A selection rule of solvent for highly aligned diketopyrrolopyrrole-based conjugated polymer film for high performance organic field-effect transistors

Abstract

Controlling the morphology of conjugated polymer film through careful selection of solvent is very important for facilitating charge transport in organic opto-electrical and electrical devices. In this report, we systematically study on a selection rule for optimum solvent choice to achieve highly aligned conjugated polymer chains with large ordered domain sizes for high performance organic field-effect transistors (OFETs) through various experimental analysis and Hansen solubility parameters. Three parameters: boiling point, solubility, and molecular interaction between conjugated polymer and solvents, are the most important to obtain optimum morphology. Similar molecular interaction values between solvent and conjugated polymer determined the formation of larger size ordered domain in films. High boiling point and relatively poor solubility solvents affect anisotropic film formation of conjugated polymer chains during off-center spin-coating. Considering these, large ordered domains with highly aligned diketopyrrolopyrrole thieno[3,2-b]thiophene (DPPT-TT) polymer chains were achieved by these important factors, and we demonstrate impressively high field-effect mobility similar to 5.89 cm(2) V-1 s(-1) with low standard deviation (13%), which is the highest reported value so far for top-gate/bottom-contact DPPT-TT OFETs.