Method of forming an inverted metamorphic multijunction solar cell with dbr layer adjacent to the top subcell

Abstract

A multijunction solar cell comprising an upper first solar subcell having a first band gap; a middle second solar subcell adjacent to the first solar subcell and having a second band gap smaller than the first band gap; a graded interlayer adjacent to the second solar subcell; the graded interlayer having a third band gap greater than the second band gap; a third solar subcell adjacent to the interlayer, the third subcell having a fourth band gap smaller than the second band gap such that the third subcell is lattice mismatched with respect to the second subcell; and a distributed Bragg reflector (DBR) layer adjacent to the upper first subcell.

1 - 20 . (canceled) 
     
     
         21 . A method of forming a multijunction solar cell comprising:
 forming an upper first solar subcell composed of InGa(Al)P;   forming a back surface field (BSF) layer directly adjacent the upper first solar subcell;   forming a distributed Bragg reflector (DBR) layer composed of a plurality of alternating layers of lattice matched materials with discontinuities in their respective indices of refraction directly adjacent the BSF layer;   forming a middle second solar subcell adjacent to said DBR layer having a GaAs base layer and a GaInP emitter layer;   forming a third solar subcell, said third solar subcell composed of an InGaAs base layer and an InGaAs emitter layer that is lattice matched to the InGaAs base layer;   wherein the DBR layer is designed such that (i) a portion of the light that enters and passes through the upper first solar subcell is reflected back into the upper first solar subcell by the DBR layer, and (ii) a portion of the light that enters and passes through the upper first solar subcell passes through the DBR layer to the middle second solar subcell and the lower third solar subcell.   
     
     
         22 . A method of forming a solar cell as defined in  claim 21 , wherein the difference in refractive indices between alternating layers is maximized in order to minimize the number of periods required to achieve a given reflectivity. 
     
     
         23 . A method of forming a solar cell as defined in  claim 21 , wherein the DBR layer includes a first DBR composed of a p type InGaAlP layer, and a second DBR layer disposed over the first DBR layer composed of a p type InAlP layer. 
     
     
         24 . A method of forming a solar cell as defined in  claim 21 , wherein the DBR layer includes a first DBR layer composed of a p type Al x Ga 1-x As layer, 0<x<1, and a second DBR layer disposed over the first DBR layer composed of p type Al y Ga 1-y As layers, where 0<y<1 and y is greater than x. 
     
     
         25 . A method of forming a solar cell as defined in  claim 21 , wherein the distributed Bragg reflector (DBR) layer is composed of a plurality of alternating layers of lattice matched materials with discontinuities in their respective indices of refraction. 
     
     
         26 . A method of forming a solar cell as defined in  claim 21 , wherein the distributed Bragg reflector layer increases the radiation hardness of the solar cell by reducing the diffusion length necessary for collection in the upper first solar subcell. 
     
     
         27 . A method of forming a solar cell as defined in  claim 21 , wherein:
 the upper first solar subcell has a first band gap and the middle second solar subcell has a second band gap smaller than said first band gap; and   further comprising forming a graded interlayer adjacent to said middle second solar subcell, said graded interlayer having a third band gap greater than said second band gap wherein the third solar subcell is disposed adjacent to said interlayer, said third solar subcell has a fourth band gap smaller than said second band gap such that said third solar subcell is lattice mismatched with respect to said middle second solar subcell.   
     
     
         28 . A method as defined in  claim 26 , wherein the graded interlayer is composed of (In x Ga 1-x ) y Al 1-y As, with 0<x<1, 0<y<1, and x and y selected such that the band gap of the interlayer material remains constant throughout its thickness. 
     
     
         29 . A method of forming a solar cell as defined in  claim 26 , wherein the lower third solar subcell has a band gap in the range of approximately 0.8 to 1.2 eV, the middle second solar subcell has a band gap in the range of approximately 1.2 to 1.6 eV, and the upper first solar subcell is disposed over and is lattice matched to the middle second solar subcell, and has a band gap in the range of 1.8 to 2.1 eV. 
     
     
         30 . A method of forming a solar cell as defined in  claim 26 , wherein the third solar cell is the bottom subcell. 
     
