Near-field scanning photocurrent measurements of polyfluorene blend devices: Directly correlating morphology with current generation

Near-field scanning photocurrent microscopy (NSPM) measurements probing the relationship between morphology and current generation in photovoltaic devices based on p-xylene processed poly(9,9'-dioctylfluorene-co-bis-N,N'-(4,butylphenyl)-bis-N,N'-phenyl-1,4-phenylene-diamine) [PFB] and poly(9,9'-dioctylfluorene-co-benzo-thiadiazole) [F8BT] blend films are presented. We find that current generation occurs primarily from within the micron-sized phase-segregated domains, with the PFB-rich phase contributing significantly more current than the surrounding F8BT-rich regions. These results are explained by nanoscale intermixing within the micron-sized domains, with differing extents of intermixing in the PFB- and F8BT-rich domains.