A guide to qualitative haze measurements demonstrated on inkjet-printed silver electrodes for flexible OLEDs

The search for alternative transparent electrodes to the commonly used indium tin oxide (ITO) in optoelectronic devices has led to solution-based approaches based on inkjet printing. As an additive manufacturing technique that allows drops to be positioned only where necessary, inkjet printing shows reduced waste of starting material compared to other methods such as spin coating. As a result, functional materials can be both coated and structured without the need for masks or lithographic pre-patterning of the substrate. For this contribution, we utilized a particle-free silver ink to produce a transparent electrode by inkjet printing. After printing, the silver ions were reduced to metallic silver by an argon plasma. The process takes place at low temperatures (ca. 40 – 50°C), making it suitable for use with flexible substrates, which are often temperature-sensitive. The printed silver layers show good electrical conductivity and optical transmittance, with a crystalline grain structure being formed and maintained during the metallization process. This structure forms a self-organized nanometer-size grid, whose structure allows light to pass through. Due to its nano-structured property, the haze of the electrode was investigated using a simple experimental setup based on a light source shining through the electrode and analyzing the size of the projected pattern. Such qualitative assessment can be a useful indication of the quality of the electrode and we provide details on how to replicate this setup. The final electrodes were implemented in solution-processed OLEDs, which showed bright luminance and overall low haze compared to ITO-based reference devices.Peer Reviewe

Formation of Acene-Based Polymers: Mechanistic Computational Study

Understanding the mechanism of linear acene decomposition and its reactivity is a prerequisite for controlling the stability of acenes and their future applications. Previously, we suggested that long acenes may undergo polymerization since the polymerization product is thermodynamically more stable than the dimerization product. However, due to kinetic considerations, the most thermodynamically stable product, the polymer, might not necessarily be formed. To elucidate the situation, we investigated the mechanisms of acene polymerization computationally, using pentacene, hexacene, and heptacene as representative examples. Similarly to dimerization, acene polymerization follows a stepwise biradical pathway. Structural and steric hindrance of the polymer backbone forces acene polymerization to proceed via the less reactive noncentral benzene rings. Consequently, dimerization is always kinetically more favorable than polymerization, irrespective of acene length. Although, for long acenes starting from hexacene, both polymerization and dimerization are barrierless pathways relative to the reactants, polymerization is thermodynamically preferred for hexacene and heptacene and even more so for longer acenes (since polymerization forms four new C–C bonds while dimerization forms only two). Indeed, reinvestigation of available experimental data suggests that acene-based polymers were probably obtained experimentally previously

Unusual Doping of Donor–Acceptor-Type Conjugated Polymers Using Lewis Acids

Conjugated polymers that can undergo unusual nonoxidative doping were designed. A series of polymers based on donor–acceptor–donor (DAD) moieties 2,1,3-benzoselenadiazole, 2,1,3-benzothiadiazole, 2,1,3-benzoxadiazolebenzo­[2,1,5]­oxodiazole, and 2-hexylbenzotriazole as acceptor fragments and 3,4-ethylenedioxyselenophene (EDOS) and 3,4-ethylenedioxythiophene (EDOT) as donor fragments was prepared. When the studied polymers were reacted with Lewis acids and bases, notable optical switching and conductivity changes were observed, evidencing the exceptional case of efficient nonoxidative doping/dedoping. Remarkably, in previously reported works, coordination of Lewis acids causes band gap shift but not doping of the conductive polymer, while in the present study, coordination of Lewis acid to highly donating EDOT and EDOS moieties led to polymer doping. The polymers show remarkable stability after numerous switching cycles from neutral to doped states and vice versa and can be switched both electrochemically and chemically. The reactivity of the prepared polymers with Lewis acids and bases of different strengths was studied. Calculation studies of the Lewis acid coordination mode, its effect on polymer energies and band gap, support the unusual doping. The reported doping approach opens up the possibility to control the conjugation, color change, and switching of states of conjugated polymers without oxidation

Unusual Doping of Donor–Acceptor-Type Conjugated Polymers Using Lewis Acids

Conjugated polymers that can undergo unusual nonoxidative doping were designed. A series of polymers based on donor–acceptor–donor (DAD) moieties 2,1,3-benzoselenadiazole, 2,1,3-benzothiadiazole, 2,1,3-benzoxadiazolebenzo­[2,1,5]­oxodiazole, and 2-hexylbenzotriazole as acceptor fragments and 3,4-ethylenedioxyselenophene (EDOS) and 3,4-ethylenedioxythiophene (EDOT) as donor fragments was prepared. When the studied polymers were reacted with Lewis acids and bases, notable optical switching and conductivity changes were observed, evidencing the exceptional case of efficient nonoxidative doping/dedoping. Remarkably, in previously reported works, coordination of Lewis acids causes band gap shift but not doping of the conductive polymer, while in the present study, coordination of Lewis acid to highly donating EDOT and EDOS moieties led to polymer doping. The polymers show remarkable stability after numerous switching cycles from neutral to doped states and vice versa and can be switched both electrochemically and chemically. The reactivity of the prepared polymers with Lewis acids and bases of different strengths was studied. Calculation studies of the Lewis acid coordination mode, its effect on polymer energies and band gap, support the unusual doping. The reported doping approach opens up the possibility to control the conjugation, color change, and switching of states of conjugated polymers without oxidation