In this paper, we present design and numerical simulations of nano-cavities for free space matching in solar cells at optical frequencies. The cavity designs are inspired by the wellknown antenna geometries that are commonly used at radio and microwave frequencies. Using such designs that have not been explored before in the context of solar cells, the electromagnetic mismatch between solar-cell surfaces and vacuum is significantly reduced, in comparison to planar interfaces and those with the conventional corrugations. This way, using the designed optimal cavities, the efficiency of solar cells can be increased without employing any matching layer that complicates the fabrication processes. All simulations and comparisons are performed in highly accurate in-house implementations of surface integral equations accelerated with the multilevel fast multipole algorithm.