Spatial Self‐Assembled Ionic Bridge Strategy for Overcoming Perovskite/PCBM Heterojunction Issues in Inverted Perovskite Solar Cell

ABSTRACT In inverted perovskite solar cells (IPSCs), perovskite (PVSK)/[6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM) heterojunction energy loss severely limits device performance and stability. Despite ionic liquids (ILs)’ unique advantages as additives and buried interface modifiers, their potential at this heterojunction remains underexplored with insufficient mechanistic insights. Here, a spatially self‐assembled ionic bridge strategy using an ILs of 1‐hexyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (HMB, composed of [TFSI − ] and [HMIM + ]) is first proposed to overcome this loss. Leveraging [TFSI − ]/[HMIM + ]’s differential interactions with PVSK and PCBM, cation‐anion spatial segregation forms at their interface ([TFSI − ] on PVSK, [HMIM + ] on PCBM). HMB thus spontaneously assembles as [PVSK‐TFSI − ]←[HMIM + ‐PCBM], reinforcing interfacial electrical coupling, passivating defects, improving PCBM film formation, and building a strong built‐in electric field. Benefiting from this strategy, defect passivation, improved interface contact, eliminated migration, and released residual stress are achieved, effectively enhancing the performance and stability of IPSCs. The high‐power conversion efficiency (PCE) of 25.24% is achieved with this strategy, which exhibits outstanding performance among the reported values for ILs‐modified PVSK/PCBM heterojunction in IPSCs. Furthermore, HMB devices retain 99.56% for 1000 h (N 2 ), 97.19% for 300 h (65°C), 84.05% for 934 h (1sun @ MPPT) of its initial PCE value, superior than that of the control devices.