Semitransparent photovoltaic device designed based on surface light reflection principle

Abstract

The invention discloses a semitransparent photovoltaic device designed based on a surface light reflection principle, which comprises at least one group of basic units, each basic unit comprises a solar cell and a reflecting surface, a reflecting layer is arranged on the light facing surface of each solar cell, and the reflecting layers are used for reflecting part or all visible light and transmitting part or all invisible light. The included angle theta between the normal direction of the light-facing surface of the solar cell and the incident light meets 0 lt; theta < lt >; the reflecting surface is used for partially or completely reflecting the light reflected by the reflecting layer; the semi-transparent photovoltaic device enables incident light to pass through at least two times of light reflection in the semi-transparent photovoltaic device to achieve equivalent light transmission. According to the semitransparent photovoltaic device structure, all solar cells can be prepared into the semitransparent photovoltaic device with excellent properties, the semitransparent photovoltaic device has excellent photoelectric properties and semitransparent properties, the preparation process is simple, the cost is low, and the semitransparent photovoltaic device structure has wide application prospects.

Description

Technical Field

[0001] The invention relates to the field of semi-transparent photovoltaic devices, and in particular to a semi-transparent photovoltaic device designed based on the principle of surface light reflection. Background Art

[0002] In recent years, solar cells, as an important component of clean and renewable energy, have been widely used in many fields, from home residences to industrial facilities. As the global demand for renewable energy continues to increase, traditional photovoltaic technology is gradually unable to meet the increasingly diverse needs in terms of application scenarios and forms.

[0003] Therefore, how to improve the functionality and applicability of photovoltaic devices, especially to achieve high-efficiency photoelectric conversion in a limited space, has become an important issue facing researchers and engineers.

[0004] Semitransparent Photovoltaics (ST-PV) is a new type of photovoltaic technology that can transmit visible light and absorb non-visible light (such as infrared and ultraviolet rays) at the same time. With this unique feature, semitransparent photovoltaic devices have shown great application potential in building integrated photovoltaics (BIPV), automotive windows, agricultural greenhouses, and wearable devices. In the field of building integrated photovoltaics, semitransparent photovoltaics can not only replace traditional windows, but also effectively convert solar energy without affecting lighting, providing green energy support for buildings. Therefore, how to design and optimize the performance of semitransparent photovoltaic devices has become an important research direction in the development of photovoltaic technology.

[0005] At present, the design of semi-transparent photovoltaic devices mostly relies on the selective regulation of light transmission and light absorption. Traditional semi-transparent photovoltaic devices usually use a transparent conductive oxide layer to ensure light transmission and current conduction. However, this design based on the transmission principle limits the photoelectric conversion efficiency of photovoltaic devices.

[0006] Since semi-transparent photovoltaic devices need to achieve effective light absorption while ensuring high visible light transmittance, their design faces two major challenges: 1. Excessive non-visible light transmission will reduce the effective absorption of photovoltaic materials; 2. The light absorption range of existing photovoltaic materials often does not match the visible light band, thus affecting light utilization.

[0007] Although semi-transparent photovoltaic devices have significant application prospects, existing technologies still face some limitations. For example, many high-efficiency photovoltaic technologies (such as silicon-based photovoltaics, cadmium telluride, copper indium gallium selenide, etc.) are difficult to prepare into semi-transparent photovoltaic devices due to their structural characteristics.

[0008] In addition, although the current mainstream organic photovoltaic devices can achieve visible light transmission and non-visible light absorption conversion, there are still difficulties in balancing the photoelectric conversion efficiency and visible light transmittance. This balance problem leads to the fact that the light utilization rate of semi-transparent photovoltaic technology can reach 20% in theory, but in practical applications, the highest efficiency is usually only about 6%. Therefore, the technical development of semi-transparent photovoltaic devices is still relatively lagging behind. Summary of the invention

