A tandem two-dimensional photovoltaic cell defined by ferroelectric domains and a preparation method thereof

Abstract

The invention discloses a tandem two-dimensional photovoltaic cell defined by ferroelectric domains and a preparation method thereof. The photovoltaic cell structure is a ferroelectric functional layer, a metal electrode, a two-dimensional semiconductor and an insulating silicon substrate from top to bottom. The device preparation step is to prepare a transition metal chalcogenide two-dimensional semiconductor on a substrate, use ultraviolet lithography or electron beam exposure combined with thermal evaporation and stripping process to prepare a metal electrode as the source and drain of a semiconductor channel, then use a spin coating method to prepare a ferroelectric film to cover the structure, and then use piezoelectric force microscopy to write positive and negative domain structures to the two channels respectively, so that the ferroelectric domain can regulate the two sides of the bipolar two-dimensional semiconductor to present hole and electron conduction respectively, forming an in-plane PNPN junction. The tandem PN junction formed by this method has the characteristic of doubling the open circuit voltage compared with a single PN junction, and the preparation process is simple, the device size is small, and the device stability is good.

Description

Technical Field

[0001] The present invention relates to a two-dimensional semiconductor photovoltaic device, in particular to a series-connected two-dimensional photovoltaic cell defined by a ferroelectric domain and a preparation method thereof. Background Art

[0002] Photovoltaic devices can be used to convert solar energy into electrical energy. Light irradiated on the device is absorbed by the semiconductor material, generating electron-hole pairs, which are separated by the built-in electric field of the photovoltaic device. The separated electrons and holes generate photovoltage and photocurrent at the junction. The PN junction is a typical photovoltaic device.

[0003] The open circuit voltage value (Voc) is a key factor in improving cell efficiency. It shows the number of charge carriers in the cell when light shines on the solar cell, which can effectively improve the performance of the solar cell. However, the output voltage of the solar cell is usually limited by the incident light intensity and band gap of the semiconductor material. In order to increase the output voltage, semiconductor materials such as amorphous silicon can be used to make photovoltaic arrays. This photovoltaic array connects the PN junctions in series through electrodes. This process usually involves processes such as photolithography, chemical etching, laser etching, and mechanical scribing. The process is cumbersome and the process is complicated.

[0004] In recent years, two-dimensional materials have shown great development potential in the field of optoelectronic devices due to their high surface area ratio, flexibility and good conductivity. PN junction photovoltaic devices made of two-dimensional materials have received great attention. Two-dimensional material PN junctions include heterojunctions and homojunctions. Among them, two-dimensional material heterojunction structure photovoltaic devices usually stack p-type materials and n-type materials vertically together to form a PN junction. At present, the most reported heterojunction structure is MoS 2 -WSe 2 PN junction, where the conversion efficiency of a single-layer stack is 0.2%. The power conversion efficiency of a multi-layer stack is 3.4% [Chemical Society Reviews, 2018, 47(9): 3339]. 2 -WSe 2 In addition to the PN junction, various two-dimensional heterostructures have also appeared due to the diversity of p-type and n-type two-dimensional materials. However, due to the recombination of carriers during the charge transfer process between the two layers of materials, the open circuit voltage of the two-dimensional material heterojunction structure is much smaller than that of the two-dimensional materials that make up the heterojunction, generally not exceeding 0.3eV, and very few can reach 0.5eV. Compared with the heterojunction, the open circuit voltage of the two-dimensional material homojunction is usually larger, but due to the relatively small space charge area, the power conversion efficiency is lower. The current methods for preparing two-dimensional material homojunctions include electrostatic doping, elemental doping, chemical doping, etc. These methods are relatively complex and the doping level is usually difficult to control.

[0005] The two-dimensional material PN junctions constructed by the above methods are all single PN junctions. Therefore, the present invention uses the strong local field generated by the ferroelectric material to control the two-dimensional material, so that a continuous "P region N region P region N region" appears on the same two-dimensional material, thereby forming a series of two-dimensional material PN junction photovoltaic solar cells, and finally achieving the effect of doubling the open circuit voltage. This invention promotes the application of two-dimensional materials in solar cells. Summary of the invention

[0006] The present invention proposes a ferroelectric domain-defined series-connected two-dimensional photovoltaic cell and a preparation method thereof, thereby realizing the application of two-dimensional semiconductor series-connected photovoltaic cells.

