Methylammonium-Free Ink for Blade-Coating of Pure-Phase α-FAPbI Perovskite Films in Air.

The α-c (α-FAPbI) has been extensively employed in the fabrication of high-efficiency perovskite solar cells, yet heavily relied on multiple additives in upscalable fabrication in air. In this work, a simple α-FAPbI ink is developed for the blade-coating fabrication of phase-pure α-FAPbI in ambient air free from any additives containing extrinsic ions. The introduction of 2-imidazolidinone (IMD) to the FAPbI precursor inks leads to the formation of intermediate phases that change the phase transition pathway from δ-FAPbI to α-FAPbI by tilting the PbI octahedrons with strong coordination to Pb. Furthermore, the IMD ligands in the intermediate phase gradually escape from the perovskite film during the annealing, leaving a phase-pure α-FAPbI film vertically grown with large grains. Consequently, the small-sized PSCs fabricated with blade-coated α-FAPbI film achieve an efficiency of up to 23.14%, and the corresponding mini-module yields an efficiency of 19.66%. The device performance is among the highest reported for phase-pure α-FAPbI PSCs fabricated in the air without non-native cations or chloride additives, offering a simple and robust fabrication approach of phase-pure α-FAPbI films for PV application.