Origins of Low Quantum Efficiencies in Quantum Dot LEDs

Abstract

The promise for next generation light‐emitting device (LED) technologies is a major driver for research on nanocrystal quantum dots (QDs). The low efficiencies of current QD‐LEDs are often attributed to luminescence quenching of charged QDs through Auger‐processes. Although new QD chemistries successfully suppress Auger recombination, high performance QD‐LEDs with these materials have yet to be demonstrated. Here, QD‐LED performance is shown to be significantly limited by the electric field. Experimental field‐dependent photoluminescence decay studies and tight‐binding simulations are used to show that independent of charging, the electric field can strongly quench the luminescence of QD solids by reducing the electron and hole wavefunction overlap, thereby lowering the radiative recombination rate. Quantifying this effect for a series of CdSe/CdS QD solids reveals a strong dependence on the QD band structure, which enables the outline of clear design strategies for QD materials and device architectures to improve QD‐LED performance.

Electric Field Modulation of Semiconductor Quantum Dot Photoluminescence: Insights Into the Design of Robust Voltage-Sensitive Cellular Imaging Probes

“…The entire device sits within a Sawyer−Tower serial capacitor circuit that exploits a reference capacitor, C ref , and fundamental principles of series circuitry in order to permit the calculation of the potential drop across the QD-containing polymer layer (Figure 1). 11 The active device area, including both SiO 2 layers and the QD/PMMA film, is treated as three separate capacitors, with capacitance C ox for the SiO 2 layers and C QD for the QD/PMMA layer. Both the input potential, V 0 , and the potential before the reference capacitor, V ref , are measured.…”

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

“…Due to such hybridized heterojunction structures, the efficiency of QD-LEDs is significantly influenced by the conductivity of the current injection/transport layers, as well as the interface energy barriers. 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.…”

High-Efficiency All-Solution-Processed Light-Emitting Diodes Based on Anisotropic Colloidal Heterostructures with Polar Polymer Injecting Layers

“…The effects of positive or negative charging of QD by electron transfer from or to polymer interlayers or ZnO nanoparticles in both direct and inverted structure LEDs have been recently investigated by several groups showing detrimental effects on the device efficiency and stability 21,[64][65][66][67] . In order to test charging/quenching effects by our polymer materials, we measured the PL efficiency and dynamics of CdSe/CdS DiRs on glass and deposited on 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 top of ~60 nm films of each polar polymer.…”