Here we report results of time-of-flight (ToF) measurements on blends of different ratios of poly(9,9-dioctylfluorene-cobis-
N,N'-(4-methoxylphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine) (PFMO) and the structurally similar poly(9,9-
dioctylfluorene-co-N-(4-methoxyphenyl)diphenylamine) (TFMO). It is shown that the hole mobility can be tuned over
three orders of magnitude with a mobility minimum at 10% PFMO and 90% TFMO. We also use Raman microscopy to
demonstrate that the blends do not phase separate within the one micron resolution of our experiment.