Dual-Bidentate Thiophene-Derived Interface Engineering in Perovskite Solar Cells: Synergistic Management of Defect Passivation and Strain Relaxation

With advances in photoelectric conversion efficiency of perovskite solar cells (PSCs), intrinsic instability originating from interfacial defects and residual tensile strain is becoming a great challenge. Herein, a versatile dual-bidentate thiophene-derived molecule, 2,2'-bithiophene-4,4'-dicarboxylic acid (BTDA), is introduced to build a bilateral interface bridge layer for synergistically enabling buried defect passivation and perovskite film strain relaxation. Combined DFT calculations and experimental results verify that the two carboxylic acid groups of BTDA act as precise bilateral grippers to preferentially chelate the uncoordinated Sn⁴⁺ upon SnO₂, while its thiophene moieties function as deployed bidentate anchoring groups to stabilize the uncoordinated Pb²⁺ in perovskites. Particularly, the BTDA buried interlayer, as proven by HRTEM, GIXRD, and in situ XPS measurements, induces crystal lattice compression in perovskites beneficial for relaxing the residual tensile strain of the perovskite film and the enhanced thermal stability of the perovskite film. The BTDA-modified PSC yields a boosted power conversion efficiency (PCE) from 21.91% to 24.09% and sustains nearly 80% (unmodified, 57.1%) of its original PCE after 1000 h of aging under ambient conditions (25 °C, 20-50% RH). This work proposes an effective BTDA strategy to concurrently manage bilateral defect passivation and strain relaxation through dual-bidentate anchoring toward efficient and stable PSCs.