Abstract:
A solar cell and a manufacturing method thereof. A method of manufacturing a solar cell includes: forming an emitter layer on a first surface of a semiconductor substrate; forming an insulation layer on the emitter layer; applying a chemical compound including a dopant having a conductive type of the emitter layer on the insulation layer according to a pattern; forming a high concentration emitter portion by removing a portion of the insulation layer corresponding to a positioning of the chemical compound and diffusing the dopant toward the emitting layer; removing the chemical compound; and forming a first electrode electrically connected to the high concentration emitter portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0134211, filed on Dec. 29, 2005, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a solar cell and a manufacturing method thereof.  
         [0004]     2. Description of the Related Art  
         [0005]     A conventional solar cell generates electrical energy from solar energy. The solar cell is environmentally friendly, and its energy source is virtually endless. In addition, the solar cell has a long lifespan. Examples of the solar cell include a silicon solar cell and a dye-sensitized solar cell.  
         [0006]     The silicon solar cell includes a semiconductor substrate and an emitter layer that constitute a p-n contact area having different conductive types, an insulation layer and a front electrode that are formed on the emitter layer, and a rear electrode formed on the semiconductor substrate.  
         [0007]     The emitter layer is formed by doping a first surface of the semiconductor substrate with a dopant. In consideration of a contact resistance between the front electrode and the emitter layer, the doping may be performed with a high concentration of the dopant.  
         [0008]     However, in order to minimize recombination occurring at a surface of the solar cell, the doping may be performed with a low concentration of the dopant. As such, when the emitter layer is formed with a uniform doping concentration, necessary characteristics of the solar cell cannot be entirely satisfied (or met).  
         [0009]     A silicon solar cell has been provided in which a high concentration emitter portion is formed together with an emitter layer at a region where the front electrode is formed. In order to form the high concentration emitter portion, a dopant is additionally applied after an insulation layer is patterned through photolithography and etching processes. However, since the above may require expensive equipment and materials to pattern the insulation layer, as well as an additional application of the dopant, a manufacturing process of the silicon solar cell may be complex.  
       SUMMARY OF THE INVENTION  
       [0010]     Aspects of the present invention respectively provide a solar cell and a manufacturing method thereof by which a solar cell having a high concentration emitter portion can be manufactured using a simple and inexpensive process.  
         [0011]     According to an embodiment of the present invention, a method of manufacturing a solar cell includes: forming an emitter layer on a first surface of a semiconductor substrate; forming an insulation layer on the emitter layer; applying a chemical compound including a dopant having a conductive type of the emitter layer on the insulation layer according to a pattern; forming a high concentration emitter portion by removing a portion of the insulation layer corresponding to a positioning of the chemical compound and diffusing the dopant toward the emitting layer; removing the chemical compound; and forming a first electrode electrically connected to the high concentration emitter portion.  
         [0012]     The dopant may include phosphorus (P), and the chemical compound may further include phosphorus pentoxide (P 2 O 5 ) and/or phosphorus chloride oxide (POCl 3 ).  
         [0013]     The chemical compound may be applied by using a process selected from the group consisting of screen printing, dispensing, electroless-plating, electroplating, and combinations thereof.  
         [0014]     The high concentration emitter portion may be formed by performing a thermal annealing process for diffusing the dopant.  
         [0015]     The thermal annealing process may be performed at a temperature in a range from about 850° C. to about 950° C.  
         [0016]     The pattern of the chemical compound may correspond to a pattern by which the first electrode is formed.  
         [0017]     The method may further include forming a second electrode on a second surface of the semiconductor substrate, the second electrode being electrically connected to the semiconductor substrate.  
         [0018]     According to another embodiment of the present invention, a solar cell includes: a semiconductor substrate; an emitter layer disposed on the semiconductor substrate; a first electrode disposed on the emitter layer and electrically connected to the emitter layer; and an insulation layer disposed on one or more regions of the emitter layer where the first electrode is not disposed. The emitter layer includes a high concentration emitter portion corresponding to a positioning of the first electrode. The insulation layer includes a substantially uneven surface in contact with the first electrode. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention.  
         [0020]      FIGS. 1A, 1B ,  1 C,  1 D,  1 E,  1 F,  1 G,  1 H and  1 I are cross-sectional views illustrating a method of manufacturing a solar cell according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]     In the following detailed description, only certain exemplary embodiments of the present invention are shown and described, by way of illustration. As those skilled in the art would recognize, the described exemplary embodiments may be modified in various ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.  
