The renaissance of polythiophene organic solar cells

The past decade has witnessed tremendous advances in the power conversion efficiency (PCE) of organic photovoltaic cells. Concomitantly, the chemical structures of present high-efficiency photovoltaic polymers have become more complex, leading to tedious and harsh synthetic processes and high batch-to-batch variations. By comparison, polythiophenes have gained considerable traction and hold tremendous promise in terms of cost and scalability. In this review, we present state-of-the-art developments in polythiophene solar cells, with a focus on those made of poly(3-hexylthiophene) (P3HT) and nonfullerene small-molecule acceptors. First, the structural optimization of polythiophenes is briefly discussed. Then, we provide a concise discussion of two notable aspects (miscibility matching and crystallization control) for performance optimization and associated research highlights in the past 5 years. We also highlight guidelines to ascertain the scientific challenges for polythiophene:nonfullerene solar cells. The development of new polythiophenes and their bulk-heterojunction blends will help to stimulate advances in many kinds of cost-effective electronics.