversion layer is 0.67 nm to 100 nm.

7. The photovoltaic device as described in claim 1, characterized in that, The photovoltaic device satisfies at least one of the following conditions: (1) The material of the first conductive layer includes at least one of graphene and transparent conductive material; (2) The material of the second conductive layer includes at least one of graphene, metallic conductive material and transparent conductive glass; (3) The thickness of the first conductive layer is 0.34 nm to 100 nm; (4) The thickness of the second conductive layer is 0.34 nm to 1 μm; (5) The light transmittance of the first conductive layer is ≥10%.

8. The photovoltaic device as described in claim 1 or 7, characterized in that, The photovoltaic device further includes a first encapsulation layer and a second encapsulation layer, wherein the first encapsulation layer is disposed on the side of the first conductive layer away from the photoelectric conversion layer; and the second encapsulation layer is disposed on the side of the second conductive layer away from the photoelectric conversion layer.

9. The photovoltaic device as described in claim 8, characterized in that, The material of the first encapsulation layer includes boron nitride.

10. The photovoltaic device as described in claim 8, characterized in that, The material of the second encapsulation layer includes at least one of boron nitride and silicon oxide.

11. The photovoltaic device as described in claim 8, characterized in that, The thickness of the first encapsulation layer is 1nm~100nm.

12. The photovoltaic device as described in claim 8, characterized in that, The thickness of the second encapsulation layer is 1 nm to 1 μm.

13. An application of the photovoltaic device according to any one of claims 1-12, characterized in that, The photovoltaic device is used to manufacture solar cells, photodetectors, or photoelectric chips.

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