Molecular coordination stabilizes built-in electric fields for efficient perovskite solar cells

The efficiency of perovskite solar cells (PSCs) based on bulk heterojunctions fundamentally relies on their built-in electric fields (BIEFs) to drive charge carrier separation and extraction. However, high-quality perovskite films usually exhibit an intrinsically low carrier density (∼10¹⁴ cm⁻³) compared with the photoinjected electron-hole pair density (10¹⁵–10¹⁶ cm⁻³) under 1-sun illumination. This fundamental contradiction makes BIEFs vulnerable to dynamical screening under operational conditions. Herein, we report a molecular coordination strategy to stabilize the BIEF with 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T). By creating a concentration gradient near the perovskite surface, PO-T2T effectively coordinates with undercoordinated Pb²⁺ sites to form high-density local dipoles (∼10¹⁶ cm⁻³), significantly stabilizing the BIEF under illumination. Consequently, the resulting PSC delivers a power conversion efficiency (PCE) of 27.01% (certified 26.71%) with improved operational stability. These results underscore the pivotal role of PO-T2T in suppressing field screening, providing critical insights for designing high-efficiency heterojunction solar cells.