With the random copolymerizationstrategy, Jenekhe et al. then developed a series of NDIselenophene/PDI–selenophene random copolymers, xPDI [92].They found the crystallinity of xPDI varies with the molar ratiosof PDI/NDI in the polymers. They investigated the impact ofcrystallinity on the blend compatibility, blend morphology,and performance of OSCs. They found that 30PDI (P17) whichcomposed of 30 mol% of PDI units in the backbone (Fig. 6)exhibited the desired crystallinity with more favorable blendmorphology.