Abstract:
A solar module with a bypass diode integrated therein, fabricated on the basis of the standard thin film solar module. By connecting a series of p-n junction to a non-functional p-n junction in anti-parallel, the non-functional p-n junction in the standard thin film solar module is used as the bypass diode. Hence no additional bypass diode is needed in the design.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to a thin film solar module and, more particularly, to a thin film solar module with a bypass diode integrated therein. 
       BACKGROUND OF THE INVENTION 
       [0002]    A solar module is generally composed of many solar cells. Solar cells are typically modeled as diodes that respond to illumination by becoming forward biased and establishing a voltage across the cell. For supplying larger power, solar cells are usually connected in series. 
         [0003]      FIG. 1  shows a conventional thin film solar module with a series of solar cells. The solar module  70 ′ comprises of a substrate  10 , first conductive layers  21 , semiconductor layers  31 , the second conductive layers  41 , and two contacts  51  and  52 , wherein the first conductive layers  21  and the second conductive layers  41  act as front electrodes and back electrodes, respectively. A solar cell in the solar module  70 ′ comprises a semiconductor layer  31 , a first conductive layer  21 , and a second conductive layer  41 , wherein the semiconductor layer  31  is sandwiched by the first conductive layer  21  and the second conductive layer  41 . Each of the semiconductor layers  31  has a p-n junction formed by an n-doped region and a p-doped region. Alternatively, each of the semiconductor layers  31  may include a p-i-n junction formed by a p-doped region, intrinsic semiconductor region, and a n-doped region. The two contacts  51  and  52  are respectively a p-contact formed on the back electrode connected to the p-doped region in the semiconductor layer  31  of one solar cell and an n-contact formed on the back electrode connected to the n-doped region in the semiconductor layer  31  of another solar cell. The two contacts  51  and  52  are formed for connecting to a load (not shown). The p-n junctions in the semiconductor layers  31  are connected in series, which means the n-doped region (p-doped region) in one semiconductor layer  31  is electrically connected to the p-doped region (n-doped region) in an adjacent semiconductor layer  31  through the electrodes. The structure of the solar module is accomplished through standard process of fabrication of semiconductors, which is already known in the art and is not described in detail in the specification. 
         [0004]    During the fabrication of a thin film solar module, a process called “edge isolation” is performed to isolate the edge portions from the main body of the solar module. The isolated edge portions (the portions at the outer sides of isolation trenches  43  as shown in  FIG. 1 ) are usually of undesired property so that they need to be isolated from the series of solar cells and are thus wasted in the conventional solar module. Sometimes the edge portions of the solar modules are cut and discarded. 
         [0005]    As shown in  FIG. 1 , except for the last solar cell in the series (the solar cell at the right side in  FIG. 1 ), the back electrode of any one of the solar cells is connected to the front electrode of the adjacent solar cell. Through the configuration, when connecting to a load (not shown), the internal current in the solar module  70 ′ flows along the dashed line in  FIG. 1 . It shall be noted that due to the structure fabricated by the standard process, the p-n junction in the semiconductor layer  31  below the p-contact does not act as a solar cell and is non-functional in the solar module  70 ′. Generally, the non-functional p-n junction in the semiconductor layer  31  is wasted in the conventional solar module. 
         [0006]    For protecting the solar modules from damage, a bypass diode is usually connected across a solar module. Conventionally, in order to ensure a shaded or failed solar module is not the bottleneck of the solar system, each module usually comes with an externally connected bypass diode. However, the externally connected bypass diode adds undesirable cost to the solar module. 
         [0007]    Therefore, there exists a need for providing a solar module with a bypass diode monolithically integrated therein such that no externally connected diode or additional discrete diode is needed in the module. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect, a solar module with a bypass diode monolithically integrated therein is provided. The solar module comprises: a substrate; a plurality of first conductive layers formed on the substrate; a plurality of semiconductor layers formed on the first conductive layers, wherein the plurality of semiconductor layers each comprises a p-n junction, and wherein the p-n junctions are electrically connected in series; a plurality of second conductive layers formed on the semiconductor layers; a first contact and a second contact connected to two of the second conductive layers, wherein the p-n junctions electrically coupled between the first contact and the second contact function as a series of solar cells and one of the rest of the p-n junctions functions as the bypass diode; and a conductor connecting the series of solar cells to the bypass diode in anti-parallel. 
