Side-Chain Engineering of Diketopyrrolopyrrole-based Copolymer Using Alkyl Ester Group for Efficient Polymer Solar Cell

The new diketopyrrolopyrrole-based copolymer, referred to as PDPPBDTE, bearing linear alkyl ester groups, was synthesized with the objective of improving the miscibility between the donor polymer and [6,6]-phenyl C-71 butyric acid methyl ester (PC71BM). PDPPBDTA bearing ethylhexyl side-chains was also synthesized as a control polymer. The PDPPBDTE:PC71BM blend film showed a relatively small crystalline domain size compared to the PDPPBDTA:PC71BM blend film. A polymer solar cell fabricated with PDPPBDTE and PC71BM exhibited twofold higher power conversion efficiency than that employing PDPPBDTA.