Air-Stable n–i–p Planar Perovskite Solar Cells Using Nickel Oxide Nanocrystals as Sole Hole-Transporting Material

Development of low-cost solution processable inorganic hole-transporting materials (HTM) in n–i–p perovskite solar cells (PSCs) is still a challenge toward stable and cost-effective devices. Here, we report the synthesis, surface functionalization, and application of hydrophobic nickel oxide nanocrystals (ho-NiOx) as HTM in planar n–i–p PSCs. The morphological and electrical properties of ho-NiOx layers were evaluated by atomic force microscopy (AFM) and conductivity measurements as well as ultraviolet photoelectron spectroscopy (UPS) and surface photovoltage (SPV) measurements. Compared to the state-of-the-art Spiro-OMeTAD, our results suggested a better energy band alignment between ho-NiOx and (FAPbI3)0.78(MAPbBr3)0.14(CsPbI3)0.08 perovskite. Noticeably, ho-NiOx-based devices exhibit a power conversion efficiency (PCE) of 12.71% and a stabilized power output (SPO) of 10.99%, the best performance reported so far employing NiOx as the sole top transport layer. Notably, a low photovoltage suggests that the Voc could be enhanced by reducing possible recombination paths at the perovskite/HTM interface. Moreover, unencapsulated PSC employing ho-NiOx exhibited an outstanding stability under high moisture levels (∼65% RH) retaining ∼90% of initial PCE after 1008 h of fabrication, paving the way toward scalable and solution processed fully inorganic blocking layer PSCs.