         [0022]      FIGS. 1A, 1B ,  1 C,  1 D,  1 E,  1 F,  1 G,  1 H and  11  are cross-sectional views illustrating a method of manufacturing a solar cell according to an embodiment of the present invention.  
         [0023]     Referring first to  FIG. 1A , a p-type semiconductor substrate  10  formed of silicon is prepared (or provided). However, embodiments of the present invention are not limited thereto, and thus an n-type semiconductor substrate may be prepared. In addition, the semiconductor substrate may be formed by any of various suitable semiconductor materials other than (or in addition to) silicon.  
         [0024]     To improve characteristics of the solar cell, a pre-process may be carried out in which impurities are removed by using a washing solution after the semiconductor substrate  10  is etched by using an alkaline aqueous solution and/or an acid blend solution. A damaged part in (or of) the semiconductor substrate  10  is removed through etching, and a surface of the semiconductor substrate  10  accordingly becomes uneven. Here, it is possible to reduce a loss of solar energy.  
         [0025]     As shown in  FIG. 1B , a front surface of the semiconductor substrate  10  is doped with a dopant. An n-type emitter layer  12  is thereby formed. Although phosphorus (P) is used as the dopant by way of example in one embodiment to form the n-type emitter layer  12 , any of various suitable materials other than (or in addition to) phosphorus may be used as the dopant. Embodiments of the present invention are not limited thereto, and thus any of various suitable materials can be used such that a conductive type of the emitter layer  12  is opposite with respect to that of the semiconductor substrate  10 . Therefore, when an n-type semiconductor substrate is used, a p-type emitter layer should be formed.  
         [0026]     The front surface of the semiconductor substrate  10  may be doped using any of various suitable doping methods such as a high-temperature diffusion method, a spray method, a screen printing method, and/or an ion shower method.  
         [0027]     After the doping, a process for removing nonessential phosphorus silicate glass (PSG) using a fluoric acid aqueous solution may be carried out.  
         [0028]     As shown in  FIG. 1C , an insulation layer  14  is formed on the emitter layer  12 . The insulation layer  14  may be a silicon nitride layer, a silicon oxide layer, and/or a titanium oxide layer formed by using any of various suitable methods such as a plasma enhanced chemical vapor deposition method, an electron beam deposition method, a screen printing method, and/or a spray method.  
         [0029]     The insulation layer  14  serves not only to reduce reflection of solar rays that are incident thereto, but also to reduce (or prevent) electron loss that may occur at a surface of the semiconductor substrate  10 . That is, electron loss may occur at the surface of the semiconductor substrate  10  due to dangling bonds, and this can be reduced (or prevented) by forming the insulation layer  14 .  
         [0030]     As shown in  FIG. 1D , in one embodiment, a chemical compound  16  containing phosphorus (P) is applied to the insulation layer  14  by using a screen printing method. However, embodiments of the present invention are not limited thereto. That is, the chemical compound  16  may be applied to the insulation layer  14  by using any of various suitable methods such as screen printing, a dispensing method, an electroless-plating method, and/or an electroplating method. The chemical compound  16  is applied to correspond to a pattern by which a first electrode  22  (see, for example,  FIG. 1I ) is to be provided on the emitter layer  12 , such that a high concentration emitter portion  12   a  (see, for example,  FIG. 1E ) is located below the first electrode  22 .  
         [0031]     In the chemical compound  16 , phosphorus may exist in the form of phosphorus pentoxide (P 2 O 5 ) and/or phosphorus chloride oxide (POCl 3 ). Although phosphorus is used as the dopant in the present embodiment, embodiments of the present invention are not limited thereto. That is, any of various suitable materials may be used as the dopant so long as the dopant of the chemical compound  16  has a same conductive type as the emitter layer  12 . In addition, embodiments of the present invention are not limited to a conductive type of the dopant and the emitter layer (i.e., the invention is not limited to a type of major carriers in the dopant and the emitter layer). In one embodiment, a portion of the insulation layer  14  is etched by the chemical compound  16  including the dopant through a thermal annealing process.  
         [0032]     As shown in  FIG. 1E , the portion of the insulation layer  14  is etched to form an insulation layer  14   a , and the high-concentration emitter portion  12   a  is formed by performing the thermal annealing process on the semiconductor substrate  10  having the emitter layer  12 , the insulation layer  14 , and the chemical compound  16  applied thereon. That is, during the thermal annealing process, phosphorus pentoxide (P 2 O 5 ) and/or phosphorus chloride oxide (POCl 3 ) contained in the chemical compound  16  removes (or eliminates) the portion of the insulation layer  14  located below the chemical compound  16 , and phosphorus contained in the chemical compound  16  is diffused towards the semiconductor substrate  10  at the removed portion of the insulation layer  14 . The high concentration emitter portion  12   a  of the semiconductor substrate  10  is thereby formed.  
