Symmetric\nPolar Molecule Optimized Buried Interface\nfor Stable Flexible Perovskite Solar Cells

Molecular\nanchoring at the buried interface of flexible perovskite\nsolar cells is an efficient approach to address the low adhesion,\neasy substrate deformation and defects passivation. Herein, we introduce\na polar, symmetric small molecular (DPBCA) between the ETL and perovskite\nlayer as a buffer layer. The strong polar functional groups (–CO\nand −CN) in DPBCA molecules exhibit strong adhesion on the\nfragile ETL/perovskite interface, improving the toughness of the buried\ninterface and reducing residual stress, thereby enhancing the mechanical\nstability of devices. The results indicate that the symmetric structure\nof DPBCA provides a sufficient number of ligands to synergistically\npassivate multisite defects, and the collective interaction strength\nof the symmetric functional groups on both sides is greater than that\nof the isolated interactions on one side. The carbonyl and cyano groups\nin the DPBCA molecules can passivate noncoordinated Pb<sup>2+</sup>/Sn<sup>4+</sup>. Additionally, the carbonyl and hydroxyl groups\nin DPBCA can interact with iodine(I), synergistically passivating\nI vacancies and suppressing the migration of I, which further enhances\nthe passivation effect. This synergistic passivation greatly lowers\ndefect density and increases the lifespan of charge carriers in the\nperovskite film. As a result, the efficiency of (0.34 cm<sup>2</sup>) devices based on FA<sub>0.85</sub>MA<sub>0.15</sub>PbI<sub>3</sub> is improved by 33% (maximum 23.05%). Under different environmental\nconditions, after bending test cycles, the target devices show noticeably\nbetter stability against exposure to light, water, and temperature\nwhile retaining over 81.3% of their initial PCE.