Ultrathin Monolayer Perovskites via Microstructure-Induced Capillary Flow for Efficient Pure-Blue Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for next-generation displays. However, the performance of pure-blue PeLEDs based on quasi-2D perovskites remains challenging due to abundant inner grain boundaries resulting from their inevitable multi-layered grain stacking. Here, we report a simple strategy to construct quasi-2D perovskites with ultrathin monolayer structures by utilizing substrate microstructure-induced capillary action for liquid film thinning and flattening. The resulted architecture features highly oriented ∼6.3 nm thick grains with eliminated inner transverse grain boundaries, suppressing carrier trapping and ion migration, and promoting radiative recombination. Adopting this structure, we demonstrated pure-blue (466 nm, CIE: 0.132, 0.065) PeLED with a peak external quantum efficiency of 15.0% at 56.54 cd m −2 , and a maximum luminance of 947 cd m −2 accompanied by stable electroluminescence spectra. Our strategy provides a novel pathway for regulating perovskite film structures by utilizing microstructure-induced surface effects and liquid film morphology modulation.