One of the limitations of current amorphous silicon/crystalline silicon heterojunction solar cells are optical losses in the amorphous silicon (a-Si:H) layers that limit the short circuit current. In this work, we propose to replace amorphous silicon layers by a thin crystalline gallium phosphide (GaP) layer in heterojunctions solar cells. We show that the better transparency of GaPcompared to a-Si:H promises gain in the UV region. However, the annealing in the MOCVD chamber before GaP growth that is necessary for high quality GaP epitaxial growth degrades the bulk silicon minority carrier lifetime. This degradation is attributed to fast diffusing species and can be overcome by a gettering process.