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

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.