A New sp²-sp²Dialkylethylene-Bridged Heptacyclic Ladder-Type Arene for High Effi ciency Polymer Solar Cells

A new dithienobenzo-carbazole (DTBC) heptacyclic arene using sp ²-sp² dialkylethylene moiety as the bridge was successfully synthesized by Suzuki-Miyaura cross-coupling reaction. This facile benzoannulation planarizes the conjugated framework with the concomitant introduction of four octyl substituents, making the newly designed copolymer PDTBCDTBT exhibit solution processability, superior absorption ability, lower-lying HOMO energy level, and crystalline nature. The solar cell using PDTBCDTBT has produced a high effi ciency of 6.2%, which outperforms the corresponding sp 3 -hybridized C-bridged, Si-bridged and N-bridged analogous polymers.