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

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.