Iron-induced phase engineering for high color-purity blue LEDs in perovskites

Blue emission in perovskite light-emitting diodes (PeLEDs) remains challenging due to the inherently high bandgap energy. Quasi-two-dimensional (quasi-2D) perovskites have emerged as promising blue PeLEDs, where cascading energy transfer among distinct 2D phases plays a critical role in achieving high device performance. Herein, we propose an additive-assisted phase engineering strategy by incorporating iron additives (FeBr₃ and FeCl₃) into quasi-2D perovskites. The introduction of iron additives effectively suppresses low-n phases and promotes high-n phases, enabling bandgap modulation and resulting in a significant narrowing of the photoluminescence full width at half maximum (FWHM). Density functional theory (DFT) calculations reveal that the iron additives thermodynamically stabilize high-n phases, accounting for the observed phase redistribution. Blue PeLEDs incorporating FeCl₃ achieve an enhanced external quantum efficiency (EQE) of 6.01% and luminance of 227.6 cd m^-2 compared to pristine devices (3.72%, 177.8 cd m^-2). These results suggest that additive-assisted phase engineering provides an effective pathway toward stable, high color-purity blue PeLEDs.