Control of Crystallite Orientation in Diketopyrrolopyrrole-Based Semiconducting Polymers via the Tuning of Intermolecular Interactions.

Considerable previous studies have focused on the notion that semiconducting polymers with edge-on dominant orientation are advantageous for horizontal charge transport while polymers with face-on dominant orientation are advantageous for vertical charge transport, since the crystallite orientation determines the π-π stacking direction, which in turn affects the interchain charge transport direction. Here, we report that the crystallite orientation is dependent on the intermolecular interactions in the semiconducting polymer. In this study we control the intermolecular interactions in a donor-acceptor (D-A) semiconducting polymer via side-chain engineering. To perform side-chain engineering, we use two different polymers, in the first instance with side chains only on A units (PDPP-B), and then in the second instance, side chains on both D and A units (PDPP-C8). We observe that PDPP-C8 is characterized by weaker intermolecular interactions due to the additional side-chains on D units. An morphology analysis reveals that PDPP-B and PDPP-C8 films have microstructures, which are characterized by edge-on and face-on dominant orientation, respectively. Therefore, we demonstrate that our strategies effectively control intermolecular interactions and, consequently, the crystallite orientation. Finally, we compare the vertical and horizontal mobilities of both polymer films. These results show that crystallite orientation has significant influence on charge transport behaviors.