A two-dimensional van der waals heterojunction structure for light emission and photovoltaics

Abstract

The application provides a two-dimensional van der Waals heterojunction structure for light emission and photovoltaic, which comprises (alpha-In2Se3) single-layer units and (GaS) single-layer units from top to bottom, and the heterojunction structure is divided into P↑ state and P↓ state according to the ferroelectric polarization direction, when the middle Se atom layer of the (alpha-In2Se3) single-layer unit is close to the upper side, the heterojunction structure is in P↑ state, and when the middle Se atom layer of the (alpha-In2Se3) single-layer unit is close to the lower side, the heterojunction structure is in P↓ state. The heterojunction structure has two polarization states P↑ state and P↓ state which can be converted by applying an external electric field, and is respectively a type I heterojunction which can be used for a light-emitting device and a type II heterojunction which can be used for a photovoltaic device, so that multiple purposes of the heterojunction are realized, and the application field and use range of the heterojunction are greatly expanded.

Description

Technical Field

[0001] This invention belongs to the technical field of optoelectronic materials, specifically relating to a two-dimensional van der Waals heterojunction structure that can be used for both light emission and photovoltaic purposes. Background Technology

[0002] Since the successful exfoliation of graphene in 2004, two-dimensional materials such as graphene, transition metal dichalcogenides, and phosphorene have attracted widespread attention due to their excellent physicochemical properties. The continuous emergence of novel two-dimensional materials has given them broad application prospects. In the research and exploration of two-dimensional materials, researchers have discovered a good form that allows two-dimensional materials to more effectively utilize their advantages: van der Waals heterojunction structures composed of two or more two-dimensional materials stacked together. Graphene / transition metal dichalcogenide and transition metal dichalcogenide / transition metal dichalcogenide heterojunctions, such as graphene / MoS2 and WSe2 / MoS2, have been studied, and these structures have been found to have good application prospects in the optoelectronic field. In two-dimensional optoelectronic material heterojunctions, in addition to the properties inherent in the individual materials, the band structure at the interface of the two-dimensional material heterojunction often affects the formation, drift, and recombination of photogenerated carriers, and the charge transfer between the interfaces often occurs in the range of 50 fs to sub-picoseconds, further affecting the electrical and optical performance of two-dimensional optoelectronic material heterojunction devices. Based on the band alignment of the constituent materials, double-layer van der Waals heterojunctions are classified into Type I heterojunctions (cross-junctions), Type II heterojunctions (misaligned heterojunctions), and Type III heterojunctions (gap-broken heterojunctions). Type I heterojunctions allow for rapid recombination of electrons and holes and are commonly used in light-emitting devices (such as LEDs); Type II heterojunctions effectively separate electrons and holes and are commonly used in photovoltaic devices (such as heterojunction cells); Type III heterojunctions facilitate electron tunneling and are primarily used in tunneling field transistors (ECT).

[0003] Among two-dimensional materials, two-dimensional ferroelectric materials (such as CuInP2S6 and α-In2Se3) are a special class. They possess two or more polarization states that can be switched by applying an external electric field, and each polarization state has a different Fermi level. When two-dimensional ferroelectric materials form heterojunctions with other materials, their Fermi levels will shift and eventually unify, accompanied by changes in band alignment. Therefore, using two-dimensional ferroelectric materials and other materials to construct van der Waals heterojunctions allows for different heterojunction types corresponding to different polarization states, enabling multiple applications of a single heterojunction and greatly expanding its application areas and scope. Currently, research on switchable heterojunction types is limited, and many undiscovered two-dimensional van der Waals heterojunctions still possess potentially better performance and application structures. Therefore, it is necessary to further research and develop switchable two-dimensional van der Waals heterojunctions to provide more possibilities and choices for the development of next-generation optoelectronic devices. Therefore, in order to realize a convertible two-dimensional van der Waals heterojunction and further explore the potential of two-dimensional optoelectronic materials, this invention provides a two-dimensional van der Waals heterojunction structure that can be used for both light emission and photovoltaic purposes. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a two-dimensional van der Waals heterojunction structure that serves both light emission and photovoltaic purposes, thereby resolving the technical issues raised in the background section.

[0005] This invention provides the following technical solution: a two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications, wherein the heterojunction structure comprises, from top to bottom, ( )α-In2Se3 monolayer units and ( GaS monolayer unit cell, the heterojunction structure is divided into P↑ state and P↓ state according to its ferroelectric polarization direction, the ( When the middle Se atom layer of the α-In2Se3 monolayer unit cell is close to the top, the heterojunction structure is in the P↑ state. When the middle Se atom layer of the α-In2Se3 monolayer unit cell is close to the bottom, the heterojunction structure is in the P↓ state, and the lattice mismatch rate of the heterojunction structure is less than 2%.

