Multijunction metamorphic solar cell

Abstract

A multijunction solar cell including a tandem vertical stack of a least an upper solar subcell, a first middle solar subcell, and bottom solar subcell; a first lateral conduction interlayer disposed adjacent to and beneath the second solar subcell; a blocking p-n diode or insulating layer disposed adjacent to and beneath the first lateral conduction interlayer; and a second lateral conduction layer disposed adjacent to and beneath the blocking p-n diode or insulating layer.

1 . A multijunction solar cell including a terminal of first polarity and a terminal of second polarity, comprising:
 (a) a semiconductor body including a tandem vertical stack of epitaxial subcells including at least an upper solar subcell, a first middle solar subcell, and a bottom solar subcell, the upper subcell having a top contact connected to the terminal of the first polarity, and the bottom solar subcell having a top contact and a bottom contact;   (b) an epitaxial first lateral conduction interlayer disposed adjacent to and beneath the second solar subcell to provide an electrical contact to the bottom of the second solar subcell to provide an electrical contact to the bottom of the second solar subcell;   (c) an epitaxial blocking p-n diode or insulating layer disposed adjacent to and beneath the first lateral conduction interlayer; and   (d) an epitaxial second lateral conduction layer disposed adjacent to and beneath the blocking p-n diode or insulating layer, wherein the bottom solar subcell is disposed adjacent to and beneath the second lateral conduction layer.   
     
     
         2 . A solar cell as defined in  claim 1 , wherein the first lateral conduction layer is compositionally graded to substantially lattice match the first middle solar subcell on one side and the bottom solar subcell on the other side, and is composed of any As, P, N, Sb based III-V compound semiconductors subject to constraints of having an in-plane lattice parameter less than or equal to that of the second solar subcell and greater than or equal to that of the bottom solar cell of the respective semiconductor region. 
     
     
         3 . A solar cell as defined in  claim 1 , further comprising:
 a first electrical contact disposed on the first lateral conduction layer and a second electrical contact disposed on the second lateral conduction layer.   
     
     
         4 . A solar cell as defined in  claim 1 , wherein the respective tandem vertical stack includes a second middle solar subcell, so that at least a four junction solar cell is formed, wherein the respective upper and first and second middle solar subcells are current mismatched from the bottom solar subcell. 
     
     
         5 . A solar cell as defined in  claim 4 , wherein the bottom subcell has a band gap of approximately 0.67 eV, the second middle subcell has a band gap in the range of approximately 1.3 to 1.5 eV, the first middle solar subcell has a band gap in the range of 1.65 to 1.8 eV, and the upper subcell has a band gap in the range of 1.8 to 2.0 eV. 
     
     
         6 . A solar cell as defined in  claim 4 , wherein the bottom solar subcell has a band gap of approximately 0.67 eV, the second middle solar subcell has a band gap in the range of approximately 1.41 eV and 1.31 eV, the first middle solar subcell has a band gap in the range of approximately 1.65 to 1.8 eV and the upper solar subcell of the first and second semiconductor regions has a band gap in the range of 2.0 to 2.20 eV. 
     
     
         7 . A solar cell as defined in  claim 4 , wherein the first lateral conduction interlayer is composed of In x Al y Ga 1-x-y As or In x Ga 1-x P with 0<x<1, 0<y<1, and x and y selected such that the band gap is in the range of 1.41 eV to 1.6 eV and may vary throughout its thickness, and is compositionally graded to substantially lattice match the second solar subcell on one side and the bottom solar subcell on the other side. 
     
     
         8 . A solar cell as defined in  claim 4 , wherein the upper subcell is composed of indium gallium aluminum phosphide (InGaAlP);
 the second middle solar subcell includes an emitter layer composed of indium gallium phosphide (InGaP), indium aluminum gallium arsenide (InAlGaAs) or indium gallium arsenide phosphide (InGaAsP), and a base layer composed of indium aluminum gallium arsenide or indium gallium arsenide phosphide (InGaAsP);   the first middle solar subcell is composed of indium gallium arsenide;   the fourth subcell is composed of germanium or SiGeSn, GaSb, InGaAsN, InGaAsNSb, InGaAsNBi, InGaAsNSbBi, InGaSbN, InGaBiN, InGaSbBiN; and   the first and second lateral conduction interlayers are composed of In x Al y Ga 1-x-y As or In x Ga 1-x P with 0<x<1, 0<y<1, and x and y selected such that the band gap is in the range of 1.41 eV to 1.6 eV and may vary throughout its thickness.   
     
     
         9 . A solar cell as defined in  claim 4 , wherein:
 the upper subcell has a band gap in the range of 2.0 to 2.20 eV and is composed of indium gallium aluminum phosphide (InGaAlP);   the second middle solar subcell has a band gap in the range of approximately 1.65 to 1.8 eV and includes an emitter layer composed of indium gallium phosphide (InGaP), indium aluminum gallium arsenide (InGaAs) or indium gallium arsenide phosphide (InGaAsP), and a base layer composed of indium aluminum gallium arsenide or indium gallium arsenide phosphide (InGaAsP);   the first middle solar subcell has a band gap in the range of approximately 1.3 to 1.41 eV and is composed of indium gallium arsenide; and   the bottom solar subcell is composed of germanium or SiGeSn, GaSb, InGaAsN, InGaAsNSb, InGaAsNBi, InGaAsNSbBi, InGaSbN, InGaBiN, InGaSbBiN; the upper first subcell is composed of indium gallium aluminum phosphide.   
     
