Mitigating Photothermal‐Induced Burn‐In in Perovskite Solar Cells via a Multidentate Phosphonic Acid Polymer Network

ABSTRACT The burn‐in loss in perovskite solar cells (PSCs) during the initial operational stage induces substantial heterogeneous power output, as non‐uniform degradation among sub‐cells rapidly amplifies series‐parallel mismatch to compromise both efficiency and long‐term stability at module level. Most monomeric self‐assembled monolayers (M‐SAMs) suffer severe burn‐in loss under harsh photothermal stress, and the early‐stage performance decay dynamics and relevant degradation mechanisms remain unclear. Here, we find that the burn‐in loss under light‐heat conditions mainly originates from coordination relaxation/dissociation at the buried SAM/perovskite interface and the resultant rapid ion migration within the initial tens of hours. Further, we developed polymeric SAMs (P‐SAMs) featuring a multidentate phosphonic acid polymer network that enhances interfacial chemical coupling and mechanical robustness. Notably, it boosts interfacial fracture strength by nearly eightfold to 9.11 MPa and improves large‐area film uniformity. Consequently, P‐SAMs exhibit a certified efficiency of 26.61% for small‐area PSCs (0.06734 cm 2 ) and 22.83% for large‐area modules (62.37 cm 2 ). Under continuous AM1.5G (one‐sun) maximum power point tracking at 85 °C, the P‐SAM device reduces the initial efficiency loss from 35.6% to 4.3%, eliminating burn‐in behavior to enhance long‐term stability with a T 90 lifetime of 1695 h.