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

Abstract

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 × 10−3 cm2 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 light‐emitting diodes (PLEDs) achieve more preferable device performances than the poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]‐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.

De novo design of polymers embedded with platinum acetylides towards n-type organic thermoelectrics

“…Notably, the significantly enhanced σmix could be not only attributable to the increased contents of CF3SO3 ¬ anions (Figure S3), but also the gradually enhanced anion radical concentrations at the surfaces (Figure 1d). Wherein, the formation of anion radicals may stem from the anion-induced electron transfer between the CF3SO3 ¬ anions and the protonated π-acidic diazosulfide moieties (Scheme S2) that feature an identifiable n-type self-doping at the surface (Figure 1d) [61]. In addition, the n-type doping behavior can also be confirmed by the following XPS results.…”

Significantly Reduced Thermal-Activation Energy for Hole Transport via Simple Donor Engineering: Understanding the Role of Molecular Parameters for Thermoelectric Behaviors

“…The UV–vis–NIR absorption spectra both in chloroform solution and film state have been measured and the details are presented in Table and Figure S4. In comparison with the absorption peaks of PCZ-DPP (696 nm in chloroform solution and 726 nm in film state), the peaks for PDTP-DPP were significantly red-shifted to 855 and 858 nm, respectively, which can be ascribed to the obviously strengthened intramolecular charge transfer (ICT) state . Correspondingly, their optical band gaps ( E g,opt ) were dramatically decreased from 1.57 eV (PCZ-DPP) to 1.21 eV (PDTP-DPP).…”

“…In comparison with the absorption peaks of PCZ-DPP (696 nm in chloroform solution and 726 nm in film state), the peaks for PDTP-DPP were significantly red-shifted to 855 and 858 nm, respectively, which can be ascribed to the obviously strengthened intramolecular charge transfer (ICT) state. 55 Correspondingly, their optical band gaps (E g,opt ) were dramatically decreased from 1.57 eV (PCZ-DPP) to 1.21 eV (PDTP-DPP). Cyclic voltammetry measurements in acetonitrile solution were executed to determine the energy levels of the polymers.…”

Design of multibranched diketopyrrolopyrrole polyelectrolytes as versatile materials for efficient photocatalytic hydrogen evolution and organic solar cells

“…A straightforward way to adjust the self-doping characteristics is to modify the conjugated backbones and counterion species. 49,50 These polyelectrolytes' bromide anions and their n-type moieties participate in self-doping behaviors and radical generation, which were determined by performing electron spin resonance (ESR) spectroscopy on the polyelectrolytes. The electron donating TIP and amine functionality (pyridine and imidazole) have been shown to donate electrons to the electron-deficient DPP, resulting in self-doping characteristics.…”