Patent Publication Number: US-2019172963-A1

Title: Solar cell sheet and preparation method thereof, solar cell string and photovoltaic module

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims foreign priority benefits under 35 U.S.C. § 119(a)-(d) or 35 U.S.C. § 365(b) to Chinese Patent Application No. 201711268793.5, filed Dec. 5, 2017, titled “Solar cell sheet and preparation method thereof, solar cell string and photovoltaic module”, and Chinese Patent Application No. 201721672980.5, filed Dec. 5, 2017, titled “Double-sided power generation solar cell sheet, cell string and double-sided power generation photovoltaic module”, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to the technical field of solar energy, and in particular, relates to a solar cell sheet and a preparation method thereof, a solar cell string and a photovoltaic module. 
     BACKGROUND 
     With the development of solar cell technology, heterojunction solar cell has become one of the mainstream solar cells with its high efficiency and high stability. According to different installation methods and installation environments, the actual outdoor power generation of the heterojunction solar cells is 15%-30% higher than the actual outdoor power generation of conventional crystalline silicon cell. An important indicator for evaluating the performance of the heterojunction solar cells is the short-circuit current density Jsc. The larger the short-circuit current density Jsc is, the higher the efficiency of the heterojunction solar cell is. 
     SUMMARY 
     The first aspect of the present disclosure provides a solar cell sheet, the solar cell sheet includes: a conductive connection member; and a first electrode, a first transparent conductive layer, a first doped layer of a first conductivity type, a first passivation layer, a monocrystalline silicon wafer, a second passivation layer, a second doped layer of a second conductivity type, a second transparent conductive layer, and a second electrode arranged in an order from top to bottom, one end of the conductive connection member is electrically connected to the first electrode, the other end of the conductive connection member extends to a side of the second transparent conductive layer adjacent to the second electrode, and the conductive connection member is insulated from the second transparent conductive layer and the second electrode. 
     The second aspect of the present disclosure further provides a method for preparing a solar cell sheet, and the method for preparing the solar cell sheet includes: 
     providing a first through hole in a monocrystalline silicon wafer, the monocrystalline silicon wafer comprising first and second surfaces which are opposite; 
     performing a texturing operation and a cleaning operation on both of the first and the second surfaces; 
     forming a first passivation layer and a first doped layer on the first surface sequentially, and forming a second passivation layer and a second doped layer on the second surface sequentially; 
     forming a first transparent conductive layer on a surface of the first doped layer away from the first passivation layer, and forming a second transparent layer on the surface of the second doped layer away from the second passivation layer; and 
     preparing a first electrode on a surface of the first transparent conductive layer away from the first doped layer, preparing a second electrode on a surface of the second transparent conductive layer away from the second doped layer, and preparing a conductive connection member located in the first through hole when preparing the first electrode or preparing the second electrode, such that one end of the conductive connection member is connected to the first electrode, and the other end of the conductive connection member extends to a side of the second transparent conductive layer adjacent to the second electrode. 
     A third aspect of the present disclosure further provides a solar cell string, including: a plurality of the solar cell sheets, the plurality of solar cell sheets are electrically connected together. 
     The fourth aspect of the present disclosure further provides a photovoltaic module, including a front plate, a first bonding layer, a solar cell string, a second bonding layer, and a backing plate in an order from top to bottom; wherein the solar cell string is the above solar cell string. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural schematic diagram of a solar cell sheet according to some embodiments of the present disclosure. 
         FIG. 2  is a schematic diagram of a cross section structure of a first solar cell sheet according to some embodiments of the present disclosure. 
         FIG. 3  is a schematic diagram of a cross section structure of a second solar cell sheet according to some embodiments of the present disclosure. 
         FIG. 4  is a schematic diagram of a cross section structure of a third solar cell sheet according to some embodiments of the present disclosure. 
         FIG. 5  is a structural schematic diagram of a through hole provided by a solar cell sheet according to some embodiments of the present disclosure. 
         FIG. 6  is a structural schematic diagram of a solar cell string according to some embodiments of the present disclosure. 
         FIG. 7  is a structural schematic diagram of a solar cell string according to some embodiments of the present disclosure. 
         FIG. 8  is a structural schematic diagram of a photovoltaic module according to some embodiments of the present disclosure. 
         FIG. 9  is a first flowchart of a method for preparing a solar cell sheet according to some embodiments of the present disclosure. 
         FIG. 10  is a second flowchart of a method for preparing a solar cell sheet according to some embodiments of the present disclosure. 
         FIG. 11  is a third flowchart of a method for preparing a solar cell sheet according to some embodiments of the present disclosure. 
         FIG. 12  is a flow chart showing the preparation method of the step  5  in  FIG. 9  to  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments of the present disclosure are described in detail below, and the examples of the embodiments are illustrated in the drawings, wherein the same or similar reference numerals are used to refer to the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are intended to be illustrative and explain the present disclosure only, and are not to be construed as limiting. 
     In the related art, the heterojunction solar cell has the characteristic of double-sided power generation. Therefore, both electrodes on two opposite surfaces of the heterojunction solar cell include a plurality of fine gate lines and a main gate line which are spaced apart. Since the main gate line blocks a part of a light receiving area of the heterojunction solar cell, the short-circuit current density of the heterojunction solar cell is reduced; accordingly, the photoelectric conversion efficiency of the heterojunction solar cell is reduced. The main gate line is made of silver material. Therefore, when the main gate line is made of a large amount of silver material, the cost of preparing the main gate line is very high. 
     In addition, the existing solar cell sheet cooperates with a special back plate integrated with positive and negative electrodes by a Metal Wrap Through (MWT) back contact technology to achieve an interconnection between two adjacent solar cells. However, since the special back plate integrated with the positive and negative electrodes is non-transparent, when the back plate of the solar cell is the special back plate integrated with positive and negative electrodes, the solar cell cannot realize the double-sided power generation function. Moreover, since the special back plate integrated with positive and negative electrodes is generally expensive, it is not conducive to the control of industrialization costs. 
