The thin-film properties of a polymer library consisting of novel conjugated low-bandgap poly(diketopyrrolopyrrole-co-benzothiadiazole-co-fluorene) (poly(DPP-co-BTD-co-F)) polymers are investigated. The content of the monomer units in the copolymers is systematically varied. Structure–property relationships are obtained for the ink characteristics, the film formation qualities, and their optical properties. Toluene/o-DCB in a ratio 90/10 and a concentration of 5 mg mL−1 is found to be a suitable solvent system for all polymers. The polymer compositions and the choice of solvent have a significant influence on the film properties. Inkjet printing is shown to be a suitable technique for the preparation of thin-film libraries that subsequently can be characterized by combinatorial screening tools.