Novel polymer acceptors achieving 10.18% efficiency for all-polymer solar cells

Abstract Polymer acceptors based on extended fused ring π skeleton has been proven to be promising candidates for all-polymer solar cells (all-PSCs), due to their remarkable improved light absorption than the traditional imide-based polymer acceptors. To expand structural diversity of the polymer acceptors, herein, two polymer acceptors PSF-IDIC and PSi-IDIC with extended fused ring π skeleton are developed by copolymerization of 2,2'-((2Z,2'Z)-((4,4,9,9-tetrahexadecyl-4,9-dihydro-s-indaceno [1,2-b:5,6-b']dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC-C16) block with sulfur (S) and fluorine (F) functionalized benzodithiophene (BDT) unit and silicon (Si) atom functionalized BDT unit, respectively. Both polymer acceptors exhibit strong light absorption. The PSF-IDIC exhibits similar energy levels and slightly higher absorption coefficient relative to the PSi-IDIC. After blended with the donor polymer PM6, the functional atoms on the polymer acceptors show quite different effect on the device performance. Both of the acceptors deliver a notably high open circuit voltage (VOC) of the devices, but PSi-IDIC achieves higher VOC than PSF-IDIC. All-PSC based on PM6:PSi-IDIC attains a power conversion efficiency (PCE) of 8.29%, while PM6:PSF-IDIC-based device achieves a much higher PCE of 10.18%, which is one of the highest values for the all-PSCs reported so far. The superior device performance of PM6:PSF-IDIC is attributed to its higher exciton dissociation and charge transport, decreased charge recombination, and optimized morphology than PM6:PSi-IDIC counterpart. These results suggest that optimizing the functional atoms of the side chain provide an effective strategy to develop high performance polymer acceptors for all-PSCs.