In this Review, we discuss the scientific origins, practical approaches of designing the low-bandgap polymers/molecules, and their associated physical properties. We then provide a synopsis of major advances in the above-mentioned applications that particularly require small bandgap materials (with an emphasis on solar cells). Future developments in materials design and potential applications will also be addressed to stimulate innovation and creativity in the future. In this Review, we focus on the solution-processable organic materials with optical bandgap smaller than 1.6 eV (near-IR absorbing), and only limited numbers of representative molecules are chosen for discussion. This Review emphasizes the correlation between chemical structures, physical properties, and resulting device performance of the solution-processed polymers/small molecules, and tries to provide a comprehensive understanding from materials design to a variety of device applications. For a more complete description of the chemical structures and synthetic routes of different organic semiconductors for solar cells and FETs, please see recent review articles。

http://pubs.acs.org/doi/full/10.1021/acs.chemrev.5b00165