         [0009]    In another aspect, a method of forming solar module with a bypass diode monolithically integrated therein is provided. The method comprises: providing a substrate; forming a plurality of first conductive layers on the substrate; forming a plurality of semiconductor layers on the first conductive layers, wherein the plurality of semiconductor layers each comprises a p-n junction, and wherein the p-n junctions are electrically connected in series; forming a plurality of second conductive layers on the semiconductor layers; forming a first contact and a second contact connected to two of the second conductive layers, wherein the p-n junctions electrically coupled between the first contact and the second contact function as a series of solar cells and one of the rest of the p-n junctions functions as the bypass diode; and providing a conductor connecting the series of solar cells to the bypass diode in anti-parallel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]      FIG. 1  is a side cross-sectional view illustrating a conventional thin film solar module; 
           [0011]      FIG. 2  is a schematic electrical circuit showing that a solar cell assembly is connected in anti-parallel to a bypass diode; 
           [0012]      FIG. 3  is a side cross-sectional view showing the connection between a series of solar cells and a integrated bypass diode; 
           [0013]      FIGS. 4-8  are side cross-sectional views illustrating the fabricating process of a solar module in accordance with the embodiment of the present invention; 
           [0014]      FIG. 9  is a top view of the solar module in accordance with the embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The object of the invention is to utilize the unused (non-functional) p-n junction in the solar cell of the solar modules as a bypass diode. As shown in  FIG. 3 , to achieve the object of the invention, an electrical connection, represented as the line connecting from the second conductive layer  41  to the first conductive layer  21 , between the n-doped region in the semiconductor layer  31  below the n-contact and the p-doped region in the semiconductor layer  31  below the p-contact is needed. By the connection, the configuration as shown in  FIG. 2  is achieved, in which the series of solar cell and the bypass diode  34  are connected in an anti-parallel configuration such that the bypass diode  34  is reverse biased when the solar cells are illuminated. 
         [0016]    To achieve the object of the invention, a preferred embodiment of the solar module with a bypass diode integrated therein is provided by performing the following fabricating process. 
         [0017]      FIGS. 4-8  are schematic diagrams illustrating the fabricating process of a solar module  70  in accordance with the preferred embodiment of the invention, in which a bypass diode  34  is integrated in the solar module  70 . 
         [0018]    As shown in  FIG. 4 , a substrate  10  is provided. To allow the sunlight pass through the substrate  10 , a transparent material such as glass, for example, is used as the substrate  10 . The first conductive layer  20  is formed, by a deposition process, on the substrate  10 . The deposition process may be implemented by plasma-enhanced chemical vapor deposition (PECVD) or other deposition techniques, which can consist of several different deposition techniques. 
         [0019]    Subsequently, as shown in  FIG. 4 , first trenches  22  are formed in the first conductive layer  20  by etching away parts of the conductive layer  20 . The etching process may be implanted by, for example, laser scribing, chemical etching, mechanical scribing, ion beam writing, or other related techniques. Since the deposition process and the etching process are conventional techniques which are known in the art, they are not described in detail in the following steps. 
         [0020]    After the etching process, the first conductive layer  20  was divided into several first conductive layers  21  to be used as the front electrodes of the solar cells in the solar module  70 . The number of the first conductive layers  21  is determined based on the desired number of the solar cells in series. In the exemplary embodiment, for easy illustration, four first conductive layers are formed. 
         [0021]    In  FIG. 5 , a semiconductor layer  30  is then deposited over the first conductive layers  21  such that the semiconductor layer  30  is formed on the first conductive layers  21  and fills the first trenches  22 . Similarly, to allow the sunlight pass through the first conductive layers  21 , a conductive and transparent material such as transparent conductive oxide (TCO) may be used to form the first conductive layers  21 . 
