Patent ID: 9691929
Date: 2017-06-27
CPC Classifications: H01L,Y02E,Y02P

Claim:
1. A multijunction solar cell comprising: an upper first solar subcell having a first band gap, the upper first solar subcell including an InGaP emitter layer and an InGaP base layer; a second solar subcell below the first solar subcell and having a second band gap smaller than the first band gap, a base and emitter of the second solar subcell forming a radiation hard heterojunction, wherein the emitter layer of the second solar subcell is composed of InGaP and the base layer of the second solar subcell is composed of GaAs; a first upper barrier layer below the second solar subcell, the first upper barrier layer being composed of InGaP; a first graded interlayer, composed of InGaAlAs, disposed below and adjacent to the first upper barrier layer, wherein the first graded interlayer has a third band gap greater than the second band gap, and wherein the band gap of the first graded interlayer remains constant at 1.5 eV throughout its thickness; a first lower barrier layer disposed below and adjacent to the first graded interlayer, the first lower barrier layer being composed of InGaP and having a composition different from that of the first upper barrier layer; a third solar subcell below the first lower barrier layer, 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, a base and emitter of the third solar subcell forming a radiation hard heterojunction, wherein the emitter layer of the third solar subcell is composed of InGaP and the base layer of the third solar subcell is composed of InGaAs, and wherein the first graded interlayer provides a gradual transition in lattice constant from the second solar subcell to the third solar subcell; a second upper barrier layer below the third solar subcell; a second graded interlayer, composed of InGaAlAs, disposed below and adjacent to the second upper barrier layer, wherein the second graded interlayer has a fifth band gap greater than the fourth band gap, and wherein the band gap of the second graded interlayer remains constant at 1.1 eV throughout its thickness; a second lower barrier layer disposed below and adjacent to the second graded interlayer; and a lower fourth solar subcell below the second lower barrier layer, wherein the fourth subcell has a sixth band gap smaller than the fourth band gap such that the fourth solar subcell is lattice mismatched with respect to the third solar subcell, wherein an emitter layer and base layer of the fourth solar subcell are composed of InGaAs, and wherein the second graded interlayer provides a gradual transition in lattice constant from the third solar subcell to the lower fourth solar subcell, wherein each of the first upper barrier layer and the first lower barrier layer has a respective-composition different from the first graded interlayer, wherein each of the second upper barrier layer and the second lower barrier layer has a composition different from the second graded interlayer, and wherein the first upper barrier layer, the first lower barrier layer, the second upper barrier layer and the second lower barrier layer collectively help prevent threading dislocations from propagating into adjacent solar subcells in a direction of growth of the solar cell and in a direction opposite the direction of growth.