Boosting the overall stability of organic solar cells by crosslinking vinyl-functionalized polymer derived from PM6

In the past decade, the study on organic solar cells (OSCs) has made great progress. For commercial application, achieving high efficiency OSCs with the prominent stability is a crucial issue. Here, two crosslinkable vinyl-functionalized D-A-D-D-1-type polymers PM6-Ax (x: 5 or 15) were successfully synthesized by introducing a crosslinkable benzodithiophene (D-1) unit with vinyl functionality into the D-A polymer PM6. As expected, the un-crosslinked PM6-A5:Y6-based OSC process an outstanding PCE (15.20%) without additives, which is higher than that of the reference PM6:Y6-based OSCs (13.65%) by the D-A-D-D-1 strategy. It is found that polymers PM6-Ax can be crosslinked to some extent after annealing at 150 degrees C for a certain period of time. Meanwhile, by thermal crosslinking of the active layer, the PM6-Ax:Y6-based devices were fabricated and the stability was studied. Reference PM6:Y6-based devices were also fabricated. As a result, crosslinked PM6-A5:Y6-based devices retained 91.0% of the initial PCE under 48 h of continuous 60 degrees C thermal aging and 92.8% of the initial PCE under 72 h continuous white LED light illumination, whereas the reference PM6:Y6-based devices retained 81.9% and 72.7% under the same aging conditions. Moreover, crosslinked PM6-A5:Y6-based devices showed superior shelf-life stability over the reference devices. These results demonstrate that crosslinking of the PM6-A5:Y6-based active layer can significantly boost overall stability (including thermal-stability, photo-stability, and storage-stability) of the OSCs.