Fig. 3: QLED with a SnO2-ZnO bilayer ETL.

a Device structure. b L-J-V of QLEDs with s-ZnO or SnO2/s-ZnO as ETL. c EL spectra of QLEDs with s-ZnO or SnO2/s-ZnO as ETL. d EQE and current efficiency of QLEDs with s-ZnO or SnO2/s-ZnO as ETL. e Operational lifetime tests of QLEDs with s-ZnO or SnO2/s-ZnO as ETL (under a constant current density of 170 mA cm−2). The s-ZnO-based QLEDs were tested after being shelf-stored for 20 days.