     As shown in  FIG. 1 , in view of the above problems, some embodiments of the present disclosure provide a solar cell sheet. Compared with the heterojunction solar cell disclosed in the related art, the solar cell sheet has a relatively large light-receiving surface area, so that the short-circuit current density of the solar cell is higher than that of the heterojunction solar cell disclosed in the related art. Since the short-circuit current density of the solar cell sheet is higher than the short-circuit current density of the heterojunction solar cell disclosed in the related art, the photoelectric conversion efficiency of the solar cell sheet is high with respect to the photoelectric conversion efficiency of the heterojunction solar cell disclosed in the related art. 
     In conjunction with  FIG. 1  to  FIG. 4 , a solar cell sheet  100  provided by some embodiments of the present disclosure includes: a conductive connection member  102 ; and a first electrode  10 , a first transparent conductive layer  20 , a first doped layer  30  of a first conductive type, a first passivation layer  40 , a monocrystalline silicon wafer  50 , a second passivation layer  60 , a second doped layer  70  of a second conductive type, a second transparent conductive layer  80 , and a second electrode  90  arranged from top to bottom for one time. One end of the conductive connection member  102  is electrically connected to the first electrode  10 , and the other end of the conductive connection member  102  extends to a side of the second transparent conductive layer  80  adjacent to the second electrode  90 . 
     It may be understood that, as shown in  FIG. 1  to  FIG. 4 , when the other end of the conductive connection member  102  extends to a side of the second transparent conductive layer  80  adjacent to the second electrode  90 , the conductive connection member  102  and the second transparent conductive layers  80  are insulated from each other, and the conductive connection member  102  and the second electrode  90  are insulated from each other. In some embodiments, when the other end of the conductive connection member  102  extends to a side of the second transparent conductive layer  80  adjacent to the second electrode  90 , the other end of the conductive connection member  102  and the second electrode  90  are both located on the surface of the second transparent conductive layer  80  away from the second doped layer  70 . From the perspective of electrical connection, since one end of the conductive connection member  102  is electrically connected to the first electrode  10 , and the other end of the conductive connection member  102  extends to a side of the second transparent conductive layer  80  adjacent to the second electrode  90 , a current extraction end of the first electrode  10  is located on a side of the second transparent conductive layer  80  adjacent to the second electrode  90 . Since the current extraction end of the first electrode  10  is located on a side of the second transparent conductive layer  80  adjacent to the second electrode  90 , the current extraction end of the first electrode  10  and a current extraction end of the second electrode  90  are in the same plane. Since the current extraction end of the first electrode  10  and the current extraction end of the second electrode  90  are in the same plane, by connecting the conductive connection member included in one of the two solar cell sheets  100  to the second electrode included in the other of the two solar cells, the series connection of the two solar cells  100  can be achieved. Moreover, since the conductive connection member included in the solar cell sheet  100  does not occupy the plane of the first electrode  10  (i.e., the first transparent conductive layer  20  is far away from the surface of the first doped layer  30 ), the solar cell sheet  100  provided by some embodiments of the present disclosure reduces a blocking ratio of the conductive connection member  102  (equal to the main gate line in the related art) to the light receiving surface of the solar cell sheet  100 , so that the light receiving area of the solar cell sheet  100  is increased. Since the light receiving area of the solar cell sheet  100  is increased, the photoelectric conversion efficiency of the solar cell sheet  100  is improved. 
     In addition, the solar cell sheet  100  provided by the embodiments of the present disclosure does not need to use a special back plane integrated with positive and negative electrodes. Therefore, the solar cell sheet  100  provided by the embodiments of the present disclosure can realize double-sided solar power generation. 
     In some embodiments, the conductive connection member  102  described above may be made of metal. 
     In some embodiments, as shown in  FIG. 1  to  FIG. 3 , the conductive connection member  102  is a connector formed by filling a silver paste. At this time, the connector formed by filling the silver paste is used to make the conductive connection member instead of the pure silver material, which can reduce the manufacturing cost of the solar cell sheet  100  and simplify the manufacturing method of the solar cell sheet  100 . 
     In some embodiments, as shown in  FIG. 1  to  FIG. 3  and  FIG. 6 , the first electrode  10  includes a plurality of first gate lines b 1 . The plurality of first gate lines b 1  join together, so that an intersection of the plurality of first gate lines b 1  forms a first confluence point  11 . One end of the conductive connection member  102  is electrically connected to the first confluence point  11 . For example, one end of the conductive connection member  102  is electrically connected to the first confluence point  11  by contacting with each other. 
     A width of each of the plurality of first gate lines b 1  is generally set to be from 30 μm to 90 μm. For example, the width of each of the plurality of first gate lines b 1  is 30 μm, 90 μm, 45 μm, or 70 μm. A width direction of each of the plurality of first gate lines b 1  is perpendicular to a linear direction of a corresponding first gate line of the plurality of first gate lines b 1 . 
     In some embodiments, as shown in  FIG. 6 , the second electrode  90  includes a plurality of second gate lines b 2 . The plurality of second gate lines b 2  join together, so that an intersection of the plurality of second gate lines b 2  forms a second confluence point  91 . A width of each of the plurality of first gate lines b 2  is generally set to be from 30 μm to 90 μm. The width of each of the plurality of first gate lines b 2  is set to 30 μm, 90 μm, 45 μm or 70 μm. A width direction of each of the plurality of second gate lines b 2  is perpendicular to a linear direction of a corresponding second gate line of the plurality of second gate lines b 2 . 
     In some embodiments, as shown in  FIG. 1  to  FIG. 4  and  FIG. 6 , although the other end of the conductive connection member  102  extends to the side of the second transparent conductive layer  80  adjacent to the second electrode  90 , because the second electrode  90  includes a plurality of second gate lines b 2 , the formed second electrode  90  is the second electrode  90  of a grid structure. That is, the second electrode  90  has a hollow portion. Based on this, it is required to ensure that when the other end of the conductive connection member  102  extends to the side of the second transparent conductive layer  80  adjacent to the second electrode  90 , the other end of the conductive connection member  102  extends to a side of the second transparent conductive layer  80  adjacent to the hollow portion of the second electrode  90 , so that it is possible to prevent the conductive connection member  102  electrically connected to the first confluence point  11  from being electrically connected to the second confluence point  91 . Since the conductive connection member  102  electrically connected to the first confluence point  11  is not electrically connected to the second confluence point  91 , in the above solar cell sheet  100 , the first electrode  10  and the second electrode  90  are not electrically connected, thereby short-circuit will not occur in the solar cell sheet  100 . 
