A new concept of the optical collector including a three-dimensional photonic crystal (3D PhC) is proposed in the study for microcrystalline silicon photovoltaic cells. The goal is to couple the normally incident light into various modes diffracted and guided in the collector structure. To achieve a higher absorption, a 3D periodic structure is patterned within the presented collector as an intermediate layer providing the absorption enhancement mechanism. By select proper PhC or photonic sponge architectures, the spectral positions of the induced modes can be controlled so as to improve the light harvesting.