Spiro Linkage as an Alternative Strategy for Promising Nonfullerene Acceptors in Organic Solar Cells. (27th August 2015) - Wu, Xiao‐Feng
Abstract : This work focuses on developing diketopyrrolopyrrole (DPP)‐based small molecular nonfullerene acceptors for bulk heterojunction (BHJ) organic solar cells. The materials, SF‐DPP s, have an X‐shaped geometry arising from four DPP units attached to a spirobifluorene (SF) center. The spiro‐dimer of DPP‐fluorene‐DPP is highly twisted, which suppresses strong intermolecular aggregation. Branched 2‐ethylhexyl (EH), linear n ‐octyl (C8), and n ‐dodecyl (C12) alkyl sides are chosen as substituents to functionalize the N, N ‐positions of the DPP moiety to tune molecular interactions.SF‐DPPEH, the best candidate inSF‐DPP s family, when blended with poly(3‐hexylthiophene) (P3HT) showed a moderate crystallinity and gives a J sc of 6.96 mA cm −2, V oc of 1.10 V, a fill factor of 47.5%, and a power conversion efficiency of 3.63%. However, SF‐DPPC8 andSF‐DPPC12 exhibit lower crystallinity in their BHJ blends, which is responsible for their reduced J sc . Coupling DPP units with SF using an acetylene bridge yieldsSF‐A‐DPP molecules. Such a small modification leads to drastically different morphological features and far inferior device performance. These observations demonstrate a solid structure–property relationship by topology control and material design. This work offers a new molecular design approach to develop efficient small molecule nonfullerene acceptors. Abstract : A series of spiro‐diketopyrrolopyrroles‐based nonfullerene acceptors with X‐shapes is developed. The substituted alkyl side chains on the acceptors can significantly tailor their crystallinity and bulk heterojunction film morphology. When paring these acceptors with poly(3‐hexylthiophene), a dramatic variation of power conversion efficiency from 1.42% to 3.63% is observed.