     In some embodiments, as shown in  FIG. 6 , the first confluence point  11  and the second confluence point  91  are multiple. Accordingly, the number of the above-mentioned conductive connection members  102  is multiple. When the number of the first confluence point  11  and the number of the second confluence point  91  are both multiple, and the number of the conductive connection members  102  is multiple, the number of the conductive connection members  102  is in one-to-one correspondence with the number of the first confluence points  11 . In other words, each of the plurality of first junction points  11  corresponds to one conductive connection member  102 , so as to guide each of the plurality of first confluence points  11  to the surface of the second electrode  90  adjacent to the second transparent conductive layer  80 , so that the current extraction end of the first electrode  10  and the current extraction end of the second electrode  90  are located on the same side of the solar cell sheet  100 . 
     In some embodiments, as shown in  FIG. 1  to  FIG. 5 , the monocrystalline silicon wafer  50  is provided with a first through hole a 1 . The first passivation layer  40  is provided with a second through hole a 2 . The first doped layer  30  is provided with a third through hole a 3 . The second passivation layer  60  is provided with a fourth through hole a 4 . The second doped layer  70  is provided with a fifth through hole a 5 . The first transparent conductive layer  20  is provided with a sixth through hole a 6 , and the second transparent conductive layer  80  is provided with a seventh through hole a 7 . The first through hole a 1 , the second through hole a 2 , the third through hole a 3 , the fourth through hole a 4 , the fifth through hole a 5 , and the sixth through hole a 6 , the seventh through hole a 7  communicate with each other to constitute a through hole  101 . That is, the solar cell sheet  100  is provided with the through hole  101 , so that the conductive connection member  102  is disposed in the through hole  101 . 
     When the conductive connection member  102  is disposed in the through hole  101 , an orthographic projection of the conductive connection member  102  on one surface of the monocrystalline silicon wafer  50  at least overlaps with an orthographic projection of the first confluence point  11  on one surface of the monocrystalline silicon wafer  50 . At this time, the first confluence point  11  is located at an end of the sixth through hole a 6  of the first transparent conductive layer  20  away from the first doped layer  30 . At the same time, an orthographic projection of the conductive connection member  102  on one surface of the monocrystalline silicon wafer  50  and an orthographic projection of the second confluence point  91  on one surface of the monocrystalline silicon wafer  50  are independent from each other to avoid the conductive connection member  102  is electrically connected to the second confluence point  91 . 
     In some embodiments, as shown in  FIG. 1  to  FIG. 5 , when the number of the first confluence point  11  and the second confluence point  91  is multiple, and the number of the conductive connection members  102  is multiple, the number of the through hole  101  is multiple. The plurality of conductive connection members are located in the plurality of the through holes  101  in a one-to-one correspondence. 
     As shown in  FIG. 1  and  FIG. 6 , the plurality of the through holes  101  are arranged in an n×n array, where n is an integer greater than or equal to 3. For example, when n=3-8, the n×n array is a 3×3 array, a 4×4 array, . . . , an 8×8 array, or the like. 
     In some embodiments, as shown in  FIG. 1  to  FIG. 3 , the first transparent conductive layer  20  and the second transparent conductive layer  80  are both TCO glass conductive layers. 
     In some embodiments, as shown in  FIG. 1  to  FIG. 3 , the first doped layer  30  and the second doped layer  70  are combined to be a PN junction by the following two implementation manners, so that the solar cell sheet is a solar cell sheet of a PIN structure. 
     In the first implementation manner, the first doped layer  30  is an N-type amorphous silicon-based doped layer, and the second doped layer  70  is a P-type amorphous silicon-based doped layer. 
     In the second implementation manner, as shown in  FIG. 1  to  FIG. 3 , the first doped layer  30  is a P-type amorphous silicon-based doped layer, and the second doped layer  70  is an N-type amorphous silicon-based doped layer. 
     In some embodiments, as shown in  FIG. 1  to  FIG. 3 , the first passivation layer  40  and the second passivation layer  60  are both amorphous silicon basic intrinsic passivation layers. 
     In some embodiments, when the first transparent conductive layer  20  and the second transparent conductive layer  80  are both conductive layers, and when the first transparent conductive layer  20  is provided with a sixth through hole a 6 , and the second transparent conductive layer  80  is provided with a sixth through hole a 7 , a part of the conductive connection member  102  is located in the sixth through hole a 6  and the seventh through hole a 7 . At this time, the conductive connection member  102  may influence the photoelectric conversion efficiency of the solar cell sheet  100 . With respect to this problem, an inner wall of the through hole  101  is provided with an insulating film c. The material of the insulating film c is an ethylene-vinyl acetate copolymer (EVA), polyvinyl butyral (PVB) or Dai Nippon Printing (DNP) material. 
     In some embodiments, referring to  FIG. 3  and  FIG. 4 , if the conductive connection member  102  extends out of the second transparent conductive layer  80  along a direction from the second transparent conductive layer  80  to the second electrode  90 , and a portion of the conductive connection member  102  extending out of the second transparent conductive layer  80  is in contact with the surface of the second transparent conductive layer  80  adjacent to the second electrode  90 , then the first electrode  10  connected to the conductive connection member  102  is electrically connected with the second transparent conductive layer  80 . Since the first electrode  10  connected to the conductive connection member  102  is electrically connected to the second transparent conductive layer  80 , the first electrode  10  and the second electrode  90  are connected together, and then the solar cell sheet  100  has a short circuit problem. From another perspective, since the first transparent conductive layer  20  and the second transparent conductive layer  80  are both conductive layers having an electrical conductivity, in order to prevent the first transparent conductive layer  20  and the second transparent conductive layer  80  from affecting the current collection of the first electrode  10  and the second electrode  90 , it is necessary to perform an insulation treatment at a position where the first transparent conductive layer  20  and the second transparent conductive layer  80  contact the conductive connection member. Since a polarity of the first electrode  10  connected to the first transparent conductive layer  20  is the same as that of the conductive connection member  102 , the first transparent conductive layer  20  in contact with the first electrode  10  may not be performed an insulation treatment. The polarity of the second electrode  90  connected to the second transparent conductive layer  80  is opposite to the polarity of the conductive connection member  102 . Therefore, the second transparent conductive layer  80  in contact with the second electrode  90  needs an insulation treatment. 
