Multijunction solar cell

A multijunction solar cell comprising:

• first solar subcell, having an emitter layer and a base layer which form a photoelectric junction;
• a second solar subcell disposed below and adjacent to the first solar subcell, having an emitter layer and a base layer which form a photoelectric junction;
• and
• a third solar subcell disposed below the second solar subcell, having an emitter layer and a base layer which form a photoelectric junction;
• wherein at least one of the base layer and the emitter layer forming an active layer of a particular solar subcell from among the first solar subcell, the second solar subcell, and the third solar subcell, has a graded band gap throughout at least a portion of the thickness of a first region adjacent to the photoelectric junction of the particular solar subcell, and having a value in the range of 20 to 300 meV greater than the band gap in a third region in the emitter layer spaced away from the photoelectric junction or greater than the band gap in a fourth region in the base layer spaced away from the photoelectric junction in the particular solar subcell.

A method of fabricating a multijunction solar cell comprising:

• forming a first solar subcell having an emitter layer and a base layer which form a photoelectric junction;
• and
• forming a second solar subcell disposed below and adjacent to the first solar subcell, having an emitter layer and a base layer which form a photoelectric junction;
• and
• wherein at least one of the base layer and the emitter layer forming an active layer of a particular solar subcell from among the first solar subcell, the second solar subcell, and the third solar subcell, has a graded band gap throughout at least a portion of the thickness of a first region adjacent to the photoelectric junction, with the band gap in the first region being in the range of 20 to 300 meV greater than the band gap in a second region in the emitting layer, and a third region in the base layer, both the second and third regions being spaced away from the photoelectric junction in the particular solar subcell.