This book has been inspired by a growing interest in an emerging technology – printed organic electronics. We have realized that there is a considerable demand for a book that would present achievements and – perhaps even more importantly – challenges in the synthesis and processing of solution‐processable materials required for organic electronics as well as in assembling them into functional devices. Such a demand results from the fact that the industrial‐scale production of printed (and preferably also flexible) large‐area organic electronics still remains an unfulfilled promise. Several prominent scientists have kindly accepted our invitation to contribute with insights into the synthesis and processing of different materials used in organic and hybrid electronics (with particular emphasis on nanostructured materials) and also with the discussion of basic physical mechanisms governing optoelectronic properties of organic semiconductors (OSCs) and solution‐based methods of fabrication of organic electronic devices.

In the introductory chapter entitled “Precision and Purity of Conjugated Polymers – to be Ensured before Processing,” Klaus Müllen and his coworker, Thorsten Prechtl, discuss the basic design principles for conjugated polymers as well as the potential pitfalls of the synthetic methods used. The central message of this chapter is: “do not commence processing and device fabrication before having optimized and ensured the integrity of the macromolecular structure as well as its reliable and reproducible synthesis.”

The chapter on the synthesis of solution‐processable nanoparticles of inorganic semiconductors applicable in organic electronics and photonics written by two groups of authors led by Adam Pron and by Kwang‐Sup Lee presents a broad range of semiconducting nanocrystals with a detailed analysis of the role of ligands. The authors describe recently developed advanced materials such as photopatternable nanocrystals or perovskite nanomaterials, analyze energy and charge transfer phenomena in semiconducting nanocrystal‐based hybrid materials, and present possible applications.

Krzysztof Matyjaszewski with coworkers reviews the most advanced method of synthesis of inorganic high k nanoparticles by means of controlled radical polymerization, which allows precise control over material composition, dispersibility, and interfacial interactions. Incorporation of high k nanoparticles into polymeric matrices with high breakdown strength yields novel solution‐processable materials with excellent dielectric performance. Control and tuning of interfacial interactions allows improvement of each parameter of the dielectric material in order to satisfy the requirements of specific applications.

In the chapter on polymer blending and phase behavior in organic electronics, Paul Blom with coworkers presents two excellent examples of beneficial use of blending materials to develop novel materials with extraordinary properties. The applied innovative blending procedures employ liquid–liquid demixing during solution casting of the active layer. The authors represent an approach enabling a construction of a phase diagram based on Flory–Huggins theory. The first of the described cases illustrates how trapping phenomena in semiconducting and electroluminescent polymers can be reduced by blending them with an insulating polymer, which results in doubling of the organic light‐emitting diode (OLEDs) efficiency. In the second case, it is shown how the nonsolvent‐induced phase separation of solutions of the ferroelectric polymer influences the quality of materials used for the production of organic capacitive memory devices. On the basis of these examples, the authors present general observations on the role of liquid–liquid demixing in thin film device processing.

Anna Köhler and Heinz Bässler, in their chapter on photogeneration of charge carriers in solution‐processable OSCs, explain how photoexcitation can result free electrons and holes. After a brief introduction into established concepts to account for photocurrent generation in a single OSC phase, the authors discuss the photogeneration of charges when a more electronegative acceptor material with a less electronegative electron donor material is combined to form a bulk heterojunction or bilayer, as is common in organic photovoltaics (OPVs). There, photogenerated electron–hole pairs should still be strongly electrostatically bound because of low dielectric permittivity of OSCs. This is in apparent contradiction with the fact that the power efficiency of modern OPVs has reached values above 10%. The authors discuss this currently most intriguing issue emphasizing the role of the initial interfacial charge transfer, subsequent dissociation of the geminately bound electron–hole pair into free charge carriers, and their collection at the electrodes or geminate or nongeminate recombination.

Another issue that is critical for the performance of organic electronic devices – charge carrier transport in OSCs – is discussed by Jaroslaw Jung and Jacek Ulanski in the subsequent chapter, with a special emphasis placed on multicomponent materials such as heavily doped semiconductors, composites, and nanocomposites. The obstacles hindering progress and widespread application of organic electronics are connected with insufficient knowledge of physical processes responsible for charge carrier transport. The basic concepts, such as density of states, Fermi energy, Fermi level or charge carrier mobility, drift currents, drift–diffusion currents, or space–charge‐limited currents, must be better recognized and understood. Some models of charge carrier transport in OSCs are presented together with selected experimental techniques allowing verification of these models.

The second part of the book, its remaining six chapters, is devoted to organic electronic devices that can be produced by solution‐based methods, including printing and roll‐to‐roll manufacturing.

