A New sp2‐sp2 Dialkylethylene‐Bridged Heptacyclic Ladder‐Type Arene for High Efficiency Polymer Solar Cells

A new dithienobenzo-carbazole (DTBC) heptacyclic arene using sp2-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 efficiency of 6.2%, which outperforms the corresponding sp3-hybridized C-bridged, Si-bridged and N-bridged analogous polymers.