Abstract
Epitaxial III-V on silicon multi-junction solar cells allow to increase the conversion efficiency of single-junction silicon devices. We report progress on the development of high-efficiency GaInP/GaAs/Si triple-junction devices over the last two years. The AM1.5g conversion efficiency has been increased from 19.7% to 22.3%, 24.3%, and finally a value of 25.9% could be achieved. The improvement was enabled by a reduction of nucleation-related crystal defects in the silicon to gallium phosphide transition and a reduction of parasitic absorption within the metamorphic GaAsP buffer structure which was limiting the current in the silicon subcell. By increasing the bandgaps in the graded buffer structure, a ∼2x reduction of the threading dislocation density was observed and the short-circuit current density increased by 22% relative. A majority barrier was identified and could be suppressed to obtain a new record conversion efficiency of 25.9% with an open-circuit voltage of 2.647 V, a short-circuit current density of 12.2 mA/cm 2 and a fill factor of 80.2%.