Naphthalenediimide (NDI) polymers for all-polymer photovoltaics

Naphthalenediimide (NDI) polymers are an important class of electron-accepting (acceptor or n-type) semiconductors for organic photovoltaic (OPV) or organic solar cell (OSC) applications. Blending them with compatible electron-donating (donor or p-type) polymers yields an OPV device known as bulk-heterojunction (BHJ) all-polymer solar cells (all-PSCs). Compared to the more extensively studied OPVs using fullerene derivatives as the acceptor material, all-PSCs provide important benefits such as chemical tunability, mechanical flexibility and ambient/stress stability. Through an extensive research on materials design and device optimization in the last five years, all-PSCs employing NDI-based polymers have achieved remarkable improvement in device power conversion efficiency (PCE), now surpassing 10% - a number that approaches the state-of-the-art organic photovoltaic (OPV) cells using fullerenes. In this review, recent development of NDI-based conjugated polymers used in all-PSCs will be highlighted.