Mg-Assisted Passivation of Defects in CsPbI Perovskite Nanocrystals for High-Efficiency Photoluminescence.

CsPbI perovskite nanocrystals (NCs) are emerging as promising materials for optoelectronic devices because of their superior optical properties. However, the poor stability of CsPbI NCs has become a huge bottleneck for practical applications. Herein, we report an effective strategy of Mg-assisted passivation of surface defects to obtain high emission efficiency and stability in CsPbI NCs. It is found that the introduced Mg ions are mainly distributed on the surface of NCs and then passivate the NC defects, enhancing radiative decay rate and reducing nonradiative decay rate. As a result, the as-prepared Mg-treated CsPbI (Mg-CsPbI) NCs exhibit the highest photoluminescence quantum yield (PLQY) of 95%. The Mg-CsPbI NC colloidal solution retains 80% of its original PLQY after 80 days of atmosphere exposure. The red perovskite light-emitting diodes based on the Mg-CsPbI NCs demonstrate an external quantum efficiency of 8.4%, which shows an almost 4-fold improvement compared to the devices based on the untreated NCs.