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

Abstract 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 Et 2 OPACz 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 Et 2 OPACz 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.