Enhanced performance in quantum-dot light-emitting diodes using self-assembled hole injection layers

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) thin film is widely used as a hole injection layer (HIL) in quantum-dot (QD) light-emitting diodes (LEDs). However, its acidic and hygroscopic nature erodes the indium tin oxide electrode, causing serious device stability issues. To overcome the limitations, QLEDs that utilize self-assembled molecules (SAMs) as the HILs have been proposed and demonstrated, offering both high efficiency and improved stability. The 4PADCB SAM forms a high-quality film characterized by excellent transmittance and low surface roughness. Crucially, it possesses a high work function, which facilitates effective hole injection into the QD layer, thereby improving charge balance and reducing the accumulation of excess charges within the QLED. Additionally, the 4PADCB’s shallow lowest unoccupied molecular orbital energy level prevents electron leakage towards the anode. As a result, the 4PADCB-based red QLED exhibits a maximum external quantum efficiency of 28.07%, a peak power efficiency of 37.24 lm/W, and an extended T₉₅ operational lifetime of 12,401 h at 1000 cd/m², significantly outperforming the device based on PEDOT:PSS. This SAM HIL approach paves the way towards commercially viable, high-performance QLEDs in next generation displays.