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

Summary

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-diundecyl-12,13-dihydro[1,2,5]thiadiazolo[3,4e]thieno[2″,3″:4′,5′]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 PYT_L, PYT_M, and PYT_H) 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 × 10⁵ cm⁻¹, we investigated the blend miscibility and device performance of all-PSCs based on a wide-band-gap polymer donor, PM6. The PYT_M-based all-PSCs exhibit an excellent PCE of 13.44%, outperforming those with PYT_L (12.55%) and PYT_H (8.61%). Our results provide insight into polymer acceptor backbone and molecular mass and suggest guidelines to rationally select polymers for all-PSCs.