In the seventh chapter, Lukasz Janasz, Wojciech Pisula, and Jacek Ulanski indicate that the overall development of organic electronics relies on progress in the research on organic field‐effect transistors (OFETs), as they (particularly ambipolar transistors) constitute basic building blocks of almost any electronic device. The authors describe methods based on mixing of n‐type and p‐type OSCs and the relationships between fabrication procedures, film morphology, and performance of ambipolar OFETs. Another approach aims to improve the properties of the active layers in OFETs, such as stretchability/bendability, air stability, and thin film processability that can be achieved by mixing a conjugated semiconductor and insulator. It is shown that fabrication of efficient and multifunctional active layers requires a controlled phase separation between insulating and semiconducting fractions. In order for this development to happen, it is crucial that comprehensive understanding of the role of the blend morphology in the overall behavior of the transistors be gained.

Fabrication of OLEDs based on solution‐processable organic materials is described by Joannis K. Kallitsis and coworkers. They demonstrate the importance of selection of optimal device components, not only OSCs but also electrodes and carrier injection layers. Proper choice of the materials with appropriate properties results in custom‐made OLEDs exhibiting desired performance levels. As a consequence of the tuning and tailoring of the OSC properties and of the device preparation process, it is possible to produce both rigid and flexible OLED devices. The authors argue that the fabrication method also plays an essential role in the commercialization of OLEDs as it affects the total manufacturing cost. From this point of view, wet fabrication processes such as spin‐casting or inkjet printing are preferable especially when addressing large‐area display devices.

Marek Zdzislaw Szymanski and Beata Luszczynska, in their chapter on OPVs, focus on the device physics and modeling. After brief introduction to device modeling, it has been shown how the simulations can be run using a free open‐source software such as oedes (www.oedes.org). Such simulations can provide critical insights into the performance of emerging OPV devices, enabling the estimation of parameters that cannot be directly measured. The authors focus on the drift–diffusion modeling as it is the most fundamental approach to modeling of photovoltaic devices and is applicable to inorganic, organic, dye‐sensitized, and perovskite solar cells. The chapter also presents several examples of simulations. The authors underline the overall importance of concepts of electrical and optical modeling in the development of all electronic devices.

In the chapter on solution‐processed organic photodiodes, Raphaël Clerc et al. present an introduction to this class of devices from chemistry and processing to device physics and applications. The main materials, processes, device architectures, operation principles, and figures of merits are described, followed by an analysis of state of the art of solution‐processed organic photodiodes. This comprises not only photodiodes working in the visible spectral domain but also application of organic photodiodes to X‐ray imaging, photodiodes working in the NIR spectral domain, and organic photodiodes integrated into complementary metal oxide semiconductor (CMOS) imagers. Additionally, the chapter presents the main current approaches to modeling of performance of the organic photodetectors, including the drift–diffusion models.

Jiri Pfleger has contributed with a chapter on organic electronic memory devices based on solution‐processable materials. He argues that in spite of the importance of data storage in electronic applications, the main effort in the development of printed organic electronics has so far been on devices such as OFETs, OLEDs, OPVs, and sensors. For this reason, the progress in printable organic memory devices is less spectacular. The chapter presents basic information on classification of electronic memory devices and principles of data storage with the main focus on the resistive memory operation mechanisms. What follows is the characterization of the materials for printable memory devices, including resistive RAM device, polymer ferroelectrics for OFET memory devices, OFET memory devices with charge‐trapping mechanism, OFET memory with floating electrode, and vertical organic transistors memory devices. It has been predicted that although currently the organic electronic memories can predominantly introduce an added value in rather simplified structures in low‐cost, low‐end consumer electronics, there are promising emerging applications for organic materials in multilevel logic in neuromorphic systems.

The last chapter, written by Stergios Logothetidis and Argiris Laskarakis, presents the latest state of the art in intelligent manufacturing of organic electronic devices by roll‐to‐roll (r2r) manufacturing processes. The described unique r2r pilot line was designed for the fabrication of the large‐area and flexible OPVs and equipped with robust in‐line optical metrology and ultrafast pulsed laser patterning processes. The authors demonstrate that one of the most promising methods to be used as a quality control tool for the r2r manufacturing processes is spectroscopic ellipsometry. This approach has opened a way for introducing intelligence into production lines in nanomanufacturing of a vast variety of organic electronic devices as it afforded the capability of real‐time monitoring and control of the end properties of the printed nanomaterials.

We do hope that this book will be helpful for scientists and students involved in the field of organic electronics and that it will inspire and guide engineers in their efforts for industrial implementation of printed organic electronics technology.

Beata Łuszczyńska

Krzysztof Matyjaszewski

Jacek Ulański