Spin coating of conjugated polymers for electronic and optoelectronic applications

Experimental and theoretical study of the spin coating deposition of thin and ultrathin films from dilute solutions of four conjugated polymers, including poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), regioregular poly(3-hexylthiophene), poly(9,9-dioctylfluorenyl-2,7-yleneethynylene), and poly(2,2′-(3,3′-dioctyl-2,2′-bithienylene)-6,6′-bis(4-phenylquinoline)), is reported. Dilute solutions (0.3-2.0 wt.%) of the four conjugated polymers in chloroform were found to be Newtonian fluids with viscosities of 0.7-27.9 cp. The measured film thickness (hf) of the conjugated polymers was found to be well correlated to the initial solution concentration (x1,0) and the spin speed (ω) by the simple expression, hf=k x1,0ω−β. The exponent β is 0.5 for MEH-PPV but is reduced to 0.4 for the other three conjugated polymers. The difference in the β values can be explained by the effect of the accelerative period on the spin coating of less viscous dilute polymer solutions as verified by numerical simulation. A modified Meyerhofer's model was also found to well correlate the film thickness with the fundamental physical properties of the polymers and solvent. These experimental and theoretical results provide a basis for understanding and optimizing the preparation of thin and ultrathin films of conjugated polymers by spin coating.