[0006] Compared with existing technologies, the beneficial effects of this application are as follows: The heterojunction structure provided in this application is composed of two-dimensional ferroelectric material α-In2Se3 and two-dimensional material GaS stacked together, which has switchable P↑ and P↓ states. The P↑ state heterojunction structure is a type I heterojunction, which can rapidly recombine electrons and holes and can be used to fabricate light-emitting devices. The P↓ state heterojunction structure is a type II heterojunction, which can effectively separate electrons and holes and can be used in photovoltaic devices. This provides a heterojunction structure that achieves multiple applications, greatly expanding the application fields and scope of heterojunctions. Furthermore, the light absorption coefficients of this heterojunction structure in the ultraviolet and visible light bands are... It has a high efficiency in utilizing light energy, making it suitable for manufacturing optoelectronic devices.

[0007] Preferably, the ( The length of the α-In2Se3 monolayer unit cell is 7.114 Å in the x-direction, 7.114 Å in the z-direction, and 35 Å in the y-direction. The angle between cell edge a1 and cell edge b1 is 120°, the angle between cell edge a1 and cell edge c1 is 90°, and the angle between cell edge b1 and cell edge c1 is 90°.

[0008] Preferably, the ( The length of the GaS monolayer unit cell is 7.267 Å in the x-direction, 7.267 Å in the z-direction, and 35 Å in the y-direction. The angle between unit cell edge a2 and unit cell edge b2 is 120°, the angle between unit cell edge a2 and unit cell edge c2 is 90°, and the angle between unit cell edge b2 and unit cell edge c2 is 90°.

[0009] Preferably, the heterojunction structure has a cell edge length of 7.267 Å in the x-direction, a cell edge length of 7.267 Å in the z-direction, and a cell edge length of 35 Å in the y-direction. The angle between cell edge a3 and cell edge b3 is 120°, the angle between cell edge a3 and cell edge c3 is 90°, and the angle between cell edge b3 and cell edge c3 is 90°.

[0010] Preferably, when the heterojunction structure is in the P↑ state, the ( )α-In2Se3 monolayer units and ( The interlayer spacing of the GaS monolayer unit cell is 3.33 Å. When the heterojunction structure is in the P↓ state, the ( )α-In2Se3 monolayer units and ( The interlayer spacing of a GaS monolayer unit cell is 3.28 Å.

[0011] Preferably, when the heterojunction structure is in the P↑ state, it is a semiconductor with a band gap of 1.27 eV, and when the heterojunction structure is in the P↓ state, it is a semiconductor with a band gap of 0.92 eV.

[0012] Preferably, the ( α-In₂Se₃ monolayer units are semiconductors with a band gap of 1.36 eV. GaS monolayer units are semiconductors with a band gap of 1.56 eV.

[0013] Preferably, when the heterojunction structure is in the P↑ state, the heterojunction structure is a type I heterojunction, and its conduction band bottom and valence band top are both formed by the ( α-In2Se3 monolayers provide this.

[0014] Preferably, when the heterojunction structure is in the P↓ state, the heterojunction structure is a type II heterojunction, and its conduction band bottom and valence band top are both formed by the ( )α-In2Se3 monolayer unit cells, the ( GaS monolayer units are provided.

[0015] Preferably, the P↑ and P↓ states of the heterojunction structure can be interconverted by applying an external electric field in the polarization direction of the heterojunction structure. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a structural diagram of a two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications provided in an embodiment of the present invention, wherein (a) is ( (a) Top and front views of an α-In2Se3 monolayer unit cell in the P↑ and P↓ states, respectively. (b) is ( (c) Top and side views of a GaS monolayer unit cell; (d) Top and front views of a two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications in the P↑ and P↓ states. Figure 2 The band structure of the two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications provided in the embodiments of the present invention is shown in the diagram, wherein (a) is ( (a) Band diagram of an α-In2Se3 monolayer unit cell, (b) is ( (c) is the band structure of a GaS monolayer unit cell, and (d) is the band structure of a two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications in the P↑ state. Figure 3 The light absorption spectrum in the normal direction of the two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications provided in the embodiments of the present invention.

[0018] The present invention will be further described below with reference to the accompanying drawings and description. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain embodiments of the present invention, and should not be construed as limiting the present invention.

[0020] In the description of the embodiments of the present invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention 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. Therefore, they should not be construed as limitations on the present invention.