     In one implementation, as shown in  FIG. 4 , the insulating film c further covers the surface of the second transparent conductive layer  80  contacting the conductive connection member  102 , that is, the surface of the second transparent conductive layer  80  contacting the conductive connection member  102  is also provided with an insulating film c. The insulating film c may insulate the conductive connection member  102  from the second transparent conductive layer  80 . 
     In another implementation manner, as shown in  FIG. 3  and  FIG. 5 , an insulating hole  801  having an annular structure is formed on the second transparent conductive layer  80 . The orthographic projection of the insulating hole  801  on the plane of one of the surfaces of the monocrystalline silicon wafer  50  is an annular orthographic projection. The orthographic projection of the through hole  101  on the plane of the one of the surfaces and the orthographic projection of the conductive connection member  102  on the plane of the one of the surfaces are located in a region enclosed by the annular orthographic projection. Since the orthographic projection of the through hole  101  on the plane of the one surface is located in the region surrounded by the annular orthographic projection, the region surrounded by the second transparent conductive layer  80  corresponding to the annular orthographic projection is insulated from the region of the transparent conductive layer  80  corresponding to the outside of the annular orthographic projection. Since the region surrounded by the second transparent conductive layer  80  corresponding to the annular orthographic projection is insulated from the region of the transparent conductive layer  80  corresponding to the outside of the annular orthographic projection, and the orthographic projection of the through hole  101  on the plane of the one of the surfaces and the orthographic projection of the conductive connection member on the plane of the one of the surfaces are located within the region surrounded by the annular orthographic projection, the second transparent conductive layer  80  and the conductive connection member  102  are insulated from each other. 
     In addition, when a plurality of second gate lines b 2  included in the second electrode  90  join together at a second confluence point  91 , the second confluence point  91  should be spatially offset from the insulating hole  801  and the through hole  101  to ensure that the conductive connection member  102  disposed in the through hole  101  and the second confluence point  91  are in an insulated state. In other words, the orthographic projection of the second confluence point  91  on the plane of the one of the surfaces is outside the region enclosed by the annular orthographic projection. At this time, although the conductive connection member  102  is inserted in the region surrounded by the transparent conductive layer  80  corresponding to the annular orthographic projection, the conductive connection member  102  will not be electrically connected with the second confluence point  91  formed by joining the plurality of second gate lines b 2  included in the second electrode  90 . Therefore, although the above-mentioned conductive connection member  102  electrically connected to the first electrode is inserted in the region surrounded by the annular orthographic projection corresponding to the transparent conductive layer  80 , the first electrode  10  connected with the conductive connection member  102  will not be electrically connected to the second electrode  90  contacting the second transparent conductive layer  80 . 
     In some embodiments, referring to  FIG. 3  to  FIG. 5 , after the conductive connection member  102  is formed in the through hole  100 , if the conductive connection member  102  extends out of the second transparent conductive layer  80  along the direction from the second transparent conductive layer  80  to the second electrode  90 , and contacts the surface of the second transparent conductive layer  80  adjacent to the second electrode  90 , then a length of a portion of the conductive connection member  102  protruding from the second transparent conductive layer  80  in a radial direction of the through hole  101  is greater than a radial length of the through hole  101 . In order to ensure the insulation function of the above-mentioned insulating hole  801 , the above-mentioned insulating hole  801  should be far away from the conductive connection member  102 . Compared with the insulating manner of forming the insulating film c on the inner wall of the through hole  101  and the surface of the second transparent conductive layer  80  contacting the conductive connection member  102 , the insulating manner in which an insulating hole  801  is formed in the second transparent conductive layer  80  is simpler and easier to operate. 
     In addition, as shown in  FIG. 3 , although the first doped layer  30  and the second doped layer  70  described above are conductive, the conductivity performance thereof almost may be negligible. Therefore, it is only necessary to open the insulating hole  801  on the second transparent conductive layer  80 . 
     As shown in  FIG. 1  to  FIG. 5 , the solar cell sheet  100  provided by some embodiments of the present disclosure guides the electrode (i.e., the first electrode  10 ) on one side of the solar cell sheet  100  to the other side (i.e., the surface of the second transparent conductive layer  80  adjacent to the second electrode  90 ) of the solar cell sheet  100  by the conductive connection member  102 . When it is necessary to interconnect at least two solar cell sheets  100 , the electrodes having different polarities of adjacent two solar cell sheets  100  may be interconnected by the conductive connecting line  210 . Since the first electrode  10  and the second electrode  90  are guided to the same surface of the solar cell sheet  100 , the conductive connecting line  102  does not affect an area of the light-receiving surface on the surface on which the first electrode  10  of the solar cell sheet  100  is located. Since the conductive connecting line  102  does not affect the area of the light-receiving surface on the other surface of the solar cell, the area of the light-receiving surface of the solar cell sheet  100  is relatively increased, so that the short-circuit current density is increased. Due to the short-circuit current density of the solar cell sheet  100 , the photoelectric conversion efficiency of the solar cell sheet  100  is increased. 
     In some embodiments, as shown in  FIG. 2  to  FIG. 4 , the conductive connection member  102  is a connection member formed by filling silver paste. Compared with the method of directly using the silver paste to form the main gate line, the connection member formed by filling the silver paste can save a large amount of silver paste, therefore, the above-mentioned conductive connection member  102  being the connection member formed by filling the silver paste can greatly reduce the cost of the solar cell sheet  100 . 
     In other embodiments, when preparing the conductive connection member  102 , it is not necessary to use silver material, and only a general metal material such as a copper or a tin-plated copper is used, therefore, the manufacturing cost of the above-mentioned conductive connection member  102  is relatively low. 
     As shown in  FIG. 1  to  FIG. 5  and  FIG. 9  to  FIG. 11 , some embodiments of the present disclosure further provide a method for preparing a solar cell sheet, and the method for preparing the solar cell sheet  100  includes: step  1  (S 1 ), step  2  (S 2 ), step  3  (S 3 ), step  4  (S 4 ), and step  5  (S 5 ). 
