Suppressing Spectral Instability of Vacuum-Deposited Blue Perovskite Light Emitting Diodes via Phenanthroline-Containing Organic Passivation Agents

The current premium display market is dominated by organic light-emitting diode (OLED) technology. Based on vacuum deposition processes, OLEDs have successfully achieved large-scale production and are used in various displays such as mobile devices and TVs. Although electroluminescent quantum dot (EL-QD) LEDs were once considered the next generation of displays after OLEDs, they have faced significant commercialization challenges, particularly due to difficulties associated with solution-based processes. Metal halide perovskites, which can be synthesized using the same vacuum deposition methods as OLEDs, present a promising alternative for future displays. They offer excellent color purity due to their narrow full-width at half maximum (FWHM), enabling them to achieve a color gamut that satisfies the Rec.2020 color space standard. Additionally, they can cover the entire visible spectrum through halide composition adjustments. However, perovskites synthesized via vacuum deposition face efficiency challenges compared to those produced through solution-based methods, limiting their practical applications in display technologies. In this study, we aimed to address these efficiency challenges by synthesizing true blue perovskites with a peak emission at 460-475 nm through co-deposition of three inorganic materials: PbBr₂, CsCl, and CsBr. By adjusting the deposition rates, we achieved the optimal peak wavelength for pure blue emission. By applying hole transport layer and electron transport layer materials, we achieved pure-blue emission at 472 nm with an external quantum efficiency (EQE) of 3.13% and an FWHM of 17 nm. This represents the highest efficiency reported to date for vacuum-deposited pure blue perovskite LEDs, highlighting significant progress in this area. However, these perovskite LEDs exhibited spectral shift issues when applied bias exceeded 6.5V. To address this problem, we investigated the incorporation of an organic material containing phenanthroline groups into the perovskite structure through co-deposition. This approach maintained a peak emission at 472 nm and resulted in a device with an EQE of 2.16% and an FWHM of 17 nm. Although the EQE is slightly lower than the counterpart without the phenanthroline additives, the device exhibited much improved spectral stability. The phenanthroline groups are expected to form complexes with lead, effectively passivating the perovskite emitter. Maintaining such stability is crucial for the development of reliable and durable display technologies. These findings demonstrate substantial progress in the development of vacuum-deposited metal halide perovskites for high-efficiency, high-purity blue light-emitting applications in next-generation displays.