Multijunction solar cells having an indirect high band gap semiconductor emitter layer in the upper solar subcell

A multijunction solar cell comprising:

• a first upper solar subcell having an indirect band gap semiconductor emitter layer and a base layer forming a heterojunction solar subcell, wherein the emitter layer is an n-type AlxGa1-xAs layer with 0.7<x<1.0 and having a band gap of greater than 2.0 eV,
• wherein the emitter layer is doped with an n-type dopant selected from the group consisting of Se, Te, S, Si, Sn, and combinations thereof, and
• wherein the base layer of the upper solar subcell is a p-type AlyGazIn1-y-zP layer with 0<y<0.5 and 0<z<1;
• a second middle solar subcell disposed beneath the first upper solar subcell, wherein the second middle solar subcell has an emitter layer and a base layer forming a photoelectric junction;
• and
• a third lower solar subcell disposed beneath the second middle solar subcell, wherein the third lower solar subcell has an emitter layer and a base layer forming a photoelectric junction.

A multijunction solar cell comprising:

• a first upper solar subcell having an indirect band gap semiconductor emitter layer and a base layer forming a heterojunction solar subcell, wherein the emitter layer is an n-type AlxGa1-xAs layer with 0.7<x<1.0 and having a band gap of greater than 1.85 eV and is doped with an n-type dopant selected from the group consisting of Se, Te, S, Si, Sn, and combinations thereof, and the base layer is a p-type AlyGazIn1-y-zP layer with 0<y<0.5 and 0<z<1;
• a second middle solar subcell disposed beneath the first upper solar subcell, wherein the second middle solar subcell has a highly doped p-type AlGaAs back surface field layer, a highly doped n-type InGaP or AlGaAs layer emitter layer, a p-type AlGaAs base layer forming a photoelectric junction, and a highly doped n-type AlGaAlP window layer;
• a third middle solar subcell disposed beneath the second middle solar subcell, wherein the third middle solar subcell has an emitter layer and a base layer forming a photoelectric junction;
• and
• a fourth lower solar subcell disposed beneath the third middle solar subcell, wherein the fourth lower solar subcell has an emitter layer and a base layer forming a photoelectric junction.