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

Green-emissive CsPbBr shows promise for light-emitting diode devices superior to that of CsPbBr 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 and CsPbBr 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 CsPbBr NCs. Scrutiny of CsPbBr 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 impurity phase. Furthermore, stable green emission is observed for CsPbBr/CsPbBr nanocrystals when CsPbBr particles are well protected by the CsPbBr matrix. These CsPbBr/CsPbBr 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.