Effect of carbon hybridization in 9H-fluorene unit on the photovoltaic properties of different fluorene-based conjugated polymers

To investigate the effect of different carbon hybridization in 9H-fluorene on the resultant polymers, a series of donor–acceptor conjugated polymers have been synthesized by copolymerizing substituted 9H-fluorenes with triazoloquinoxaline. All polymers exhibit good solution-processability and broad absorption in 350–1000 nm region with narrow optical bandgaps ranging from 1.27 eV to 1.55 eV. The results indicate that fluorene functionalization via different carbon hybridization on 9-position could be an effective strategy to fine-tune the absorption, energy levels, and photovoltaic performance of the polymers. 9-Position sp 2 -hybridized carbon in fluorene could enhance absorption of ultraviolet-visible and form good morphology of blending layers, through its planar rigid structure. All polymer solar cells devices exhibited moderate performance with the best power conversion efficiency of 3.02% achieved based on P2. Compared to ladder-type multifused fluorene, carbon-hybridized 9H-fluorene units can be a very useful building block for constructing narrow bandgap polymers with facile synthesis, and even interesting optoelectronic properties.