The modeling of high efficiency, multijunction (MJ) solar cells away from the radiative limit is presented. In the model,
we quantify the effect of non-radiative recombination by using radiative efficiency as a figure of merit to extract realistic
values of performance under different spectral conditions. This approach represents a deviation from the traditional
detailed balance approximation, where losses in the device are assumed to occur purely through radiative recombination.
For lattice matched multijunction solar cells, the model predicts efficiency values of 37.1% for AM0 conditions and
52.8% under AM1.5D at 1 sun and 500X, respectively. In addition to the theoretical study, we present an experimental
approach to achieving these high efficiencies by implementing a lattice matched triple junction (TJ) solar cell grown on
InP substrates. The projected efficiencies of this approach are compared to results for the state of the art inverted-metamorphic
(IMM) technology. We account for the effect of metamorphic junctions, essential in IMM technology, by
employing reduced radiative efficiencies as derived from recent data. We show that high efficiencies, comparable to
current GaAs-based MJ technology, can be accomplished without any relaxed layers for growth on InP, and derive the
optimum energy gaps, material alloys, and quantum-well structures necessary to realize them.