Gradient Alloy Shell Enabling Colloidal Quantum Wells Light-Emitting Diodes with Efficiency Exceeding 22.

Colloidal quantum well (CQW) based light emitting diodes (LEDs) possess extra-high theoretical efficiency, but their performance still lags far behind conventional LEDs due to severe exciton quenching and unbalanced charge injection. Herein, we devised a gradient composition Cd x Zn 1- x S shell to address these issues. The epitaxial shell with gradient composition was achieved through controlling competition between Cd 2+ and Zn 2+ cations to preferentially bind to the anions S 2- . Thus, exciton quenching was suppressed greatly by passivating defects and reducing nonradiative recombination, thereby achieving near-unity photoluminescence quantum yield (PLQY). The gradient energy level of the shell reduced the hole injection barriers and increased the hole injection efficiency to balance the charge injection of LEDs. As a result, the LEDs achieved a high external quantum efficiency (EQE) of 22.83%, luminance of 111,319 cd/m 2 and a long operational lifetime ( T 95 @100 cd/m 2 ) over 6,500 h, demonstrating the state-of-the-art performance for the CQW based LEDs.