Influence of Molecular Weight on the Solidification of a Semiconducting Polymer during Time-Controlled Spin-Coating

Molecular weight (M_w) is a key material parameter governing a variety of interesting characteristics of macromolecules. Here, we systematically studied the effects of the M_w of a semiconducting polymer, poly(3-hexylthiophene) (P3HT), on the microstructure, morphology, and optical and electrical properties of the thin films prepared using a time-controlled spin-coating method. Short spinning times significantly improved the structural and electrical characteristics of all P3HT thin films prepared with different M_ws. Notably, greater chain entanglement in the high M_w-P3HT delayed solidification during spin-coating and provided more uniform and slightly thicker films. The crystallinity of high M_w-P3HT thin films prepared with short spinning times less than 10 s were comparable to that of low M_w films, and the hole mobilities of the former films reached to 0.076 cm² V^-1 s^-1, 2.7 times the values obtained from films cast over a spinning time of 60 s. These results revealed that the structural disorder due to chain entanglement could be overcome to some extent by using short spinning times.