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

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 degrees 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.