     In S 1 , a first through hole a 1  is formed in the monocrystalline silicon wafer  50 , and the monocrystalline silicon wafer  50  includes a first surface  501  and a second surface  502  which are opposite with each other. There are many ways for forming the first through hole a 1  in the monocrystalline silicon wafer  50 . For example, the first through hole a 1  is formed in the monocrystalline silicon wafer  50  by laser drilling. 
     In S 2 , the first surface  501  and the second surface  502  are both subjected to a texturing operation and a cleaning operation. The texturing operation means forming a suede having a pyramidal pattern on both the first surface  501  and the second surface  502 , and a size (a maximum span) of the pyramid is 1 μm to 10 μm. The texturing operation may reduce the reflectance of the surface of the monocrystalline silicon wafer  50 , so as to increase the photoelectric conversion efficiency of the prepared solar cell sheet  100 . 
     In S 3 , the first passivation layer  40  and the first doped layer  30  are sequentially formed on the first surface  501  described above. A second passivation layer  60  and a second doped layer  70  are sequentially formed on the second surface  502  described above. 
     In some embodiments, the sequentially forming the first passivation layer  40  and the first doped layer  30  on the first surface  501  includes: sequentially depositing a first passivation layer  40  and a first doping layer  30  on the first surface  501 , so that the first passivation layer  40  includes a second through hole a 2 , and the first doped layer  30  includes a third through hole a 3 . And the orthographic projections of the first through hole a 1 , the second through hole a 2 , and the third through hole a 3  on the plane where the first surface  501  is located are overlapped. 
     The forming sequentially the second passivation layer  60  and the second doped layer  70  on the second surface  502  includes: sequentially depositing a second passivation layer  60  and a second doped layer  70  on the second surface  502 , so that the second passivation layer  60  includes a fourth through hole a 4 , and the second doped layer  70  includes a fifth through hole a 5 . And the orthographic projections of the first through hole a 1 , the fourth through hole a 4 , and the fifth through hole a 5  on the plane of the second surface  502  are overlapped. 
     In some embodiments, the deposition method may be a Plasma Enhanced Chemical Vapor Deposition (PECVD) or a Hot Wire Chemical Vapor Deposition (HWCVD). The two passivation layers of the first passivation layer  40  and the second passivation layer  60 , and the two doped layers of the first doped layer  30  and the second doped layer  70  are deposited in the same manner. The first passivation layer  40  and the second passivation layer  60  are deposited in the same step but in different chambers. 
     Illustratively, the first passivation layer  40  and the second passivation layer  60  are simultaneously formed in the same chamber, and then the first doped layer  30  and the second doped layer  70  are formed in another chamber. 
     In some embodiments, the first doped layer  30  is an N-type amorphous silicon-based doped layer. The second doped layer  70  is a P-type amorphous silicon-based doped layer. 
     In some other embodiments, the first doped layer  30  is a P-type amorphous silicon-based doped layer. The second doped layer  70  is an N-type amorphous silicon-based doped layer. 
     In some embodiments, the first passivation layer  40  and the second passivation layer  60  are both amorphous silicon basic passivation layers. 
     In S 4 , a first transparent conductive layer  20  is formed on the surface of the first doped layer  30  away from the first passivation layer  40 . A second transparent conductive layer  80  is formed on the surface of the second doped layer  70  away from the second passivation layer  60 . 
     In some embodiments, forming the first transparent conductive layer  20  on the surface of the first doped layer  30  away from the first passivation layer  40  includes: depositing the first transparent conductive layer  20  on the surface of the first doped layer  30  away from the first passivation layer  40 , so that the first transparent conductive layer  20  includes a sixth through hole a 6 . The orthographic projections of the first through hole a 1  and the sixth through hole a 6  on the plane of the first surface  501  are overlapped. 
     The forming the second transparent conductive layer  80  on the surface of the second doped layer  70  away from the second passivation layer  60  includes: depositing the second transparent conductive layer  80  on the surface of the second doped layer  70  away from the second passivation layer  60 , so that the second transparent conductive layer  80  includes a seventh through a 7 . The orthographic projections of the first through hole a 1  and the seventh through hole a 7  on the plane of the second surface  502  are overlapped. 
     The above deposition method may be a Physical Vapor Deposition (PVD), or may be a remote plasma coating method. The remote plasma coating method is also called as Plasma Reactive Deposition (PRD). 
     The first through hole a 1 , the second through hole a 2 , the third through hole a 3 , the fourth through hole a 4 , the fifth through hole a 5 , the sixth through hole a 6 , and the seventh through hole a 7  are communicated to form the through hole  101 . 
     In some embodiments, the first transparent conductive layer  20  and the second transparent conductive layer  80  are both TCO glass conductive layers. 
     In S 5 , the first electrode  10  is prepared on the surface of the first transparent conductive layer  20  away from the first doped layer  30 . The second electrode  90  is prepared on the surface of the second transparent conductive layer  80  away from the second doped layer  70 . Moreover, the conductive connection member  102  located in the first through hole a 1  is prepared when preparing the first electrode  10  or preparing the second electrode  90 . 
     In some embodiments, the step of preparing the first electrode  10  on the surface of the first transparent conductive layer  20  away from the first doped layer  30  and the step of preparing the second electrode  90  on the surface of the second transparent conductive layer  80  away from the second doped layer  70  are performed successively. 
     The preparing the conductive connection member  102  in the first through hole a 1  when preparing the first electrode  10  or preparing the second electrode  90  includes: 
     preparing the conductive connection member  102  located in the through hole  101  when preparing the first electrode  10  or when preparing the second electrode  90 . 
