Compound photovoltaic cell

Abstract

A compound photovoltaic cell includes a substrate, a first cell made of a first semiconductor material and formed on the substrate, a tunnel layer, and a second cell made of a second semiconductor material lattice mismatched with a material of the substrate, connected to the first cell via the tunnel layer, and disposed on an incident side with respect to the first cell, wherein band gaps of the first and the second cells become smaller from an incident side to a back side, and wherein the tunnel layer includes a p-type layer disposed on the incident side and a n-type layer disposed on the back side, the p-type layer being a p + -type (Al)GaInAs layer, the n-type layer being an n + -type InP layer, an n + -type GaInP layer having a tensile strain with respect to InP or n + -type Ga(In)PSb layer having a tensile strain with respect to InP.

1 . A compound photovoltaic cell comprising:
 a first substrate;   one or more first photoelectric conversion cells configured to be made of a first compound semiconductor material and to be formed on the first substrate,   a tunnel junction layer formed on the one or more first photoelectric conversion cells; and   one or more second photoelectric conversion cells configured to be made of a second compound semiconductor material which is lattice mismatched with a material of the first substrate, to be connected to the one or more first photoelectric conversion cells via the tunnel junction layer, and to be disposed on an incident side in a light incident direction with respect to the one or more first photoelectric conversion cells;   wherein band gaps of the one or more first photoelectric conversion cells and the one or more second photoelectric conversion cells become smaller from the incident side to a back side in the light incident direction, and   wherein the tunnel junction layer includes a p-type layer disposed on the incident side and a n-type layer disposed on the back side, the p-type layer being a p + -type (Al)GaInAs layer, the n-type layer being an n + -type InP layer, an n + -type GaInP layer having a tensile strain with respect to InP or an n + -type Ga(In)PSb layer having a tensile strain with respect to InP.   
     
     
         2 . The compound photovoltaic cell as claimed in  claim 1 , wherein a band gap of the n + -type GaInP layer or the n + -type Ga(In)PSb layer is greater than or equal to a band gap of the second photoelectric conversion cell located on a backmost side in the light incident direction among the one or more second photoelectric conversion cells. 
     
     
         3 . The compound photovoltaic cell as claimed in  claim 1 , wherein the tunnel junction layer further includes a p + -type (Al)GaAs layer disposed on the incident side of the p + -type (Al)GaInAs layer. 
     
     
         4 . The compound photovoltaic cell as claimed in  claim 1 , wherein a lattice constant of the p + -type (Al)GaInAs layer is closer to a lattice constant of GaAs than a lattice constant of InP. 
     
     
         5 . The compound photovoltaic cell as claimed in  claim 1 , wherein a lattice constant of the n + -type GaInP layer or the n + Ga(In)PSb layer is closer to a lattice constant of InP than a lattice constant of GaAs. 
     
     
         6 . The compound photovoltaic cell as claimed in  claim 1 , wherein the first photoelectric conversion cell located on a foremost side in the light incident direction among the one or more first photoelectric conversion cells includes a window layer which contacts the tunnel junction layer, and
 wherein a band gap of the window layer is greater than or equal to a band gap of the second photoelectric conversion cell located on a backmost side among the one or more second photoelectric conversion cells.   
     
     
         7 . The compound photovoltaic cell as claimed in  claim 6 , wherein the window layer includes any one material of GaInP, GaPSb, GaInPSb, AlInAs, AlGaInAs, AlAsSb, AlGaAsSb, AlPSb, AlGaPSb, AlPSb and AlInPSb. 
     
     
         8 . The compound photovoltaic cell as claimed in  claim 1 , wherein the second photoelectric conversion cell located on backmost side among the one or more second photoelectric conversion cells includes a GaInAs layer having a compression strain with respect to GaAs. 
     
     
         9 . The compound photovoltaic cell as claimed in  claim 1 , wherein the one or more first photoelectric conversion cells are made of an InP lattice matching material, and
 wherein the one or more second photoelectric conversion cells are made of a GaAs lattice matching material.   
     
     
         10 . The compound photovoltaic cell as claimed in  claim 1 , wherein a number of the one or more first photoelectric conversion cells and the one or more second photoelectric conversion cells is more than or equal to three. 
     
     
         11 . The compound photovoltaic cell as claimed in  claim 1 , wherein the first substrate is an InP substrate, and
 wherein a number of the one or more first photoelectric conversion cells is more than or equal to two.