Interfacial electronic structure between a W-doped InO transparent electrode and a VO hole injection layer for inorganic quantum-dot light-emitting diodes.

The interfacial electronic structure between a W-doped InO (IWO) transparent electrode and a VO hole injection layer (HIL) has been investigated using ultraviolet photoelectron spectroscopy for high-performance and inorganic quantum-dot light-emitting diodes (QLEDs). Based on the interfacial electronic structure measurements, we found gap states in a VO HIL at 1.0 eV below the Fermi level. Holes can be efficiently injected from the IWO electrode into poly[(9,9-dioctylfluorenyl-2,7-diyl)--(4,4'-(4--butylphenyl)diphenylamine)] (TFB) through the gap states of VO, which was confirmed by the hole injection characteristics of a hole-only device. Therefore, conventional normal-structured QLEDs were fabricated on a glass substrate with the IWO transparent electrode and VO HIL. The maximum luminance of the device was measured as 9443.5 cd m. Our result suggests that the IWO electrode and VO HIL are a good combination for developing high-performance and inorganic QLEDs.