[0009] The present invention provides a semi-transparent photovoltaic device designed based on the principle of surface light reflection. The present invention provides a type of photovoltaic device structure and principle with excellent photoelectric conversion efficiency and excellent semi-transparent properties. Different from traditional semi-transparent devices, the device of the present invention mainly achieves a semi-transparent effect through two or more light reflection processes, and the working mechanism is similar to the principle of a periscope. The semi-transparent photovoltaic device includes a solar cell and a surface reflection layer, and by controlling the structure of the device surface reflection layer, such as the material, number of layers, thickness, incident angle, etc., its surface light reflection characteristics or semi-transparent properties (the spectrum after two or more reflections is the transmission spectrum of the semi-transparent photovoltaic) and photoelectric conversion efficiency can be effectively adjusted. The present invention can also prepare a semi-transparent photovoltaic device by adjusting the angle between different cells (solar cells). The semi-transparent photovoltaic device structure of the present invention can prepare all solar cells into semi-transparent photovoltaic devices with excellent properties. It not only has excellent photoelectric performance and semi-transparent properties, but also has a simple preparation process, low cost, and broad application prospects.

[0010] A semi-transparent photovoltaic device designed based on the principle of surface light reflection includes at least one group of basic units, wherein the basic unit includes a solar cell and a reflective surface, a reflective layer is provided on the light-facing surface of the solar cell, the reflective layer is used to reflect part or all of the visible light and transmit part or all of the invisible light, the angle θ between the normal direction of the light-facing surface of the solar cell and the incident light satisfies: 0<θ<90°, and the reflective surface is used to partially or completely reflect the light reflected by the reflective layer.

[0011] The semi-transparent photovoltaic device utilizes the working principle of a periscope, so that incident light can be reflected at least twice to achieve equivalent light transmission.

[0012] In the present invention, the material composition of the reflective surface may include silver, etc., and any material that can realize the function of partially or completely reflecting the light reflected by the reflective layer may be used.

[0013] In the present invention, the reflective layer can be deposited on the solar cell electrode or the transparent substrate, or the solar cell can be prepared on the reflective layer.

[0014] The present invention can realize light transmission from one side of the integrated device to the other side through integrated structural design. In some embodiments, the semi-transparent photovoltaic device may include multiple groups of basic units. Further, the reflective surface in one group of basic units may be located on the solar cell in another group of basic units.

[0015] The solar cell described in the present invention can be homemade or a commercial product can be used, including but not limited to one or more combinations of organic solar cells, perovskite solar cells, silicon solar cells, cadmium telluride solar cells, and copper indium gallium selenide solar cells.

[0016] The material composition of the reflective layer of the present invention may include but is not limited to one or more combinations of metals, oxides, fluorides, and polymer materials. Further, the material composition of the reflective layer of the present invention may include but is not limited to one or more combinations of tellurium oxide, magnesium fluoride, titanium oxide, and silicon oxide. In some embodiments, part or all of the material of the reflective layer has the property of selectively reflecting visible light.

[0017] By adjusting the material, number of layers, thickness of each layer in the reflective layer and the geometric optical structure between devices (solar cells), the reflective spectrum can be effectively controlled. In some embodiments, the main reflective band of the reflective spectrum is the visible light range.

[0018] In some embodiments, the reflective layer may be composed of tellurium oxide and magnesium fluoride. Furthermore, in the reflective layer, tellurium dioxide and magnesium fluoride may be alternately arranged.

[0019] In some embodiments, the reflective layer may be a three-layer structure arranged in sequence, wherein the first layer is 100 nm thick tellurium dioxide (TeO2), the second layer is 107 nm thick magnesium fluoride (MgF2), and the third layer is 70 nm thick tellurium dioxide, and the first layer is closest to the solar cell.

[0020] In some embodiments, the reflective layer may be a four-layer structure arranged in sequence, wherein the first layer is 70 nm thick magnesium fluoride, the second layer is 70 nm thick tellurium dioxide, the third layer is 107 nm thick magnesium fluoride, and the fourth layer is 70 nm thick tellurium dioxide, and the first layer is closest to the solar cell.

[0021] In some embodiments, the reflective layer may be a five-layer structure arranged in sequence, wherein the first layer is 100 nm thick tellurium dioxide, the second layer is 107 nm thick magnesium fluoride, the third layer is 70 nm thick tellurium dioxide, the fourth layer is 107 nm thick magnesium fluoride, and the fifth layer is 70 nm thick tellurium dioxide, and the first layer is closest to the solar cell.

