Ligand-assisted solvothermal precipitation synthesis of quantum-sized SnO2 nanoparticles and their application in quantum dot light emitting diodes

Abstract

A high-quality electron transport layer (ETL) has an extremely profound impact on the performance of quantum dot light-emitting diodes (QD-LEDs). To date, ZnO nanoparticle thin films have been usually adopted as ETLs in high-performance QD-LEDs. However, because ZnO is an amphoteric oxide, ZnO nanoparticles are chemically unstable in air, and the quantum-sized SnO₂ nanoparticles have great potential to resolve the stability issue of the ZnO nanoparticle ETL. In this work, we develop a ligand-assisted solvothermal precipitation method to prepare quantum-sized SnO₂ nanoparticles. Short-chain butyric acid and butylamine are used as the binary ligands, and ethanol is used as the solvent. Under solvothermal conditions, hydrophobic SnO₂ nanoparticles capped by butyric acid and butylamine will aggregate and form a white precipitate in ethanol. The SnO₂ nanoparticles with a particle size of 3.6 nm exhibit an optical band gap of 4.23 eV. Based on the quantum size effect, the conduction band minimum position of the quantum-sized SnO₂ nanoparticles is upshifted to −3.72 eV, which makes them suitable for use in QD-LEDs as the ETL, so that the electrons can be readily injected into the quantum dot emitting layer. As a result, QD-LEDs based on the quantum-sized SnO₂ nanoparticles exhibit a maximum external quantum efficiency of 12.9%, revealing that the quantum-sized SnO₂ nanoparticles have great potential for application in QD-LEDs as the ETL.