Eliminating Chlorine Vacancies of Perovskite Nanocrystals Using Hydrazine Cations Enables Efficient Pure Blue Light-Emitting Diodes

Mixed Br/Cl-perovskite nanocrystals (Pe-NCs) CsPbBrxCl3-x , synthesized at room temperature (RT), offer several advantages for use in light-emitting diodes (LEDs), including cost-effective processing and a narrow luminescence peak. However, achieving efficient pure blue LEDs using CsPbBrxCl3-x NCs has been proven to be challenging due to a significant number of chlorine defects. In this work, we propose a passivation strategy utilizing hydrazine cations (Hz(2+)) to eliminate chlorine defects in RT-synthesized Pe-NCs. Our investigation reveals that Hz(2+) can capture the isolated chlorine anion (Cl-) to form a Hz-Cl-Cs bridge on the Pe-NC surface, thereby effectively inhibiting the formation of chlorine vacancies. This approach significantly enhances both the photoluminescence efficiency and lifetime of Pe-NCs. Consequently, LEDs fabricated using Hz(2+)-passivated Pe-NCs achieve an outstanding external quantum efficiency (EQE) of 7.82% at 475 nm. Our findings highlight an effective passivation strategy that significantly mitigates chlorine defects in Pe-NCs, thereby advancing the development of efficient pure blue LEDs.