Controlling Molecular Mass of Low-Band-Gap Polymer Acceptors for High-Performance All-Polymer Solar Cells

Recent advances in the development of polymer acceptors and the investigation of molecular mass have boosted the power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) to approximately 11%. Here, a fused-aromatic-ring-constructed polymer acceptor PYT (Poly[(2,2'-((2Z,2'Z)-(( 12,13-bis(2-octyldodecyl)-3,9-diundecyl12,13-dihydro[1,2,5]thiadiazolo[3,4e]thieno[2 '',3 '' :40,50]thieno[2',3':4,5] pyrrolo[3,2-g]thieno[2',3' :4,5]thieno[3,2-b]-indole-2,10-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile-alt-2,5-thiophene)]) is reported, while a series of PYT polymers with different molecular masses (designated as PYTL, PYTM, and PYTH) are prepared to fine-tune the molecular crystallinity and miscibility. Benefiting from the advantages of PYT series, which possess broad absorption with a narrow band of 1.40-1.44 eV and high absorption coefficients of over 1.00 3 105 cm(-1), we investigated the blend miscibility and device performance of all-PSCs based on a wide-bandgap polymer donor, PM6. The PYTM-based all-PSCs exhibit an excellent PCE of 13.44%, outperforming those with PYTL (12.55%) and PYTH (8.61%). Our results provide insight into polymer acceptor backbone and molecular mass and suggest guidelines to rationally select polymers for all-PSCs.