[0007] The above invention introduces ferroelectric materials into transition metal chalcogenide two-dimensional semiconductor photovoltaic devices. The structure of the photovoltaic device is based on the ferroelectric field effect. The local electric field formed by ferroelectric polarization is used to adjust the carrier concentration of the two-dimensional material, so that an in-plane PNPN junction is formed on the same piece of two-dimensional material.

[0008] The present invention relates to a tandem two-dimensional photovoltaic cell defined by ferroelectric domains and a preparation method thereof, wherein the device structure is as follows from top to bottom:

[0009] - a ferroelectric functional layer 1,

[0010] -Metal electrode 2,

[0011] - Bipolar transition metal compound two-dimensional semiconductors 3,

[0012] - Silicon-on-insulator substrate 4.

[0013] The ferroelectric functional layer 1 is a polyvinylidene fluoride ferroelectric polymer film with a thickness of 60 nanometers;

[0014] The metal electrode 2 is a cubic metal electrode in which chromium is covered on a bipolar transition metal compound two-dimensional semiconductor and gold is covered on the chromium. The metal electrodes are arranged at both ends and in the middle of the bipolar transition metal compound two-dimensional semiconductor (3) respectively. The thickness of the chromium is 15 nanometers and the thickness of the gold is 25 nanometers.

[0015] The bipolar transition metal compound two-dimensional semiconductor 3 is a bipolar transition metal compound MoTe 2 , thickness 8-12 nm;

[0016] The surface of the insulating silicon substrate 4 is covered with a silicon substrate of 285 nanometers thick silicon dioxide.

[0017] The present invention relates to a ferroelectric domain-regulated MoTe 2 In-plane PNPN junction and preparation method, device preparation includes the following steps:

[0018] 1) Preparation of insulating silicon substrate

[0019] The insulating silicon substrate is a silicon substrate whose surface is covered with silicon dioxide with a thickness of 285 nanometers.

[0020] 2) Preparation and transfer of bipolar transition metal compound two-dimensional semiconductors

[0021] The bipolar transition metal compound two-dimensional semiconductor MoTe was synthesized by mechanical exfoliation. 2 Transfer to a silicon-in-insulator substrate.

[0022] 3) Metal electrode preparation

[0023] The metal electrode 3 is prepared by using ultraviolet lithography or electron beam exposure technology combined with thermal evaporation and stripping process. The electrode is composed of chromium and gold, with a thickness of 15 nanometers for chromium and a thickness of 25 nanometers for gold. The three prepared metal electrodes are respectively located at the two ends and the middle of the bipolar transition metal compound two-dimensional semiconductor (3), forming two parallel channels on the left and right.

[0024] 4) Preparation of ferroelectric functional layer

[0025] The polyvinylidene fluoride-based ferroelectric functional layer was prepared on the prepared device by spin coating, and annealed at 130°C for 2 hours to ensure the crystallization characteristics of the functional layer. The thickness of the polyvinylidene fluoride-based ferroelectric functional layer film was 60 nanometers.

[0026] 5) Polarization of ferroelectric functional layer using piezoelectric force microscopy

[0027] The piezoelectric force microscope is a microscope that uses a conductive probe to detect the amount of electro-induced deformation of a sample under an applied excitation voltage based on an atomic force microscope. The probe of the piezoelectric force microscope scans the sample in contact mode, and the voltage generated by the signal generator is applied between the piezoelectric force microscope probe and the sample electrode. The laser beam reflected by the back of the piezoelectric force microscope micro-cantilever is used to monitor the amount of electro-induced deformation. This invention uses the voltage applied to the sample by the tip of the piezoelectric force microscope to polarize P(VDF-TrFE). For 60 nanometer P(VDF-TrFE), the scanning voltage and scanning frequency are controlled to ±25V, and 1.5Hz is the most suitable. During the scanning process, a +25V scanning voltage is applied to the left side P (VDF-TrFE) of the first channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions on both sides are away from and point to the two-dimensional material respectively; similarly, a +25V scanning voltage is applied to the left side P (VDF-TrFE) of the second channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions on both sides are away from and point to the two-dimensional material respectively, and then the ferroelectric field is used to control the two-dimensional material to form an in-plane PNPN junction.