     In some embodiments, when the number of the through holes is multiple, the foregoing S 1  includes: 
     forming a plurality of first through holes a 1  on the monocrystalline silicon wafer  50  by laser drilling; and/or 
     as shown in  FIG. 1  to  FIG. 6  and  FIG. 12 , the preparing the first electrode  10  on the surface of the first transparent conductive layer  20  away from the first doped layer  30  includes step  501  (S 501 ); and/or 
     in S 501 , a plurality of first gate lines b 1  are printed on the surface of the first transparent conductive layer  20  away from the first doped layer  30  by a screen printing process to form a first electrode  10  composed of a plurality of first gate lines b 1 , the plurality of first gate lines b 1  join to form a plurality of first confluence points  11 , and the orthographic projections of the plurality of first confluence points  11  on the plane of the first surface  501  are located in the orthographic projections of the through holes  101  on the plane of the first surface  501  in a one-to-one correspondence; and/or 
     as shown in  FIG. 1  to  FIG. 6  and  FIG. 12 , the preparing the second electrode  90  on the surface of the second transparent conductive layer  80  away from the second doped layer  70  includes step  502  (S 502 ), 
     in S 502 , a plurality of second gate lines b 2  are printed on the second transparent conductive layer  80  by a screen printing process to form a second electrode  90  composed of a plurality of second gate lines b 2 , the plurality of second gate lines b 2  join to form a plurality of second confluence points  91 , and the orthographic projections of the plurality of second confluence points  91  on the plane of the second surface  502  are outside the annular orthographic projection of the insulating hole  801  on the plane of the second surface  502  in a one-to-one correspondence; and/or 
     the preparing the conductive connection member in the first through hole a 1  when preparing the first electrode  10  or when preparing the second electrode  90  includes: step  503  (S 503 ) and step  504  (S 504 ). 
     In S 503 , when printing the plurality of first gate lines b 1  or printing the plurality of second gate lines b 2 , filling the plurality of through holes a 5  with silver paste. 
     In S 504 , drying the silver paste filled in the plurality of through holes  101 , so that the silver paste filled in the plurality of the through holes  101  is solidified, thereby a plurality of conductive connection members  102  are obtained, and the plurality of conductive connection members  102  are located in the plurality of the through holes  101  in a one-to-one correspondence. 
     Since the orthographic projections of the plurality of first confluence points  11  on the plane of the first surface  501  are located within the orthographic projection of the first through hole a 1  on the plane of the first surface  501 , and the orthographic projections of the plurality of second confluence points  91  on the plane of the second surface  502  and the orthographic projection of the first through hole a 1  on the plane of the second surface  502  are independent from each other, when the plurality of conductive connection members  102  are located in the plurality of the through holes  101  in a one-to-one correspondence, one ends of the plurality of conductive connection members  102  may be electrically connected to the first confluence point  11  in a one-to-one correspondence, the other ends of the plurality of conductive connection members  102  are not electrically connected to the plurality of second confluence points  91 . 
     It may be seen that: after the plurality of conductive connection members  102  are formed in the plurality of through holes  100  in a one-to-one correspondence, the current extraction end of the first electrode  10  is led out through the plurality of conductive connection members  102  to the surface of the second transparent conductive layer  80  adjacent to the second electrode  90 , so that the current extraction end of the first electrode  10  is located on the same side as the second electrode  90 . 
     In some embodiments, the first electrode  10  and the second electrode  90  are made of the silver paste and a resin material. 
     Illustratively, the silver paste and the resin material are mixed to form a premix with a mass percent greater than 90%. The premix is printed on the surface of the second transparent conductive layer  80  away from the second doped layer  70  by the screen printing process, so that a plurality of second gate lines b 2  are formed on the surface of the second transparent conductive layer  80  away from the second doped layer  70 . Similarly, a premix is printed on the surface of the first transparent conductive layer  20  away from the first doped layer  30  by the screen printing process, so that a plurality of second gate lines b 2  are formed on the surface of the first transparent conductive layer  20  away from the first doped layer  30 . 
     In some embodiments, as shown in  FIG. 1  to  FIG. 5 , the first passivation layer  40 , the first doped layer  30 , the first transparent conductive layer  20 , the second passivation layer  60 , the second doped layer  70  and the second transparent conductive layer  80  have a thickness of nanometer, and the through hole  101  has a diameter of millimeter. Therefore, when depositing the first passivation layer  40 , the first doped layer  30 , the first transparent conductive layer  20 , the second passivation layer  60 , the second doped layer  70 , and the second transparent conductive layer  80 , an upper end of the inner wall of the first through hole a 1  (the first through hole a 1  is located at the end of the direction of the first surface  501 ) is likely to be adhered with a first deposition layer formed of the material of the first passivation layer  40 , the material of the first doped layer  30 , and the material of the first transparent conductive layer  20 . The first deposition layer is a three-layer structure formed by the material of the first passivation layer  40 , the material of the first doped layer  30 , and the material of the first transparent conductive layer  20 . The lower end of the inner wall of the first through hole a 1  (the first through hole a 1  is located at the end of the direction of the second surface) may be adhered with the second deposited layer formed of the material of the second passivation layer  60 , the material of the second doped layer  70 , and the material of the second transparent conductive layer  80 . The second deposition layer is a three-layer structure formed by the material of the second passivation layer  60 , the material of the second doped layer  70 , and the material of the second transparent conductive layer  80 . Since the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  are conductive, if the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  adhered to the inner wall of the first through hole a 1  are not removed, the conductive connection member  102  connected to the first electrode  10  may contact the second transparent conductive layer  80  connected to the second electrode  90 , thereby affecting the polarity of the conductive connection member  102 . Since the conductive connection member  102  connected to the first electrode  10  contacts the second transparent conductive layer  80  connected to the second electrode  90 , the first electrode  10  and the second electrode  90  of the solar cell sheet  100  are connected together, so that the above solar cell sheet  100  is short-circuited. Therefore, it is necessary to perform an insulation process on the inner wall of the through hole  101 . In addition, although the first doped layer  30  and the second doped layer  70  may also conduct electricity, their electrical conductivity may be almost negligible. Therefore, only the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  70  in the through hole  101  need to be processed. 
     In one embodiment, as shown in  FIG. 1  to  FIG. 4  and  FIG. 9 , after step S 4 , and before step S 5 , the method for preparing the above solar cell sheet  100  further includes step  401  (S 401 ). 
     In S 401 , the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  formed in the inner wall of the through hole  101  (for example, the forming manner is deposition manner) are removed by a corrosion process or a laser etching process. When the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  formed in the inner wall of the through hole  101  are removed by the corrosion process, it is possible to use a strong alkali to corrode the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  formed in the inner wall of the through hole  101 . The strong alkali includes an inorganic alkali such as sodium hydroxide or potassium hydroxide. 
