Comparative Study of the Nanomorphology of Spray and Spin Coated PTB7 Polymer: Fullerene Films

We present a comparative study of the nanomorphology of spray and spin coated films of a blend of thieno[3,4-b]-thiophene/benzodithiophene (PTB7) semiconducting polymer and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM). The surface morphology and inner structure of these films are investigated with optical microscopy, atomic force microscopy (AFM), and grazing incidence wide-angle X-ray scattering (GIWAXS). The spray coated PTB7: PC71BM films exhibit significant differences in the molecular packing compared with their spin-coated counterparts. Only very weak order is observed in the spraycoated films as compared to well-defined ordered periodic lamellar structure and pi-pi stacking of the PTB7 polymer of the spin-coated systems. This difference in the resulting nanomorphology is related to the different structural formation mechanisms in the two deposition techniques. (C) 2016 Society of Plastics Engineers