Abstract:
This application is related to a method of manufacturing a solar cell device comprising providing a substrate comprising Ge or GaAs; forming a first tunnel junction on the substrate, wherein the first tunnel junction comprises a first n-type layer comprising InGaP:Te, and a first alloy layer comprising AlxGa( 1 −x)As and having a lattice constant; adding a material into the first alloy layer to change the lattice constant; and forming a first p-n junction on the first tunnel junction.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a Continuation of co-pending application Ser. No. 14/161,255, filed on 22 Jan. 2014, which is a Divisional application of co-pending application Ser. No. 12/686,169 filed on 12 Jan. 2010; for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. 098100992 filed in Taiwan on 12 Jan. 2009 under 35 U.S.C. §119, the entire contents of all of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    This application is related to a tandem solar cell structure. 
         [0004]    2. Description of the Related Art 
         [0005]    The solar cell is an energy transferring optoelectronic device that receives sunlight and transfers it into electrical energy. 
         [0006]    The tandem solar cell or the multi junction solar cell stacks two or more than two p-n junction elements in series with the same or different energy bandgaps. In general, the p-n junction element which can absorb higher energy spectrum is formed as the upper layer; the p-n junction element which can absorb lower energy spectrum is formed as the bottom layer. By combining the p-n junction elements of different materials, the photon energy can be absorbed layer by layer. It can raise the absorbing rate and efficiency, and decrease the transferring loss. 
         [0007]      FIG. 1  illustrates a cross-sectional view of the conventional tandem solar cell structure including a substrate  101 , a buffer layer  102 , a tunnel junction  103  and a p-n junction  104 . Currently, the wildly used tunnel junction  103  includes a heavily doped n-type layer (n++)  1031  and a heavily doped p-type layer (p++)  1032  wherein the heavily doped n-type layer (n++) is generally doped with Silicon, Tellurium or Selenium. The heavily doped p-type layer (p++)  1032  is generally doped with Carbon, Zinc, Magnesium or Beryllium. The lattice constant of the heavily doped p-type layer (p++)  1032  is decreased after doped with Carbon. It increases the lattice constant difference of the tunnel junction  103  and the substrate  101  and impairs the epitaxial quality and the effect of the tunnel junction  103 . 
       SUMMARY 
       [0008]    This application is related to a method of manufacturing a solar cell device, comprising providing a substrate comprising Ge or GaAs; forming a first tunnel junction on the substrate, wherein the first tunnel junction comprises a first n-type layer comprising InGaP:Te, and a first alloy layer comprising Al x Ga (1−x) As and having a lattice constant; adding a material into the first alloy layer to change the lattice constant; and forming a first p-n junction on the first tunnel junction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings are included to provide easy understanding of the application, and are incorporated herein and constitute a part of this specification. The drawings illustrate embodiments of the application and, together with the description, serve to illustrate the principles of the application. 
           [0010]      FIG. 1  illustrates a cross-sectional view of the conventional tandem solar cell structure. 
           [0011]      FIG. 2A  illustrates a cross-sectional view of the tandem solar cell structure in accordance with one embodiment of the present application. 
           [0012]      FIG. 2B  illustrates a cross-sectional view of the tandem solar cell structure in accordance with another embodiment of the present application. 
           [0013]      FIG. 3  illustrates the I-V curve of the alloy layer with different concentration of Indium in the tunnel junction in accordance with one embodiment of the present application. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    Reference is made in detail to the preferred embodiments of the present application, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
         [0015]      FIG. 2A  illustrates a cross-sectional view of the tandem solar cell structure in accordance with one embodiment of the present application including a substrate  201 , a buffer layer  202 , a first tunnel junction  203  and a first p-n junction  204 . The first tunnel junction  203  includes a heavily doped n-type layer (n++)  2031  and an alloy layer  2032 . In this application, the material of the substrate  201  can be Silicon, Germanium, Si—Ge, GaAs or InP. The material of the buffer layer  202 , the heavily doped n-type layer (n++)  2031 , the alloy layer  2032  and the first p-n junction  204  contains one or more elements selected from the group consisting of Gallium, Aluminum, Indium, Arsenic, Phosphorous, Nitrogen and Silicon, such as (Al x Gal 1−x ) y In 1−y As or (Al x Gal 1−x ) y In 1−y P. 
