Here, we discuss the recent developments toward efficient GaP/Si-based photovoltaic devices and their implementation using Molecular Beam Epitaxy. The GaP/Si structural and electronic characteristics are first presented with respect to PV applications. It is shown that the presence of antiphase boundaries deeply impact both structural and electronic properties. Issues related to GaP processing are then discussed. Performances of GaP-based PV single solar cells and GaP/Si-based tandem solar cells are reviewed. While performances of photovoltaic devices are encouraging, they are still far from the theoretical limit achievable and require additional materials research. To this aim, molecular beam epitaxial techniques provide many advantages. Finally, we report on the last development of GaP/Si heterojunctions, which has the theoretical ability to surpass the efficiency of the a-Si/c-Si heterojunctions due to the higher GaP bandgap as compared to the a-Si.