     
         10 . A solar cell as defined in  claim 1 , further comprising:
 a distributed Bragg reflector (DBR) layer disposed above the bottom solar subcell and arranged so that light can enter and pass through the solar subcell disposed above the bottom subcell and at least a portion of which can be reflected back into the solar subcell located above the bottom subcell by the DBR layer, and the distributed Bragg reflector layer is composed of a plurality of alternating layers of lattice matched materials with discontinuities in their respective indices of refraction.   
     
     
         11 . A solar cell as defined in  claim 10 , wherein the thickness and refractive index of each period determines the stop band and its limiting wavelength, and the DBR layer includes a first DBR layer composed of a plurality of n or p type Al x Ga 1-x (In)As layers, and a second DBR layer disposed over the first DBR layer and composed of a plurality of n or p type Al y Ga 1-y (In)As layers, where 0<x<1, 0<y<1, and y is greater than x, and the term (In) denotes an optional inclusion of up to 10% indium. 
     
     
         12 . A solar cell as defined in  claim 4 , wherein the selection of the composition of the subcells and their band gaps maximizes the efficiency at high temperature (in the range of 40 to 100 degrees Centigrade) in deployment in space at a predetermined time after the initial deployment (referred to as the beginning-of-life or BOL), such predetermined time being referred to as the end-of-life (EOL), and the average band gap of all four cells (i.e., the sum of the four lowest direct or indirect band gaps of the materials of each subcell divided by 4) is greater than 1.44 eV. 
     
     
         13 . A solar cell as defined in  claim 4 , wherein the bottom solar subcell is comprised of a direct or indirect band gap material such that the lowest direct band gap of the material is greater than 0.75 eV, and the average band gap of the upper solar subcell, the first middle solar subcell, the second middle solar subcell and the bottom solar subcell is greater than 1.44 eV. 
     
     
         14 . A solar cell as defined in  claim 1 , further comprising a tunnel diode layer over the first lateral conduction layer. 
     
     
         15 . A solar cell as defined in  claim 1 , further comprising a first alpha layer deposited over the first lateral conduction layer of the respective semiconductor region to a thickness of between 0.25 and 1.0 micron to prevent threading dislocations from propagating, either opposite to the direction of growth or in the direction of growth into the first middle solar subcell. 
     
     
         16 . A solar cell as defined in  claim 15 , further comprising a second alpha layer deposited over the blocking p-n diode or insulating layer to a thickness of between 0.25 and 1.0 micron to prevent threading dislocations from propagating, either opposite to the direction of growth or in the direction of growth into the second solar subcell. 
     
     
         17 . A solar cell as defined in  claim 10 , further comprising a tunnel diode disposed over the first lateral conduction layer and below the distributed Bragg reflector (DBR) layer. 
     
     
         18 . A solar cell as defined in  claim 1 , wherein the bottom contact of the bottom solar subcell is connected to the terminal of second polarity. 
     
     
         19 . A multijunction solar cell including a terminal of first polarity and a terminal of second polarity, comprising:
 (a) a semiconductor body including:
 a tandem vertical stack of at least an epitaxial upper solar subcell, first middle solar subcell, second middle solar subcell and bottom solar subcell, the upper subcell having a top contact connected to the terminal of the first polarity, and the bottom solar subcell having a top contact and a bottom contact connected to the terminal of second polarity; 
   (b) an epitaxially deposited first lateral conduction interlayer disposed adjacent to and beneath the second solar subcell to provide an electrical contact to the bottom of the second solar sub cell;   (c) an epitaxially deposited blocking p-n diode or insulating layer disposed adjacent to and beneath the first lateral conduction interlayer; and   (d) an epitaxially deposited second lateral conduction layer disposed adjacent to and beneath the blocking p-n diode or insulating layer, wherein the bottom solar subcell is disposed adjacent to and beneath the second lateral conduction layer which forms an electrical contact to the top contact of the bottom solar subcell.   
     
     
         20 . A method of forming a multijunction solar cell assembly comprising:
 (a) providing an integral semiconductor body including a tandem vertical stack of epitaxially grown subcells including at least an upper solar subcell, a first middle solar subcell, a second middle solar subcell and a bottom solar subcell, the upper subcell having a top contact connected to a terminal of the first polarity, and the bottom solar subcell having a bottom contact;   an epitaxially deposited first lateral conduction layer disposed adjacent to and beneath the second solar subcell thereby forming a bottom contact to the first middle solar subcell;   an epitaxially deposited blocking p-n diode or insulating layer disposed adjacent to and beneath the first lateral conduction interlayer of the respective semiconductor region;   an epitaxially deposited second lateral conduction layer disposed adjacent to and beneath the blocking p-n diode or insulating layer, wherein the bottom solar subcell is disposed adjacent to and beneath the second lateral conduction layer;   
       (b) etching from the top surface of the semiconductor body to the first lateral conduction layer to make an electrical contact to the first lateral conduction layer and thereby to the bottom contact to the first middle solar subcell; and 
       (c) etching from the top surface of the semiconductor body to the second lateral conduction layer to make an electrical contact to the second lateral conduction layer and thereby to the top contact of the bottom solar subcell.