All solution-processed composite (ZnO+PEG)/Cs2CO3 with robust electron injection tailoring and its application to efficient inverted near ultraviolet organic light-emitting diodes

Abstract

Electron injection/extraction is always highly emphasized in tailoring optoelectronic properties of organic electronic devices. Solution-processed ZnO, ZnO doped with poly(ethylene glycol) (ZnO+PEG) and composite (ZnO+PEG)/Cs2CO3 have been synthesized and characterized with X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscopy, atomic force microscopy, X-ray/ultraviolet photoelectron spectroscopy. It is demonstrated that ZnO, ZnO+PEG and (ZnO+PEG)/Cs2CO3 exhibit superior film morphology and robust electron injection tailoring. With (ZnO+PEG)/Cs2CO3 as electron injection layer and 9-(4′-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-[1,1′-biphenyl]-4-yl)-9H-carbazole as fluorescent molecule, efficient inverted near ultraviolet organic light-emitting diode is assembled and gives satisfactory radiance of 10.6 mW cm−2 and external quantum efficiency of 1.9% with short-wavelength peaking at 409 nm and full width at half maximum of 52 nm, which are superior to the corresponding counterparts. The electron injection capacity of ZnO, ZnO+PEG and (ZnO+PEG)/Cs2CO3 are further confirmed by current-voltage characteristics, impedance spectroscopy transition curves and surface work function measurements. Such a solution-processed composite (ZnO+PEG)/Cs2CO3 also pave an alternative approach for constructing other multilayer electronic devices.