Polymer and Small Molecule Mixture for Organic Hole Transport Layers in Quantum Dot Light-Emitting Diodes

Abstract

The performance of quantum dot light-emitting diodes (QD-LEDs) was investigated for different hole transport layers with small molecules and polymers: poly(4-butyl-phenyl-diphenyl-amine), poly-N-vinylcarbazole (PVK), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-diphenyl-4,4'-diamine, 4,4',4″-tris(N-carbazolyl)-triphenyl-amine (TCTA), and 4,4'-bis(carbazole-9-yl)biphenyl (CBP). The electroluminescence performance of QD-LEDs was considerably improved by adding small molecules (TCTA or CBP) having high hole mobilily to the polymer hole transport material (PVK). The maximal current efficiency of QD-LED-based PVK was improved by 27% upon addition of 20 wt % TCTA due to the hole injection improvement. The lower turn-on voltage, the higher current density, and the higher luminance were achieved by addition of TCTA. The maximal luminance of 40900 cd/m(2) and the highest current efficiency of 14.0 cd/A with the narrow full width at half-maximum (<35 nm) were achieved by the best hole transport layer.

Solution-processed quantum dot light-emitting diodes with PANI:PSS hole-transport interlayers

“…It is well-known that the p-type conductivity and hole injection barriers of the organic hole injection/transport layer are crucial to the efficiency of QD-LEDs and organic LEDs [4,5]; the comparatively resistive organic layer causes charge imbalance of the electron/hole carriers, resulting in nonradiative processes such as carrier charging, exciton quenching, Auger recombination, and thermal decay [6][7][8][9]. Hence, considerable effort has focused on doping (or blending) the organic layer [10,11], use of hole injection layer with high work function [12] or gradient work function [13,14], insertion of additional layer for good Ohmic contact [15] and graded work function [16][17][18], chemical treatment of indium-tin oxide (ITO) electrodes or conducting polymer films to increase the work function [19,20], and insertion of intermediate hole transport layer or electron-blocking layer [2,21] to balance the charge injection for high efficiency QD-LEDs.…”

Electroluminescence from colloidal semiconductor CdSe nanoplatelets in hybrid organic–inorganic light emitting diode

“…A large number of papers has been devoted to research and development of hybrid light emitting diodes based on a flat emitting layer of quantum dots placed between the electron and hole transporting layers. Most of these works concerned the realization of quantum dot -organic light emitting diodes (QD-OLEDs) using spherical-shaped quantum dots like Si or PbSe [4,5] as well as core-shell and coredouble-shell QD-structures like CdZnSe, CdSe/ZnS, CdSe/CdS, ZnSe/CdSe/ZnS [6][7][8][9][10][11][12]. Recently the electroluminescence from a single active layer of QD-LED device based on colloidal CdSe/CdS core-arm tetrapod nanostructures has been reported [13].…”

Solution-Processable MoO<italic>x</italic>for Efficient Light-Emitting Diodes Based on Giant Quantum Dots

“…Recently, many studies have put more efforts to cost-down while still remaining highly efficient performance of QLEDs. The architecture design of QLEDs have been focused as an intrinsically important role to achieve simple and cost-effective fabrication process allowing devices with high performance and long lifetime [4][5]. While ZnO nanoparticles (NPs) have been the outstanding electron injection/transport material due to the suitable band-gap offset, high mobility, air stability, and solution-processability, both in QLEDs and polymer LEDs (PLEDs) [1,6], the hole injection materials of similar quality are still in demand.…”

“…On the other hand, inorganic hole injection materials with low-lying valence bands that match with QDs are the desirable candidates for stable and long-lived devices [1,5]. Sputtered metal oxides including NiO, WO3, or Zn2SnO4 (ZTO) have been successfully utilized to replace PEDOT:PSS in initially [9][10][11].…”