Highly efficient green, red, and blue perovskite light‐emitting diode based metal‐oxide charge injection layers are demonstrated. This is an important step toward the realization of next‐generation solid‐state lighting and devices for use in full‐color large‐area display applications.

Zinc-oxide (ZnO) is widely used as an n-type electron transporting layer (ETL) for quantum dot (QD) light-emitting diode (QLED) because various metal doping can be possible and ZnO nanoparticle can be processed at low temperatures. We report here a Li- and Mg-doped ZnO, MLZO, which is used for ETL of highly efficient and long lifetime QLEDs. Co-doping, Mg and Li, in ZnO increases its band gap and electrical resistivity and thus can enhance charge balance in emission layer (EML). It is found also that the O-H concentration at the oxide surface decreases and exciton decay time of QDs on the metal oxide increases by co-doping in ZnO. The inverted green QLEDs with MLZO ETL exhibits the maximum current efficiency (CE) of 69.1 cd/A, power efficiency (PE) of 73.8 lm/W, and external quantum efficiency (EQE) of 18.4%. This is at least two times higher compared with the efficiencies of the QLEDs with Mg-doped ZnO ETL. The optimum Li and Mg concentrations are found to be 10% each. The deep-red, red, light-blue, and deep-blue QLEDs with MLZO ETLs exhibit the CE of 6.0, 22.3, 1.9, and 0.5 cd/A, respectively. The MLZO introduced here can be widely used as ETL of highly efficient QLEDs.

Zinc oxide (ZnO) nanoparticles (NPs) are widely used as electron-transport layers in quantum dots (QDs) light-emitting diodes (QLEDs). In this work, we show that the size of the NPs can be tuned with the sol–gel synthesis temperature while keeping a constant mass yield. As the NP size decreases, the surface defect density reduces and the band gap broadens. In return, it prevents exciton quenching at the ZnO NPs/emitting QDs (core–shell CdSe@ZnS) interface. Moreover, as the conductivity of the ZnO NP films decreases, the electron–hole balance in QLEDs improves. When the synthesis temperature decreases from 60 to 0 °C, the diameter of the NPs shrinks from 5.4 to 2.8 nm. The optical band gap broadens from 3.44 to 3.66 eV and the energy of the minimum of the conduction band increases from −3.81 to −3.64 eV below the Fermi level. Consequently, the radiative decay rate of a CdSe@ZnS QDs layer coated on ZnO NP films increases from 11.62 to 13.75 ns. The smaller NPs exhibit a faceted surface with a lower density of defects. Under UV illumination, the intensity of the band to band emission from the ZnO NPs increases while the emission from defects decreases as the NPs diameter becomes smaller. The conductivity of the ZnO film decreases by more than 1 order of magnitude, and the current efficiency of QLEDs increases from 35.8 to 50.8 cd/A.

PSS:WOx) and n-type metal oxide (lithium doped zinc oxide, LZO). The effective charge generation in solution processed p-n junction was confirmed by capacitance-voltage (C-V) and current density-electric field characteristics. It is also demonstrated that the performances of CGL based QLEDs are very similar when various substrates with different work functions are used.

We report highly efficient inverted quantum-dot light emitting diodes (QLEDs) using an Al doped ZnO (AZO)/Li doped ZnO (LZO) stack electron transport layer (ETL). An introduction of the LZO layer on AZO improved the current and power efficiencies of the green (G-) QLEDs from 10.5 to 34.0 cd A and from 5.4 to 29.6 lm W, respectively. The red (R-), G-, and blue (B-) QLEDs fabricated in this work exhibited the maximum external quantum efficiencies (EQEs) of 8.4, 12.5, and 4.3%, respectively. It is found from time-resolved photoluminescence (PL) and transient electroluminescence (EL) decay that exciton loss at the interface between the ETL and the emission layer can be significantly reduced by introducing LZO.