(129a) Printing Semiconductor Polymers to Order

Controlled morphology evolution via directed assembly has played a central role in the development of modern electronic, optical and clean energy materials. In comparison to conventional ‘hard’ materials, polymer-based functional materials can be easily processed into diverse form factors by low-cost, high-throughput methods such as roll-to-roll printing and 3D printing. The printing conditions intimately couple with the assembly process and sensitively modulate the solid-state properties in the fabricated devices.

We are particularly interested in semiconducting polymers with p-conjugated molecular structures. Recent years, conjugated polymers have emerged as a new class of electronic and photoelectronic materials that are light-weight, flexible and solution printable. Conjugated polymers have demonstrated potential uses in a diverse range of applications from transistors, thermoelectrics, sensors, light-emitting diodes to solar cells etc. However, major challenges remain, in controlling the nucleation, growth and aggregation of conjugated polymers during solution printing and coating, which critically impact the printed device performance by orders of magnitude. The rapid printing process creates a complex environment with coupled physics that drive the polymer assembly far from equilibrium.

In our work, we combine printing experiments, morphology and device characterizations with governing-equation-based modeling and simulations to present new insights and strategies for controlling multi-scale assembly of semiconducting polymers. We learn from living systems and design bioinspired assembly processes, allowing molecules to put themselves together cooperatively into highly ordered structures otherwise not possible with significantly improved electronic properties. We develop free energy models and apply in situ morphology characterization methods to understand the critical role of interfaces in guiding polymer nucleation and the ensuing assembly process. We establish tools for investigating flow-induced morphology transition that accompanies change in printing regimes. High degree of morphology control from molecular to device scale further enables new insights into charge transport properties of semiconducting polymers and realizes advanced electronic device applications.