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

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 Cs2HfCl6 (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 similar to 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.