[0028] The advantages of the present invention are: the strong local field generated by the ferroelectric material with opposite polarization direction is used to regulate the internal carriers of the two-dimensional material to form an in-plane PNPN junction, and the open circuit voltage value is doubled. Different from the traditional back-gate field tube device, which requires an external gate voltage to adjust the Fermi energy level of the two-dimensional material to form electron or hole injection, the present invention polarizes the ferroelectric material through the tip of the piezoelectric force microscope, so that the polarization of both ends is upward and downward, and the strong local field formed by the residual polarization of the ferroelectric material is used to realize the in-plane PNPN junction on the same two-dimensional material. The residual polarization of the ferroelectric material can be stably maintained, and no external gate voltage is required during operation, which reduces energy consumption. And the spatial width of the ferroelectric domain is within 10 nanometers, which gets rid of the spatial size limitation of the gate electrode. In addition, the realization of the two-dimensional semiconductor PNPN junction often requires four materials to be superimposed together. This process is accompanied by cumbersome process processes such as transfer and degumming, which may cause the performance degradation of the device. The use of ferroelectric materials can realize the in-plane PNPN junction on the same two-dimensional material, which can avoid these processes from polluting the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Different bipolar transition metal chalcogenide two-dimensional semiconductors MoTe in three implementation cases 2 The thickness does not affect the final test, and the test data are basically consistent.

[0030] Figure 1 Ferroelectric domain-tuned MoTe 2 Schematic diagram of the working state of the series in-plane PN junction.

[0031] In the figure: 1 ferroelectric functional layer, 2 metal electrode, 3 bipolar transition metal chalcogenide two-dimensional semiconductor MoTe 2 , 4 insulating silicon substrate, 5 the tip of a piezoelectric force microscope that applies voltage to the surface of the ferroelectric functional layer for scanning.

[0032] Figure 2 Ferroelectric domain-tuned MoTe 2 Schematic diagram of the in-plane PNPN junction band structure.

[0033] Figure 3 It is the volt-ampere characteristic curve of a single PN junction and a PNPN junction of the device.

[0034] Figure 4 , Figure 5 Ferroelectric domain-tuned MoTe 2 The open circuit voltage-optical power relationship diagram and short circuit current-optical power relationship diagram of the in-plane PNPN junction. DETAILED DESCRIPTION

[0035] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings:

[0036] The present invention has developed a two-dimensional semiconductor photovoltaic device that introduces ferroelectric materials into transition metal chalcogenide compounds. The structure of the photovoltaic device is based on the ferroelectric field effect. The local electric field formed by ferroelectric polarization is used to adjust the carrier concentration of the two-dimensional material, so that an in-plane PNPN junction is formed on the same piece of two-dimensional material.

[0037] The specific steps for implementing Case 1 are as follows:

[0038] 1) Preparation of insulating silicon substrate

[0039] The insulating silicon substrate is a silicon substrate whose surface is covered with silicon dioxide with a thickness of 285 nanometers.

[0040] 2) Preparation and transfer of bipolar transition metal compound two-dimensional semiconductors

[0041] The 8-nanometer bipolar transition metal compound two-dimensional semiconductor MoTe was prepared by mechanical exfoliation. 2 Transfer to a silicon-in-insulator substrate.

[0042] 3) Metal electrode preparation

[0043] The metal electrode 3 is prepared by using ultraviolet lithography or electron beam exposure technology combined with thermal evaporation and stripping process. The electrode is composed of chromium and gold, with a thickness of 15 nanometers for chromium and a thickness of 25 nanometers for gold. The three prepared metal electrodes are respectively located at the two ends and the middle of the bipolar transition metal compound two-dimensional semiconductor (3), forming two parallel channels on the left and right.

[0044] 4) Preparation of ferroelectric functional layer

[0045] The polyvinylidene fluoride-based ferroelectric functional layer was prepared on the prepared device by spin coating, and annealed at 130°C for 2 hours to ensure the crystallization characteristics of the functional layer. The thickness of the polyvinylidene fluoride-based ferroelectric functional layer film was 60 nanometers.

[0046] 5) Polarization of ferroelectric functional layer using piezoelectric force microscopy

[0047] The piezoelectric force microscope is a microscope that uses a conductive probe to detect the amount of electro-induced deformation of a sample under an applied excitation voltage based on an atomic force microscope. The probe of the piezoelectric force microscope scans the sample in contact mode, and the voltage generated by the signal generator is applied between the piezoelectric force microscope probe and the sample electrode. The laser beam reflected by the back of the piezoelectric force microscope micro-cantilever is used to monitor the amount of electro-induced deformation. This invention uses the voltage applied to the sample by the tip of the piezoelectric force microscope to polarize P(VDF-TrFE). For 60 nanometer P(VDF-TrFE), the scanning voltage and scanning frequency are controlled to ±25V, and 1.5Hz is the most suitable. During the scanning process, a +25V scanning voltage is applied to the left side P (VDF-TrFE) of the first channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions on both sides are away from and point to the two-dimensional material respectively; similarly, a +25V scanning voltage is applied to the left side P (VDF-TrFE) of the second channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions on both sides are away from and point to the two-dimensional material respectively, and then the ferroelectric field is used to control the two-dimensional material to form an in-plane PNPN junction.

