Nano structure evolution in P3HT:PC₆₁BM blend films due to the effects of thermal annealing or by adding solvent

Crystallographic dynamics of blend films of regioregular poly(3-hexylthiophene) (P3HT) mixed with 6-6--phenyl-C61-butyric acid methyl ester (PC₆₁BM) treated by thermal annealing or by adding solvent 1,8-diiodooctane (DIO) are characterized by 2D-grazing incidence x-ray diffraction (2D-GIXRD). The results show that the P3HT chains are primarily oriented with the thiophene ring edge-on to the substrate, with a small fraction of chains oriented plane-on. The interplanar spacing becomes narrow after being treated by DIO, and the coherence length of the P3HT crystallites increases after being treated by thermal annealing or DIO, which is accompanied by a change in the orientation angle of the P3HT lamellae. The increased ordering of P3HT packing induced by thermal annealing or adding DIO contributes to enhanced photovoltaic performance.