Regulating the Ni3+/Ni2+ ratio of NiOx by plasma treatment for fully vacuum-deposited perovskite solar cells

Inorganic p-type NiOx was considered as an idea hole-transport layer (HTL) for perovskite solar cells due to its good transmittance in visible region and outstanding chemical stability. The p-type behavior of NiOx is mainly derived from its nonstoichiometric nature and determined by the Ni cation deficiency. Thus, the synthesizing methods play an important role to the electronic properties of NiOx films. And for most of the inverted PSCs with NiOx HTL, the hole-extraction efficiency was limited by the unmatched valence band and too much surface defects of NiOx, causing poor performance of the device. To date, solution-based synthesizing methods and surface treatments were widely used for achieving high efficiencies of the PSCs. But the vacuum-based synthesizing methods and surface treatments are rarely reported. Herein, we developed a facile plasma post-treatment for the electron-beam evaporated NiOx to regulate its Ni3+/Ni2+ ratio and improve its electronic performance. By using O2 plasma treatment, we successfully enhanced the conductivity of the NiOx and optimized the charge-extraction capability. As a result, the all-vacuum deposited PSCs based on the O2 plasma-treated NiOx HTL achieved a champion PCE of 17.84%. This facile approach is expected to be further developed for fabricating high-efficiency PSCs on textured silicon solar cell.