Suppressed Thermal Quenching via Tetrafluoroborate-Induced Surface Reconstruction of CsPbBr₃ Nanocrystals for Efficient Perovskite Light-Emitting Diodes

Although metal-halide perovskite nanocrystals (NCs) have garnered significant attention for optoelectronic applications, the presence of electrically insulating organic ligands in CsPbBr₃ NCs hinders efficient charge injection and transportation in light-emitting diodes (LEDs). A common approach to address this issue involves ligand exchange with shorter ligands and precise control of the surface ligand density through additional purification steps. Nevertheless, the practical application of these methods has been hindered by their poor structural integrity and high surface-defect density, which remain a challenge. Our investigation reveals that NOBF₄ treatment effectively replaces native ligands with BF₄^- anions, in which BF₄^- anions are readily coordinated with the positively charged CsPbBr₃ surface metal centers, thereby improving the photoluminescence quantum yield (PLQY) and thermal stability. In particular, the presence of BF₄^- anions coordinated at CsPbBr₃ surfaces efficiently suppresses the pathway of excitons toward thermally activated nonradiative recombination, leading to minimal thermal quenching and superior device performance in green-emitting PeLEDs. Notably, PeLEDs based on CsPbBr₃ NCs with the reconstructed surface via NOBF₄ treatment exhibit an improved current efficiency of 31.12 cd/A and an external quantum efficiency of 11.24%, increased by 2.8 times compared to that of the pristine sample, indicating the enhanced hole-electron injection and transport into the CsPbBr₃ NCs. Therefore, our results highlight the potential of NOBF₄ as a versatile reagent for the ligand exchange and surface passivation of CsPbBr₃ NCs, thereby offering promising prospects for the development of stable, high-performance PeLEDs.