Surface Energy Modulation of NiO_x through In Situ Click-Cross-Linked Networks for Air-Processed Flexible Blue Perovskite Light-Emitting Diodes

Air-processed flexible blue perovskite light-emitting diodes (PeLEDs) are crucial for advancing flexible displays and wearable optoelectronic devices. However, the NiO_x functional layer in such a flexible device faces a critical challenge of surface energy control within an extremely narrow polarity range to balance water resistance and perovskite precursor wettability. Herein, we demonstrate the postpolymerization modification strategy of click-cross-linking that in situ constructs polymer networks, which significantly improves the mechanical flexibility of the NiO_x film and the interfacial contact between NiO_x and perovskite. Furthermore, the polymer network precisely modulates the surface energy of the NiO_x film based on the selective hydrogen bond interaction between the polymer and solvent molecules (H₂O and DMSO). The flexible NiO_x film is capable of simultaneously achieving good DMSO wetting and H₂O resistance, which facilitates the perovskite film fabrication under ambient conditions. Consequently, we realize the first air-processed flexible blue PeLEDs, achieving a peak external quantum efficiency (EQE) of 1.32% with exceptional bending durability, retaining over 80% of the initial EQE after 2000 bending cycles. This work offers a guideline for surface energy modulation to achieve a robust flexible inorganic hole transport layer for air-processed blue perovskite fabrication, opening an avenue for advancing flexible perovskite displays.