An n‐Type Polythiophene Derivative as Electron Transport Layer for Stable and Efficient Dion–Jacobson Perovskite Solar Cells

ABSTRACT N‐type conjugated polymers based on non‐fused‐ring electron‐deficient building blocks offer significant advantages, including simpler structures and lower production costs, compared with counterparts based on complex fused‐ring building blocks. Nonetheless, they have been scarcely investigated as electron transport layer (ETLs) in hybrid perovskite solar cells (HPSCs), probably limited by the small number of non‐fused‐ring electron‐deficient building blocks developed to date. Here, a thiophene‐based n‐type polymer (n‐PT3) composed of very simple non‐fused‐ring building blocks is employed as ETL in inverted Dion–Jacobson (DJ) HPSCs. Compared to the control polymer (P5O) with fused‐ring building blocks, n‐PT3 exhibits the merits of a planar conformation, electron‐rich backbones, and higher hydrophobicity, resulting in superior charge transport and defect passivation, as well as enhanced water resistance. Consequently, n‐PT3 as an ETL yields more efficient, reproducible, and stable devices that achieve a power conversion efficiency (PCE) of 14.86%, representing a remarkable 83% improvement compared to the control device. More importantly, devices using n‐PT3 as ETL retain 94.68% of their initial PCEs after aging in air for 1669 h, compared to 46.66% for the control device. These results demonstrate great potential of n‐type polymers with non‐fused‐ring electron‐deficient building blocks for efficient and stable DJHPSCs.