Electronic structures of all inorganic rare-earth element, such as gadolinium (Gd) and neodymium (Nd), double perovskite crystals (Cs₃GdCl₆ and Cs₃NdCl₆) were characterized for application of photovoltaic devices with photovoltaic performance. The band structure, density of state, electron density distribution, and the real and imaginary parts of the dielectric function of Cs₃GdCl₆ and Cs₃NdCl₆ double perovskite crystals were approximated using first-principles calculations, with GGA-PBE approximation. The Cs₃GdCl₆ and Cs₃NdCl₆ double perovskite crystals had a narrow band dispersion with direct band gaps of 1.0 eV and 0.7 eV. The band structure of the Cs₃GdCl₆ crystal consisted of 5d and 4f orbitals of Gd ions near the valence band (VB) state,the 5d orbital of Gd ions ,and the 6s orbital of Cs ions near the conduction band (CB) state. The band structure of the Cs₃NdCl₆ crystal consisted of the 5p orbital of Cl ions near the VB state, and the 5d orbital of Nd ions near the CB state. The charge transfer and carrier generation related to electron mobility will be caused by the overlap of the 5d orbital of Gd and Nd ions and the 6s orbital of Cs ions near the CB state. The real and imaginary parts of the dielectric function in both cases were obtained in the range of 0 – 1 eV. The photon energies correspond to transition between the energy levels of the split 5d and 4f orbitals of Gd andNd ions coordinated with Cl ions as ligands in the crystal field with charge distribution. The Cs₃GdCl₆ and Cs₃NdCl₆ double perovskite crystals have high potential for the application of photovoltaic devices with photovoltaic performance.