Development of high-performance GaInAsP solar cells for tandem solar cell applications

Recent results in the development of high-efficiency, low-bandgap GaInAsP solar cells epitaxially grown and lattice matched on InP substrates are presented. Such cells are intended to be used as optimum bottom cell components in tandem solar cells. Assuming that a GaAs-based top cell is used, computer simulation of the potential bottom cell performance as a function of the cell bandgap and incident spectrum indicates that two particular alloys are desirable: Ga_0.47In _0.53As (E_g=0.75 eV) for space applications and Ga_0.25In_0.75As_0.54P _0.4$ (E_g=0.95 eV) for terrestrial applications. In each of these materials, solar cells with new record-level efficiencies have been fabricated. The efficiency boost available to tandem configurations from these low-bandgap cells is discussed