In situ molecular passivation for improved performance and spectral stability in thermally evaporated pure blue perovskite light-emitting diodes

Pure blue perovskite light-emitting diodes (PeLEDs) produced via vacuum deposition have limited efficiency and spectral stability due to defect-induced non-radiative recombination and halide migration. In this study, we report a pure blue PeLED with improved performance, featuring a thermally evaporated perovskite layer passivated in situ using 4,7-di(9H-carbazol-9-yl)-1,10-phenanthroline (BUPH1), a newly introduced phenanthroline-based small molecule designed to coordinate under-coordinated Pb²⁺ ions. The bidentate coordination of BUPH1 effectively passivates halide vacancies and suppresses ion migration, resulting in improved film morphology, enhanced photoluminescence quantum yield, reduced trap density, and increased exciton binding energy. The optimized perovskite film emits at 472 nm with a narrow full width at half maximum of 19 nm, exhibiting pure blue emission suitable for Recommendation ITU-R BT.2020, an industrial standard for color gamut. The corresponding PeLED achieves an external quantum efficiency of 3.10%, the highest value reported for thermally evaporated pure blue PeLEDs. In addition, the device maintains excellent spectral and color stability under electrical bias, with no noticeable peak shift or change in chromaticity coordinates across varying voltages. This work demonstrates that in situ molecular passivation is an effective strategy to overcome key limitations of thermally evaporated perovskite emitters and supports their potential for next-generation high-resolution display technologies.