An A−D−A oligomer, DTS(F 2 BT) 2 , was synthesized; its structural evolution was studied with DSC, POM, 2D-WAXD, and in-situ GI-XRD. The structural evolution of DTS(F 2 BT) 2 is stepwise and kinetically slow. Both rapid drying and the presence of PC 71 BM trapped DTS(F 2 BT) 2 in a less ordered nematic (N) phase. PDMS-assisted crystallization enabled a pristine DTS(F 2 BT) 2 thin film to attain a more ordered equilibrium phase, and enhanced the OFET mobility of DTS(F 2 BT) 2 . In OPV devices, DIO additive drove the DTS(F 2 BT) 2 domains in the DTS(F 2 BT) 2 :PC 71 BM blended film from the N phase toward the equilibrium phase, and resulted in enhanced OPV performances. These results reveal the slow ordering process of the A−D−A oligomer, and the importance of monitoring the degree of structural evolution of the active thin films in organic optoelectronics.

Molecular conformation and the assembly structure determine the spatial arrangements of the constituent units and the functions of a molecule. Although, fullerene hexa-adducts (FHAs) have been known as functional materials with great versatility, their conformational preferences and phase stability remain a complicate issue. By choosing bithiophene (T2 ) and dodecyl bithiophene (C12 T2 ) as the peripheral units of FHA, and using microscopic, scattering and diffraction characterizations, our study reveals how the intramolecular interaction and environmental stimulus affects the conformational preferences and phase stability of FHAs.