         [0033]     Here, since the portion of the insulation layer  14  is removed by the chemical compound  16  that has been screen printed, as shown in an exploded partial perspective view in  FIG. 1F , a substantially uneven part (or surface)  14   b  is formed on the insulation layer  14   a  according to a screen mesh pattern.  
         [0034]     As described above, in the present embodiment, a photolithography process or a mask etching process is not required when the insulation layer  14  is patterned according thereto. Thus, expensive equipment and/or materials are not required, and a manufacturing cost can be significantly reduced as a result. In addition, since the high concentration emitter portion  12   a  can be formed without using an additional doping process, the manufacturing process can be simplified.  
         [0035]     The thermal annealing process may be carried out at a temperature in a range from 850° C. to 950° C. At a high temperature above 950° C., the semiconductor substrate  10  is more likely to be damaged by the thermal annealing process. At a low temperature below 850° C., diffusion may not occur to a sufficiently high degree.  
         [0036]     An infrared lamp, a furnace, or the like may be used as a heat source in the thermal annealing process. For example, when the infrared lamp is used, the thermal annealing process may be carried out for a period in a range from 10 seconds to 10 minutes.  
         [0037]     As shown in  FIG. 1G , ultra-pure water may be used to wash the semiconductor substrate  10 , thereby removing the chemical compound  16 . Here, a surfactant may be used in consideration of materials composing the chemical compound  16 .  
         [0038]     As shown in  FIG. 1H , in one embodiment, an aluminum paste is screen-printed on a rear surface of the semiconductor substrate  10 , and a thermal annealing process is then carried out. As a result, a second electrode  18  electrically connected to the semiconductor substrate  10  is formed. However, embodiments of the present invention are not limited thereto. That is, the second electrode  18  may be formed of any of various suitable materials other than (or in addition to) aluminum.  
         [0039]     Aluminum is diffused over the rear surface of the semiconductor substrate  10  through the thermal annealing process to a certain thickness (which may be predetermined), and thus a p+ type of rear electric field layer  20  is formed. The rear electric field layer  20  forms an electric field such that optically excited electrons are blocked (or prevented) from moving to the rear surface of the semiconductor layer  10 .  
         [0040]     As shown in  FIG. 1I , the first electrode  22  is formed on the front surface of the semiconductor substrate  10  such that the first electrode  22  corresponds to a region from where the chemical compound  16  was removed, that is, a region adjacent to the high concentration emitter portion  12   a . The first electrode  22  may be formed by using any of various suitable methods such as screen printing, an electroless-plating method, an electroplating method, an inkjet method, and/or a dispensing method. For example, the first electrode  22  may be formed of silver (Ag).  
         [0041]     In the solar cell of the present embodiment, a contact resistance can be effectively reduced since the first electrode  22  is formed on the high concentration emitter portion  12   a . Moreover, since the relatively low concentration emitter layer  12  is formed on a region where the first electrode  22  is not formed, a charge loss may be reduced.  
         [0042]     When light is incident to the solar cell produced according to the manufacturing method of embodiments of the present invention, pairs of positive holes and electrons formed by a photoelectric effect are divided. Accordingly, the electrons are accumulated on the n-type emitter layer  12 , and the positive holes are accumulated on the p-type semiconductor substrate  10 , thereby generating an electrical potential difference. The electrical potential difference allows current to flow through the first electrode  22 , the second electrode  18 , and an external circuit. As described above, the conductive type of the semiconductor substrate  10  and the conductive types of the emitter layer  12  and the high concentration emitter portion  12   a  can be modified in any of various suitable forms, which are included in the scope of the present invention.  
         [0043]     According to a method of manufacturing a solar cell of embodiments of the present invention, an insulation layer can be patterned at a low cost by using a chemical compound for etching the insulation layer. The chemical compound includes a dopant having the same conductive type as the emitter layer, and thus a high concentration emitter portion can be formed concurrently with the patterning of the insulation layer without an additional doping process. Therefore, the solar cell having the high concentration emitter portion can be manufactured using simple processes.  
         [0044]     In addition, a contact resistance can be reduced since the first electrode is formed on the high concentration emitter portion. Moreover, since a relatively low concentration emitter layer is formed at a region where the first electrode is not formed, it is possible to reduce charge loss. Consequently, various characteristics of the solar cell can be improved.  
         [0045]     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.