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

Green-emissive Cs₄PbBr₆ shows promise for light-emitting diode devices superior to that of CsPbBr₃ 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 CsPbBr₃ and Cs₄PbBr₆ 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 Cs₄PbBr₆ NCs. Scrutiny of Cs₄PbBr₆ microscopic and optical data in addition to their emission quenching study with a hole-withdrawing molecule reveals that the green emission originates from the CsPbBr₃ impurity phase. Furthermore, stable green emission is observed for CsPbBr₃/Cs₄PbBr₆ nanocrystals when CsPbBr₃ particles are well protected by the Cs₄PbBr₆ matrix. These CsPbBr₃/Cs₄PbBr₆ 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.