Facilely solution-processed ZnO + Cs2CO3 for robust electron injection in ultraviolet organic light-emitting diode with inverted architecture

Abstract Electron injection governs electro-optic performance of organic light-emitting diodes (OLEDs) with intractable inverted architecture. Solution process with low cost and scalable manufacturing drives a lab-to-fab journey of electron injection layer (EIL) in OLEDs. Herein, a facilely solution-processed composite EIL of ZnO + Cs2CO3 with robust electron injection has been explored for constructing ultraviolet OLED with inverted architecture. Using 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole as emitter, attractive short-wavelength emission of 380 nm and full-width at half-maximum of 37 nm are demonstrated in the inverted ultraviolet OLED. It achieves maximum radiance of 2.42 mW/cm2 and external quantum efficiency of 0.85% with improved operation durability, which are superior or comparable to the corresponding references using single EILs of Cs2CO3, ZnO and LiF, or double-stacked EIL of ZnO/Cs2CO3. X-ray photoelectron spectroscopy analysis clarifies that the Cs2CO3, ZnO and ZnO + Cs2CO3 exhibit exceptional electronic properties. The current-voltage characteristics and impedance spectroscopy analysis of electron-only cells confirm that ZnO + Cs2CO3 behaves robust electron injection and accounts for excellent device performance. Our results pave an alternative approach for advancing ultraviolet OLED with inverted architecture and facile solution process.