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

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 cm²) and 22.83% for large-area modules (62.37 cm²). 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 T₉₀ lifetime of 1695 h.