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 (Voc), 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.