Influence of Quantum Dot Purification on a Blue Quantum Dot Light-Emitting Diode

Quantum dots (QDs) have demonstrated their potential in QD light-emitting diodes (QLEDs) with high brightness and color purity. The short lifetime of blue QLEDs is currently a big obstacle for QLED commercialization. Ligands passivate surface defects of QDs and play a vital role in QLED performance. However, QDs must be purified using the precipitation-centrifuge-redissolution (PCR) method to remove residuals before application. Purification leads to ligand loss and thus an inevitable increase in surface defects, which is detrimental to device performance. In this study, we synthesized and characterized blue QDs with a ZnCdSe/ZnSe/ZnCdS structure and investigated the influence of PCR purification cycles on QD thin film morphologies. We then investigated the effect of morphology on QLED performance. It was found that the QD film with minimal residuals and the lowest roughness demonstrated the highest current efficiency of 10.3 cd/A, the highest EQE of 15.3%, and the longest T95 operation time at a luminance of 1000 cd/m2 (T95@1000 cd/m2) of 105 h. Our work demonstrates the significance of an optimized purification process for achieving stable blue QLEDs.