Inverted quantum-dot light-emitting diodes with solution-processed aluminium–zinc oxide as a cathode buffer

Abstract

We report an inverted structure of quantum-dot light emitting diodes (QLEDs) with a metal oxide as a cathode buffer. The Al doped zinc oxide (AZO) with Al concentration from 0 to 30% was used as a charge transport layer in QLEDs which were processed at the temperature of 225 °C. It is found that the conductivity of AZO decreases with increasing Al concentration, but the luminance intensity increases from 6380 to 26 700 cd m⁻². The current and power efficiencies at 1000 cd m⁻² increase from 3.03 to 4.63 cd A⁻¹ and 2.75 to 3.64 lm W⁻¹, respectively, as the Al concentration increases from 0 to 30%. The luminance intensity for the QLED with 30% AZO increases further to 31 030 cd m⁻² and the current efficiency to 5.21 cd A⁻¹ by increasing the thickness of the electron transport layer from 33 to 50 nm. It is concluded therefore that a solution processed AZO can be an effective cathode buffer for an inverted structure of QLEDs.