Self-Doping Cathode Interfacial Material Simultaneously Enabling High Electron Mobility and Powerful Work Function Tunability for High-Efficiency All-Solution-Processed Polymer Light-Emitting Diodes

A variety of N-hydrogenated/N-methylated pyridinium salts are elaborately designed and synthesized. Thermogravimetric and X-ray photoelectron spectra analysis indicate the intensities of the N. H covalent bonds are strengthened step-by-step from 3,3'-(5'-(3-(pyridin-3-yl) phenyl)-[1,1': 3', 1.terphenyl]-3,3.-diyl) dipyridine (Tm)-HCl to Tm-HBr and then Tm-TfOH, which results in gradually improved cathode interfacial modification abilities. The larger dipole moments of N+. H containing moieties compared to those of the N+-CH3 endow them with more preferable interfacial modification abilities. Electron paramagnetic resonance signals reveal the existence of radical anions in the solid state of Tm-TfOH, which enables its self-doping property and high electron mobility up to 1.67 x 10(-3) cm(2) V-1 s(-1). Using the Tm-TfOH as the cathode interfacial layers (CILs), the phenyl-substituted poly(para-phenylene vinylene)-based all-solution-processed polymer lightemitting diodes (PLEDs) achieve more preferable device performances than the poly[(9,9-bis(3'-(N, N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9dioctylfluorene)]-based ones, i.e., high current density of nearly 300 mA cm(-2), very high luminance over 15 000 cd m(-2) at a low bias of 5 V. Remarkably, the thickness of the CILs has little impact on the device performance and high efficiencies are maintained even at thicknesses up to 85 nm, which is barely realized in PLEDs with small-molecule-based electron transporting layers.