     Since a total thickness of the first passivation layer  40 , the first doped layer  30 , the first transparent conductive layer  20 , the second passivation layer  60 , the second doped layer  70 , and the second transparent conductive layer  80  is nanometer scale, for convenience of operation, the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  formed on the inner wall of the through hole  101  consisting of the first through hole a 1 , the second through hole a 2 , the third through hole a 3 , the fourth through hole a 4 , the fifth through hole a 5 , the sixth through hole a 6 , and the seventh through hole a 7  may be corroded for one time, in this way, the method of removing the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  is simple and convenient to operate, and has a high reliability. 
     Illustratively, the first doped layer has a thickness of 6 nm, the second doped layer has a thickness of 8 nm, and the first transparent conductive layer  20  and the second transparent conductive layer  80  both have a thickness of 80 nm. 
     In some embodiments, as shown in  FIG. 2 ,  FIG. 4 ,  FIG. 5  and  FIG. 9 , after step S 4 , and before step S 5 , the method for preparing the solar cell sheet  100  further includes step  402  (S 402 ). 
     In S 402 , an insulating film c is prepared on the inner wall of the through hole  101  and the surface of the second transparent conductive layer  80  for contacting the conductive connection member  102 . The insulating film c is an ethylene-vinyl acetate copolymer (EVA) material layer, a polyvinyl butyral material layer or a Dai Nippon Printing (DNP) plastic layer. Since the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  are conductive materials, in order to prevent the material of the first transparent conductive layer  20  and the material of the second transparent conductive layer  80  on the inner wall of the through hole  101  from affecting the current collection by the electrode, in particular, it is necessary to provide an insulating film on the inner wall of the sixth through hole a 6  included in the through hole  101  and the inner wall of the seventh through hole a 7  included in the through hole  101 . Since the first passivation layer  40 , the first doped layer  30 , the first transparent conductive layer  20 , the second passivation layer  60 , the second doped layer  70 , and the second transparent conductive layer  80  have a total thickness of nanometer scale, the insulating film c is entirely provided on the inner wall of the through hole  101 , and it is not necessary to define the position where the insulating film c is formed, so that it is convenient to form the insulating film c on the inner wall of the through hole  101 . Further, providing the insulating film c entirely on the inner wall of the through hole  101  can also ensure a good insulation between the conductive connection member  102  and the first transparent conductive layer  20 , the second transparent conductive layer  80 . 
     Referring to  FIG. 3 , if the conductive connection member  102  extends out of the second transparent conductive layer  80  along the direction from the second transparent conductive layer  80  to the second electrode  90 , and a portion of the conductive connection member  102  extending out of the second transparent conductive layer  80  is in contact with the lower surface of the second transparent conductive layer  80  (the surface adjacent to the second electrode  90 ), then the first electrode  10  connected to the conductive connection member  102  is electrically connected with the second transparent conductive layer  80 . In order to prevent the first electrode  10  connected to the conductive connection member  102  from being electrically connected to the second transparent conductive layer  80 , the above insulating film c is also formed on the surface of the second transparent conductive layer for contacting the conductive connection member, so that the conductive connection member  102  is insulated from the second transparent conductive layer  80  by the insulating film c, thereby preventing the first electrode  10  connected to the conductive connection member  102  from electrically connecting to the second electrode  90  in contact with the second transparent conductive member  80 . 
     In some other embodiments, as shown in  FIG. 3 ,  FIG. 5 , and  FIG. 10 , the insulation process may be performed after S 4 , and prior to S 5 . At this time, after S 4 , and before the step S 5 , the method for preparing the solar cell sheet  100  further includes: step  403  (S 403 ). 
     In S 403 , an annular insulating hole  801  is formed in the second transparent conductive layer  80 , so that the orthographic projection of the insulating hole  801  on the plane of the second surface  502  is an annular orthographic projection. The orthographic projection of the seventh through hole a 7  included in the through hole  101  on the plane of the second surface  502  is located in the region surrounded by the annular orthographic projection. The orthographic projection of the seventh through hole a 7  included in the through hole  101  on the plane of the second surface  502  and the orthographic projection of the conductive connection member  102  on the plane of the second surface  502  are both located in the region enclosed by the annular orthographic projection, and the orthographic projection of the second confluence point  91  on the plane of the second surface  502  is outside the region enclosed by the annular orthographic projection. At this time, the region surrounded by the second transparent conductive layer  80  corresponding to the annular orthographic projection is not only insulated from the outer region of the second transparent conductive layer  80  corresponding to the annular orthographic projection, but also insulated from the second electrode  81 . Since the region surrounded by the second transparent conductive layer  80  corresponding to the annular orthographic projection is electrically connected to the conductive connection member  102 , by providing the insulating hole  801  on the second transparent conductive layer  102 , the insulating holes  801  may insulate the conductive connection members  102  from the second transparent conductive layer  80  and the second electrode  90 . 
     The manner in which the second transparent conductive layer  80  and the conductive connection member  102  are insulated by the insulating holes  801  is simpler and easier to operate. The first transparent conductive layer  20  is in contact with the first electrode  10 , and the conductive connection member  102  is electrically connected to the first electrode, therefor the polarity of the first transparent conductive layer  20  is the same as that of the conductive connection member  102 , and the conductive connection members  102  can be insulated from the second transparent conductive layer  80  and the second electrodes by only providing the insulating holes  801  in the second transparent conductive layer  80 . 
       FIG. 6  shows a first cell string, wherein the portion for connecting in parallel the first cell string by an interconnecting strip is omitted, and those skilled in the art may understand in accordance with conventional technical means. 
     As shown in  FIG. 6 , an embodiment of the present disclosure further provides a solar cell string  200 . The solar cell string  200  includes a plurality of solar cell sheets  100  that are electrically connected together. 
     Compared with the related art, the beneficial effects of the solar cell string  200  provided by the embodiments of the present disclosure are the same as those of the solar cell sheet  100  provided by the above embodiments, which are not described herein. 
     It should be understood by those skilled in the art that, as shown in  FIG. 6  and  FIG. 7 , when the plurality of solar cell sheets  100  are electrically connected together, the electrical connection manner may be a series connection or a parallel connection. When the electrical connection manner is the series connection, the first electrode  10  of one of the adjacent two solar cell sheets  100  and the second electrode  90  of the other solar cell sheet  100  are connected by a conductive connecting line  210 . When the electrical connection mode is the parallel connection, the first electrode  10  of one of the adjacent two solar cell sheets  100  and the first electrode  10  of the other solar cell sheet  100  are connected by the conductive connecting line  210 . 
