Ultrathin PVK charge control layer for advanced manipulation of efficient giant CdSe@ZnS/ZnS quantum dot light-emitting diodes

An efficient green quantum dot light-emitting diode (QLED) consisted of giant CdSe@ZnS/ZnS quantum dots (QDs) with the gradient composition was reported. The electroluminescence (EL) enhancement was demonstrated by utilizing a poly(9-vinlycarbazole) (PVK) charge control layer (CCL) to regulate the injection charge inside QD emitters. With lower electron mobility and high triplet energy for the possibility of efficient resonance energy transfer, the ultrathin PVK CCL possessed the capability of increasing the radiative recombination of excitons by reducing the predominant electrons, adjusting the charge injection rate, and thus suppressing QD charging effect. As a consequence, the QLED with a CCL demonstrated excellent performance (external quantum efficiency (EQE) ∼ 4.3% and maximum luminance (Lmax) ∼41900 cd/m2) superior to that of previously published "Type-II″ devices with similar organic/polymer carrier transporting materials. Furthermore, neither noticeable increase of turn-on voltage nor photon emission from PVK were observed after inserting this PVK CCL in right position. This demonstration creates a new route to design impact QLED architecture for next generation displays.