The importance of renewable energy has become ever more important with the increasing environmental costs of using fossil fuels and their limited supply. The Sun is the most abundant source of renewable energy. There are two routes for the conversion of sunlight into a usable form of energy: the solar thermal approach, whereby solar energy is converted to heat and then electricity, and the solar photovoltaic route, where semiconductors are used to convert solar radiation directly into electricity. The photovoltaic solar cell has been identified as one of the most promising conversion devices for solar energy because it is both clean and scalable.

Photovoltaic technology has gone through many changes over the last four decades. These changes have now been classified into different generations of photovoltaic technology. Type I photovoltaic technology was based on crystalline silicon; it is expensive, but can give high power conversion efficiencies. Type II photovoltaic technology is based on thin film technology, with films containing polycrystalline silicon, cadmium telluride and copper indium disulphide. It is cheap compared with Type I photovoltaic technology, but offers lower efficiencies. Type III photovoltaic technology, the topic of this book, is based on solution-processed semiconducting nanostructured materials, which are both cheap and efficient. Nanostructured materials include atomic clusters or layered assemblies as thin films in which one of the dimensions is <100 nm. The properties of these materials are remarkably different from the bulk materials. Type III photovoltaic solar cells include organic polymer:fullerene macromolecules, inorganic nanoparticles or hybrids, dye-sensitised solar cells, hybrid polymer and perovskite solar cells.

The materials for Type III solar cells have branched into a series of generic groups. These include: organic ‘small molecule’ and polymer-conjugated structures, fullerenes, quantum dots, copper indium gallium selenide nanocrystal films, dyes/TiO₂ for Grätzel cells, hybrid organic/inorganic composites, and perovskites. Although the power conversion efficiencies of organic solar cells are modest compared with other Type III photovoltaic materials, plastic semiconductors provide a cheap route to manufacturing through solution processing and offer flexible devices. However, other types of material are proving to be compatible with this type of processing while providing higher device efficiencies. As a result, the field is experiencing healthy competition between technologies and this is pushing progress at a fast rate. In particular, perovskite solar cells have emerged as a highly disruptive technology, with power conversion efficiencies now just over 22%. Perovskite cells, however, still have to address stability and environmental issues.

With such a diverse range of materials, it is timely to capture the different technologies in a single volume of work. The aim of this book is to give a collective insight into the different parts played by nanostructured materials in Type III solar cells. It aims to be an essential text for those working with any of the devices highlighted here, providing a fundamental understanding and appreciation of the potential and challenges associated with each of these technologies. This book gives an overview of recent developments in the synthesis and use of these nanostructured materials in photovoltaic technology. It is divided into two major sections, although the first chapter critically and importantly deals with the accuracy of photovoltaic cell measurements and is essential reading for those who make and test devices. The next six chapters of the book cover the development and working principles of organic solar cells, while the last seven chapters highlight the progress made in the synthesis, properties and the use of inorganic nanostructured materials in photovoltaic technology.

Peter Skabara and Mohammad Azad Malik