     In some embodiments, as shown in  FIG. 7 , a plurality of the solar cell sheets  100  connected together constitute at least two cell substrings  200   a  connected in parallel. The plurality of cell substrings  200   a  are connected in parallel by an interconnecting strips  400  to form the solar cell string  200 . 
     As shown in  FIG. 6 , in each of the plurality of cell substrings  200   a , the conductive connection member  102  included in one of the adjacent two solar cell sheets  100  and the second electrode  90  included in the other solar cell sheet are electrically connected through the conductive connecting line  210 , so that the adjacent two solar cell sheets  100  are connected in series. 
     As shown in  FIG. 7 , when the solar cell string  200  is formed in parallel, one of the interconnecting strips  400  connects the conductive connection members  102  included in the bottommost solar cell sheets included in the adjacent two cell substrings  200   a , thus the first electrodes  10  of the plurality of cell substrings are electrically connected together; and the other interconnecting strip  400  electrically connects the second electrodes  90  included in the bottommost solar cell sheets included in the adjacent two cell sub-strings  200   a , thus the second electrodes  90  of the plurality of cell substrings are electrically connected, in this way, a solar cell string  200  is obtained. 
     In some embodiments, as shown in  FIG. 1  to  FIG. 6 , when the two adjacent two solar cell sheets  100  are connected in series, the first electrode  10  included in one of the adjacent two solar cell sheets  100  is electrically connected to the second electrode  90  included in the other solar cell sheet. 
     Illustratively, as shown in  FIG. 1  to  FIG. 6 , the first electrode  10  included in one of the adjacent two solar cell sheets  100  and the second electrode  90  included in the other solar cell sheet are connected by a conductive connecting line  210 . At this time, it is necessary to connect the first confluence point  11  included in one of the adjacent two solar cell sheets  100  and the second confluence point  91  included in the other solar cell sheet by the conductive connecting line  210 . Since the first confluence point  11  in each solar cell sheet  100  is electrically connected to the conductive connection member  102 , and the other end of the conductive connection member  102  extends to the surface of the second transparent conductive layer  80  away from the second doped layer  70 , when the first confluence point  11  included in one of the adjacent two solar cell sheets  100  and the second confluence point  91  included in the other solar cell sheet are connected by the conductive connecting line  210 , the conductive connection member  102  included in one of the adjacent two solar cell sheets  100  and the second confluence point  91  included in the other solar cell sheet are connected by the conductive connecting line  210 . 
     Illustratively, the conductive connection member  102  has a thickness of 0.01 mm to 0.2 mm and a width of 0.6 mm to 12 mm. Compared with the conventional silver main gate line, the above-mentioned conductive connecting line  102  is also smaller in size, which reduces the shielding of the light receiving surface of the solar cell sheet  100 , thereby improving the conversion efficiency of the solar cell sheet  100 . 
     It may be understood that, as shown in  FIG. 1  to  FIG. 4 , the first confluence point  11  in the solar cell sheet  100  is guided by the conductive connection member  100  to the surface of second transparent conductive layer  80  which is coplanar with the second confluence point  91  and is away from the second doped layer  70 . In other words, the first confluence point  11  and the second confluence point  91  are already located on the same surface of the solar cell sheet  100 , therefore, one surface of the solar cell sheet  100  realizes the series connection of two adjacent solar cell sheets  100  by the conductive connecting line  210 , and the influence of the conductive connecting line  210  on the light receiving surface of the solar cell sheet  100  can be reduced, thereby improving the photoelectric conversion efficiency of the solar cell sheet  100 . 
     The shapes of the first confluence point  11  and the second confluence point  91  in  FIG. 6  are different, which is only for distinguishing the first confluence point  11  and the second confluence point  91 , and is not intended to limit the shapes of the first confluence point  11  and the second confluence point  91 . 
     In some embodiments, the above conductive connecting line  210  is made of a copper strip. The copper strip may be a pure copper strip or a tinned copper strip, but the present disclosure is not limited thereto. 
     Illustratively, the outer surface of the above conductive connecting line  210  is coated with a layer of insulating material. For example, the insulating material is preferably a rubber or plastic. 
     When the conductive connection member  200  included in one of the adjacent two solar cell sheets  100  of the plurality of cell sub-strings is electrically connected to the second electrode  90  included in the other solar cell sheet, it is only necessary to expose the inner tinned copper strip by spot welding or gluing the insulating material at the end of the conductive connecting line  210  to ensure the electrical conductivity. 
     In some embodiments, the temperature of the spot welding described above does not exceed 200 degrees. The temperature of the above low temperature curing does not exceed 220 degrees. 
     In addition, as shown in  FIG. 7 , when the conductive connecting line  210  is electrically connected to the adjacent two cell sub-strings  200   a , insulation is realized by providing an insulating film on the outside of the conductive connecting line  210 , and the insulating film is the ethylene-vinyl acetate copolymer (EVA) material layer, the polyvinyl butyral (PVB) material layer or the Dai Nippon Printing (DNP) material layer. 
     As shown in  FIG. 5 , some embodiments of the present disclosure also provide a photovoltaic module  300 . The photovoltaic module  300  includes a front plate  310 , a first bonding layer  320 , a solar cell string  200 , a second bonding layer  330 , and a backing plate  340  in an order from top to bottom. The solar cell string  200  is the solar cell string  200  provided in any of the above embodiments. 
     Compared with the related art, the beneficial effects of the photovoltaic module  300  provided by some embodiments of the present disclosure are the same as those of the solar cell sheet  100  described above, and are not elaborated herein. 
     In some embodiments, the first bonding layer  320  and the second bonding layer  330  are both ethylene-vinyl acetate copolymer (EVA) material layer and polyvinyl butyral (PVB) material layer, a polyolefin elastomer (POE) material layer or a thermoplastic silicone layer. 
     The structures, features and effects of the present disclosure have been described in detail above with reference to the embodiments shown in the drawings. The above is only the preferred embodiment of the present disclosure, but the disclosure does not limit the scope of the implementation as shown in the drawings. All changes which come within the spirit and scope of the present disclosure are intended to be included within the protection scope of the present disclosure.