Synthesis of 6H-benzo[c]chromene as a new electron-rich building block of conjugated alternating copolymers and its application to polymer solar cells

Abstract

For the purpose of reducing the bandgap of a fluorene-based semiconducting polymer, we introduced a strong electron-donating oxygen atom into fluorene (F) to synthesize benzochromene (BC), which was then polymerized with electron deficient dithienyl benzothiadiazole (DTBT) and diketopyrrolopyrrole (DPP2T) to afford two low-bandgap polymers, PBCDTBT and PBCDPP2T, respectively. The PBCDTBT-based solar cell exhibits a high power conversion efficiency (PCE) of 5.74%, which is much higher than that of the reference polymer (PFDTBT) (2.56%). The higher PCEs of BC-based polymers are mainly attributed to higher J_SC, which arises from stronger and broader absorption, higher exciton generation rate, more effective charge separation and higher hole mobility as compared to fluorene-based polymers.