Development of non-fullerene electron acceptors for efficient organic photovoltaics

Compared to fullerene based electron acceptors, n-type organic semiconductors, so-called non-fullerene acceptors (NFAs), possess some distinct advantages, such as readily tuning of optical absorption and electronic energy levels, strong absorption in the visible region and good morphological stability for flexible electronic devices. The design and synthesis of new NFAs have enabled the power conversion efficiencies (PCEs) of organic photovoltaic (OPV) devices to increase to around 19%. This review summarises the important breakthroughs that have contributed to this progress, focusing on three classes of NFAs, i.e. perylene diimide (PDI), diketopyrrolopyrrole (DPP) and acceptor–donor–acceptor (A-D-A) based NFAs. Specifically, the PCEs of PDI, DPP, and A-D-A series based non-fullerene OPVs have been reported up to 11%, 13% and 19%, respectively. Structure–property relationships of representative NFAs and their impact on OPV performances are discussed. Finally, we consider the remaining challenges and promising directions for achieving high-performing NFAs.

Star-Shaped Non-Fullerene Small Acceptors for Organic Solar Cells

Over the past decade, organic solar cells (OSCs) have received considerable attention from the scientific community and are considered one of the most important sources of low-cost electricity production. Recently, OSC-based on star-shaped small-molecule (SM) non-fullerene acceptors (NFAs) have developed rapidly, and the highest power conversion efficiency (PCE) has exceeded 10 %. The star-shaped SM NFAs not only have three-dimensional charge-transport characteristics similar to fullerenes but also have a strong light absorption capacities and easily tunable energy levels. They are potential candidates as outstanding acceptor materials. In this Review, research progress in of star-shaped SM NFAs OSCs is reviewed specifically. Moreover, the influence of molecular structure, central unit, and peripheral linking group on OSC performance has been evaluated systematically. This Review could stimulate inspiration for designing high-performance OSC acceptor materials in the future.