A Self-Formed Stable PbI 2 /NiO x Interface with Increased Ni 3+ Centers for Perovskite Photovoltaics.

Nickel oxide (NiO x ) is a promising hole transport material (HTM) for perovskite photovoltaics owing to its chemical stability and low cost. However, most NiO x based solar cells deliver relatively weak performance because of its insufficient electrical property and interfacial contact. In this work, a self-formed PbI 2 /NiO x interface was developed to stabilize the Ni 3+ centers, which was beneficial for electrical transport and band alignment in perovskite solar cells. Combined with ultraviolet ozone treatment (UVO) and sequential deposition, the density of Ni 3+ centers was greatly increased and could be stabilized by the PbI 2 interface. These merits contributed coordinately to the fast hole extraction and low energy loss across the PbI 2 /NiO x interface, yielding power conversion efficiencies (PCEs) of over 19 %.