Systems, methods and apparatus related to a multijunction solar cell. The apparatus comprises a first sub-solar cell, a second sub-solar cell in series with the first sub-solar cell and one or more quantum wells. At least some of the quantum wells are disposed in a region of the first sub-solar cell, and have a thickness and a bandgap sized such that a bandgap in selected quantum wells are less than a bandgap of a material of the first sub-solar cell and greater than a bandgap of a material of the second sub-solar cell resulting in radiative coupling between the first sub-solar cell and the second sub-solar cell.