Highly stable hetero-structured green-emitting cesium lead bromide nanocrystals via ligand-mediated phase control.

Green-emissive Cs ₄ PbBr ₆ shows promise for light-emitting diode devices superior to that of CsPbBr ₃ NCs owing to their stability and high photoluminescence efficiency. Nevertheless, there is still no consensus regarding the basis of their green emission, which decelerates their advance in light-emitting applications. Herein, a systematic investigation on the concentration of capping ligands (oleylamine and oleic acid), which determines the predominant phase between CsPbBr ₃ and Cs ₄ PbBr ₆ for a given Cs to Pb feed ratio, is conducted. This study deduces that oleylamine to oleic acid ratio plays a crucial role in obtaining either green-emissive or non-emissive Cs ₄ PbBr ₆ NCs. Scrutiny of Cs ₄ PbBr ₆ microscopic and optical data in addition to their emission quenching study with a hole-withdrawing molecule reveals that the green emission originates from the CsPbBr ₃ impurity phase. Furthermore, stable green emission is observed for CsPbBr ₃ /Cs ₄ PbBr ₆ nanocrystals when CsPbBr ₃ particles are well protected by the Cs ₄ PbBr ₆ matrix. These CsPbBr ₃ /Cs ₄ PbBr ₆ films remained highly luminescent even after UV exposure for hours or annealing at ∼150 °C for days in addition to their long-term stability under an ambient atmosphere, which are the desirable properties for various practical applications.