Orientation-Engineered Interfacial Bi-Anchoring Molecules for Efficient and Stable Perovskite Solar Cells

Self-assembled monolayers as hole-transport materials have been a milestone in the advancement of inverted perovskite solar cells (PSCs). However, its strong-acidity and weak-interface-bonding inherences remain great challenges for commercially desirable PSCs. To overcome the limitation, we proposed the orientation-engineered interfacial bi-anchoring molecules with a symmetric linear donor-acceptor-donor (D-A-D) structured N-oxide-based building block. The D-A-D structure with intramolecular push-pull electron effects features superior hole-selective ability than the widely used donor units, endowing effective hole-transport planar. However, the bilateral N-oxide functional groups (N⁺-O^-) in the acceptor bipyridine introduce a steric effect to drive the D-A-D planar in both in-plane and out-of-plane directions, effectively promoting the hole extraction. Moreover, the reversely oriented N⁺-O^- function groups can firmly adsorb on ITO substrate and perovskite buried surface, respectively, constructing an interfacial bi-anchoring connection. This molecular configuration considerably promotes the photothermal tolerance, connective strength as well as energy-level alignment at perovskite/HTLs interface, enabling superior charge extraction and durability. Consequently, BPyDO-TPA-based inverted PSCs achieve an impressive efficiency of 26.53%, ranking as one of the highest efficiencies among nonphosphonic acid small-molecule transporting materials. BPyDO-TPA-based devices also demonstrate excellent operational stability, retaining 94.82% of its initial efficiency after MPP tracking for 1000 h at 85 °C.