[0022] In some embodiments, the reflective layer may be a six-layer structure arranged in sequence, wherein the first layer is 70 nm thick magnesium fluoride, the second layer is 70 nm thick tellurium dioxide, the third layer is 107 nm thick magnesium fluoride, the fourth layer is 70 nm thick tellurium dioxide, the fifth layer is 107 nm thick magnesium fluoride, and the sixth layer is 70 nm thick tellurium dioxide, and the first layer is closest to the solar cell.

[0023] In some embodiments, the reflective layer may be composed of silicon oxide and titanium oxide.

[0024] In some embodiments, the reflective layer may be a 46-layer structure arranged in sequence, wherein the first layer is closest to the solar cell, and the material composition and thickness of each layer are as follows: .

[0025] Compared with the prior art, the present invention has the following beneficial effects: The semi-transparent (integrated) photovoltaic device structure designed by the present invention based on the surface reflection principle breaks the limitation of traditional semi-transparent photovoltaic devices on opaque photovoltaic devices. On the one hand, all solar cells (including silicon-based cells that were originally difficult to achieve semi-transparent structures) can achieve spectral selective semi-transparency and are no longer affected by light transmission and transparent back electrodes; on the other hand, the structure can achieve a better balance between selective light transmission and high photoelectric conversion efficiency, thereby further improving the performance of semi-transparent photovoltaic devices and making them easier to integrate with buildings. Therefore, the present invention not only adds more possibilities to semi-transparent photovoltaic devices, but also greatly promotes the development and industrial application of semi-transparent photovoltaic technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of a semi-transparent photovoltaic device designed based on the principle of surface light reflection to achieve semi-transparency according to the present invention.

[0027] Figure 2 Schematic diagram of the organic photovoltaic device and the corresponding reflective layer structure according to Examples 1-4 of the present invention.

[0028] Figure 3 : is the structural formula diagram of PCP-2F-Li used in the embodiments of the present invention, wherein n is a positive integer.

[0029] Figure 4 The photovoltaic characteristic curve diagram of the solar cell provided with a reflective layer in the semi-transparent photovoltaic device of Examples 1-4 of the present invention.

[0030] Figure 5 EQE spectra and reflectivity spectra of solar cells provided with a reflective layer in the semi-transparent photovoltaic devices of Examples 1-4 of the present invention.

[0031] Figure 6 This is a reflectivity spectrum diagram of the reflective layer A-layer in Example 5 of the present invention.

[0032] Figure 7 This is a photovoltaic characteristic curve diagram of a solar cell with a reflective layer in the silicon photovoltaic and its semi-transparent photovoltaic device of Example 5 of the present invention, in which w / o represents an initial cell without a reflective layer.

[0033] Figure 8 EQE spectra of the silicon photovoltaic and the solar cell with a reflective layer in its semi-transparent photovoltaic device according to Example 5 of the present invention.

[0034] Fig. 9 This is a photovoltaic characteristic curve diagram of a solar cell provided with a reflective layer in the photovoltaic device involved in Examples 6 to 9 of the present invention and its semi-transparent photovoltaic device, wherein w / o represents an initial cell without a reflective layer.

[0035] Fig.10 This is a graph of external quantum efficiency (EQE) of a solar cell provided with a reflective layer in the photovoltaic device and the semi-transparent photovoltaic device according to Examples 6 to 9 of the present invention, wherein w / o represents an initial cell without a reflective layer. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0037] Figure 1 The schematic diagram of the photovoltaic device (integrated) structure designed based on the principle of surface light reflection of the present invention is shown, which includes solar cells and reflective layers. The structure of the reflective layer on the surface of the device is controlled. By designing the number of layers, thickness, etc., the translucent properties and photoelectric conversion efficiency can be effectively adjusted. After the solar cells are integrated, translucency can be achieved by adjusting the angle.

[0038] The reflective layer can be deposited on the solar cell electrode or transparent substrate, or the solar cell can be prepared on the reflective layer, and the direction of the reflective layer is the direction of light incident on the solar cell. Through the integrated structure design, light can be transmitted from one side of the integrated device to the other side.

[0039] Solar cells include all solar cells such as organic solar cells, perovskite solar cells and silicon solar cells.

