Interfacial Embedding for High‐Efficiency and Stable Methylammonium‐Free Perovskite Solar Cells with Fluoroarene Hydrazine

Abstract Perovskite solar cells (PSCs) with state‐of‐the‐art efficiencies contain thermally unstable methylammonium (MA). Here, interfacial passivation with pentafluorophenylhydrazine (5F‐PHZ) to fabricate efficient and stable MA/Br‐free PSCs is introduced. The 5F‐PHZ surface treatment quenches the PbI 2 and δ‐perovskite phase formed in the pristine film. The surface passivation ameliorates the film chemistries at the surface with modulation of interface band alignment as a consequence of halogen bonding with fluoroarene moieties or NH–NH 2 terminals. This results in a much longer carrier lifetime with the passivation at the surface and grain boundaries trap centers. As a result, it boosts the power conversion efficiency (PCE) (area ≈ 1 cm 2 ) from 18.10% to 22.29% ( V OC ≈ 1.096–1.178 V) with superior operational thermal stability. A certified PCE of 21.01% with a large area of ≈1.026 cm 2 is also achieved. It is found that the surface passivation forms an interfacial embedded layer subsequent to attenuation of defect densities and suppression of ion migration, which is supported by density‐function‐theory calculation. Importantly, this approach is effective in enhancing the PCE of narrow and wide bandgap perovskite systems. Thus, this work opens up a new technique for interface modulation with fluoroarene functional derivatives to achieve superior device performance and stability.