Organic/Inorganic Hybrid EIL for All‐Solution‐Processed OLEDs

Abstract

AbstractSolution processing metal cathodes to fabricate all‐solution‐processed organic light‐emitting diodes (OLEDs) could significantly reduce their production cost. However, the challenge to realize all‐solution‐processed OLEDs lies in the electron injection layer (EIL) between the light emission layer and the high‐work‐function solution‐processed cathode. Aside from offering efficient electron injection, the EIL should resist the solvent, and prevent the solvent from permeating through to damage the organic functional layers beneath. Combining the advantages of both organic and inorganic EILs, a novel poly[9,9‐bis(60‐(N,N‐diethylamino)hexyl)‐fluorene‐alt‐9,9‐bis(3‐ethyl‐(oxetane‐3‐ethyloxy)‐hexyl)‐fluorene] (PFN‐OX)/ZnO hybrid EIL achieves all the necessary functions. To characterize the solvent‐proof capability quantitatively for the first time, a “solvent detector” is developed by detecting the poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)'s lateral conductivity. The PFN‐OX/ZnO hybrid EIL not only shows better electron injection than the organic PFN‐OX EIL, but also retains the inorganic ZnO EIL's solvent resistance and solvent‐proof capability. Based on the PFN‐OX/ZnO hybrid EIL, all‐solution‐processed OLED devices are fabricated with spin‐coated Ag nanoparticles as the cathode. The poly(dibenzothiophene‐S,S‐dioxide‐co‐9,9‐dioctyl‐2,7‐fluorene) blue emission device reaches 1000 cd m−2 at only 6.2 V with the luminous efficiency of 2.1 cd A−1.