Thiadiazoloquinoxalines: Tuning Physical Properties through Smart Synthesis

The synthesis of π-conjugated acceptors based on thiadiazoloquinoxaline (TQ) derivatives is described. Apart from reporting on the functionalization of the TQ core, the influence of the substituents was studied by UV−vis absorption and emission spectroscopy, cyclic voltammetry measurements, and DFT calculations. By changing the donor as well as the π-spacer, a fine-tuning of the photo- and electrochemical properties was achieved

Tertiary Carbonate Side Chains: Easily Tunable Thermo-labile Breaking Points for Controlling the Solubility of Conjugated Polymers

We present a new class of solubilizing groups for conjugated polymers that enable solution processing of multilayer devices. Conjugated polymers in organic devices are sometimes difficult to process, because of their limited solubility. Well-soluble polymers decorated with alkyl side chains, however, introduce new challenges for thin-film deposition. Using the same solvent for multiple layers can dissolve the already applied layers. In this work, we introduce a new class of thermo-labile groups, which reduce the solubility of conjugated polymers after thermal treatment. Following a very modular approach, we can tune the temperature of the thermo-cleavage between 140 °C and 200 °C. This enables the fabrication of organic solar cells and field-effect transistors (FETs) with robust, solvent-resistant active layers

From Thia- to Selenadiazoles: Changing Interaction Priority

The synthesis, optical, and electrochemical properties as well as solid-state structures of a series of alkynylated, benzannulated selenadiazoles are reported. This set of compounds is compared to the lighter homologue series, the thiadiazoles. The selenadiazoles show head-to-head dimerization in the solid state, while packing of the thiadiazoles was dominated by the steric bulk of the side groups. The Se–N interaction is a supramolecular motif that should drive the effective self-assembly and modulate charge transport when these compounds are used as thin films in devices

From Thia- to Selenadiazoles: Changing Interaction Priority

The synthesis, optical, and electrochemical properties as well as solid-state structures of a series of alkynylated, benzannulated selenadiazoles are reported. This set of compounds is compared to the lighter homologue series, the thiadiazoles. The selenadiazoles show head-to-head dimerization in the solid state, while packing of the thiadiazoles was dominated by the steric bulk of the side groups. The Se–N interaction is a supramolecular motif that should drive the effective self-assembly and modulate charge transport when these compounds are used as thin films in devices

Emissive Polyelectrolytes As Interlayer for Color Tuning and Electron Injection in Solution-Processed Light-Emitting Devices

Herein we present a solution-processed hybrid device architecture combining organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) in a bilayer architecture. The LEC interlayer promotes the charge injection from an air-stable Ag cathode as well as permits the color tuning of the device emission. To this end, we used an alcohol-soluble anionic polyfluorene derivative, the properties of which were investigated by absorption and photoluminescence spectroscopy as well as by cyclic voltammetry. The bilayer device exhibited operating voltages ∼6 V and a color tuning of the emission spectrum dependent on the LEC interlayer thickness. The hybrid devices presented a color emission ranging from the yellow (<i>x</i> = 0.39, <i>y</i> = 0.47) toward the green region (<i>x</i> = 0.29, <i>y</i> = 0.4) of the Commission Internationale de I’Eclairage (CIE) 1931 chromaticity diagram

High-Performance Electron Injection Layers with a Wide Processing Window from an Amidoamine-Functionalized Polyfluorene

In this work, we present organic light-emitting diodes (OLEDs) utilizing a novel amidoamine-functionalized polyfluorene (PFCON-C) as an electron injection layer (EIL). PFCON-C consists of a polyfluorene backbone to which multiple tertiary amine side chains are connected via an amide group. The influence of molecular characteristics on electronic performance and morphological properties was tested and compared to that of the widely used, literature known amino-functionalized polyfluorene (PFN) and polyethylenimine (PEI). PFCON-C reduces the turn-on voltage (<i>V</i>_ON) of poly­(<i>p</i>-phenylene vinylene) (PPV)-based OLEDs from ∼5 to ∼3 V and increases the maximum power efficiency from <2 to >5 lm W^–1 compared to that of PFN. As a result of its semiconducting backbone, PFCON-C is significantly less sensitive to the processing parameters than PEI, and comparable power efficiencies are achieved for devices where thicknesses of PFCON-C are between 15 and 35 nm. Atomic force microscopy (AFM) measurements indicate that the presence of nonpolar side chains in the EIL material is important for its film-forming behavior, while Kelvin probe measurements suggest that the amount of amine groups in the side chains influences the work-function shift induced by the EIL material. These results are used to suggest strategies for the design of polymeric electron injection layers

Soluble Diazaiptycenes: Materials for Solution-Processed Organic Electronics

The synthesis and characterization of soluble azaiptycenes is reported. Optical and physical properties were studied and compared with those of the structurally consanguine azaacenes. Electrochemical experiments and quantum-chemical calculations revealed the electronic structure of the iptycene derivatives. Their crystallization behavior was examined. A highly fluorescent amorphous diazatetracene derivative was integrated into a simple organic light-emitting diode, showing enhanced performance compared with that of previously reported, structurally similar tetracenes

Soluble Diazaiptycenes: Materials for Solution-Processed Organic Electronics

The synthesis and characterization of soluble azaiptycenes is reported. Optical and physical properties were studied and compared with those of the structurally consanguine azaacenes. Electrochemical experiments and quantum-chemical calculations revealed the electronic structure of the iptycene derivatives. Their crystallization behavior was examined. A highly fluorescent amorphous diazatetracene derivative was integrated into a simple organic light-emitting diode, showing enhanced performance compared with that of previously reported, structurally similar tetracenes

Photo-Cross-Linkable Polymeric Optoelectronics Based on the [2 + 2] Cycloaddition Reaction of Cinnamic Acid

We report the synthesis of cinnamic acid-functionalized conjugated polymers, which are cross-linked via [2 + 2] cycloaddition by UV illumination, reducing their solubility. The cross-linking reaction was investigated by a combination of FTIR and optical spectroscopy, and an optimum condition for the solubility modulation of thin films, a major challenge in the solution-phase fabrication of layered optoelectronic devices, was reached. As proof of concept, OLEDs were fabricated, using these conjugated polymers as emissive layers

Naphthalene Tetracarboxydiimide-Based n‑Type Polymers with Removable Solubility via Thermally Cleavable Side Chains

Multilayer solution-processed devices in organic electronics show the tendency of intermixing of subsequently deposited layers. Here, we synthesize naphthalene tetracarboxydiimide (NDI)-based n-type semiconducting polymers with thermally cleavable side chains which upon removal render the polymer insoluble. Infrared and photoelectron spectroscopy were performed to investigate the pyrolysis process. Characterization of organic field-effect transistors provides insight into charge transport. After the pyrolysis homogeneous films could be produced which are insoluble in the primary solvent. By varying curing temperature and time we show that these process parameters govern the amount of side chains in the film and influence the device performance