Chemical synthesis of nonstoichiometric NiOx nanoparticles using different nickel salts and application as an additive or interface layer in photovoltaic devices

Abstract

The stoichiometric nickel oxide is an insulator while it becomes a p-type semiconductor with the presence of divalent and trivalent states. Here nonstoichiometric nickel oxide nanoparticles (NiO${}_{x}$NPs) were synthesized via a chemical route using two different starter salts; nickel chloride hexahydrate and nickel nitrate hexahydrate. The nanoparticles were investigated by X-ray diffraction and transmission electron microscopy, scanning electron microscopy, to determine the crystal structure, morphology, and particle size. The effect of different nickel salts in the reaction and the formation of NiO${}_{x\ }$nanoparticles were observed for the first time in the literature. Because of the high uniformity and stability, nitrate-based inks were employed as additives and interface layers for planar perovskite solar cells, using a two-step deposition for regular (n-i-p) and one-step antisolvent washing method for inverted (p-i-n) configurations. Photovoltaic performances were improved in the case of NiO${}_{x}$ applied as an interface layer between P3HT and Ag for regular solar cells and both as an additive in sol-gel based NiO${}_{x}$ and interface layer between HTL and perovskite in inverted solar cells.