     
         31 . A method of forming a solar cell comprising:
 providing a first substrate;   depositing on a first substrate a sequence of layers of semiconductor material, including a contact layer and a sequence of layers forming a plurality of solar subcells over the contact layer;   mounting and bonding a surrogate substrate on top of the sequence of layers; and   removing the first substrate;   wherein the step of depositing on a first substrate a sequence of layers of semiconductor material forming a plurality of solar cell subcells includes depositing a distributed Bragg reflector (DBR) layer adjacent to the first deposited solar subcell.   
     
     
         32 . A method of forming a solar cell as defined in  claim 31 , wherein the distributed Bragg reflector (DBR) layer is composed of a plurality of alternating layers of lattice matched materials with discontinuities in their respective indices of refraction. 
     
     
         33 . A method of forming a solar cell as defined in  claim 31 , wherein the Bragg reflector layer increases the radiation hardness of the solar cell by reducing the diffusion length necessary for collection in the upper first solar subcell. 
     
     
         34 . A method of forming a solar cell as defined in  claim 31 , wherein the difference in the refractive indices between alternating layers is maximized in order to minimize the number of periods required to achieve a given reflectivity, and the thickness and refractive index of each period determines its stop band and limiting wavelength. 
     
     
         35 . A method of forming a solar cell as defined in  claim 31 , wherein the DBR layer includes a first DBR layer composed of a p type InGaAlP layer, and a second DBR layer disposed over the first DBR layer composed of a p type InAlP layer. 
     
     
         36 . A method of forming a solar cell as defined in  claim 31 , wherein the DBR layer includes a first DBR layer composed of a p type Al x Ga 1-x As layer, 0<x<1 and a second DBR layer disposed over the first DBR layer composed of p type Al y Ga 1-y As layers 0<y<1, and where y is greater than x. 
     
     
         37 . A method of forming a solar cell as defined in  claim 31 , wherein:
 the upper first solar subcell has a first bandgap; the middle second solar subcell has a second band gap smaller than said first band gap, and further comprising forming a graded interlayer adjacent to said middle second solar subcell, said graded interlayer having a third band gap greater than said second band gap wherein the lower third solar subcell is disposed adjacent to said interlayer, said lower third solar subcell having a fourth band gap smaller than said second band gap such that said lower third solar subcell is lattice mismatched with respect to said middle second solar subcell.   
     
     
         38 . A method of forming a multijunction solar cell comprising:
 forming an upper first solar subcell composed of InGa(Al)P and having a first band gap;   forming a back surface field (BSF) layer directly adjacent the upper first solar subcell;   forming a distributed Bragg reflector (DBR) layer composed of a plurality of alternating layers of lattice matched materials with discontinuities in their respective indices of refraction directly adjacent the BSF layer;   forming a middle second solar subcell adjacent to said DBR layer and having a second band gap smaller than said first band gap, and having a GaAs base layer and a GaInP emitter layer;   forming a graded interlayer adjacent to said middle second solar subcell, said graded interlayer having a third band gap greater than said second band gap; and   forming a lower third solar subcell adjacent to said interlayer, said lower third solar subcell composed of an InGaAs base layer and an InGaAs emitter layer that is lattice matched to the InGaAs base layer and having a fourth band gap smaller than said second band gap such that said lower third subcell is lattice mismatched with respect to said middle second solar subcell;   wherein the DBR layer is designed such that (i) a portion of the light that enters and passes through the upper first solar subcell is reflected back into the upper first solar subcell by the DBR layer, and (ii) a portion of the light that enters and passes through the upper first solar subcell passes through the DBR layer to middle second solar subcell and the lower third subcell.   
     
     
         39 . The method of forming a solar cell as defined in  claim 38 , wherein the difference in refractive indices between alternating layers is maximized in order to minimize the number of periods required to achieve a given reflectivity, and the thickness and refractive index of each period determines its stop band and limiting wavelength. 
     
     
         40 . The method of forming a solar cell as defined in  claim 38 , wherein the DBR layer includes (i) a first DBR layer composed of a p type InGaAlP layer, and a second DBR layer disposed over the first DBR layer composed of a p type InAlP layer, or (ii) the first DBR layer composed of a p type Al x Ga 1-x As layer, 0<x<1, and the second DBR layer disposed over the first DBR layer composed of a p type Al y Ga 1-y As layers, 0<y<1, where y is greater than x.