         [0022]    The semiconductor layer  30  may be any kind of semiconductor materials suitable for using as solar cell, wherein the semiconductor layer  30  is doped to form an n-doped region and a p-doped region. In the preferred embodiment, an amorphous silicon is utilized for forming the semiconductor layer  30  and the semiconductor layer  30  is doped such that the bottom side of the semiconductor layer  30  is a p-doped region and the upper side of the semiconductor layer  30  is an n-doped region. In addition, an intrinsic semiconductor region would be inserted between the p-doped region and the n-doped region in the case of amorphous silicon solar cells. Alternatively, the semiconductor layer  30  may be doped in an opposite manner. Moreover, if the sunlight comes in from the other side, the position of the p-doped region and the n-doped region formed in the semiconductor layer  30  may be exchanged according to a different design. 
         [0023]    In  FIG. 6 , second trenches  32  are formed in the semiconductor layer  30  by an etching process such that some portions of the first conductive layers  21  are exposed. The semiconductor layer  30  was divided into several semiconductor layers  31  by the second trenches  32 . A contact trench  33  is formed at the edge of the solar module, as shown at the left side of the solar module  70 . The contact trench  33  is prepared for the connection between the series of solar cells and the bypass diode. 
         [0024]    As shown in  FIG. 7 , a second conductive layer  40  is deposited over the semiconductor layers  31  such that the second conductive layer  40  is formed on the semiconductor layers  31  and fills the second trenches  32  and the contact trench  33 . The material of the second conductive layer  40  may be copper or any other transparent or opaque materials of desired conductivity. 
         [0025]    In  FIG. 8 , third trenches  42  are then formed in the semiconductor layers  31  and the second conductive layers  40  so as to expose some portions of the surface of the first conductive layers  21 . In addition, edge isolation is performed by forming the isolation trenches  43  at the edges of the solar module  70 . Through the edge isolation, the edge portions of the solar cells at the two sides of the solar module  70  are isolated from the series of solar cells. Since the isolated portions are usually of undesired property, usually they are not utilized for acting as solar cells or bypass diodes. 
         [0026]    Subsequently, a first contact  51  and a second contact  52  are then formed on two of the second conductive layers  41  as the contacts of the series of solar cells. When the two contacts are connected to a load (not shown), the internal current in the solar module  70  flows along the dashed line in  FIG. 8 , which does not flow through the semiconductor layer below the second contact  52 . Therefore, in the solar module  70 , the p-n junction in the semiconductor below the second contact  52  is an “unused” or “non-functional” p-n junction, which is not used for a solar cell. 
         [0027]    In the subject invention, the unused p-n junction of the semiconductor layer is utilized as a bypass diode by connecting to the series of the solar cells in an anti-parallel configuration. As shown in  FIG. 8 , a third contact  53  is formed on the second conductive layer  41  on the isolated portion adjacent to the second contact  52 . The third contact  53  is electrically connected to the p-doped region of the semiconductor layer  31  below the second contact  52  through the second conductive layer  41  and the first conductive layer  21 . 
         [0028]      FIG. 9  is a top-view of the solar module  70  shown in  FIG. 8 . In the preferred embodiment of the subject invention, a conductor, more specifically a conductive ribbon  60  is formed between the third contact  53  and the first contact  51  for connecting the two contacts electrically. By the connection, the unused p-n junction below the second contact  52  is now used as a bypass diode  34  which is connected in anti-parallel to the series of solar cells in the solar module  70 . 
         [0029]    It is appreciated that although the unused p-n junction below the second contact  52  is electrically connected in parallel with the series of solar cells through the ribbon  60 , the first contact  51 , and the third contact  53 , one skilled in the art will know that the connection may be in any desired form so as to achieve the electrical circuit shown in  FIG. 2 . 
         [0030]    While the illustrative embodiment of the invention has been shown and described, numerous variations and alternate embodiment will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention as defined in the appended claims.