[0040] The reflective layer can be a material that selectively reflects visible light. As one of the preferred materials for the emitting layer, tellurium dioxide and magnesium fluoride are alternately evaporated. By adjusting the number and thickness of each layer, the reflective spectrum can be effectively controlled. The main reflection band of the reflective spectrum is the visible light range.

[0041] The semi-transparent photovoltaic device structure of the present invention is different from the currently commonly used semi-transparent photovoltaic devices designed based on the principle of transmitted light. This structure can make any photovoltaic device semi-transparent and is no longer affected by light transmission and the transparent back electrode. While ensuring that more light passes through one side of the integrated device to the other side, it ensures that it has excellent photoelectric conversion efficiency and improves its light utilization rate. Example 1

[0042] See also Figure 2 The preparation process of the organic photovoltaic device and the corresponding reflective layer thereon is as follows: the transparent glass substrate is ultrasonically washed with detergent, isopropanol, ethanol, and acetone for 15 minutes in sequence, and after UV-ozone treatment, 100 nm silver is deposited on the transparent glass substrate as the anode. Subsequently, a 10 nm PCP-2F-Li film and a 30 nm poly (3,4-ethylenedioxythiophene): polystyrene sulfonate) (PEDOT:PSS) film are spin-coated as the hole transport layer. Among them, PCP-2F-Li is an interfacial layer that can effectively connect the silver electrode and the hole transport layer of PEDOT:PSS. Its structure is as follows Figure 3 As shown. PM6 was used as the donor material, L8-BO:BTP-eC9 was used as the acceptor material, and a 16 mg / mL solution was prepared at a mass ratio of 1:0.6:0.6. A 100 nm active layer was spin-coated. PDINN was used as the electron transport layer, and 10 nm was spin-coated. 10 nm silver was evaporated as the cathode.

[0043] The reflective layer is set on the cathode and consists of three layers (3-layer). From bottom to top, 100 nm tellurium dioxide, 107 nm magnesium fluoride, and 70 nm tellurium dioxide are evaporated in sequence to obtain the reflective layer. The photoelectric conversion efficiency of the device at different angles (this angle refers to the angle θ between the normal direction of the reflective layer and the incident light, the same below) is: 0 degrees is 11.35%, 30 degrees is 10.84%, 45 degrees is 10.78%, 60 degrees is 10.58%, the average visible light reflectivity at 0 degrees is 45.0%, and the average visible light utilization efficiency (LUE) at 0 degrees is 5.11%. The photovoltaic characteristic curve test results are as follows Figure 4 The external quantum efficiency test (EQE) and reflectivity test results are shown in Figure 5 shown. Example 2

[0044] The only difference from Example 1 is the composition of the reflective layer, and the rest are the same.

[0045] The reflective layer of this embodiment is composed of four layers (4-layer), and 70 nm magnesium fluoride, 70 nm tellurium dioxide, 107 nm magnesium fluoride, and 70 nm tellurium dioxide are evaporated from bottom to top to obtain the reflective layer. The photoelectric conversion efficiency of the device at different angles is: 10.92% at 0 degrees, 10.65% at 30 degrees, 10.45% at 45 degrees, and 10.32% at 60 degrees. The average visible light reflectivity at 0 degrees is 48.1%, and the average visible light utilization efficiency (LUE) at 0 degrees is 5.25%. The photovoltaic characteristic curve test results are shown in the figure. Figure 4 As shown, the EQE test and reflectivity test results are as follows Figure 5 shown. Example 3

[0046] The only difference from Example 1 is the composition of the reflective layer, and the rest are the same.

[0047] The reflective layer of this embodiment is composed of 5 layers (5-layer), and 100 nm tellurium dioxide, 107 nm magnesium fluoride, 70 nm tellurium dioxide, 107 nm magnesium fluoride, and 70 nm tellurium dioxide are evaporated from bottom to top to obtain the reflective layer. The photoelectric conversion efficiency of the device at different angles is: 7.89% at 0 degrees, 7.43% at 30 degrees, 7.58% at 45 degrees, and 7.56% at 60 degrees. The average visible light reflectivity at 0 degrees is 54.4%, and the average visible light utilization efficiency (LUE) at 0 degrees is 4.29%. The photovoltaic characteristic curve test results are shown in the figure. Figure 4 As shown, the EQE test and reflectivity test results are as follows Figure 5 shown. Example 4

[0048] The only difference from Example 1 is the composition of the reflective layer, and the rest are the same.

