Oxidized Nickel films as highly transparent HTLs for inverted planar perovskite solar cells

Inverted planar perovskite solar cells (PSCs) with nickel oxide (NiO) as a hole transporting layer were fabricated in an ambient atmosphere. Nickel (Ni) film synthesized at optimized evaporation conditions using low-cost thermal evaporation were transformed from island-like structure to compact porous thin films of NiO after oxidation at 580 degrees C. The formation of highly transparent NiO films without any impurity was confirmed from UV-visible spectroscopy and energy dispersive x-ray analysis. These optically tailored NiO films with island-like morphology conceived minimum absorption to the visible light than that of compact porous thin films. The NiO island-like films coated with single cationic CH3NH3PbI3 perovskite overlayer in ambient conditions via a modified two-step method showed higher hole quenching than the compact porous NiO thin films. PSCs consisting of NiO island-like films showed 39.3% improvement in power conversion efficiency (PCE), and 41.4% enhancement in current density (J(SC)) compared to the compact porous NiO thin films. Overall, the present approach of utilizing optically engineered island-like inorganic films with single cationic CH3NH3PbI3 perovskite overlayer has opened up a novel approach toward the improvement in high-performance optoelectronic devices fabricated at an ambient atmosphere.