Photochemical Iodine Immobilization for Stabilizing Wide-Bandgap Perovskite Solar Cells

Halide segregation remains a critical challenge for wide-bandgap perovskite solar cells. Iodide oxidation and diffusion at the perovskite heterointerface play pivotal roles in this process, as light-induced generation of I2 leads to compositional demixing. To address this issue, we developed a styrene-functionalized molecule (CBP-V) as an interfacial buffer atop the perovskite layer that covalently immobilizes I2 via photochemical addition, suppressing the formation of more reactive iodine species and preventing the degradation of perovskites. The π-conjugated carbazole within CBP-V passivates undercoordinated Pb2+ on the surface, reducing defect density and suppressing nonradiative recombination. This dual-function approach enables 1.77 eV perovskite solar cells with a power conversion efficiency (PCE) of 19.51% and a VOC of 1.28 V. Moreover, CBP-V treatment markedly enhances solar cell stability, with devices retaining over 80% of their initial PCE under continuous operation (200 h), 85% under thermal stress (65 °C, 400 h), and 90% during long-term storage (1000 h), substantially outperforming the control devices.