Bifunctional Multidentate Linker Tailoring Interfacial Dipole and Residual Stress to Enhance Photovoltaic Performance

Buried layer crystallization at an electron transport layer interface is seldom discussed but crucial for obtaining a high-quality perovskite layer. This study demonstrates a novel interfacial engineering concept by using 2-aminoethylphosphonic acid (APA) to bridge the mechanical and electronic disparities at the SnO ₂ /perovskite interface. The bifunctional synergy of the APA molecule, which serves as both an electronic dipole and a mechanical geometrical tuner. The flexible backbone of APA renders it to alleviate the strain by over 20% through releasing residual compressive stress. The electron-withdrawing phosphonate and electron-donating amino headgroups anchor preferred-orientationally onto SnO ₂ and perovskite terminal facets. The directional dipole and releasing stress help expand the quasi-Fermi level splitting and accelerate electron transfer from the perovskite layer to the electron transport layer of SnO ₂ . The champion device can achieve power conversion efficiency of 22.92% with over 1,500 h stability in air without encapsulation. By harmonizing molecular orientation with mechanical stress relief, this study establishes a new paradigm for high-performance and durable perovskite photovoltaics.