High-performance top-emitting quantum dot light-emitting diodes by balancing electrical conductance and light outcoupling

We present a method for fabricating top-emitting quantum dot light-emitting diodes (TE-QLEDs) with high performance through a solution-based process. The ITO as an interfacial layer can effectively improve the hydrophilicity of the glass substrate/Al, addressing the difficulty in depositing a smooth poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) film on the Al electrode. Additionally, the ITO layer also reduces the barrier of hole injection between the glass substrate/Al and the PEDOT:PSS film. Simulation reveals that the wide-angle interference in the normal direction becomes destructive as the ITO thickness increases. The waveguide mode confines more photons and inhibits the light outcoupling, thus decreasing the efficiency of the TE-QLEDs. By balancing electrical conductance and light outcoupling, an optimized performance is achieved at an ITO layer thickness of 5 nm. The red-emitting TE-QLEDs exhibit a maximum luminance and external quantum efficiency of 175 000 cd m⁻² and 20.1%, respectively. The consistency between the experimental data and the simulation results supports the significance of the ITO thickness in determining the device's efficiency. This study provides important insight into the preparation of high-performance TE-QLEDs through the interfacial modification of the metal oxides.