(581b) Understanding Crystallization of Oriented Domains in Solution Printed Organic Semiconductor Thin Films

Solution coating has been widely adopted in studies of functional materials because of its potential application as a high-throughput, low-cost, energy-efficient method for large area coating. Control in molecular assembly, crystallization and multi-scale morphology has significant impact on the development of solution-processable electronics. Although out-of-plane molecular orientation with respect to the substrate is a critical factor determining the performance of a wide range of organic electronic devices, it remains a central challenge to control molecular orientation due to complex molecular assembly mechanism in the far-from-equilibrium solution coating processes. On the other hand, there is a lack of generally applicable design rules for controlling molecular orientation, which results in trial and error condition tuning in molecular orientation studies.

In this work, we employed diverse characterization methods to understand and develop generally applicable design rules for molecular orientation and morphology control in conjugated polymer thin films. We hypothesize that the out-of-plane molecular orientation of a semiconducting polymer is jointly determined by intermolecular interactions (thermodynamic driving force) and the rate of aggregation near the polymer-substrate interface (kinetic pathway), both of which are sensitively modulated by the solution coating conditions and the polymer and substrate properties. We directly obtained the crystallization kinetics of conjugated polymers by monitoring polymer aggregation in situ during solution coating. We also evaluated polymer self-interactions and polymer-substrate interactions to help determine the thermodynamically favored molecular orientation. Our work will enable rational design approaches for controlling out-of-plane molecular orientation and the resulting electronic properties of advanced (opto)electronic devices, as well as having a broad and profound impact that goes far beyond organic heterojunction devices.