Flexible Colloidal Light-Emitting Diodes of Self-Assembled Quantum Well Monolayers

Quasi-2D semiconductor nanocrystals, also known as colloidal quantum wells (CQWs), with their high quantum yield in the visible range, ultra-narrow emission, and in-plane oriented transition dipole moments, provide potentially an excellent platform for flexible light-emitting diodes (f-LEDs). In this study, it is proposed and demonstrated colloidal f-LEDs of a single layer face-down oriented CdSe/CdZnS core/hot injection shell-grown CQWs employed as an emissive monolayer in a flexible platform for the first time. The obtained f-LEDs are shown to be immune to a large number of bending, enabled by the use of only a single emitter layer and their configuration all being face-down in the layer. These f-LEDs exhibit a maximum external quantum efficiency of 14.12%, an intense luminance of ≈33 700 cd m^-2, a low turn-on voltage of <2 V, and a highly saturated red color. Here, orienting these CQWs only in face-down configuration is essential to efficient charge injection thanks to its extremely low roughness and increased outcoupling efficiency owing to in-plane oriented transition dipoles. Therefore, these f-LEDs of face-down CQW monolayers, with their excellent luminance properties and stable emission, stand out as exceptional candidates for future advanced flexible display and lighting applications as well as wearables.