Solvothermal derived crystalline NiOx nanoparticles for high performance perovskite solar cells

• Ultra-small crystalline NiOx nanoparticles were prepared by a hydrothermal method.
• NiOx thin films were spin coated from the NiOx nanoparticle solution.
• Planar perovskite solar cells were fabricated using NiOx films as hole contacts.
• The NiOx-based devices output a reproducible high PCE of 16.68%.

A solvothermal method is employed to synthesize NiOx nanoparticles with good dispersibility. The synthesized NiOx nanoparticles are very homogenous with an average size of about 3–5 nm, and the X-ray diffraction suggests a good crystallinity for the nanoparticles. NiOx films are spin coated from a colloid precursor which is prepared by dispersing the NiOx nanoparticles into ethanol using a certain amount of acetic as the stabilizer. To obtain an efficient hole extraction layer, an annealing process at 300 °C degree is necessary to remove the residual acetic in the NiOx film. Finally, hysteresis-less NiOx-based perovskite solar cells with good reproducibility are achieved, and a highest power conversion efficiency (PCE) of 16.68% and a constant steady state PCE of 16.49% are also demonstrated.

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