Self-assembled monolayer modified nickel oxide surface for air-processed blue perovskite light-emitting diodes

Ambient-air fabrication of blue perovskite light-emitting diodes (PeLEDs) presents a significant pathway toward accelerating the commercialization of perovskite displays. However, a primary challenge still remains in deteriorating perovskite crystallization caused by absorption of moisture on the substrate surface. Herein, we engineered a novel composite interface comprising an inorganic transport layer and an ultra-thin self-assembled monolayer (SAM) to significantly enhance the crystallization quality of air-processed blue perovskites. The molecule of (2-(3,6-dibromo-9H-carbazol-9-yl)ethyl) phosphonic acid (Br-2PACz) features a hydrophobic carbazole headgroup and a strongly anchoring phosphonic acid (P–OH) tail group. The tail group establishes robust covalent P–O–Ni bonding with NiOx nanoparticles, which effectively passivates the surface defects on the NiOx surface and concurrently creates an enhanced interfacial dipole moment, thereby facilitating superior hole injection. Simultaneously, the peripheral carbazole headgroup enhances interfacial hydrophobicity of the NiOx layer, thereby optimizing the crystallization of perovskites in ambient air. Ultimately, the air-processed blue perovskite films on the Br-2PACz-modified layer exhibit suppressed defect densities and enhanced photoluminescence quantum yield (PLQY), leading to a substantial improvement in the external quantum efficiency (EQE) for blue PeLEDs from 0.73% to 3.32% in ambient air (T ≈ 21 °C, RH ≈ 20%).