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 NiO_x 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 NiO_x 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 NiO_x 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.