Preface

To achieve broader deployment of photovoltaic (PV) technology, new generation photovoltaic devices need to be produced from low-cost, non-toxic, and earth-abundant materials using environmentally friendly and scalable processes. Organics/polymer-based photovoltaics (OPV) have the potential to fulfil all these requirements and therefore have attracted significant global attention. When compared with inorganic-based photovoltaic cells, the advantages of OPVs include their potential to be manufactured at extremely high throughput with ultra low production cost using a solution-based, continuous roll-to-roll coating process. Their features of ultra light weight and high flexibility also distinguish OPVs from traditional photovoltaic technology. With these unique properties, OPVs offer good form factors for various new applications, and therefore have extremely high commercial value. Over the past few years, the performance of OPVs has improved significantly, from ∼7% in 2009 to ∼12% in 2015, and now reaches a level that can be considered for some specific PV applications. As the interest in polymer solar cell research continues to grow, this book aims to provide a comprehensive, up-to-date review of the recent advancements in OPV technology.

This book consists of 13 chapters contributed by leading experts in the OPV field covering the areas of new chemistry, design and synthesis of OPV materials, interface engineering, photophysics, morphology control and characterizations, new device concepts and advanced manufacturing process. As the development of new materials is key to the continuous improvement of the performance of OPVs, a major portion of the book will be dedicated to discussing the design concept and synthesis of novel organic semiconductors for OPV applications.

In Chapter 1, Li and Bo provide an overview of the key chemistry, including Stille coupling, Suzuki coupling and direct C–H arylation, for the synthesis of conjugated polymers used for OPVs. The reaction mechanism and the pros and cons of each type of coupling reaction are discussed in detail. In Chapter 2, Hou and co-workers present the design criteria for developing state-of-the-art polymer donors for highly efficient OPVs. The polymer structure–device performance relationships for a few important classes of polymers are discussed. In Chapter 3, Matsuo provides a comprehensive discussion on the design concepts and synthesis of new fullerene acceptors for OPVs. The effects of chemical functionalization, multi-adduct modification and the crystal structure of fullerenes on the OPV device performance are also discussed. In Chapter 4, Yan and co-workers review the recent development of efficient n-type semiconducting polymers and their applications as electron acceptor materials for all polymer-based OPVs. The effects of molecular weight, side chains, crystallinity of polymers and processing conditions on the bulk heterojunction morphology, as well as the device performance, are thoroughly discussed. In Chapter 5, Welch and co-workers highlight the synthesis and structure of several important classes of small molecule donors that enable the fabrication of highly efficient OPVs, and their structure–property–function relationships are discussed. In Chapter 6, Huang and co-workers give an overview of interface engineering for OPVs. The functions and the design criteria for efficient interfacial materials and their effects on OPV performance are discussed. In Chapter 7, Choy explains the functions and effects of solution processed metal oxide-based interfacial materials for OPVs. Different preparation methods for the metal oxide interlayers and their performance in both conventional and inverted OPVs are compared. In addition, the concepts of using chemical and metal nanoparticle doping of the oxide interlayer to introduce plasmonic-electrical effects to improve the performance of OPVs are presented. In Chapter 8, Heeger and co-workers describe how they discovered the ultrafast electron transfer process in nanostructured bulk heterojunctions and also discuss the ultrafast experimental results for both the polymer:fullerene and small molecule:fullerene films. They also present a general strategy to produce highly ordered and aligned semiconducting polymer films with exceptional high charge carrier mobilities. In Chapter 9, Russell and co-workers review some of the significant advances that have been made in understanding and manipulating the morphology of the OPV bulk heterojunction (BHJ) layers. Several key characterization techniques for morphological study are discussed. In addition, the major factors that affect the BHJ morphologies are discussed from both thermodynamic and kinetic aspects. In Chapter 10, Zhong discusses the current understanding of the photocurrent generation mechanism in OPVs, covering the electronic processes including charge generation, charge recombination, and charge transport. In Chapter 11, Furlan and Janssen discuss the design, working principle, modeling and characterizations of multi-junction OPVs. An overview of the high performance multi-junction OPVs with respect to the material choice, interconnection layer and device configuration is also provided. In Chapter 12, Yip and Jen provide an overview of the state-of-the-art semitransparent OPVs for power generating window applications. Several important factors that are required to achieve high performance semitransparent OPVs, including the development of new transparent electrodes, efficient low-bandgap materials, new device structures, and optical engineering, are discussed. Finally, in Chapter 13, Youn and Guo discuss the scalability issues of OPVs, covering cost evaluation, material choice, and large-scale manufacturing of OPVs based on roll-to-roll coating processes.

With the comprehensive, up-to-date reviews on the recent advancements in OPV technology from the leading experts around the world, we hope that this book will provide a useful source of information and a practical guide for scientists, engineers and graduate students that are interested in this field.

Fei Huang

Hin-Lap Yip

Yong Cao