High‐Performance Tandem Quantum‐Dot Light‐Emitting Diodes Based on Bulk‐Heterojunction‐Like Charge‐Generation Layers

In this study, the fundamental but previously overlooked factors of charge generation efficiency and light extraction efficiency (LEE) are explored and collaboratively optimized in tandem quantum-dot light-emitting diodes (QLEDs). By spontaneously forming a microstructured interface, a bulk-heterojunction-like charge-generation layer composed of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/ZnO bilayer is fabricated and an ideal charge-generation efficiency surpassing 115% is obtained. The coupling strength of the waveguide mode for the top unit and the plasmon polariton loss for the bottom unit are highly suppressed using precise thickness control, which increases the LEE of the tandem devices. The red tandem QLED achieves an exceptionally low turn-on voltage for electroluminescence at 4.0 V and outstanding peak external quantum efficiency of 42.9%. The ultralow turn-on voltage originates from the sequential electroluminescence turn-on of the two emissive units of the tandem QLED. Benefiting from its unique electroluminescent features, an easily fabricated optical-electrical dual anti-counterfeiting display is built by combining a dichromatic tandem QLED with masking technology.