[0021] 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 one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0022] In the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "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. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0023] In embodiments of the present invention, such as Figure 1As shown, a two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications is disclosed. The heterojunction structure comprises, from top to bottom, (…). )α-In2Se3 monolayer units and ( GaS monolayer unit cell, the heterojunction structure is divided into P↑ state and P↓ state according to its ferroelectric polarization direction, the ( When the middle Se atom layer of the α-In2Se3 monolayer unit cell is close to the top, the heterojunction structure is in the P↑ state. When the middle Se atom layer of the α-In2Se3 monolayer unit cell is close to the bottom, the heterojunction structure is in the P↓ state, and the lattice mismatch rate of the heterojunction structure is less than 2%.

[0024] like Figure 1 As shown in (a), the ( The length of the α-In₂Se₃ monolayer unit cell is 7.114 Å at cell edge a₁ in the x-direction, 7.114 Å at cell edge b₁ in the z-direction, and 35 Å at cell edge c₁ in the y-direction. The angle between cell edge a₁ and cell edge b₁ is 120°, the angle between cell edge a₁ and cell edge c₁ is 90°, and the angle between cell edge b₁ and cell edge c₁ is 90°. α-In2Se3 monolayer units also possess two states, namely the P↑ state and the P↓ state, when the ( When the middle Se atom layer of α-In2Se3 monolayer unit cell is close to the upper side, the... ) α-In2Se3 monolayer unit cells are in the P↑ state, the ( When the middle Se atom layer of α-In2Se3 monolayer unit cell is close to the bottom, the... The α-In2Se3 monolayer unit cell is in the P↓ state.

[0025] like Figure 1 As shown in (b), the ( The length of the GaS monolayer unit cell is 7.267 Å in the x-direction, 7.267 Å in the z-direction, and 35 Å in the y-direction. The angle between unit cell edge a2 and unit cell edge b2 is 120°, the angle between unit cell edge a2 and unit cell edge c2 is 90°, and the angle between unit cell edge b2 and unit cell edge c2 is 90°.

[0026] like Figure 1 As shown in (c), the length of cell edge a3 in the x direction of the heterojunction structure is 7.267 Å, ​​the length of cell edge b3 in the z direction is 7.267 Å, ​​the length of cell edge c3 in the y direction is 35 Å, the angle between cell edge a3 and cell edge b3 is 120°, the angle between cell edge a3 and cell edge c3 is 90°, and the angle between cell edge b3 and cell edge c3 is 90°. And when the heterojunction structure is in the P↑ state, the ( )α-In2Se3 monolayer units and ( The interlayer spacing of the GaS monolayer unit cell is 3.33 Å. When the heterojunction structure is in the P↓ state, the ( )α-In2Se3 monolayer units and ( The interlayer spacing of GaS monolayer unit cells is 3.28 Å, which is within the range of van der Waals forces.

[0027] exist Figure 2 In the middle, the light gray band is ( ) α-In2Se3 monolayer unit cell band and heterojunction composed of ( The energy bands contributed by the α-In2Se3 monolayer unit cell; the dark gray energy band is ( The band structure of GaS monolayer unit cells and heterojunctions is composed of ( The energy band contributed by the GaS monolayer unit cell.

[0028] like Figure 2 (a) Figure 2 As shown in (b), the ( α-In₂Se₃ monolayer units are semiconductors with a band gap of 1.36 eV. GaS monolayer units are semiconductors with a band gap of 1.56 eV.

[0029] like Figure 2 (c) Figure 2 As shown in (d), when the heterojunction structure is in the P↑ state, it is a semiconductor with a band gap of 1.27 eV; when the heterojunction structure is in the P↓ state, it is a semiconductor with a band gap of 0.92 eV. Meanwhile, since α-In2Se3 is a ferroelectric material, the polarization state can be switched by applying an external electric field in the polarization direction. Therefore, the P↑ state and P↓ state of the heterojunction structure can be switched to each other by applying an external electric field in the polarization direction of the heterojunction structure.

[0030] Furthermore, when the heterojunction structure is in the P↑ state, the heterojunction structure is a type I heterojunction, and its conduction band bottom and valence band top are both determined by the ( The α-In2Se3 monolayer unit cell provides the ability to rapidly recombine electrons and holes when the heterojunction structure is a type I heterojunction, which can be used to fabricate light-emitting devices (such as LEDs).

[0031] Furthermore, when the heterojunction structure is in the P↓ state, the heterojunction structure is a type II heterojunction, and its conduction band bottom and valence band top are both determined by the ( )α-In2Se3 monolayer unit cells, the ( GaS monolayer units provide the ability to effectively separate electrons and holes when the heterojunction structure is a type II heterojunction, which can be used in photovoltaic devices (such as heterojunction cells).

