Synergistic effect of side-chain and backbone engineering in thieno[2,3-f]benzofuran-based conjugated polymers for high performance non-fullerene organic solar cells

Abstract

Most polymer donors developed so far for high-performance polymer solar cells (PSCs) are designed in planar molecular geometries containing benzodithiophene (BDT) units. In this study, three two-dimensional conjugated polymers, PTBF_EH-BDD, PTBFS_DO-BDD and PTBFS_EH-BDD, based on thieno[2,3-f]benzofuran (TBF) building blocks with different side-chains are designed and synthesized. It is found that the TBF unit can inherit and integrate the advantages of both the BDT and benzo[1,2-b:4,5-b′]difuran (BDF) building blocks. Due to the synergistic effects of oxygen and sulfur in the backbone and the optimized side chain, PTBF_EH-BDD shows a higher absorption coefficient, more suitable aggregation and improved hole mobility in comparison with PTBFS_DO-BDD and PTBFS_EH-BDD, which improves the J_SC and FF in PSCs. The PSCs based on PTBF_EH-BDD:ITIC achieve a power conversion efficiency (PCE) of 11.13% with a J_SC of 17.76 mA cm⁻², a V_OC of 0.893 V, and a FF of 70.16%, which is comparable with its BDT counterparts. Moreover, the PSCs based on these three TBF-based devices do not need any extra post treatments or additives. This study demonstrates that the TBF-based polymers are promising candidates for highly efficient non-fullerene PSCs.