Efficient MAPbI3 Perovskite Solar Cells Employing Sputtered p-Type NiOx Hole Transport Layer on Dependence of Oxygen Partial Pressure

In this paper, the effect of NiO x thin film prepared by a radio-frequency sputtering process under different oxygen partial (Ar:O 2 ratio) pressures on the photovoltaic properties of planar-type MAPbI 3 perovskite solar cells (PSCs) was investigated. The electrical, optical, morphological, and structural properties of sputtered NiO x thin films deposited under varied process oxygen gas condition are scrutinized. In particular, this study demonstrates that the properties of NiO x thin film with Ni 3+ /Ni 2+ ratio are dependent on process oxygen gas condition. The influence of Ni vacancies on the chemistry and electronic structure of NiO x thin films is investigated using X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The sputtered NiO x thin film with lower Ni 3+ /Ni 2+ ratio exhibits appropriate conductivity, hole mobility, high transmittance, and uniform surface morphology as well as a preferred in-plane orientation of the (220) plane under pure Ar gas atmosphere. When 5% (Ar:O 2 =19:1) or 10% (Ar:O 2 =18:2) oxygen is injected during the process, the conductivity of NiO x thin films with higher Ni 3+ /Ni 2+ ratio is higher, but at the expense of optical transmittance. Additionally, this work exhibits the effect of perovskite active layer crystallinity and device performance using sputtered NiO x thin film under different oxygen partial pressures (Ar:O 2 ratio) as hole transport layer for PSCs. The power conversion efficiency (PCE) of PSC obtains the highest PCE of 15.74% at the optimized NiO x thin film under pure Ar atmosphere. Compared to that, the efficiencies of the PSCs using the NiO x thin films processed at 5% and 10% oxygen partial pressure is 4.17% and 1.39%, respectively. Therefore, this study elucidate the effect of NiO x thin films deposited under different oxygen partial (Ar:O 2 ratio) pressures on the performance of PSCs.