[0048] The specific steps for implementing Case 2 are as follows:

[0049] 1) Preparation of insulating silicon substrate

[0050] The insulating silicon substrate is a silicon substrate whose surface is covered with silicon dioxide with a thickness of 285 nanometers.

[0051] 2) Preparation and transfer of bipolar transition metal compound two-dimensional semiconductors

[0052] The 10-nanometer bipolar transition metal compound two-dimensional semiconductor MoTe was prepared by mechanical exfoliation. 2 Transfer to a silicon-in-insulator substrate.

[0053] 3) Metal electrode preparation

[0054] The metal electrode 3 is prepared by using ultraviolet lithography or electron beam exposure technology combined with thermal evaporation and stripping process. The electrode is composed of chromium and gold, with a thickness of 15 nanometers for chromium and a thickness of 25 nanometers for gold. The three prepared metal electrodes are respectively located at the two ends and the middle of the bipolar transition metal compound two-dimensional semiconductor (3), forming two parallel channels on the left and right.

[0055] 4) Preparation of ferroelectric functional layer

[0056] The polyvinylidene fluoride-based ferroelectric functional layer was prepared on the prepared device by spin coating, and annealed at 130°C for 2 hours to ensure the crystallization characteristics of the functional layer. The thickness of the polyvinylidene fluoride-based ferroelectric functional layer film was 60 nanometers.

[0057] 5) Polarization of ferroelectric functional layer using piezoelectric force microscopy

[0058] The piezoelectric force microscope is a microscope that uses a conductive probe to detect the amount of electro-induced deformation of a sample under an applied excitation voltage based on an atomic force microscope. The probe of the piezoelectric force microscope scans the sample in contact mode, and the voltage generated by the signal generator is applied between the piezoelectric force microscope probe and the sample electrode. The laser beam reflected by the back of the piezoelectric force microscope micro-cantilever is used to monitor the amount of electro-induced deformation. This invention uses the voltage applied to the sample by the tip of the piezoelectric force microscope to polarize P(VDF-TrFE). For 60 nanometer P(VDF-TrFE), the scanning voltage and scanning frequency are controlled to ±25V, and 1.5Hz is the most suitable. During the scanning process, a +25V scanning voltage is applied to the left side P (VDF-TrFE) of the first channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions on both sides are away from and point to the two-dimensional material respectively; similarly, a +25V scanning voltage is applied to the left side P (VDF-TrFE) of the second channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions on both sides are away from and point to the two-dimensional material respectively, and then the ferroelectric field is used to control the two-dimensional material to form an in-plane PNPN junction.

[0059] The specific steps for implementing Case 3 are as follows:

[0060] 1) Preparation of insulating silicon substrate

[0061] The insulating silicon substrate is a silicon substrate whose surface is covered with silicon dioxide with a thickness of 285 nanometers.

[0062] 2) Preparation and transfer of bipolar transition metal compound two-dimensional semiconductors

[0063] A 12-nanometer bipolar transition metal compound two-dimensional semiconductor MoTe was prepared by mechanical exfoliation. 2 Transfer to a silicon-in-insulator substrate.

[0064] 3) Metal electrode preparation

[0065] The metal electrode 3 is prepared by using ultraviolet lithography or electron beam exposure technology combined with thermal evaporation and stripping process. The electrode is composed of chromium and gold, with a thickness of 15 nanometers for chromium and a thickness of 25 nanometers for gold. The three prepared metal electrodes are respectively located at the two ends and the middle of the bipolar transition metal compound two-dimensional semiconductor (3), forming two parallel channels on the left and right.

[0066] 4) Preparation of ferroelectric functional layer

[0067] The polyvinylidene fluoride-based ferroelectric functional layer was prepared on the prepared device by spin coating, and annealed at 130°C for 2 hours to ensure the crystallization characteristics of the functional layer. The thickness of the polyvinylidene fluoride-based ferroelectric functional layer film was 60 nanometers.

