Uniform inkjet-printed films with single solvent

Highlights: • Uniform film of polymer is inkjet-printed from single solvent dissolved ink. • High boiling point solvent slows down the outward capillary flow. • High concentration ink weakens the outward capillary flow. • High substrate temperature accelerates the solvent's evaporation rate of solvent. - Abstract: To fabricate solution-processed full-color display, a single solvent suitable for all the primary-color inks which could be printed on the substrate at room temperature, is much preferred. Uniform red, green, and blue polymer films without coffee-ring are achieved by inkjet-printing single solvent, o-dichlorobenzene (o-DCB), dissolved poly(dibenzothiophene-S,S-dioxide-co-9,9-dioctyl-2,7-fluorene) (PPF-SO) inks. It's discovered that first, the solvent with high boiling point slows down the outward capillary flow, reducing the coffee-ring effect. Second, the coffee-ring effect decreases monotonically with the viscosity difference between the ink and the solvent. Third, as the concentration of the ink increases, the interaction between the solutes becomes stronger, thereby weakening the outward capillary flow. Fourth, high substrate temperature accelerates the evaporation rate of solvent, leading to enhanced coffee ring. Uniform line film of PPF-SO is inkjet-printed from o-DCB dissolved PPF-SO ink with concentration of 15 mg/mL, and droplet-spacing of 70 μm. The substrate temperature is set at 25 °C. The red and green emitting inks are made by mixing a small amount of the PPF-SO derivatives into the blue host ink PPF-SO with the same solvent. Therefore, the printing conditions are kept the same to obtain uniform red and green films.