Organic Sulfonium‐Stabilized High‐Efficiency Cesium or Methylammonium Lead Bromide Perovskite Nanocrystals

Abstract Herein, we report a new X‐type ligand, i.e., organic sulfonium bromide, for high‐efficiency CsPbBr 3 and MAPbBr 3 (MA=methylammonium) perovskite nanocrystals (PNCs). We first confirmed the facile synthesis of the titled ligands in N,N‐dimethylformamide at room temperature. By reacting dodecylmethylsulfide with allyl bromide, (3‐bromopropyl)trimethoxysilane, and 1,4‐dibromobutane, respectively, three representative ligands (named DAM, DSM, and DMM) are acquired. All of them result in CsPbBr 3 and MAPbBr 3 PNCs with near‐unity photoluminescence quantum yield (PLQY) and decent ambient stability (no less than 90 % PLQY after 2 months) using a room‐temperature ligand‐assisted reprecipitation technique. Among them, DSM and DMM endow CsPbBr 3 PNCs with higher thermal/light stability arising from the cross‐linkable or bidentate ligand structure. Further, DSM‐CsPbBr 3 PNCs can be incorporated into polystyrene through in situ thermal polymerization and the composite shows a record‐high PLQY of 93.8 %.