Low-temperature processed nickel oxide hole-transporting layer for perovskite solar cell

In this study, we demonstrated low-temperature sol–gel processed nickel oxide (NiO) film as the hole transporting layer (HTL) of the CH₃NH₃PbI₃ (MAPbI₃) perovskite solar cells. The NiO film, which was solution-processed and annealed at a temperature of 300 °C showed rms surface roughness of 2.86 nm, optical transmittance of ~ 82 to 87% in the visible wavelength, and the band gap energy of 3.82 eV. The perovskite coated on the NiO showed a good surface coverage with negligible pinholes, a typical grain size of 100–300 nm, photoluminescence peak of 767 nm, and the Urbach energy of 60 meV. The perovskite solar cells fabricated with NiO HTL produced the power conversation efficiency (PCE) of 8.13%, short circuit current density (J_sc) of 14.78 mA/cm², open circuit voltage (V_oc) of 1.05 V, and filling factor (FF) of 52.4%. This indicates that, although the device performance should be further developed by optimizing the NiO, the low-temperature processed NiO has a substantial potential as the HTL of the perovskite solar cells.