Scalable and room-temperature preparation of Cs2HfCl6 double perovskites with recorded photoluminescence efficiency and robust stability.

[Display omitted] Mass production of Bi3+ and Te4+ co-doped vacancy-ordered Cs 2 HfCl 6 (CHC) double perovskites (DPs) under room temperature (RT) was reported, which was enabled by the rationally designed ligand of [Hmim]Cl. The resultant CHC DPs exhibit overall excellent performance with robust photostability and superior PL QY of 96.4%, ∼2 times to the highest one of the analogues obtained at RT ever reported. • The PLQY of CHC DPs can be optimized to 96.4% with the assistance of [Hmim]Cl. • The multi-functional effects of [Hmim]Cl ligand have been clarified. • The mass production of high-quality CHC DPs at room temperature has been achieved. Vacancy-ordered double perovskites (DPs) are promising candidates for modern white light-emitting-diodes (WLEDs) due to their low toxicity and unique optical properties. However, the grand challenge is that DPs synthesized at room temperature (RT) typically have a low photoluminescence quantum yield (PLQY), most of which reported below 51 %, making them impractical for applications. Here, we present a facile strategy for the mass production of Bi3+ and Te4+ co-doped Cs 2 HfCl 6 (CHC) DPs at RT, to realize single-component dual-band emission with a high color rendering index. It is witnessed that the rationally designed ligand [Hmim]Cl facilitates a strong chemical interaction between the ligand and DPs. This interaction allows [Hmim]Cl to coordinate with undercoordinated Hf4+ ions and provide excess chloride ions to the surface of the DPs. Consequently, it effectively controls the crystallization of DPs, protects them against moisture, reduces surface defects, and increases the migration barrier of halogen ions. As a result, the DPs exhibit excellent overall performance with robust photostability and a superior PLQY of 96.4 %, which is ∼ 2 times the highest reported value for similar DPs synthesized at RT. Current work presents a potential pathway for the mass production of high-quality DPs under mild conditions, leading to the development of signal-component WLEDs. [ABSTRACT FROM AUTHOR]