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

Abstract

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 NiO_x nanoparticles, which effectively passivates the surface defects on the NiO_x surface and concurrently creates an enhanced interfacial dipole moment, thereby facilitating superior hole injection. Simultaneously, the peripheral carbazole headgroup enhances interfacial hydrophobicity of the NiO_x 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%).