New nickel-based hybrid organic/inorganic metal halide for photovoltaic applications.

In this work, we have synthesized and fabricated solar cells with the hybrid metal halide compounds with the general formula ABX, where the A cation is methylammonium, the B cation is nickel, and the X anion is chlorine or a mixture of chlorine and iodine. We obtained experimental evidence that this material is a semiconductor with an orthorhombic crystalline structure which pertains to the space group Cmcm. The bandgap can be modulated from 1.4 eV to 1.0 eV by changing the chlorine anion to iodine. Therefore, we were able to obtain solar cells with efficiencies up to 0.16% with the CHNHNiClI composition. We have also studied by means of first-principles calculations, taking into account van der Waals dispersive forces, the ground state properties of these materials such as their crystal structure and formation and decomposition energies. We have found that these energies are lowered by the lighter mass anion, and the calculated decomposition energies show that only CHNHNiCl is stable with respect to the most probable decomposition pathway. The electronic band structure and band edge alignments have been calculated using quasiparticle effects through the GW approximation; these materials show an indirect bandgap with the valence band maxima at -6.93 and -5.49 eV with respect to vacuum and the conduction band minima at -5.62 and -4.60 eV with respect to vacuum for CHNHNiCl and CHNHNiI, respectively. This work provides a pathway to explore new hybrid ABX-type semiconductor materials.