Structural optimization in the same polymer backbones for efficient polymer solar cells: Relationship between steric hindrance and molecular weight

[Display omitted] •New polymers by structural modification in the same backbones were designed and synthesized.•This effects of the polymers were and proved through computing simulation and XRD, SCLC etc.•The best device of P-C4 was reached to 8.9% with 250nm. Structural optimization by using donor–acceptor (D–A) conjugated polymers is a promising strategy for improving the power conversion efficiencies (PCEs) of polymer solar cells (PSCs). In this study, we report the best PCE of 8.9% based on PC71BM that was achieved by using a 250nm thick active layer in an inverted device through the optimization of side chains of P(2DBDT-DTffBT) backbones. Specifically, by varying the alkyl side chain lengths and shapes in the acceptor unit of polymers, the effect of side chain engineering on photovoltaic performance was systematically studied in terms of the relationship between steric hindrance and molecular weight.