Synthesis methods of NiOx nanoparticles and its effect on hole conductivity and stability of n-i-p perovskite solar cells

Herein, nickel oxide nanoparticles (NPs) with different routes were synthesized and used as HTLs for MAPbI3-based PSCs. UV-Vis absorption spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), steady-state photoluminescence (PL) spectra, space-charge limited current (SCLC) model, water droplet contact angle and current voltage (I-V) measurements were used to investigate the characteristics of synthesized NiOx, photovoltaic parameters and stability of constructed n-i-p perovskite solar cells. It was found that employing nickel chloride hexahydrate (NiCl2·6H2O) (labeled as NiCl2) as Ni reagent in the synthesis process could be obtained more desirable NiOx NPs for the HTL role in PSC devices. Results showed NiCl2-based NiOx HTL facilitates hole extraction to a gold electrode and suppresses electron-hole recombination rate in PSCs. NiCl2-based NiOx HTL brings a champion power conversion efficiency (PCE) of 12.57% for PSCs, higher than HTL-free PSCs with a champion PCE of 6.78%. In addition, the stability of NiOx-containing PSCs was considerably higher than that of a device without NiOx HTL. NiCl2-based PSC maintained 86% of its initial PCE after keeping in ambient air (25–40% RH) for 45 days, outperforming the control device that only retained ∼ 48% of its initial PCE after 25 days of the stability test. This work provides a deep understanding for efficiency and stability of the NiOx based perovskite solar cells and an approach to improve the using of low-cost HTLs.