Boosting the efficiency of inverted quantum dot light-emitting diodes by balancing charge densities and suppressing exciton quenching through band alignment

Abstract

We report an inverted and multilayer quantum dot light emitting diode (QLED) which boosts high efficiency by tuning the energy band alignment between charge transport and light emitting layers. The electron transport layer (ETL) was ZnO nanoparticles (NPs) with an optimized doping concentration of cesium azide (CsN) to effectively reduce electron flow and balance charge injection. This is by virtue of a 0.27 eV upshift of the ETL's conduction band edge, which inhibits the quenching of excitons and preserves the superior emissive properties of the quantum dots due to the insulating characteristics of CsN. The demonstrated QLED exhibits a peak current efficiency, power efficiency and external quantum efficiency of up to 13.5 cd A, 10.6 lm W and 13.4% for the red QLED, and correspondingly 43.1 cd A, 33.6 lm W and 9.1% for green, and 4.1 cd A, 2.0 lm W and 6.6% for the blue counterparts. Compared with QLEDs without optimization, the performance of these modified devices shows drastic improvement by 95.6%, 39.4% and 36.7%, respectively. This novel device architecture with heterogeneous energy levels reported here offers a new design strategy for next-generation high efficiency QLED displays and solid-state lighting technologies.

Ten micrometer pixel, quantum dots color conversion layer for high resolution and full color active matrix micro‐LED display

“…The quantum‐dots (QDs) have been attracted as the one of material for next generation displays replacing organic light emitting diodes (OLEDs) because of its big advantages such as solution process, easy color tuning by controlling QD core size, and higher color purity (narrow full width at half maximum [FWHM]) . Due to the advantages of QDs, they can be used for the color conversion layer (CCL) replacing commercial color filter (CF) for back light unit (BLU), liquid crystal display (LCD), and LED …”

Colloidal quantum dot light-emitting diodes employing solution-processable tin dioxide nanoparticles in an electron transport layer

“…[9][10][11] Although ZnO ETLs are widely employed and considered a standard platform for high-efficiency QD-LEDs, ZnO has been oen indicated as the main reason for undesirable behavior of QD-LED performance such as efficiency roll-off, EL quenching, and short lifetime. [12][13][14] These behaviors are attributable to excessive electron injection from ZnO into the QDs, which lead to non-balancing of electron and hole densities in the QD emissive layer. 15 To move one step closer to commercialization, it is currently necessary to study other alternatives that can potentially supplement or even replace ZnO.…”

Stability of Quantum-Dot Light Emitting Diodes with Alkali Metal Carbonates Blending in Mg Doped ZnO Electron Transport Layer

“…Compared to the thermal evaporation process, the thickness control is one of key issues in the solution process to form a uniform and ultra-thin layer. However, the uniform and easier thickness controllable EIL/electron transporting layer (ETL) can be achieved without an additional interlayer deposition process when the alkali metal carbonate is doped into metal oxide [25][26][27].…”