Ionic surfactants of different dipole moments as anti-solvent additives for air-processing MAPbI_3−xCl_x perovskite thin films

Three ionic surfactants, didodecyldimethylammonium bromide (DDABr), sodium lauryl ether sulfate (NaLES) and sodium lauryl sulfate (NaLS), with different dipole moment values: 0.907, 17 and 212 Debye, respectively, have been used as anti-solvent additives to remove the moisture from perovskite precursor solutions. The three additives impact in different ways on the crystallinity, wettability and morphology of perovskite thin films, as well as on the stability and efficiency of air-processed perovskite solar cells (PSCs). The hydrophobic groups of the additives at the surface of perovskite thin films help to increase the stability of PSCs, especially DDABr of the lowest dipole moment. On the other hand, NaLES, of the highest dipole moment, is the most efficient to extract moisture from the perovskite precursor coatings, increasing the average power conversion efficiency (PCE) of NaLES-based PSCs from 16.16 ± 0.94% to 17.21 ± 0.32% in comparison with that of the reference. Furthermore, the synergy between NaLES and the perovskite precursor additive, KI, achieves the best photovoltaic performance of the PSCs, leading to an average PCE of 17.42% and the best PCE of 18.75%. It is concluded that ionic surfactants of different dipole moments are good candidates as anti-solvent additives to improve the efficiency and stability of air-processed PSCs.