Advances and Potentials of NiO_x Surface Treatments for p−i−n Perovskite Solar Cells

The performances of perovskite solar cells (PSCs) largely depend on the perovskite compositions and the selection of electron and hole transport layers (ETLs and HTLs). The p-type NiO_x films are largely used as HTLs in p-i-n PSCs, thanks to their high transparency, processing versatility, cost-effectiveness, and easy integration within tandem devices. Several studies have shown that surface modifications on NiO_x films remove the surface defects, increase the NiO_x conductivity, and alter the band offset, consequently improving the interfaces between NiO_x films and the perovskite active layer. Indeed, besides improving the NiO_x intrinsic properties, the surface treatments also lead, in many cases, to superior perovskite quality driving high photovoltaic performance.