[0032] like Figure 3 As shown, in Figure 3 In the diagram, the gradient shaded area from 380 to 780 nm represents the visible light wavelength range, and the normal direction of the heterojunction structure is the z-axis direction. The light absorption coefficients of the heterojunction structure in the ultraviolet and visible light bands in the normal direction (z-axis) of this invention are... Its absorption spectrum is relatively high, with little difference between the P↑ and P↓ states, reaching a maximum of 36 μm in the ultraviolet band. -1 In the visible light band, it exceeds 23μm. -1 Both polarization states have high light energy utilization rates in the ultraviolet and visible light bands, making them suitable for fabricating optoelectronic devices.

[0033] In summary, the two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications provided in this embodiment is composed of a stack of two-dimensional ferroelectric material α-In₂Se₃ and two-dimensional material GaS. It possesses switchable P↑ and P↓ states. The P↑ state heterojunction is a type I heterojunction, capable of rapid recombination of electrons and holes, and can be used to fabricate light-emitting devices. The P↓ state heterojunction is a type II heterojunction, capable of effectively separating electrons and holes, and can be used in photovoltaic devices. This provides a heterojunction structure that achieves multiple applications, greatly expanding the application fields and scope of heterojunctions. Furthermore, the light absorption coefficients of this heterojunction structure in the ultraviolet and visible light bands are [not specified in the original text]. It has a high efficiency in utilizing light energy, making it suitable for manufacturing optoelectronic devices.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications, characterized in that, The heterojunction structure includes, from top to bottom, ( )α-In2Se3 monolayer units and ( GaS monolayer unit cell, the heterojunction structure is divided into P↑ state and P↓ state according to its ferroelectric polarization direction, the ( When the middle Se atom layer of the α-In2Se3 monolayer unit cell is close to the top, the heterojunction structure is in the P↑ state. When the middle Se atom layer of the α-In2Se3 monolayer unit cell is close to the bottom, the heterojunction structure is in the P↓ state, and the lattice mismatch rate of the heterojunction structure is less than 2%. The heterojunction structure has a cell edge length of 7.267 Å in the x direction, a cell edge length of 7.267 Å in the z direction, and a cell edge length of 35 Å in the y direction. The angle between cell edge a3 and cell edge b3 is 120°, the angle between cell edge a3 and cell edge c3 is 90°, and the angle between cell edge b3 and cell edge c3 is 90°. When the heterojunction structure is in the P↑ state, the ( )α-In2Se3 monolayer units and ( The interlayer spacing of the GaS monolayer unit cell is 3.33 Å. When the heterojunction structure is in the P↓ state, the ( )α-In2Se3 monolayer units and ( The interlayer spacing of a GaS monolayer unit cell is 3.28 Å.

2. The two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications according to claim 1, characterized in that, The ( The length of the α-In2Se3 monolayer unit cell is 7.114 Å in the x-direction, 7.114 Å in the z-direction, and 35 Å in the y-direction. The angle between cell edge a1 and cell edge b1 is 120°, the angle between cell edge a1 and cell edge c1 is 90°, and the angle between cell edge b1 and cell edge c1 is 90°.

3. The two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications according to claim 1, characterized in that, The ( The length of the GaS monolayer unit cell is 7.267 Å in the x-direction, 7.267 Å in the z-direction, and 35 Å in the y-direction. The angle between unit cell edge a2 and unit cell edge b2 is 120°, the angle between unit cell edge a2 and unit cell edge c2 is 90°, and the angle between unit cell edge b2 and unit cell edge c2 is 90°.

4. The two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications according to claim 1, characterized in that, When the heterojunction structure is in the P↑ state, it is a semiconductor with a band gap of 1.27 eV; when the heterojunction structure is in the P↓ state, it is a semiconductor with a band gap of 0.92 eV.

5. The two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications according to claim 1, characterized in that, The ( α-In₂Se₃ monolayer units are semiconductors with a band gap of 1.36 eV. GaS monolayer units are semiconductors with a band gap of 1.56 eV.

6. The two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications according to claim 1, characterized in that, When the heterojunction structure is in the P↑ state, the heterojunction structure is a type I heterojunction, and its conduction band bottom and valence band top are both formed by the ( α-In2Se3 monolayer units provide this.

7. The two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications according to claim 1, characterized in that, When the heterojunction structure is in the P↓ state, the heterojunction structure is a type II heterojunction, and its conduction band bottom and valence band top are both formed by the ( ) α-In2Se3 monolayer unit cells, the ( GaS monolayer units are provided.

8. The two-dimensional van der Waals heterojunction structure for both light emission and photovoltaic applications according to claim 1, characterized in that, The P↑ and P↓ states of the heterojunction structure can be interconverted by applying an external electric field in the polarization direction of the heterojunction structure.

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