Modification of Nickel Oxide via Self-Assembled Monolayer for Enhanced Performance of Air-Processed FAPbl3 Perovskite Solar Cells

Fabricating formamidinium lead iodide (FAPbI3) in ambient air has shown great promise for reducing its fabrication costs and promoting future large-scale production of perovskite solar cells (PSCs). Compared with the regular structure, the inverted counterpart exhibits advantages in low-temperature-fabricated and dopant-free charge transport materials. However, the commonly used hole transport material NiOx suffers from a large amount of surface defects, which results in severe nonradiation recombination at the interface as well as poor perovskite film grown on top. Herein, we report an interfacial engineering strategy via a self-assembled monolayer (SAM) to modify the interface between NiOx and air-processed FAPbI3, among which the 4-(3,6-dimethyl-9H-carbazol-9-yl)butyl phosphonic acid (Me-4PACz) modified device shows the best efficiency. With Me-4PACz, not only the interfacial defects are passivated, but also the energy alignment between NiOx and FAPbI3 is optimized, thus facilitating charge extraction. Moreover, the crystallization process of air-processed perovskite film is slowed down, leading to enlarged grain size in both lateral and vertical directions, which benefits charge transport in the perovskite film. After optimization, the air-processed inverted FAPbI3 PSCs achieve a dramatically improved power conversion efficiency (PCE) of 17.3%, outperforming that of the control device with 11.3%. This work provides a feasible way towards low-cost and efficient FAPbI3 PSCs in a humid environment.