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 C2-symmetric syn-type bifacial donor-pi-donor (D-pi-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 pi-core. In addition to this bifacial amphiphilic pi-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 PbI2 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.

Automated summary

In this study, a novel molecular concept of a C2-symmetric syn-type bifacial donor-pi-donor (D-pi-D) passivation molecule was introduced to enhance the power conversion efficiency of organic-inorganic lead halide perovskite solar cells. The experimental results showed that this molecule could effectively stabilize the surface of the solar cells, facilitate hole transfer, reduce the remnant PbI2, and change the perovskite orientation, leading to an increase in the maximum efficiency of the cells.