         [0016]    The alloy layer  2032  comprises a heavily doped p-type layer containing an element with atomic number larger than that of Gallium. A p-type impurity with high doping concentration and an element with atomic number larger than that of Gallium are added in the p-type layer in the epitaxial process to form the alloy layer  2032  having a heavily doped p-type layer with an element with atomic number larger than that of Gallium. The lattice constant of the alloy layer  2032  is increased by the content of the added element with atomic number larger than that of Gallium to decrease the lattice mismatch of the alloy layer  2032  and the substrate  201  so the quality of the epitaxial layers improved. Besides, the energy gap of the alloy layer  2032  is decreased by adding the element with atomic number larger than that of Gallium. The Jp (current density), and the Jp/Vp (slope of current density to voltage) of the alloy layer are increased and the tunneling current of the first tunnel junction  203  is increased. The material of the element with atomic number larger than that of Gallium can be selected from Indium, Thallium, Antimony, Bismuth, Tin, Lead, Bismuth, Polonium, Cadmium, and Mercury. The concentration of the element with atomic number larger than that of Gallium can be 1˜2%, which is equal to 3.5×10 21 ˜1.7×10 22  (l/cm 3 ). 
         [0017]      FIG. 2B  illustrates a cross-sectional view of the tandem solar cell structure in accordance with another embodiment of the present application including a substrate  201 , a buffer layer  202 , a first tunnel junction  203 , a first p-n junction  204 , a second tunnel junction  205  and a second p-n junction  206 . The first tunnel junction  203  and the second tunnel junction  205  include heavily doped n-type layers (n++)  2031 ,  2051  and alloy layers  2032 ,  2052 . 
         [0018]    In this application, the material of the substrate  201  can be Silicon, Germanium, Si—Ge, GaAs or InP. The material of the buffer layer  202 , the heavily doped n-type layers (n++)  2031 ,  2051 , the alloy layers  2032 ,  2052 , the first p-n junction  204  and the second p-n junction  206  contains one or more elements selected from the group consisting of Gallium, Aluminum, Indium, Arsenic, Phosphorous, Nitrogen and Silicon, such as (Al x Gal 1−x ) y In 1−y As or (Al x Gal 1−x ) y In 1−y P. 
         [0019]    The alloy layers  2032 ,  2052  comprise a heavily doped p-type layer containing an element with atomic number larger than that of Gallium. A p-type impurity with high doping concentration and an element with atomic number larger than that of Gallium are added in the p-type layer in the epitaxial process to form the alloy layer  2032 ,  2052  having a heavily doped p-type layer with an element with atomic number larger than that of Gallium. The lattice constant of the alloy layers  2032 ,  2052  is increased by the content of the added element with atomic number larger than that of Gallium to decrease the lattice mismatch of the alloy layers  2032 ,  2052  and the substrate  201  so the quality of the epitaxial layers is improved. Besides, the energy gap of the alloy layers  2032 ,  2052  is decreased by adding the element with atomic number larger than that of Gallium. The Jp (current density), and the Jp/Vp (slope of current density to voltage) of the alloy layers are increased and the tunneling current of the first tunnel junction  203  is also increased. The material of the element with atomic number larger than that of Gallium can be selected from Indium, Thallium, Antimony, Bismuth, Tin, Lead, Bismuth, Polonium, Cadmium, and Mercury. The concentration of the element with atomic number larger than that of Gallium can be 1˜2%, which is equal to 3.5×10 21 ˜1.7×10 22  (l/cm 3 ). 
         [0020]    In one embodiment, the material of the substrate  201  is Germanium. The material of the heavily doped n-type layers (n++)  2031 ,  2051  of the first and the second tunnel junction  203 ,  205  is InGaP:Te. The material of the alloy layer  2032 ,  2052  is Al x Ga (1−x) As:C+ and is doped with In to form the In y Al x Ga (1−x) As alloy. The alloy layer can decrease the lattice mismatch and increase the tunneling current of the tunnel junction. 
         [0021]      FIG. 3  illustrates the I-V curve of the alloy layer with different concentration of Indium in the tunnel junction in accordance with one embodiment of the present application. By increasing the adding concentration of Indium, the slope of the I-V curve is increased and the tunnel current through the first and the second tunnel junction  203 ,  205  is also increased. 
         [0022]    In other embodiment of this application, a third tunnel junction can be formed on the second p-n junction  206  and a third p-n junction can be formed on the third tunnel junction. The tunnel junctions and the p-n junctions can be stacked repetitively based on the requirement of the product and there is no need to limit the number of the p-n junction in the tandem solar cell. The design of the tunnel junction is substantially the same as the embodiment mentioned above and can be referred thereto. 
         [0023]    Although the drawings and the illustrations above are corresponding to the specific embodiments individually, the element, the practicing method, the designing principle, and the technical theory can be referred, exchanged, incorporated, collocated, coordinated except they are conflicted, incompatible, or hard to be put into practice together. 
         [0024]    Although the present application has been explained above, it is not the limitation of the range, the sequence in practice, the material in practice, or the method in practice. Any modification or decoration for present application is not detached from the spirit and the range of such.