[0049] The reflective layer of this embodiment is composed of 6 layers (6-layer), which are deposited from bottom to top in order of 70 nm magnesium fluoride, 70 nm tellurium dioxide, 107 nm magnesium fluoride, 70 nm tellurium dioxide, 107 nm magnesium fluoride, and 70 nm tellurium dioxide to obtain the reflective layer. The photoelectric conversion efficiency of the device at different angles is: 5.34% at 0 degrees, 5.04% at 30 degrees, 5.11% at 45 degrees, and 5.37% at 60 degrees. The average visible light reflectivity at 0 degrees is 58.6%, and the average visible light utilization efficiency (LUE) at 0 degrees is 3.31%. The photovoltaic characteristic curve test results are shown in the figure. Figure 4 As shown, the EQE test and reflectivity test results are as follows Figure 5 shown. Example 5

[0050] By sputtering a reflective layer on a commercial silicon cell (Si-PV efficiency of 26.54%) and setting a reflective surface, a double-surface reflective semi-transparent device based on silicon photovoltaics can be obtained, wherein the reflective layer is a photonic crystal layer (A-layer) composed of alternating titanium dioxide and silicon dioxide. Its specific composition is shown in Table 1, where the first layer is closest to the cell and the reflection spectrum is shown in Figure 6 As shown, the photoelectric conversion efficiency of the device at different angles is: 13.32% at 0 degrees, 13.48% at 30 degrees, 14.40% at 45 degrees, and 14.13% at 60 degrees. The average visible light reflectivity at 0 degrees is 94.65%, and the average visible light utilization efficiency (LUE) at 0 degrees is 12.61%. The photovoltaic characteristic curve test results are shown in Figure 1. Figure 7 As shown, the EQE test results are as follows Figure 8 shown.

[0051] Table 1

[0052] Example 6 By setting a reflective surface on a commercial copper indium gallium selenide cell (CIGS efficiency is 17.90%) and sputtering the same reflective layer (A-layer) in Example 5, a double-surface reflective semi-transparent device based on CIGS photovoltaic can be obtained. The photoelectric conversion efficiency of the device at 0 degrees is 8.78%, the average visible light reflectivity at 0 degrees is 94.65%, and the average visible light utilization efficiency (LUE) at 0 degrees is 8.31%. The photovoltaic characteristic curve test results are shown in Figure 2. Fig. 9 As shown, the EQE test results are as follows Fig.10 shown. Example 7

[0053] By setting a reflective surface on an organic photovoltaic device (OPV efficiency of 19.30%) and sputtering the same reflective layer (A-layer) in Example 5, an OPV-based double-surface reflective semi-transparent device can be obtained. The device has a photoelectric conversion efficiency of 6.90% at 0 degrees, an average visible light reflectivity of 94.65% at 0 degrees, and a LUE of 6.53% at 0 degrees. The photovoltaic characteristic curve test results are shown in Fig. 9 As shown, the EQE test results are as follows Fig.10 shown. Example 8

[0054] By setting a reflective surface on a commercial cadmium telluride cell (CdTe-PV efficiency is 18.06%) and sputtering the same reflective layer (A-layer) in Example 5, a double-surface reflective semi-transparent device based on cadmium telluride photovoltaics can be obtained. The photoelectric conversion efficiency of the device at 0 degrees is 8.86%, the average visible light reflectivity at 0 degrees is 94.65%, and the LUE at 0 degrees is 8.39%. The photovoltaic characteristic curve test results are shown in Fig. 9 As shown, the EQE test results are as follows Fig.10 shown. Example 9

[0055] By setting a reflective surface on the perovskite cell (Perovskite efficiency is 25.40%) and sputtering the same reflective layer (A-layer) in Example 5, a double-surface reflective semi-transparent device based on perovskite photovoltaics can be obtained. The photoelectric conversion efficiency of the device at 0 degrees is 3.97%, the average visible light reflectivity at 0 degrees is 94.65%, and the LUE at 0 degrees is 3.76%. The photovoltaic characteristic curve test results are shown in Fig. 9 As shown, the EQE test results are as follows Fig.10 shown.

