Surface Passivation of Lead Halide Perovskite Solar Cells by a Bifacial Donor-π-Donor Molecule.

Surface passivation is key to the power conversion efficiency (PCE) of organic-inorganic lead halide perovskite solar cells (PSCs). Herein, we report a novel molecular concept of a C 2 -symmetric syn -type bifacial donor-π-donor (D-π-D) passivation molecule (a racemic mixture of enantiomers) with hydrophobic phenyls and hydrophilic tetraethylene glycol-substituted phenyls on each face of the indeno-[1,2- b ]fluorene π-core. In addition to this bifacial amphiphilic π-core unit, triphenylamine, a well-established passivation donor, effectively passivated the PSC surface, facilitated hole transfer, and increased the maximum PCE from 18.43 to 19.74%. Another notable effect is the removal of remnant PbI 2 and the change in the perovskite orientation on the surface by the syn -type molecule. In contrast, the anti -type isomer degraded its long-term stability. We characterized the electrostatic and electronic properties of these molecules and highlighted the advantage of molecular strategy based on a bifacial structure and its stereochemistry.