Core Extended Conjugation in Thiophene‐Based Cations Enables Open‐Circuit Voltage Improvement in Inverted Perovskite Solar Cells

Interface engineering plays a pivotal role in enhancing the performance and stability of perovskite solar cells (PSCs). Here, we explore the influence of core conjugation in thiophene‐based ammonium cations as surface passivation agents in the inverted (p–i–n) device architecture. The increased bonding strength observed with the conjugation extension allows specific defect suppression at the perovskite/PCBM interface, confirmed by combined spectroscopic analysis and density functional theory simulations. This passivation strategy yields a remarkable increase in the device open‐circuit voltage ( V oc ), resulting in a champion power conversion efficiency of 22.8%, compared to 20.8% in the control device. This study highlights the importance of molecular conjugation and halide choice in designing efficient surface passivation strategies for effective surface defect passivation in high‐performance PSCs.