“…Applying this methodology we were able to visualize the morphology of polymer:fullerene blend films and identify the scale of phase separation, estimate fullerene content and degree of crystallinity, study the effect of the fullerene type on film morphology and prepare a 3D reconstruction of the BHJ morphology in working devices. [37][38][39][40] In this study, we harness a comprehensive set of techniques to monitor BHJ morphology evolution during thermal annealing over a wide range of time and length scales, from initial molecular precipitation associated with the ''burn-in'' effect, to micrometer size aggregation. The model system we chose is poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3 00 0 -di(2octyldodecyl)-2,2 0 ;5 0 ,2 00 ;5 00 ,2 00 0 -quaterthiophen-5,5 00 0 -diyl)]:phenyl-C 61 -butyric acid methyl ester (PCE11:PCBM, Fig.…”