Monolithic tandem voltage-matched multijuntion solar cells

Abstract

Voltage-matched monolithic thin film multijunction solar cell and methods of producing cells having a first pn junction with a first band-gap energy, a second pn junction with a second band-gap energy and an insulating layer between the first and second pn junctions. The voltage-matched monolithic thin film multijunction solar cells further include a parallel connection between the first and second pn junctions to form a two-terminal photonic device.

What is claimed is: 
     
         1 . A voltage-matched monolithic thin film multijunction solar cell comprising:
 a first pn junction having an n-type region, a p-type region and a first band-gap energy;   a second pn junction having an n-type region, a p-type region and a second band-gap energy;   a transparent electrically insulating layer between the first pn junction and the second pn junction; wherein the first and second pn junctions are connected in parallel to form a two-terminal photonic device.   
     
     
         2 . The voltage-matched monolithic thin film multijunction solar cell of  claim 1  further comprising:
 a transparent first front contact and a transparent first back contact associated with the first pn junction, wherein the transparent back contact is positioned between the transparent electrically insulating layer and the first pn junction and wherein the transparent first front contact and the transparent first back contact provide for electrical connection to the first pn junction from a first side of the solar cell; and 
 a transparent second front contact and a second back contact associated with the second pn junction, wherein the transparent second front contact is positioned between the transparent electrically insulating layer and the second pn junction and wherein the transparent second front contact and the second back contact provide for electrical connection to the second pn junction from a second side of the solar cell. 
 
     
     
         3 . The voltage-matched monolithic thin film multijunction solar cell of  claim 1  further comprising:
 at least one of crystalline, polycrystalline or amorphous first pn junction; and 
 at least one of crystalline, polycrystalline or amorphous second pn junction. 
 
     
     
         4 . The voltage-matched monolithic thin film multijunction solar cell of  claim 2  wherein the first pn junction and the second pn junction comprise layers of at least one of; CIGS, CZTS, a-Si, polycrystalline Si, microcrystalline Si, CdTe, or CdTe alloyed with Zn, Se or S. 
     
     
         5 . The voltage-matched monolithic thin film multijunction solar cell of  claim 1  further comprising:
 a first string of serially connected sub-cells defined within the first pn junction; 
 a second string of serially connected sub-cells defined within the second pn junction; and 
 a parallel connection between the first string of serially connected sub-cells and the second string of serially connected sub-cells. 
 
     
     
         6 . The voltage-matched monolithic thin film multijunction solar cell of  claim 1  wherein the transparent electrically insulating region further comprises one or more low index of refraction layers providing for enhanced photon recycling or light trapping. 
     
     
         7 . The voltage-matched monolithic thin film multijunction solar cell of  claim 1  wherein at least one of the first pn junction or the second pn junction comprises a vertically stacked set of multiple pn junctions that are connected in series with tunnel junctions. 
     
     
         8 . A voltage-matched thin film multijunction solar cell comprising:
 a first pn junction comprising;
 an n-type region; 
 a p-type region; and 
 a first bandgap; 
   a second pn junction comprising a doped Si, Ge or GaAs wafer;   a transparent electrically insulating region separating the first pn junction and second pn junction;   a transparent first front contact and a transparent first back contact associated with the first pn junction, wherein the transparent back contact is positioned between the transparent electrically insulating region and the first pn junction; and   an interdigitated p-type and n-type back contact associated with the second pn junction on the side of the wafer opposite the electrically insulating layer, wherein the first pn junction and the second pn junction are connected in parallel to form a two-terminal photonic device.   
     
     
         9 . The voltage-matched thin film multijunction solar cell of  claim 8  further comprising at least one of a crystalline, polycrystalline or amorphous first pn junction. 
     
     
         10 . The voltage-matched thin film multijunction solar cell of  claim 9  wherein the first pn junction comprises layers of at least one of; CIGS, CZTS, a-Si, polycrystalline Si, microcrystalline Si, CdTe, or CdTe alloyed with Zn, Se or S. 
     
     
         11 . The voltage-matched thin film multijunction solar cell of  claim 8  wherein the second pn junction further comprises a textured surface. 
     
     
         12 . The voltage-matched thin film multijunction solar cell of  claim 8  further comprising:
 a first string of serially connected sub-cells defined within the first pn junction; 
 a second string of serially connected sub-cells defined within the second pn junction; and 
 a parallel connection between the first string of serially connected sub-cells and the second string of serially connected sub-cells. 
 
