Scheme 1.

Schematic illustration of the morphology evolution of the PffBT4T-2OD:PC₇₁BM blends after post thermal annealing. After thermal annealing, the originally ordered PffBT4T-2OD around the interface (dotted line region of unannealed sample) was disarranged at the interface (dotted line region of annealed sample), due to the aggregation of the PC₇₁BM. Meanwhile, the size of the pure PffBT4T-2OD phase increases from L1 to L2, due to the aggregation of the donor during thermal annealing process.