Synergistic aggregation inhibition and radical-catalyzed doping in 3D crosslinked electron transport layer for efficient and stable inverted perovskite solar cells

Conventional PCBM electron transport layers (ETLs) in inverted perovskite solar cells (PerSCs) suffer from self-aggregation and poor charge transport after crosslinking. To overcome these challenges, a family of three-dimensional (3D) crosslinkable electron transport materials (ETMs)—POSS-PDI4, POSS-PDI6, and POSS-PDI8—by integrating perylene diimide (PDI) units with a 3D polyhedral oligomeric silsesquioxane (POSS) core are designed. The optimized thiol-ene crosslinked C-POSS-PDI4 addresses these challenges through three synergistic innovations. First, it suppresses PCBM self-aggregation, forming uniform and pinhole-free ETLs, while introducing a hydrophobic and passivating barrier against moisture and ion penetration. Second, a radical-catalyzed n-doping strategy is introduced, where TEMPO dramatically enhances the efficiency of N,N′-4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (NDMBI) dopants. This reduces the activation energy, leading to a three-order-of-magnitude conductivity increase. As a result, devices incorporating the co-doped ETL with NDMBI and TEMPO (C-POSS-PDI4 + PCBMNT) achieve a record PCE of 25.65% and excellent stability (98% PCE retention after 3000 h in dark storage under nitrogen atmosphere). In addition, the synthesis cost of ETL is reduced by 77.1% compared to PCBM. This work presents a synergistic design strategy that integrates 3D crosslinked architectures with radical-catalyzed n-doping to simultaneously enhance device efficiency, stability, and cost-effectiveness, offering a promising pathway toward the commercialization of high-performance PerSCs.