     
     
         13 . The voltage-matched thin film multijunction solar cell of  claim 8  wherein the transparent electrically insulating region further comprises one or more low index of refraction layers providing for enhanced photon recycling or light trapping. 
     
     
         14 . The voltage-matched thin film multijunction solar cell of  claim 8  wherein the first pn junction comprises a vertically stacked set of multiple pn junctions that are connected in series with tunnel junctions. 
     
     
         15 . A method of fabricating a tandem voltage-matched solar cell comprising:
 providing a transparent substrate;   forming a first crystalline, polycrystalline or amorphous pn junction comprising an n-type region, a p-type region and a first band-gap energy, in contact with a first surface of the substrate;   forming a second crystalline, polycrystalline or amorphous pn junction comprising an n-type region, a p-type region and a second band-gap energy in contact with a second surface of the substrate, opposite the first surface; and   connecting the first pn junction and the second pn junction in parallel to form a two-terminal photonic device.   
     
     
         16 . The method of  claim 15  further comprising:
 forming first front contacts and first back contacts associated with the first pn junction, which first front contacts and first back contacts are accessible from a surface of the first pn junction opposite the transparent substrate; and 
 forming second front contacts and second back contacts associated with the second pn junction, which second front contacts and second back contacts are accessible from a surface of the second pn junction opposite the transparent substrate. 
 
     
     
         17 . The method of  claim 16  wherein the first front and first back contacts and the second front contacts are formed of a transparent conducting oxide. 
     
     
         18 . The method of  claim 16  further comprising providing a transparent glass substrate. 
     
     
         19 . The method of  claim 16  wherein the first pn junction and the second pn junction each comprise at least one of CIGS, CZTS, a-Si, polycrystalline Si, microcrystalline Si, CdTe, or CdTe alloyed with Zn, Se or S. 
     
     
         20 . The method of  claim 16  further comprising:
 forming a first string of serially connected sub-cells defined within the first pn junction; 
 forming a second string of serially connected sub-cells defined within the second pn junction; and 
 forming a parallel connection between the first string of serially connected sub-cells and the second string of serially connected sub-cells. 
 
     
     
         21 . The method of  claim 16  further comprising forming at least one of the first or second pn junctions as a vertically stacked set of multiple pn junctions that are connected in series with tunnel junctions. 
     
     
         22 . A method of fabricating a voltage-matched thin film multijunction solar cell comprising:
 providing a bottom pn junction comprising;
 a doped Si, Ge or GaAs region; and 
 interdigitated p-type and n-type back contacts; 
   forming an insulating layer in contact with the bottom pn junction, opposite the interdigitated p-type and n-type back contacts;   forming an upper pn junction in contact with the insulating layer, wherein the upper pn junction comprises;
 an n-type region, 
 a p-type region; 
 a transparent front contact; and 
 a transparent back contact, wherein the transparent back contact is positioned between the insulating layer and the upper pn junction; and 
   connecting the bottom pn junction and the upper pn junction in parallel to form a two-terminal photonic device.   
     
     
         23 . The method of  claim 22  further comprising forming a crystalline, polycrystalline or amorphous upper pn junction. 
     
     
         24 . The method of  claim 22  wherein the upper pn junction comprises at least one of;
 CIGS, CZTS, a-Si, polycrystalline Si, microcrystalline Si, CdTe, or CdTe alloyed with Zn, Se or S. 
 
     
     
         25 . The method of  claim 22  further comprising forming the transparent front contact and the transparent back contact associated with the upper pn junction from a transparent conducting oxide. 
     
     
         26 . The method of  claim 22  further comprising exposing the transparent back contact associated with the upper pn junction by scribing or chemically removing a portion of the upper pn junction and the transparent front contact associated with the upper pn junction. 
     
     
         27 . The method of  claim 22  further comprising texturing a surface of the bottom pn junction. 
     
     
         28 . The method of  claim 22  further comprising:
 forming a first string of serially connected sub-cells defined within the bottom pn junction; 
 forming a second string of serially connected sub-cells defined within the upper pn junction; and 
 forming a parallel connection between the first string of serially connected sub-cells and the second string of serially connected sub-cells. 
 
     
     
         29 . The method of  claim 22  further comprising forming the upper pn junction as a vertically stacked set of multiple pn junctions that are connected in series with tunnel junctions.