The production of electronic devices using solution based (“wet”) deposition technologies has some decisive technical and commercial advantages compared to competing approaches like vacuum based (“dry”) manufacturing. Particularly, the potential to scale up production processes to large areas and high volumes by introducing continuous roll-to-roll (R2R) methods on flexible substrates has been the topic of intense studies from both applied research institutes and industry already for some years. Decisive steps forward have been achieved during that time, resulting in the dawn of commercial applications for a number of processes, while additional development work is still needed in some other fields. This review summarizes the work published during the last few years on the R2R printing and wet coating of electronic devices. An overview is presented of the basic operational principles for the most commonly used R2R printing and coating methods and techniques for proper web handling in R2R lines. Then, the most commonly used types of flexible substrate materials are introduced, followed by a review of the work published in the application areas of transparent conductor materials, printed electric connections, light emitting devices, photovoltaic energy generation, printed logic, and sensing.

Operational lifetime is a critical performance parameter of organic electronic devices and can be cut short by multiple degradation mechanisms. One supposed cause is metal migration between the electrodes, which, however, is difficult to study independently of other failure modes. We present a setup, which excludes such competing processes and demonstrates that silver (Ag) electrochemical migration through organic optoelectronic materials occurs predominantly by cation transport. Metal dendrites form at the cathode, eventually causing short circuits between the electrodes. Lifetime studies with organic light-emitting diodes containing Ag electrodes suggest that results obtained with our setup can provide relevant information about degradation in real devices.

The large volume production of flexible electronics by solution based roll-to-roll (R2R) manufacturing technologies is a promising upscaling strategy for the organic electronics industry. Typical optoelectronic devices like organic light emitting diodes (OLEDs) consist of a complex stack of functional layers. Solution deposition of these structures eliminates the need for expensive vacuum processing. This contribution presents approaches for solution based R2R production methods of functional OLED layers on flexible polymer substrates. The development of a R2R line with two slot-die coating stations is discussed which can deposit two uniform layers consecutively in a single run (“tandem coating”) at web speeds up to 30 m/min. Furthermore, it offers the unique feature that there is no contact between the rollers and the top side of the substrate where the functional coating is deposited. Thereby, an important source of particle contamination and other damage to the device is eliminated. In addition to continuous deposition, stripe and intermittent coating techniques have been developed, allowing the production of patterned layers. Finally, examples will be shown of OLEDs where two functional materials are deposited by R2R processing from solution.

Inkjet printing (IJP) is a highly versatile and useful tool for product development, prototyping, and even small-scale manufacturing in the printed electronics industry. This chapter discusses a number of printed electronic (PE) applications. PE applications make use of inkjet-printed electrically conductive structures. At first sight, IJP might not seem the most obvious method for the manufacturing of these structures and as a result, it is rather new for PE manufacturing. The potential of IJP for PE applications has been demonstrated recently in a variety of academic and industrial research laboratories. These examples are, however, usually achieved on a sheet-to-sheet (S2 S) basis and only on a small scale. Various types of functional electronic materials can be processed into functional structures and devices by IJP. Examples include conductive metallic inks, organic semiconductors, insulators, and many others.

The necessary metal-based inks typically consist of silver nanoparticles dispersed in a liquid carrier medium. In order to keep the ink stable and printable, the agglomeration and sedimentation of these functional components need to be prevented as long as they are not printed onto a substrate. This is typically done by the addition of organic (usually polymeric) stabilizers that induce repulsion between the metal nanoparticles. Process optimization involves the screening of a wide range of materials, temperatures, and sintering times and typically the resulting resistance is measured only at the end of the process. The measuring probe consists of an evaporated metal line that is covered with a thin isolating layer. In order to prevent direct electrical contact between the probe line and the conductive ink to be tested, the probe line is covered by an insulating layer.