A photonic crystal design that significantly enhances the absorption of tandem thin-film solar cells composed by amorphous and microcrystalline silicon (i.e., a-Si:H/μc-Si:H tandem cell) is proposed. The top junction with a-Si:H is nanopatterned as a one-dimensional photonic crystal. Considering the photocurrent matching, we optimally design the junction thickness and the configuration of the nanopattern; moreover, both transverse electric and magnetic incidences with various illuminating angles are taken into account. Calculations by rigorous coupled-wave approach and finite-element method show that the nanophotonic crystal design can improve the absorption and output photocurrent by over 20%, which shows very low sensitivity to the incident polarization. Moreover, the proposed structure is able to sustain the performance for a very wide angle ranges from 0° to ~80°.