Bi-Ligand Synergy Enables Threshold Low Voltage and Bandgap Stable Pure-Red Mix-Halide Perovskite LEDs

Abstract

Perovskite light-emitting diodes (LEDs) emitting in the pure-red range of 630–640 nm show promise in meeting the requirement of the Rec.2100 standard for high-resolution displays. However, the high-performing LEDs (external quantum efficiency, EQE >20%) in the pure-red range suffer from half-life time (luminance drop to 50% of the initial luminance) of <1.6 h, resulting from the injection/transportation barrier and surface-defects–induced charge carrier quenching. Herein, a bi-ligand synergy strategy is developed to address the T50 issue: the introduction of iodide-rich ligands with different chain length increases the vacancy formation energy of halogen ions and enhances the exciton binding energy, resulting in a high photoluminescence quantum yield of over 92%. The treated CsPbBrx/I3−x films exhibit 34-fold improved material stability related to the control at continuous aging at 100 °C. As a result, pure-red LEDs with CIE coordinates of (0.698, 0.301) approaching the Rec.2100 standard are reported. These pure-red LEDs exhibit a low turn-on voltage of 1.8 V, which is the lowest among reported pure-red perovskite LEDs, and even 0.15 V lower than the optical bandgap energy (1.95 eV); and a maximum EQE of ≈21% with fourfold enhanced T50 relative to the best previous pure-red perovskite LEDs.