Dioctylfluorene-thiophene based conjugated copolymers for bulk heterojunction solar cells and enhanced power conversion efficiency via methanol treatment

Sensible design and synthesis of conjugating polymers is important to the development of polymer solar cells (PSCs). In this work, we synthesized and characterized two dioctylfluorene-thiophene based conjugated copolymers, PFTDPP and PFTpBT, having different acceptor groups on the backbone. The photovoltaic properties of the copolymers blended with 6,6-phenyl-C61-butyric acid methyl ester (PC61BM) as an electron acceptor were obtained. The PSC based on a conventional device configuration ITO/PEDOT:PSS/ Polymer:PC61BM/LiF/Al showed power conversion efficiencies (PCEs) of 2.42% and 3.02% for PFTDPP and PFTpBT, respectively. Methanol treatment was introduced to further optimize device performance, and the solvent treatment gave a dramatic increase in PCE. The best PCEs could reach 4.25% and 4.20% after methanol treatment under AM 1.5G illumination with an intensity of 100 mW cm−2 from a solar simulator. © 2015 Society of Chemical Industry