Split InAlAs top cell enabled four-junction solar cell lattice matched to InP

We have demonstrated for the first time a proof of concept four junction solar cell grown on an InP substrate. The split top cell design uses two 1.45 eV InAlAs subcells in series to take advantage of the large portion of the solar spectrum with energies higher than this bandgap. The prototype cell has an open circuit voltage of 2.44 V and short circuit current density of 1.8 mA/cm
²
. Further optimization may allow this cell to have performance comparable with high quality triple-junction GaAs cells. This architecture may be useful in other systems where high quality wide bandgaps are not available or in materials systems where carrier collection is strongly limited by the diffusion length within the material.