Suppressing Residual Low-Dimensional Phases in Bromide Perovskite LEDs Using a Dimethyl Phosphate Ionic Liquid

Perovskite light-emitting diodes (PeLEDs) are promising for display applications owing to their excellent color purity and efficiency. However, they often face the challenge of maintaining high efficiency at high luminance (>1000 cd m^-2). The unintended formation of low-dimensional phases and defects during the crystallization of 3D perovskites is considered to be one of the detrimental factors limiting device performance. Here, we introduce an ionic liquid, tributyl(methyl)phosphonium dimethyl phosphate (TDP), into the precursor of a light-emitting bromide perovskite. This process is found to form perovskite emissive layers with suppressed low-dimensional phases, improved film morphology, and reduced defect density. The resultant green PeLEDs achieve peak external quantum efficiency (EQE) exceeding 20% at 1000 cd m^-2, a high brightness of 3.7 × 10⁵ cd m^-2, and a T₅₀ lifetime of 47 h at an initial luminance of 1000 cd m^-2. Our work highlights the effectiveness of dimethyl phosphate ionic liquids in controlling the formation of 3D perovskites, contributing to the advancement of high-performance green PeLEDs.