Achieving Ultrahigh Efficiency Vacancy‐Ordered Double Perovskite Microcrystals via Ionic Liquids

Abstract Lead‐free perovskites have gained much interest for photovoltaic and optoelectronic applications. But instability and low quantum efficiency significantly limit their prospects for future applications. Here, a general route is reported to synthesize highly stable lead‐free perovskites on a large scale with remarkably enhanced quantum efficiency. Two typical vacancy‐ordered double perovskites (Cs 2 ZrCl 6 and Cs 2 SnCl 6 ) and their corresponding Bi 3+ or Sb 3+ doped samples are synthesized in ionic liquids (ILs) solutions via a simple solution method. These prepared perovskite samples all exhibit high‐quality crystalline structures and their photoluminescence quantum yields (PLQYs) all show an increase close to 200% compared to the samples prepared in the hydrochloric acid system. The PLQY of Sb‐doped Cs 2 ZrCl 6 with excellent thermal stability can reach up to 90.2%, which is the highest value reported for this system (Cs 2 ZrCl 6 :Sb). Density functional theory calculations reveal that the corresponding interaction between the ILs and the samples can effectively improve the crystal quality and reduce energy loss. The potential applications of the prepared samples for high‐performance white light‐emitting diodes and optical anti‐counterfeiting are also demonstrated. The findings provide a straightforward way to obtain ultrahigh quantum efficiency vacancy‐ordered double perovskites with good thermal stability and excellent optoelectronic properties.