Ligand modification enhanced quantum dot LEDs: principles and methods

Abstract

Many academics are exploring using quantum dots (QDs) to make better LED devices due to their narrow emission band, low reaction temperature, low self-absorption effect, and high photoluminescence quantum yields (PLQYs). Solid-state, colorful, and display technology applications with quantum dot light-emitting diodes (QD-LEDs) are promising. Ligand modification could enhance QD-LED luminescence. Several ligand surface modification techniques, principles, and effects are reviewed. These ligands include X-type (alkyl ammonium halides, alkyl thiols, alkyl sulfates, alkyl phosphates, sulfonic acids, and inorganic ions), L-type (alkyl phosphines), amino acids, aromatic ammonium halides, and other special ligands. Ligand modification reduces deep-level defects, balances carrier transport, and maintains crystal structures and stability to increase QD-LED emission efficiency. Electron–hole compounding in QD-LEDs occurs via two mechanisms: radiative and non-radiative recombination. Band-to-band, defect, sensitized, and Förster resonance energy transfer luminescence are four basic types of radiation recombination. SRH and Auger recombination dominate non-radiative recombination. The properties of high-performing ligands, prospects and challenges of ligand modification in QD-LEDs are also discussed.