Effect of Spacer Length of Siloxane-Terminated Side Chains on Charge Transport in Isoindigo-Based Polymer Semiconductor Thin Films

A series of isoindigo-based conjugated polymers (PII2F-CmSi, m = 3-11) with alkyl siloxane-terminated side chains are prepared, in which the branching point is systematically moved away from the conjugated backbone by one carbon atom. To investigate the structure-property relationship, the polymer thin film is subsequently tested in top-contact field-effect transistors, and further characterized by both grazing incidence X-ray diffraction and atomic force microscopy. Hole mobilities over 1 cm(2) V-1 s(-1) is exhibited for all soluble PII2F-CmSi (m = 5-11) polymers, which is 10 times higher than the reference polymer with same polymer backbone. PII2F-C9Si shows the highest mobility of 4.8 cm(2) V-1 s(-1), even though PII2F-C11Si exhibits the smallest - stacking distance at 3.379 angstrom. In specific, when the branching point is at, or beyond, the third carbon atoms, the contribution to charge transport arising from - stacking distance shortening becomes less significant. Other factors, such as thin-film microstructure, crystallinity, domain size, become more important in affecting the resulting device's charge transport.