[0068] 5) Polarization of ferroelectric functional layer using piezoelectric force microscopy

[0069] The piezoelectric force microscope is a microscope that uses a conductive probe to detect the amount of electro-induced deformation of a sample under an applied excitation voltage based on an atomic force microscope. The probe of the piezoelectric force microscope scans the sample in contact mode, and the voltage generated by the signal generator is applied between the piezoelectric force microscope probe and the sample electrode. The laser beam reflected by the back of the piezoelectric force microscope micro-cantilever is used to monitor the amount of electro-induced deformation. This invention uses the voltage applied to the sample by the tip of the piezoelectric force microscope to polarize P(VDF-TrFE). For 60 nanometer P(VDF-TrFE), the scanning voltage and scanning frequency are controlled to ±25V, and 1.5Hz is the most suitable. During the scanning process, a +25V scanning voltage is applied to the left side P (VDF-TrFE) of the first channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions on both sides are away from and point to the two-dimensional material respectively; similarly, a +25V scanning voltage is applied to the left side P (VDF-TrFE) of the second channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions on both sides are away from and point to the two-dimensional material respectively, and then the ferroelectric field is used to control the two-dimensional material to form an in-plane PNPN junction.

[0070] The present invention relates to a ferroelectric domain-regulated MoTe 2 In-plane PNPN junction and preparation method. The structural device has the characteristics of simple preparation, no limitation on the physical size of the gate electrode, and doubled open circuit voltage, which accelerates the application of two-dimensional semiconductor materials in the field of solar cells.

Claims

1. A tandem two-dimensional photovoltaic cell defined by ferroelectric domains, comprising a ferroelectric functional layer (1), a metal electrode (2), a bipolar transition metal compound two-dimensional semiconductor (3), and an insulating silicon substrate (4), characterized in that: The structure of the tandem two-dimensional photovoltaic cell is, from top to bottom, a ferroelectric functional layer (1), a metal electrode (2), a bipolar transition metal compound two-dimensional semiconductor (3), and an insulating silicon substrate (4), wherein: The ferroelectric functional layer (1) is a polyvinylidene fluoride-based ferroelectric polymer film with a thickness of 60 nanometers; The metal electrodes (2) are three metal electrodes in the shape of cubes, with chromium covering the bipolar transition metal compound two-dimensional semiconductor and gold covering the chromium, which are respectively arranged at the two ends and the middle of the bipolar transition metal compound two-dimensional semiconductor (3), with the thickness of chromium being 15 nanometers and the thickness of gold being 25 nanometers; The bipolar transition metal compound two-dimensional semiconductor (3) is a bipolar transition metal compound MoTe2, and has a thickness of 8-12 nanometers; The insulating silicon substrate (4) is a silicon substrate whose surface is covered with silicon dioxide with a thickness of 285 nanometers; The method for preparing the ferroelectric domain defined tandem two-dimensional photovoltaic cell comprises the following steps: 1) using a mechanical exfoliation transfer method to transfer a bipolar transition metal compound two-dimensional semiconductor (3) to a surface of an insulating silicon substrate (4); 2) using ultraviolet lithography or electron beam exposure technology, combined with thermal evaporation and lift-off processes, to prepare three metal electrodes (2), and the three metal electrodes are respectively located at the two ends and the middle of the bipolar transition metal compound two-dimensional semiconductor (3), forming two parallel channels on the left and right; 3) preparing the ferroelectric functional layer (1) by spin coating, and annealing at 130° C. for 2 hours to ensure the crystallinity of the functional layer; 4) polarizing the ferroelectric functional layer using a piezoelectric force microscope, specifically, using the following method: polarizing P(VDF-TrFE) by applying a voltage to the ferroelectric functional layer (1) using the tip of a piezoelectric force microscope, wherein the scanning voltage and scanning frequency are controlled to be ±25V and 1.5Hz, respectively. During the scanning process, a +25V scanning voltage is applied to the left side of the P(VDF-TrFE) of the first channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions of the two sides are opposite, and the polarization directions point to and away from the two-dimensional material, respectively. Similarly, a +25V scanning voltage is applied to the left side of the P(VDF-TrFE) of the second channel from the left of the material, and a -25V scanning voltage is applied to the right side, so that the polarization directions of the two sides are away from and toward the two-dimensional material, respectively, and then the ferroelectric field is used to control the two-dimensional material to form an in-plane PNPN junction.

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