SELECTIVE CRYSTALLIZATION OF CONJUGATED POLYMERS INTO NANOWIRES ON WELL-DEFINED NUCLEATION SITES
Daniel Acevedo-Cartagena1, Ryan Hayward1, Emily Pentzer2, Elvira Trabanino3, Jiaxin Zhu1, Alejandro Briseno1, Todd Emrick1, Stephen Nonnenmann1.
1University of Massachusetts Amherst, Amherst, MA, 2Case Western Reserve University, Cleveland, OH, 3California State Polytechnic University, Pomona, CA.
Efficient devices for energy generation from renewable sources are crucial in order to preserve the environment and improve our quality of life. Solution crystallization of conjugated polymers is a suitable route for obtaining hierarchical structures capable of improving the performance of organic electronics, especially solar cells. By adding well-defined nucleation sites to supersaturated solutions, crystallization can be induced permitting control over structural features. We have been able to modify the hysteresis in the crystallization of poly(3-hexylthiophene) (P3HT) by tuning the polymer solubility in a marginal solvent. The hysteresis window between crystallization and dissolution temperatures of P3HT is tuned using temperature-controlled fractionation. This process produces supersaturated solutions in a metastable state at room temperature which suppresses homogenous crystallization, but is suitable for studying heterogeneous crystallization upon the addition of nucleation sites. We show that in these metastable solutions, crystalline nanowires are selectively grown on a variety of nucleation sites such as graphene, highly orientated pyrolytic graphite, and short P3HT nanowires.