Effects of fluorination position on all-polymer organic solar cells

Abstract

In organic solar cells, fluorination has a great influence on the performance of non-fullerene acceptors, however there are very few studies on the effects of fluorination position on polymerized small molecule acceptors. In this article, two polymer acceptor materials (PAL1 and PAL2) with different fluorine substitution positions are investigated to study the influence of fluorinated forms on polymerized small molecule acceptor materials and the all-polymer solar cell performance. The end group fluorinated polymer acceptor material PAL1 and the π-bridge fluorinated polymer acceptor material PAL2 have similar absorption spectra and energy levels. While the blend film based on the polymer donor PM6:PAL1 has smaller roughness, finer phase separation, and tighter molecular packing, compared to the blend film of PM6:PAL2. Thus PM6:PAL1-based all-polymer organic solar cells (all-PSCs) have longer carrier life, faster carrier mobilities, and less bimolecular recombination.These polymer properties can simultaneously enhance the Jsc and FF of PM6:PAL1 based devices, finally achieving a device efficiency of 13.53%, which is significantly better than PM6:PAL2 based devices (9.16%). More importantly, the device based on PM6:PAL1 has excellent stability. When stored in a nitrogen atmosphere for 90 days, the PCE attenuation is only 4.2%. This work enriches the types of polymer acceptor materials and provides new ideas for the design of high-performance all-PSCs.