Siloxane-Terminated Side Chain Engineering of Acceptor Polymers Leading to Over 7% Power Conversion Efficiencies in All-Polymer Solar Cells.

To investigate the influence of functional pendent groups on acceptor polymers and photovoltaic properties of all-polymer solar cells (all-PSCs), two novel acceptor polymers containing siloxane-terminated side chains are synthesized and characterized. Increasing the content of siloxane-terminated side chains can reduce π-π stacking distance and improve crystalline behavior, yet lead to poorer solubility of the acceptor polymers. By modulating the proper loadings of siloxane-terminated side chains on the acceptor polymers, the PBDB-T:PNDI-Si25 all-PSC attains a maximal power conversion efficiency (PCE) of 7.4% with an outstanding fill factor of 0.68. The results provide new insights for developing high-performance all-PSCs through functional group engineering on the acceptor polymers, to achieve good solubility, polymer miscibility, and blend morphology.