Constructing low efficiency roll-off InP-based QLEDs by enhancing hole injection and suppressing electron leakage

Indium phosphide (InP)-based quantum dot light-emitting diodes (QLEDs) have attracted considerable attention due to their excellent color purity and high external quantum efficiency (EQE). However, InP-based QLEDs exhibit severe efficiency roll-off, which limits their applications in high-brightness devices. In this Letter, we demonstrate low-efficiency roll-off red InP-based QLEDs by employing an ionic salt-doped poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as the hole injection layer (HIL), in combination with poly(9-vinylcarbazole) (PVK) as the hole transport layer. The work function and conductivity of PEDOT:PSS HIL were effectively modulated by introducing ionic liquids, while the electron leakage of QLEDs was suppressed by PVK with a shallower lowest occupied molecular orbital level by constructing a stepped hole transport layer, thereby achieving improved charge balance within the device. As a result, the parasitic emission of the device was suppressed, and the EQE was improved from 10.2% to 15.6%, especially at 100 mA cm^-2. Notably, the efficiency roll-off was effectively reduced to only 11% relative to the peak EQE. The structural engineering of devices significantly enhances the potential of QLEDs to operate efficiently at high luminance.