Bicontinuous Phase Structure in Poly(3,3′′′-didodecylquaterthiophene) (PQT-12)/[6,6]-Phenyl-C71-Butyric Acid Methyl Ester (PC71BM) Blend Films

Bicontinuous phase structure in Poly(3,3 -didodecylquaterthiophene) (PQT-12)/[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) blend films was formed by using thiophene as solvent to suppress the compatibility between PC71BM and side chains of PQT-12. The interaction between PQT-12 chains was enhanced and the interaction between PC71BM and PQT-12 was weakened in thiophene because of the good compatibility of thiophene with PQT-12 and its planar molecular structure. Thus, the energy barrier for PC71BM nucleation was overcome. As a result, spherical PC71BM domains surrounded by the continuous phase of PQT-12 were formed after spin-coating. This structure was not stable and secondary phase separation was induced by thermal annealing. During thermal annealing, adjacent spherical PC71BM domains grew and connected together, which cut off PQT-12 continuous phase. Subsequently, the PQT-12 phase grew further and connected again. At last, bicontinuous structure was formed. The power conversion efficiency of the device prepared from solution in thiophene was almost 1.9 times of the one from chloroform.