sp ³ -Hybridized Self-Assembled Monolayers with Asymmetric Steric Effect for Perovskite Solar Cells

Incorporating symmetric substituents into self-assembled monolayers is an effective strategy for suppressing aggregation. However, the resulting symmetric steric effect often weakens the π-interactions. To better balance steric effect and π-interactions, we design two SAMs with an asymmetric steric effect through an sp3-hybridized 9,10-dihydroacridine core, 4PADMeAC and 4PADPhAC. Compared to the methyl group, the phenyl group creates a larger twist angle and more effective π-π interactions, leading to smaller micelles and more efficient hole transport. Therefore, the 4PADPhAC film exhibits improved uniformity and higher conductivity, resulting in perovskite films with higher crystalline quality and lower trap densities. As a result, devices based on 4PADPhAC achieve a 25.34% efficiency and improved stability, retaining 85% of its initial efficiency after 3026 h in air of RH 45 ± 10% (ISOS-D-1) and 94% of its initial efficiency after 500 h of MPPT under 1 sun at 45 ± 5 °C and RH 70 ± 10% in air (ISOS-L-3).