Molecular Tailoring of Self‐Assembled Monolayers via Polar Ether Linker for Highly Efficient and Mechanically Robust Flexible Perovskite Solar Cells

Flexible perovskite solar cells (f-PSCs) are promising candidates for next-generation portable, wearable, and building-integrated photovoltaics. However, conventional self-assembled monolayer (SAM) molecules often exhibit weak interfacial binding and limited mechanical coupling, leading to incomplete coverage and poor contact on rough flexible substrates. Here, a molecularly tailored SAM design is presented that addresses these challenges through rational linker engineering. Replacing common alkyl chains with a polar ether linker modulates the electron density around the phosphonic acid anchoring group, while the ether oxygen atom acts as an effective hydrogen-bond acceptor. This dual functionality promotes Et₂OPACz to assemble into a dense, uniform layer on flexible substrates, thereby strengthening interfacial adhesion, improving perovskite film quality, and facilitating hole extraction. As a result, f-PSCs incorporating Et₂OPACz SAM achieve a remarkable power conversion efficiency (PCE) of 25.11% (certified 24.59%), among the highly reported for f-PSCs. The devices retain 94% of their initial PCE after 1000 h of continuous operation and 92.6% after 5000 bending cycles at a radius of 3 mm. These results demonstrate that polar ether linker engineering provides a powerful strategy to simultaneously optimize interfacial contact, charge transport, and mechanical durability in high-performance f-PSCs.