CdSe/CdSeS Nanoplatelet Light-Emitting Diodes with Ultrapure Green Color and High External Quantum Efficiency.

Colloidal II-VI group nanoplatelets (NPLs) possess ultranarrow emission line widths, for which they have great promise in achieving the purest display color in solution-processed light-emitting diodes (LEDs). Red NPL-LEDs have shown extremely saturated red color with high efficiency, while the green and blue ones lag far behind. Herein, we report green NPL-LEDs with the purest color in accordance with the Rec. 2020 standard and the peak external quantum efficiency (EQE) of 9.78%. By carefully controlling the aspect ratio, capping ligands, and purifications of CdSe/CdSeS core/alloyed-crown NPLs, NPL films with excellent flatness and unity photoluminescence quantum yields (PLQYs) are realized, laying a solid foundation for improving LED performance. Furthermore, via tuning the carrier injection balance, the record-high EQE for green NPL-LEDs is achieved. The electroluminescence (EL) exhibits an extremely saturated green color with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.163 0.786), which demonstrates their great potential in applications of ultrahigh-definition display technology. Our findings would help to further improve the performance of all NPL-LEDs.