[0056] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A semi-transparent photovoltaic device designed based on the principle of surface light reflection, characterized in that: It comprises at least one group of basic units, wherein the basic unit comprises a solar cell and a reflecting surface, a reflecting layer is arranged on the light-facing surface of the solar cell, the reflecting layer is used to reflect part or all of the visible light and transmit part or all of the invisible light, the angle θ between the normal direction of the light-facing surface of the solar cell and the incident light satisfies: 0<θ<90°, the reflecting surface is used to partially or completely reflect the light reflected by the reflecting layer; the semi-transparent photovoltaic device enables the incident light to undergo at least two light reflections therein to achieve equivalent light transmission.

2. The semi-transparent photovoltaic device according to claim 1, characterized in that: The semi-transparent photovoltaic device comprises a plurality of groups of basic units, wherein the reflective surface in one group of basic units is located on the solar cells in another group of basic units.

3. The semi-transparent photovoltaic device according to claim 1, characterized in that: The solar cell includes one or more combinations of organic solar cells, perovskite solar cells, silicon solar cells, cadmium telluride solar cells, and copper indium gallium selenide solar cells.

4. The semi-transparent photovoltaic device according to claim 1, characterized in that: The material composition of the reflective layer includes one or more combinations of metals, oxides, fluorides, and polymer materials.

5. The semi-transparent photovoltaic device according to claim 1, characterized in that: The material composition of the reflective layer includes one or more combinations of tellurium oxide, magnesium fluoride, titanium oxide, and silicon oxide.

6. The semi-transparent photovoltaic device according to claim 1, characterized in that: The reflective layer is composed of tellurium oxide and magnesium fluoride, and tellurium dioxide and magnesium fluoride are arranged alternately; The reflective layer is a three-layer structure arranged in sequence, wherein the first layer is 100 nm thick tellurium dioxide, the second layer is 107 nm thick magnesium fluoride, and the third layer is 70 nm thick tellurium dioxide, and the first layer is closest to the solar cell.

7. The semi-transparent photovoltaic device according to claim 1, characterized in that: The reflective layer is composed of tellurium oxide and magnesium fluoride, and tellurium dioxide and magnesium fluoride are arranged alternately; The reflective layer is a four-layer structure arranged in sequence, wherein the first layer is 70 nm thick magnesium fluoride, the second layer is 70 nm thick tellurium dioxide, the third layer is 107 nm thick magnesium fluoride, and the fourth layer is 70 nm thick tellurium dioxide, and the first layer is closest to the solar cell.

8. The semi-transparent photovoltaic device according to claim 1, characterized in that: The reflective layer is composed of tellurium oxide and magnesium fluoride, and tellurium dioxide and magnesium fluoride are arranged alternately; The reflective layer is a five-layer structure arranged in sequence, wherein the first layer is 100 nm thick tellurium dioxide, the second layer is 107 nm thick magnesium fluoride, the third layer is 70 nm thick tellurium dioxide, the fourth layer is 107 nm thick magnesium fluoride, and the fifth layer is 70 nm thick tellurium dioxide, and the first layer is closest to the solar cell.

9. The semi-transparent photovoltaic device according to claim 1, characterized in that: The reflective layer is composed of tellurium oxide and magnesium fluoride, and tellurium dioxide and magnesium fluoride are arranged alternately; The reflective layer is a six-layer structure arranged in sequence, wherein the first layer is 70 nm thick magnesium fluoride, the second layer is 70 nm thick tellurium dioxide, the third layer is 107 nm thick magnesium fluoride, the fourth layer is 70 nm thick tellurium dioxide, the fifth layer is 107 nm thick magnesium fluoride, and the sixth layer is 70 nm thick tellurium dioxide, and the first layer is closest to the solar cell.

10. The semi-transparent photovoltaic device according to claim 1, characterized in that: The reflective layer is composed of silicon oxide and titanium oxide, and has a 46-layer structure arranged in sequence, wherein the first layer is closest to the solar cell, and the material composition and thickness of each layer are as follows: 。

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