Ligand-stripping approach to modulate carrier transport in a bilayer structure achieving charge balance for efficient and stable quantum dot light-emitting diodes

Abstract

Charge balance is a decisive factor for the efficiency and operational stability of blue quantum dot light-emitting diodes (QD-LEDs). In these devices, electron transport is typically excessive relative to hole transport, causing recombination imbalance. Such disparity leads to exciton quenching and accelerates device degradation, limiting performance. Here, we demonstrate a strategy to improve charge balance through controlled ligand stripping in the emissive layer, enabling bidirectional tuning of hole and electron transport. Colloidal-state stripping (CSS) partially removed ligands, introducing trap states that reduced both hole and electron currents, whereas film-state stripping (FSS) extensively removed ligands, facilitating tunneling and markedly enhancing transport. Single-carrier measurements confirmed that CSS decreased hole and electron currents by ∼56% and ∼55%, respectively, while FSS increased them by factors of 2.8 and 7.6. Building on these complementary behaviors, we designed a bilayer emissive configuration combining FSS quantum dots adjacent to the hole-transport layer and CSS quantum dots adjacent to the electron-transport layer, thereby independently regulating hole and electron transport to improve charge balance. As a result, the bilayer QD-LED achieved a maximum current efficiency of 16.1 cd A−1 and an LT50 of 85.4 h at 650 cd m−2, representing a 4.4-fold improvement in stability compared to the control device. These findings establish ligand stripping as a practical strategy for engineering carrier-transport-modulated bilayer structures that deliver charge balance, high efficiency, and long operational lifetime.